CAF-Interpreting Blueprint for Cages

HOW TO USE THIS COMPETENCY BASED LEARNING MATERIAL

Welcome to the module in Reviewing, Designing and Interpreting Blueprint for
Cages and Pens. This module contains training materials and activities for you to complete.

The unit of competency " Construct Aquaculture Facilities_" contains knowledge, skills and
attitudes required for Aquaculture. It is one of the specialized modules at National Certificate
level (NCII).

You are required to go through a series of learning activities in order to complete each
learning outcome of the module. In each learning outcome are Information Sheets and
Resources Sheets (Reference Materials for further reading to help you better understand the
required activities). Follow these activities on your own and answer the self-check at the end of
each learning outcome. You may remove a blank answer sheet at the end of each module (or
get one from your facilitator/trainer) to write your answers for each self-check. If you have
questions, don’t hesitate to ask your facilitator for assistance.

Recognition of Prior Learning (RPL)

You may already have some or most of the knowledge and skills covered in this learner's
guide because you have:

• been working for some time
• already completed training in this area.

If you can demonstrate to your trainer that you are competent in a particular skill or skills,
talk to him/her about having them formally recognized so you don't have to do the same training
again. If you have a qualification or Certificate of Competency from previous trainings, show it to
your trainer. If the skills you acquired are still current and relevant to the unit/s of competency
they may become part of the evidence you can present for RPL. If you are not sure about the
currency of your skills, discuss this with your trainer.

At the end of this module is a Learner’s Diary. Use this diary to record important dates, jobs
undertaken and other workplace events that will assist you in providing further details to your
trainer or assessor. A Record of Achievement is also provided for your trainer to complete
once you complete the module.

This module was prepared to help you achieve the required competency, in Constructing
Aquaculture Facilities. This will be the source of information for you to acquire knowledge and
skills in this particular trade independently and at your own pace, with minimum supervision or
help from your instructor.

1. Talk to your trainer and agree on how you will both organize the Training of this unit.
Read through the module carefully. It is divided into sections, which cover all the skills,
and knowledge you need to successfully complete this module.

2. Work through all the information and complete the activities in each section. Read
information sheets and complete the self-check. Suggested references are included to
supplement the materials provided in this module.

3. Most probably your trainer will also be your supervisor or manager. He/she is there to
support you and show you the correct way to do things.

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4. Your trainer will tell you about the important things you need to consider when you are
completing activities and it is important that you listen and take notes.

5. You will be given plenty of opportunity to ask questions and practice on the job. Make
sure you practice your new skills during regular work shifts. This way you will improve
both your speed and memory and also your confidence.

6. Talk to more experience workmates and ask for their guidance.

7. Use the self-check questions at the end of each section to test your own progress.

8. When you are ready, ask your trainer to watch you perform the activities outlined in this
module.

9. As you work through the activities, ask for written feedback on your progress. Your
trainer keeps feedback/ pre-assessment reports for this reason. When you have
successfully completed each element, ask your trainer to mark on the reports that you
are ready for assessment.

10. When you have completed this module (or several modules), and feel confident that you
have had sufficient practice, your trainer will arrange an appointment with registered
assessor to assess you. The results of your assessment will be recorded in your
competency Achievement Record.

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QUALIFICATION : AQUACULTURE NC II
UNIT OF COMPETENCY
MODULE : Construct Aquaculture Facilities

: Reviewing, Designing and Interpreting Blueprint for
Cages and Pens

INTRODUCTION:

This module is focused on the functional requirements and needed facilities to place the farm in
effective operational condition. It is concerned with the general provision of the necessary size
and number of pens and cages suited to the available area.

This module covers the process of determining the appropriate cages and pen sizes and the
number to be constructed given the available area of body of water. It also deals with the proper
selection of the required construction materials suitable to the features of the area and the to
the target organisms. Other issues are more essential to farm operations such as the type of
nets and the size of the net mesh to be used for fingerlings. Lastly, it is also concerned with the
identification of other farm facilities supportive of the pen and cage culture.

LEARNING OUTCOMES:

At the end of this module you will be able to:

1. Determine pen and cages size, number to be constructed as to availability of the given
area.

2. Selecting framing materials, type of nets to be used as to the availability and suitability of
the area and species cultured.

3. Identify net mesh size base on the available size of fingerlings
4. Determine materials based on site selected
5. Identify other farm facilities necessary to the culture module

ASSESSMENT CRITERIA:

1. Pen and cages size are determined
2. Number of pen and cages to be constructed are identified as to the available area
3. Quality framing materials are selected
4. Guide in choosing type of nets are explained
5. Materials selected are suitable to the area and the species cultured
6. Criteria in choosing appropriate size of nets are explained
7. Net mesh which suits to the species of fingerlings being cultured are identified.
8. Materials are identified based on the site selected
9. Other farm facilities are properly identified and laid out

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QUALIFICATION : AQUACULTURE NC II
UNIT OF COMPETENCY
MODULE : Construct Aquaculture Facilities

LEARNING OUTCOME #1 : Mobilizing Resources and Carry-out Installation of
Facilities of Pens and Cages

: Determine pen and cages size, number to be
constructed as to availability of the given area

ASSESSMENT CRITERIA:

1. Pen and cages size are determined
2. Number of pen and cages to be constructed are identified as to the available area

RESOURCES:

Equipment and Facilities Tools and Instrument Supplies and Materials
1. record book
none none 2. pen
3. tracing paper
4. pencil

REFERENCES:

Cagauan, A. G. and Z. P. Bartolome, 2004.Fisheries Information Material:Tilapia cage
culture.College of Fisheries and Freshwater Aquaculture Center,Central Luzon State
University. Science City of Muñoz, Nueva Ecija 3120

SEAFDEC, 2001

Pen culture (enclosure culture) as an aquaculture system3.htm

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5.

Learning Outcome #1: Determine pen and cages size, number to be constructed as to
availability of the given area

LEARNING ACTIVITIES SPECIAL INSTRUCTIONS

1. Read the following information sheets: ƒ Information sheet #1-1: “Fish pen and

ƒ Information sheet #1-1: “Fish pen and cages”
cages” ƒ Information sheet # 1-2: “Cage

ƒ Information sheet # 1-2: “Cage structure structure and design”
and design” ƒ Information sheet # 1-3: “Pen

ƒ Information sheet # 1-3: “Pen structure structure and design”
and design”
Information sheet # 1-4: “Finding proper Information sheet # 1-4: “Finding
location”
proper location”

2. Do Activity sheet # 1-1 • Activity sheet # 1-1: “Making plan in
constructing pens and cages”
3. Do Self-Check
4. Check your answer • Self-Check # 1-1

• Answer Key # 1-1

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INFORMATION SHEET #1-1

FISH PEN AND CAGES

Size and shape of fish pen and cages

Both fish pens and cages are built around the same basic design concept: a net enclosure
supported by a rigid framework. They differ, however, in a number of respects. Firstly, a pen
does not have a net bottom; the edges of its net wallings/fencings are anchored to the lake
bottom/substrate by means of bamboo pegs and the lake bottom is the pen bottom. In
comparison, a cage is like an inverted mosquito net with the cage bottom made of the same
netting material used for its four sides.

Secondly, fish pens theoretically have no limit to their size/area while cages cannot exceed
1000m2 in area for reasons of the quantity of material required for cage construction (due to the
need for a flooring) and manageability of operation.

Thirdly, design of the structures and methods of construction are different. Fish pens are fixed
structures; fish cages may either be fixed or floating. Fish pens for milkfish culture in Laguna de
Bay consist of a nursery pen within the grow-out pen/enclosure. Cages are individual units for
either seed production or grow-out; they are , however, usually installed in cluster or modules
with a common framework.

Pens and cages come in various shapes and sizes and are made of different types of materials.
Most pens and cages are rectangular or square although some may be circular.

The size of existing pens varies from less than one ha to 100 ha. The present trends have
shown however an increase in pen size up to 400 ha by large corporations.

Various shapes of fish pen exist and those found to be technically feasible are the square,
rectangular, and circular. The two latter shapes along with proper wind orientation during
construction deflect added load caused by drifting water hyacinths and other flotsams and
increased height of waves during stormy weather.

Difference between pen and cage

Different terms have been used for fish culture in an artificially enclosed area of a natural water
body. The term 'Enclosure' is the general term applied to a culturing unit in such types of
culture.

'Cage' refers to the type of culturing units consisting of a framed net open at the top and floating
on the surface, or when completely enclosed, the cage is kept below the water surface by
adjustable buoyancy or suspending from the surface. Meanwhile 'Pen' refers to that type of
culturing unit where one part of the natural water body is enclosed by a fence-like wall resting
on the bottom.

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Fish cage culture

Fish cage culture is an aquaculture method of confining aquatic animals in small floating cages
in ponds that cannot be drained, reservoirs and lakes, and even sea (at coastal areas). It is
employed primarily in freshwater situations, but also found applications in coastal regions.

Fish pen culture

Fish pen culture is the rearing of fish in net enclosure with supporting framework. Fish pen
culture facility is usually built in shallow lakes with fertile water. This type of culture is commonly
employed for bangus and tilapia in Laguna de Bay.

Advantages and disadvantages of Cages and Pens Culture?

Advantages

1. Facilitates feeding and harvesting
2. Intensify fish production
3. Desirable market size is easily controlled
4. Easily built
5. Less cost on construction compared to fish pond
6. Water is reliable unlike in the pond

Disadvantages

1. Crowding can have negative impacts on water quality within the cages
2. Increase problems associated with diseases
3. Perennial threat of damage to infrastructure and escape of stock arising from frequent

typhoons
4. Large accumulation of water hyacinth between fish pens and along navigational

channels makes accessibility to fish pens difficult. This also makes continuous pressure
and abrasion on the net resulting to breakage or portion of the framework to collapse.
5. The intrusion of pollutants and organic sediments from lake’s tributaries as well as
phytoplankton die off contribute to depletion of dissolved oxygen resulting to fish kill.
6. Bamboos are short-lived
7. Poaching

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INFORMATION SHEET # 1-2

CAGE STRUCTURE AND DESIGN

Cage Size: Depends upon production goal and availability of capital. The sizes of fish
cages used in the country are:

Cage size Width Length (m) Depth (m)
Small (cm)
Medium/semi-commercial 1 1 – 1.5
Large/commercial 1 2–3 1.5 – 2
2 3–4 2–3
3 5 – 10 2–3
5
25 50 5
10 30 3

Types of Cage

A. Fixed (suitable for relatively shallow areas)

Common in Laguna de Bay, Lake Bato, Lake Buhi, Lake Buluan and Lake Mainit.

Structure

1. Basic framework consists of nylon or polyethylene netting sewn similarly to an
inverted mosquito net (“hapa”).

2. Bamboo poles stakes firmly 30 cm below the bottom substrate holds the net in
place.

3. Net flooring may or may no touch the substration while the upper rim is kept at
least 0.5 m above the water level.

4. Cover of cages may or may not be installed. A cover provides additional
protection from flooding or poaching.

5. Position covered cages underwater so as to minimize damage due to floating
objects during typhoon.

Design

1. Arranges cages in clusters or modules of 2-20 units per module.
2. In each module, the area of each cell is ½ - 1 m wider than the size of the net

cage. In the outside parameter, bamboos are spaced 1 m apart. Inside,
spacing between bamboos is 2 meters.

B. Floating Type (Suitable for depths exceeding 5 meters. It is type of cage used in
lakes of San Pablo City.

Structure

1. Cages are made of floating frames from which the net cages are suspended

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2. Lead sinkers are attached to the net flooring to stabilize the structure.
3. Framework is held is place by concrete structure with a nylon rope. A

freeboard of 1 m is left above the waterline.

Design

1. There are many variations in the design of floating cages using bamboo
rafts, oil drums or styrofoams as floats.

General Designs of Cages

1. Square or Rectangular

Arranged in clusters. Cages can be subdivided into smaller compartments.

Source: SEAFDEC, 2001

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2. Circular Cage
Arranged in cover clusters. The frame is resistant to water current and wind since
there are no corner connections. However, it can’t be subdivided into smaller
compartments.

Source: SEAFDEC, 2001

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INFORMATION SHEET # 1-3

PEN STRUCTURE AND DESIGN
Types of enclosures

Fig. 1-3. Types of enclosures

We have referred to the three types of pens earlier (Fig.1-2) -i.e. the completely enclosed pen
with net/rigid structures on all four sides in the middle of a bay/open water in lake without any
foreshore; a shore enclosure with a forshore extending to deepwater surrounded by a net
structure (c.f. osland enclosure) and a bay or lock/fiord enclosure with an embankment or net
barrier only at the entrance (of the bay).

While all the pens would come under the above 3 categories, we can deal with the design and
construction of pens, in a different classification, as indicated below:

1. Rigid pens
a. Embanked pens
b. Net enclosures

2. Flexible pens (netting)
3. Outer barrier nets.

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The embanked pens and net enclosures have already been referred to under ‘pen culture in
different parts of the world’, but here we shall describe the design (structural details) and
construction more particularly. Under ‘Net enclosures’ material selection, fouling and corrosion
will not be dealt with here, as these topics have been covered under ‘Cage Culture’. However,
structural details, and fouling and other effects will be referred to briefly as pertinent to the
points in question; some mention of these have already been made under ‘Site Selection’. The
“outer barrier nets” will not be discussed separately, but discussion on these is incorporated
under the section on “net enclosures”.
As a section under “Rigid enclosure - net enclosures”, the milk -fish pens (nets and bamboo
poles) are also discussed.
1. Rigid enclosures
1.1 Embanked Pens
Intertidal enclosures such as those at Adoike in the Inland Sea in Japan and Ardtoe in Britain
are examples of rigid enclosures which have stone-pitched or concrete walls as embankments
(Fig. 5).
Since such embankments are costly, such intertidal enclosures are not being built lately.

Fig. 5. Cross section of rockfill dam at Artdoe (from Milne, 1979)

Fig. 6. Piled net barrier at Hitsuiski Japan showing cross section - restraining anchor
blocks and weighted meshnet are shown (after Milne, 1979a)

All embankments have sluices to allow water circulation Embanked pens are constructed in the
sublittoral area also. In some cases there are to barriers, in which case often one, the shorter
wall, is usually an embankment and the other a piled barrier net, as described separately. A

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general view of the Ardtoe (Scotland) embankment, which we have described earlier and a
cross section of the Ardtoe Rockfill Dam, are given in Fig. 3 and 5 respectively. The rockfill dam
has a puddle clay core as impervious barrier, and has two sluices. The Adoike embankment
has an enclosure 27 ha in area and also has two sluice gates.

1.2 Net Enclosures

We have already referred to the several rigid net enclosures (including barrier nets) in our
review of pen culture in various parts of the world, especially those at Hitsuishi, Matsumigaru
and Ieshima in Japan and those at Flogoykgolpo and Bjordal and the Osland enclosures in
Norway. While the gross descriptions have been given earlier we shall now refer to certain
specific aspects of design and construction here. The piled net barrier at Matsumigaru fish farm
in Japan is anchored on the two Anchor blooks at the two ends on the banks of the narrow
mouth of the bay - the extended length of the barrier as provided by the shape of the barrier
ensures better circulation. A vinyl covered wire not (15mm square mesh) is stretched between
steel piles and smaller concrete blocks on two sides of the barrier restrain the net barrier. The
barrier also incorporated floating boom for passage of boats.

A cross section of the piled net barrier at Hitsuishi (Japan), showing restraining anchor blocks
and weighted mesh net and other details, is given in Fig. 6.

For the net enclosures of the yellow-tail fish farm at Megishima 3 piled - net barriers are built
more or less in concentric positions - overlapping one another. Perhaps this has advantages in
that there is saving in net materials when more area is brought within the enclosure. Different
culture operations where segregation is needed can also be attended to in this kind of
concentric pens (in contiguous enclosures also - but here the level of overlap will be less in that
the net barriers will be common at the contiguous limits only). In both these cases difficulties in
cleaning and maintenance and also water circulation could drop up. Elevation and sectional
views of the pen barrier nets of Megishima are shown in Fig. 7. Anchors placed on the outside
only for restraining the nets; note the 40cm diameter piles; the 35mm horizontal steel bars for
strengthening; the double wire mesh (galvanized), 25mm square inside and 50mm diamond
outside; and the rubble piled on the top of nets stretched on two sides on the floor, for
restraining the net, as well as for protection from predators. This enclosure is also provided with
as boat lock at one end of the enclosure near the shore for boats to pass and stay. For details
of the design of moored support framework for netting barrier in deep water in a Scottish lock
(with an inner fish net and outer predator net suspended from the scaffolding framework) and
that of the 12 - M square fish enclosures at Faery Isles (Scotland) reference is made to the
description in M.Ire (1971a). The latter has a fish netting of 12mm galvanized mesh inside and
predator and trash net of 75mm mesh outside. There is also an access catwalk and another
catwalk surrounding the enclosures. The catwalk is one metre wide and facilitates access for
routine inspection, feeding, cleaning etc. The elevation of the catwalk has to be higher than the
high water mark. In this specific case the catwalk is 1.2m higher than the high water ordinary
spring tide (HWOST) and a hand rail one metre above the catwalk floor. Over 73 net enclosures
(rigid) were constructed in the Inland Sea in Japan, covering vast areas and providing a major
problem of cleaning by divers at regular intervals. Some of the Japanese net enclosures were
abandoned due to poor circulation of water (poor siting and also due to low tidal range - of less
than 1 metre). Also often the standard fishing nets used fouled easily and circulation was
restricted and nets damaged by water currents combined with wind and wave action.

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Fig. 7. Elevation and section view of net enclosure at yellow-tail fish farm at Megishima,
Japan, showing net fixing arrangements (after Milne, 1979a)

Successful enclosures have been sited only after detailed hydrographic studies especially to
ensure sufficient water exchange. Success also depends on the design and selection of net ting
structure (see selection of netting materials under ‘Cage Culture’). A successful net enclosure is
the one built in 1968 at Sakaide (Takamatsu) in Japan. The enclosure is of 8 ha. and uses
galvanized chain link mesh for the main fish netting to reduce marine fouling and subsequent
maintenance and cleaning (1973) harvest here was 1000,000 yellow tail weighing 300g each)
(Milne, 1979b).

In Scotland galvanized wildmesh and galvanized scaffolding were chosen as the most suitable
materials for the construction of 12M square fish enclosures at Faery Isles, Loch Sweed in
Argyll. In loch Sween there is a tidal range of 1.5m only and therefore, was suitable (Low tide
range) for access catwalk. The netting materials chosen was so good that an inspection by
divers after 5 years showed that the original galvanized mesh netting was still in good condition
(Milne, 1979b). Galvanized scaffolding and weldmesh are acceptable because of the ease of
erection and subsequent lesser maintenance.

1.2.1 .Square corner and round corner in rigid pens

In Faery Isles the corners of the enclosures were curved to a 1.5m radius, assuming that
square corners were not useful in a fish using a sliding screen. Subsequently in the enclosures
built in ardtoe in 1972, (7 × 3m enclosures) square corners were adopted.

1.2.2. Predator control (see also “requirements of pen” earlier)

When fish are stocked at high density predators such as sea birds and others are attracted. To
avoid this surface covers of galvanized weldmesh were provided at catwalk level. The surface
covers were of 2" (51mm) spacing net and were light and were hinged at the centre of the
enclosure enabling easy ascess.

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We have already referred to the sublittoral enclosures in Norway (Flogyjolpo and Volkjolpo) for
Atlantic salmion farming.
A sublittoral rigid enclosure is the one built in Loch Moidart in 1974. Here there is a tidal range
of 5m and therefore any structure rising above the tides will have to be very high. To reduce this
problem a 40 M3 pen with a top cover with its upper surface just above the low water neap tide
level, ensuring access to the enclosure at the low tide level, was constructed. This is example of
an enclosure (pen) with a top cover which can be submerged and by definition a pen with the
natural floor as the bottom.

1.3. Osland Enclosure

We have already referred to the Osland enclosure (Fig 8A, B & C) of Norway usually installed
near a sloping shore. About 25m from the shore line the depth is to be about 10m. Concrete or
timber dock piles are driven with the sea bed, forming a horse shoe from of about 25 × 35m. A
concrete wall is built on the shore to moor the nets. The piles are higher than spring water level.
Two nets are stretched, one inside net would hold the fish, the lower fold would work as an
effective fish seal and the outside one would keep off drift wood etc., and predators. The nets
are re-inforced by a head line, midline and a lead line. There is a provision for attaching a
hauling rope (see Fig. 8C) to the midline so the nets can be pulled up for inspection. The
hauling rope move through a hole in the cross bar and a cremp fixed near the bottom of the pile.
Other details are given in the figure, (see Fig. 8B, C).

1.4. Milk fish pen - bamboo poles and net

1.4.1 Design and construction

In designing the fish pen structure, effects of three forces, namely, wind, waves and drifting
water hyacinth (Eicchornia) have to be considered. The wind force acting on the fish pen can be
calculated from the wind pressure and the surface areas on which the wind acts.

Fig. 8a. Osland enclosure - plan view

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Fig. 8b. Elevation view of netting fixed on piles.

Fig. 8c. Attachment of net in the Osland enclosure (after Milne, 1979a)

Compared to the wave action, which is based on the wind, on the pond dykes (levees) the wave

action on fish pen structures on the lake pens in said to be the minimal. However, the waves

cause a “sail affect” on the pen structures causing the nets to drag away from the pen. Major

damage can be done by drifting water hyacienth mass (1–5 hectares spread on occasions). A
single water hyacient plant can weigh 10kg and occupy an area of 0.10M2. A hectare of water

hyacienth formed by the wind can hit the fish pen in a force equivalent to 15 tons.

1.4.2 Catfish pens in Cote d'Ivoire

The catfish, Chrysichthys nigrodigitatus and C. walkeri were tested in pens in Cote d'Ivoire by
Hem (1979), who found that in properly designed pens, using locally available materials
(enclosures made with wooden poles and nylon netting) the catfish can be successfully
cultured.

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2. Flexible Enclosures

Most of the buoyed fish net enclosures known are bag nets with a bottom net - as per our
definition this enclosure is a ‘cage’ (and not a pen/enclosure) even if the bottom net may rest on
the floor. Such enclosures are limited in their size - the largest being of 55m diameter in Japan.
A generalized plan of a milkfish pen, showed rearing, nursery area and an attached ware house
in Philippine is shown in Fig. 9. Figure 10 shows the details of a split-bamboo fencing for a
traditional milkfish pen. Different types of framing arrangements, showing bamboo poles as
piles and netting used are shown in Figures 11A and 11B. Poles have been supported either
with a simple bracing (Fig. 11A) or with double bracing (Fig. 11B). Figure 11B also shows a
double enclosure. Design of a fish pen wall defined by the Laguna Bay Development Authority,
Philippines is given in Fig. 12. Details of a pen enclosure net in use in (Philippines, described by
Alferez (1982), are given in Fig. 13. See Guerrero and Soesanto, 1982 for more details. When
the Philippine pen-culture fishery was affected greatly by typhoons, alternate designs were
considered. Since the Japanese or Faery isles piled net barrier type could not be adapted, “due
to extreme lengths of piling required to withstand typhoon conditions” in soft silt in Laguna de
Bay for considerable areas a floating net enclosure for a 10 ha area was designed (Fig. 14)
(Miline, 1974; Delmendo and Godney, 1976).

In fabricating the flexible enclosure care was taken to make use of locally available simple
materials (cf. Bamboo mat replacement), eventhough Japanese 9.5mm (3/8") nylon net, which
has antifouling properties and long life as opposed to the one-year life Philippine nylon net, was
used. Concrete block sinkers weighing 500kg were spaced 30m apart and were placed from a
boat and a chain link raiser chain was provided from the sinker for attachment to the net to
allow settlement in the soft sediment. The average depth of Laguna de Bay varied from 3 to 5m
and therefore a 7.5m height of net was chosen to allow billowing due to water current and wave
motion. In the case of the bamboo pen the fencing stretched above water surface to prevent
fish from jumping, but in the present net, a 2.5m horizontal flap was provided on top with float,
which effectively prevented fish jumps and also helped as a fish seal when water level rose
unprecedented, for the top floats help adjust the stretching of the net into a vertical wall.

A lattice work of nylon ropes, at 10m × 2.5, crosses, from the top net down to the sinkers was
provided to spread the load of the forec ‘due to water movement and wave action’. In the
construction the only Underwater work involved is the attachment of the chainlink risers to the
chain link foot rope-all the others, the lattice work of nylon ropes, nylon netting and chain link
foot ropes can be assembled on the shore and connected to previously placed buoys and
sinkers, as explained by Milne (1979).

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Fig. 9. A milkfish pen, showing nursery, rearing area and warehouse.

Fig. 10. Split bamboo fencing for milkfish pen.

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Fig. 11a. Framing arrangement in traditional milkfish pen - Poles with single bracing.

Fig. 11b. Framing arrangement in milkfish pens - double bracing, edge view (left) and double
enclosures (right)

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Fig. 12. Design of a fish pen will as defined by LLDA (from Alferez, 1982)

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Fig. 13. Details of pen enclosure net (from Alferez)

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Fig. 14. Floating fish net barrier for milkfish farming (from Milne, 1979)

The advantages are:

1. There is no need for allowances for wind forces on the exposed section of netting and
structures, especially useful in typhoon-affected areas.

2. Ease of access of boats, since no boat locks are required and smooth bottom boats may
slide over the net barrier and the engine propeller can be lifted clear or shielded (see
also boat lock described earlier).

Milne (1979b) who designed this flexible enclosure is of the view that this can be fixed
anywhere near the shore line, simplifying design and construction.

SOURCE: PEN CULTURE (ENCLOSURE CULTURE) AS AN AQUACULTURE SYSTEM3.htm

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INFORMATION SHEET # 1-4

FINDING PROPER LOCATION
Locating fish pens
You can build a pen in the shallow water of a stream, a river, a lake or a reservoir.

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The water in a pen should be no more than 1.5 metres in the deepest part. You must also be
sure that the water in a pen
will never be less than 1
metre even during the dry
season. A pen should be put
in a place where the flow of
water is gentle, not fast. It
should be protected from
wind so that the surface of
the water will be calm, not
rough. Choose a place in the
stream or lake where the
bottom is firm. It is not easy
to build a pen if the bottom is
too soft, and where the
water may become muddy
when you have to work in
the pen.

Try to find a place where you can build a
pen using very few materials, such as the
corner of a reservoir or an angle in a
stream.

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How large should your pen be?

A pen can be small or large depending on how many fish you want to raise. However, when you
first begin, start by building a small pen. You will need fewer materials, and it will be easier to
take care of. A good size pen to begin with is 10 by 10 metres This is 100 square metres Later,
when you have learned more, you can build bigger ones.

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ACTIVITY SHEET

MAKING PLAN IN CONSTRUCTING PENS AND CAGES

Materials: pencil, tracing paper, notebook, bond paper, calculator, ruler

Instructions:

1. Using the knowledge gain from the information sheets above, make a plan in
constructing pen and cages in an area of 2 ha. Include the following details in making
this plan:
ƒ Size of pen and cages
ƒ Number of pen and cages to be constructed
ƒ Lay-out of the plan, with proper labels
ƒ List and estimate of construction resources to be used, that is equipment, materials,
supplies and manpower resources.

Note: Use the Sample lay-out included in this package as your pattern

2. Submit your output to the facilitator. Be ready to discuss this.

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SELF- CHECK #1–1

A. Fill in the blanks

1. Secondly, fish pens theoretically have no limit to their size/area while cages cannot
exceed ___________in area for reasons of the quantity of material required for cage
construction (due to the need for a flooring) and manageability of operation.

2. Pens and cages come in various shapes and sizes and are made of different types of
materials. Most pens and cages are ________________ although some may be circular.

3. The size of existing pens varies from less than one ha to 100 ha. The present trends
have shown however an increase in pen size up to _______ ha by large corporations.

4. You can build a pen in the ______ water of a stream, a river, a lake or a reservoir.

5. You must also be sure that the water in a pen will never be less than ________ even
during the dry season.

B. Fill what is missing in the table Width Length (m) Depth (m)
Cage size (cm)
? 1 – 1.5
? 1 1.5 – 2
Medium/semi-commercial 2 3–4
Large/commercial 3 5 – 10 ?
5
? 50 5
30 3

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ANSWER KEY # 1-1

A. Fill in the blanks

6. Secondly, fish pens theoretically have no limit to their size/area while cages cannot
exceed 1000m2 in area for reasons of the quantity of material required for cage
construction (due to the need for a flooring) and manageability of operation.

7. Pens and cages come in various shapes and sizes and are made of different types of
materials. Most pens and cages are rectangular or square although some may be
circular.

8. The size of existing pens varies from less than one ha to 100 ha. The present trends
have shown however an increase in pen size up to 400 ha by large corporations.

9. You can build a pen in the shallow water of a stream, a river, a lake or a reservoir.

10. You must also be sure that the water in a pen will never be less than 1 metre even during
the dry season.

B. Fill what is missing in the table Width Length (m) Depth (m)
Cage size (cm)
1 1 – 1.5
Small 1 2–3 1.5 – 2
Medium/semi-commercial 2 3–4 2–3
Large/commercial 3 5 – 10 2–3
5
25 50 5
10 30 3

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QUALIFICATION : AQUACULTURE NC II
UNIT OF COMPETENCY
MODULE : Construct Aquaculture Facilities

LEARNING OUTCOME #2 : Reviewing, Designing and Interpreting Blueprint for
Cages and Pens

: Selecting framing materials, type of nets to be used as
to the availability and suitability of the area and species
cultured

ASSESSMENT CRITERIA:

1. Quality framing materials are selected
2. Guide in choosing type of nets are explained
3. Materials selected are suitable to the area and the species cultured

RESOURCES:

Equipment and Facilities Tools and Instruments Supplies and Materials
1. net mesh sizes
2. framing materials

REFERENCES:

Cagauan, A. G. and Z. P. Bartolome, 2004.Fisheries Information Material:Tilapia cage
culture.College of Fisheries and Freshwater Aquaculture Center,Central Luzon State
University. Science City of Muñoz, Nueva Ecija 3120

SEAFDEC, 2001

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Learning Outcome #2 : Selecting framing materials, type of nets to be used as to the
availability and suitability of the area and species cultured

LEARNING ACTIVITIES SPECIAL INSTRUCTIONS

1. Read the following information sheets:

ƒ Information sheet #2-1: “Floating • Information sheet #2-1: “Floating cages –
cages – design and construction design and construction

ƒ Information sheet #2-2: “Materials • Information sheet #2-2: “Materials used
used in constructing pens and in constructing pens and cages
cages

2. Perform Activity sheet # 2-1 • Activity sheet # 2-1: “Making list of
framing materials”
3. Do Self-Check
• Self- Check # 2-1

4. Check your answer • Answer key # 2-1

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INFORMATION SHEET #2-1

FLOATING CAGES – DESIGN AND CONSTRUCTION

Design of Floating Cage

The size and materials used for cage construction can vary greatly depending on locally
available long lasting materials and the ability of the former to manage the project.
Sometimes it is depended on the site and various shapes such as round, square and
hexagonal have been designed. In Malaysia square cages are usually constructed.

A unit of a floating consists of:

• Raft and floats
• Proper net cages
• Anchor

1.1 Raft Structure (Platform)

The raft structure or platform refers to the portion that floats above the water. The
structure from where the nets are suspended from depends on the shape of the nets.

In general, a raft is 3m x 3m for its internal dimension. The depth of the cage may
range from 1.5m to 5m but is usually about 3m. This depends on the depth of the site
and a minimum of 1m is allowed from he cage bottom to the sea bottom when
measured at low tide.

The platform maybe made of various materials e.g. bamboo, planks/wood or
galvanized pipes. Where bamboo is abundant, this is used, as it is cost effective but it
only last for about 1-2 years.

Wood is better and last longer. Hardwoods are normally used as they can withstand
heavy weights as well as are not easily broken by wave action. Each cage made of
hardwoods can last about 4-5 years.

Other than the main beams or structure described above, the platforms also requires:

• Planks for the platform
• Planks for holding the floats in place

The platform or catwalk is where the farmer moves around to carry out his daily
activities. The planks are usually 2.5cm thick and 20cm broad x 700cm in length.
Alternatively 2 pieces of 2.5cm x 5cm x 700cm may be used.

Side planks for holding floats in place are not absolutely necessary but helps in
stabilizing the floats and preventing more rapid deterioration. Side planks are usually
2.5cm x 20cm x 700cm.

In summary, the construction of a unit of 4 cages each measuring 3m x 3m would

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require the following materials as shown in below.

Material/Structure Measurement Total
1. main structure Wood 5cm x 7.5cm x 12 pcs
(skeletons) 700cm
2. platform Plank 2.5cm x 20cm x 12 pcs
700cm
3. side plank Plank 2cm x 20cm x 12 pcs
700cm
4. nails 6.25cm 1.8 kg
5cm 1.8 kg
5. stainless steel 1.25 x 11.25cm 36 pcs
6. bolt and nut 1.25 x 15cm 36 pcs

1.2 Floats

Floats are used to ensure the raft is constantly above water. Several different types
of floats may be used such as oil drums, plastic or fiberglass barrels, Styrofoam and
bamboo. The choice depends on availability and costs. The number of floats required
depends on the size of the cage, materials used and type of float used. The following
gives the number of floats required for a 7m x 7m unit of 4 cages.

Type of Float Number Required
Steel or plastic drum (44 gallons) 9
5 gallon plastic can 50 – 60
Plastic drums (approx. 30 gallons) 24
Styrofoam (30 x 60 x 60 cm) 18

In Pulau Ketam area, plastic drums are used while in Terengganu, Styrofoam is used.
The floats are securely tied length wise to the bottom of the platform and equally
spaced out to ensure equal floatation effect.

1.3 Anchor

In order to ensure the raft does not float away an anchor is required. Several methods
of anchoring may be used. The most common being made of iron and attached at
each corner of the raft. A standard unit of 4 cages would require 4 anchors each of
10–30 kg in weight. The rope needed should be 18 mm with a length of 3-5 times the
depth at high tide.

An Alternative anchor could be made of cement with a securing iron embedded it. An
ideal size would be half a 44-gallon drum . In Penang, farmers use a piece of
hardwood about 3m in length with a hole at the top for rope attachment. This is sunk
in the bottom and serves as the anchor.

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1.4 Net Cage

The size of the net cage varies withthe size of the raft structure and depth of the site.
A normal sized cage would be 3m x 3m with a depth of 3m. It is usually 5 sided i.e. 4
vertical sides and 1 bottom. The materials for cage construction can vary greatly e.g.,
galvanize wire mesh, synthetic plastic but are usually normal net material made of
various synthetic materials. These may be nylon, polyester or polyethylene amongst
others. Of these polyethylene is recommended because it is long lasting, easily
available and cheap compared to others.

A comparison of qualities is given in the table below:

Type Breaking Durability Erosion Cost
strength resistance
P.E. (polyethylene) High Average High Cheap
P.A. (polyamide) Very high Average Highest Very
expensive
PES (polester) High High High Very
expensive
PP (polypropyline) Very high Below Average Expensive
Average High
PVC Low High High Expensive
(polyvinychloride) Low High
PVD Average High Expensive
(polyvinylidene)
PVA High Expensive
(polyvinylacohol)

Types of Nets for Cage Fabrication

1. B-Net (1/4” mesh)
2. DD-Net (3/8” mesh)
3. CC-Net (1/2” mesh)

Net cages are constructed for 2 purposes:

1. Nursery

Nursery net cages have a small mesh size of 8 mm for fingerlings of 10-mesh
size are required. This nursery cage called ‘hapa’. Fish of 10-25 cm size have
‘hapas’ of 25mm mesh. The hapa is normally smaller than the grow-out cage.
There are no specific sizes and a farmer may choose size if it suits his style of
management. In Singapore “hapas” of 2m x 2m x 2m are common while in
Malaysia they are smaller at 2.5m x 1.2m x 1.2m. Nylon can be used as hapa
material. Care must be taken to ensure the net is properly cut.

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2. Grow-out / Production Net

The grow out or production net is used to raise the fish to marketable size. The
mesh size ranges from 25-50 mm and it increase correspondingly with the size
of the fish.

The production net must fit the internal cage structure. In Malaysia, especially on
the East Coast, the nets are 3m x 3m x 3m. While groupers in Penang are
reared in cages 1.8m x 2.1m x 1.4m and farmers at Pulau Ketam, Selangor
used 2.5m x 2.5m x 2.5m net-cages. In Singapore it is 5m x 5m x 3m. The nets
are made of material of 15-48 ply or more. Below is the recommended cage
specification for various fish sizes.

Fish Size Mesh Size Ply
< 10 cm 8 mm 4
10-20 cm 25 mm 18-24
25-32 cm 37.5 mm 27-30
>32 cm 62.5 mm > 48

2. Construction

2.1 Raft Construction

The main wooden frame for the raft is put into appropriate sizes. They are then
arranged and fastened together using bolts and nuts. If the main frame is made of
bamboo, then they are tied with galvanized wire to form a platform. The distance
between parallel main frame beams is dependent on the type of float used. The float
must fit between and under the beams.

Once the main frame is ready, it is slowly put into the water so that the floats can be
properly attached, starting with the part in water until all are attached. The floats are
secured by tying with rope. Where Styrofoam or certain type of plastic drums are
used, side planks are used to further help keep the floats in place. Once, this is done,
the planks to form the catwalk are nailed on.

2.2 Net Cage Construction

Net-ages are normally made of polyethylene net. If we wish to construct a 3m x 3m x
3m net with mesh size 2.5cm, a 15m long and 150 mesh wide double piece net is
required. Two net cages can be constructed. The net is cut into 2 parts with each part
performing an L shape. (Refer Fig. 6) the length is divided in 4 parts (A, B, C, and D)
which will form the walls of the cage while section E forms the bottom. This is a
convenient way of cutting as it limits the amount of joining required. When a larger
mesh net is used, the mesh number is less. The method of cutting into an L shape
cannot be employed but the cage sided can still be cut as a single piece.

Then, the net is joined to form a box with open ends. Piece E is sewn on one end to
form the bottom of the cage. The open end is threaded with an 18mmm rope (see fig.
7) to support the net and attach to the cage frame.

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In order to ensure the cage is always kept in shape, a weight is tied at each corner of
the net. It is normally made of cement or a brick is used. This is sufficient in areas of
slow current flow. Where the current is strong, a square shaped weight is paced at
the bottom. It is made of 4 pieces of G.I. pipe of 2.5-cm diameter or PVC pipes filled
with cement. It is appropriately joined to form the square to fit the inner bottom of the
net e.g. a 3m x 3m cage would require a 2.8m x 2.8m weight (refer Fig. 8)

It is a normal practice to have a net cover for each cage made to the size of the cage.
This is to prevent loss by jumping out and to avoid enemies such as birds.

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INFORMATION SHEET #2-2

MATERIALS USED IN CONSTRUCTING PENS AND CAGES

FRAMES for the net cages are suspended or fixed, the sides of which become
walkways for working, feeding and monitoring.

The frames should be able to withstand water current; withstand high salt
content if at sea; and resistant to fouling organisms.

The materials that can be used for frame are as follows:

Source: SEAFDEC, 2001

FLOATERS are installed to keep the frame stable above the water surface.
Commonly used materials for floaters are:

Source: SEAFDEC, 2001

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Source: SEAFDEC, 2001

MOORING keeps the whole cage in a certain location and prevents towing of the
cages by the water current. Mooring materials are made of steel with
shapes as follows:

Source: SEAFDEC, 2001

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ACTIVITY SHEET # 2-1

MAKING LIST OF FRAMING MATERIALS

INSTRUCTIONS:

Based on the plan you made in activity # 1-1, list and choose the framing materials, type of nets
and other materials to be used in constructing the frame.

Use the table below as your listing guide.

Quantity Materials Specification Remarks

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SELF-CHECK#2-1

1. What are the type of net and mesh sizes being used in making a cage?
2. Name material that are being used for framing cages and pens.
3. What are the materials which are commonly used as floaters?
4. What is the size of a normal cage?
5. What is being used to ensure the raft does not float away?
6. What is the function of production net?

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ANSWER KEY # 2-1

1. What are the types of net and mesh sizes used in making cages ?

a. B-net (1/4” mesh)
b. DD-net (3/8” mesh)
c. CC-net (1/2” mesh)

2. Name the materials that are used for framing cages.
a. Bamboo
b. Wood
c. Galvanized iron (GI) pipes
d. Polyvinyl chloride (PVC) or Polyethylene pipes

3. What are the materials which are commonly used as floaters?
a. Barrel
b. Styrofoam
c. Plastic container

4. What is the size of a normal cage?
A normal sized cage would be 3m x 3m with a depth of 3m.

5. What is being used to ensure the raft does not float away?
In order to ensure the raft does not float away an anchor is required.

6. What is the function of production net?
The grow out or production net is used to raise the fish to marketable size.

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QUALIFICATION : AQUACULTURE NC II
UNIT OF COMPETENCY
MODULE : Construct Aquaculture Facilities

LEARNING OUTCOME #3 : Reviewing, Designing and Interpreting Blueprint for
Cages and Pens

: Identify net mesh size base on the available size of
fingerlings

ASSESSMENT CRITERIA:

1. Criteria in choosing appropriate size of nets are explained
2. Net mesh which suits to the species of fingerlings being cultured are identified.

RESOURCES:

Equipment and Facilities Tools and Instruments Supplies and Materials

None None 1. Mesh nets(different sizes)
2. Different species of

fingerlings

REFERENCES:

1. Gopalakrishnan, V. and A.G. Coche.1994. Handbook on small-scale freshwater fish
farming.FAO Training Series No. 24. ISSN 0259-2533 David Lubin Memorial Library
Cataloguing in Publication Data Food and Agriculture Organization of the United
Nations. Rome

2. Kumar, Dilip, Abu Tweb Abu Ahmed S.B. Nandi And Andras Peteri.1993. Fish Seed
Rearing Manual. Institutional Strengthening In The Fisheries Sector. Ministry Of
Fisheries & Livestock, Department Of Fisheries, Government Of Bangladesh. United
Nations Development Programme.Food And Agriculture Organization Of The United
Nations.

3. Müller, F. and L. Váradi. ---. Chapter 14: Freshwater Cage for Fish Fish Culture
Research Institute .Szarvas, Hungary .

4. TILAPIA CAGE CULTURE http://www.da.gov.ph/tips/tilapia/fishcage.html#design

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Learning Outcome #3: Identify net mesh size base on the available size of fingerlings

LEARNING ACTIVITIES SPECIAL INSTRUCTIONS

1. Read and study carefully the information • Information sheet # 3-1: “Choosing a net”
below: • Information sheet # 3-2: “Net fabrication”
• Information sheet # 3-3: “Nets for
• Information sheet # 3-1: “Choosing a
net” fingerlings”

• Information sheet # 3-2: “Net • Activity # 3-1: “Choosing the appropriate
fabrication” mesh net size”

• Information sheet # 3-3: “Nets for
fingerlings”

2. Perform activity # 3-1

3. Complete Self-check # 3-1 • Self-Check # 3-1
4. Refer to the answer key • Answer key # 3-1

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INFORMATION SHEET # 3-1

CHOOSING A NET

Netting

The netting has three major functions as follows: keeping the fish stock together; protecting the
stocks against harmful external influences; allowing free water exchange between the inside
and outside water.

The most commonly used netting material is flexible nylon since it is relatively inexpensive and
it can be treated with chemicals against anti-fouling (Figure 2-1). Rigid netting material (e.g.,
rigid plastic, galvanized or plastic coated steel) are also used in some cases

The mesh size should be as large as possible, taking into account the fish size. The larger the
mesh size the better the oxygen supply of the stocks and the fouling problems are less as well.
The fouling of the net should be avoided by regular cleaning or by replacing it. Heavy fouling
reduces the water exchange through the net wall and thus causes oxygen depletion inside the
cage; increases the net drag requiring large and more expensive mooring; increases labour
requirement in cleaning and replacing the net.

Net Cage

The size of the net cage varies with he size of the raft structure and depth of the site. A normal
sized cage would be 3m x 3m with a depth of 3m. It is usually 5 sided i.e. 4 vertical sides and 1
bottom. The materials for cage construction can vary greatly e.g., galvanize wire mesh,
synthetic plastic but are usually normal net material made of various synthetic materials. These
may be nylon, polyester or polyethylene amongst others. Of these polyethylene is
recommended because it is long lasting, easily available and cheap compared to others.

A comparison of qualities is given in the table below:

Type Breaking Durability Erosion Cost
strength resistance
P.E. (polyethylene) High Average High Cheap
P.A. (polyamide) Very high Average Highest Very
expensive
PES (polester) High High High Very
expensive
PP (polypropyline) Very high Below Average Expensive
Average
PVC Low High High Expensive
(polyvinychloride) Low
PVD Average High High Expensive
(polyvinylidene)
PVA High High Expensive
(polyvinylacohol)

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Net cages are constructed for 2 purposes:

1. Nursery

Nursery net cages have a small mesh size of 8 mm for fingerlings of 10-mesh size
are required. This nursery cage called ‘hapa’. Fish of 10-25 cm size have ‘hapas’ of
25mm mesh. The hapa is normally smaller than the grow-out cage. There are no
specific sizes and a farmer may choose size if it suits his style of management. In
Singapore “hapas” of 2m x 2m x 2m are common while in Malaysia they are smaller
at 2.5m x 1.2m x 1.2m. Nylon can be used as hapa material. Care must be taken to
ensure the net is properly cut.

2. Grow-out / Production Net

The grow out or production net is used to raise the fish to marketable size. The mesh
size ranges from 25-50 mm and it increase correspondingly with the size of the fish.

The production net must fit the internal cage structure. In Malaysia, especially on the
East Coast, the nets are 3m x 3m x 3m. While groupers in Penang are reared in
cages 1.8m x 2.1m x 1.4m and farmers at Pulau Ketam, Selangor used 2.5m x 2.5m
x 2.5m net-cages. In Singapore it is 5m x 5m x 3m. The nets are made of material of
15-48 ply or more. Below is the recommended cage specification for various fish
sizes.

Fish Size Mesh Size Ply
< 10 cm 8 mm 4
10-20 cm 25 mm 18-24
25-32 cm 37.5 mm 27-30
>32 cm 62.5 mm > 48

Design of a fish pen will as defined by LLDA (from Alferez, 1982)

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Fig. 13. Details of pen enclosure net (from Alferez)

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INFORMATION SHEET # 3-2

NET FABIRCATION

The design of fish cages is determined by the behavior of the culture species. For Tilapia
nilotica, which is less active and sometimes territorial in habitat, the shape of the cage does not
affect its mobility. In this case, design rectangular cages for easy assemblage and
management. The arrangement of the cages is not a problem if there are only few of these.
However, 8 or more should be arranged depending upon the direction of the wind.

There are many kinds of nets that could be used for cage fabrication. The most common are the
B-net (1/4" mesh), DD-net (3/8" mesh) and CC-net (1/2# mesh). However, the most popular is
the B-net because smaller fingerlings do not need a nursery cage. It is cheaper per unit area
because it is wider (108 inches) than other nets, hence, labor cost in fabricating cages is much
lower, and tearing of one or two meshes do not easily provide an escape route for bigger fish.

Generally, floating net fish cages are made of nylon nettings supported on all sides and corners
with polyethelyne rope fixed by a nylon twine. Each is hung within a rectangular area, the top is
supported by bamboo braces and the bottom is provided with lead sinkers. The size of net
cages used in Magat Dam for commercial production of tilapia is 6 m deep, 6 m wide and 12 m
long. This size makes possible the full utilization of bamboo poles and nets. To do it, hang the
net cages in bamboo raft type frame which also serve as catwalk for workers allowing 1 m of
the net above the water level and fix the synthetic ropes to four corners of the poles to prevent
the fish from escaping by jumping out. The longest side of the cages is oriented perpendicular
to the direction of the wind.

Construct the net fish cages in the following manner:

• Cut the net according to desired specification
• Double-lace every mesh of the four corners using nylon twine 210 d/6, double-twine

beginning at the second mesh row using rolling hitch or clove hitch with a single hitch as
lock at intervals of 7.62 - 10.16 cm.
• Double-lace the nylon salvage net to the top edges of the cage with a nylon twine, using
either a rolling hitch or clove hitch with single hitch as lock. Start the second half from the
second mesh row.
• Rig all sinkers (No. 7) to the rib lines of the bottom side and centers. Attach the rib lines on
all sides using rolling or rib hitch with an interval of 7.62 - 10.16 cm.
• Make splices on the four corners of the hanging lines (top portion of net cage) for the
attachment of four stretching ropes with weight. Continue with the other units following the
same procedure.

Types of Nets for Cage Fabrication

1. B-Net (1/4” mesh)
2. DD-Net (3/8” mesh)
3. CC-Net (1/2” mesh)

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INFORMATION SHEET # 3-3

NETS FOR FINGERLINGS

Putting baby fish into your pen

If you are raising Tilapia nilotica you will need to put in two baby fish for each square metre of
pen. So, if you have built a small pen of 100 square metres you will need 200 baby fish. The
baby fish that you use should be at least 8 to 10 centimetres long or weigh about 15 to 20
grams each.

Note: If you need any help or want to raise a different kind of fish, your extension agent or
fishery officer will be able to give you good advice.

Just before you put the baby fish in your pen, be sure that the water they are in is not hotter or
colder than the water in the pen.

If the water the fish are in is hotter or colder, slowly add water from the pen to the water with the
fish until it reaches the same temperature.

Taking care of your fish pen

A pen can be easily damaged. If this happens your fish may get out. Check the pen fence every
day to be sure that there are no holes. At the same time, you should check that the fence is well
buried in the pen bottom.

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If you find any places where your fish can
get out, repair them right away. In
addition, you must be sure that the
openings in the fence are free of dirt and
plants so that fresh water can flow into the
pen. You can clean the fence of a pen
using a brush or a broom. However, do it
very gently so that you do not damage the
fence material.

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ACTIVITY # 3-1

CHOOSING THE APPROPRIATE MESH NET SIZE

Instructions:

Visit a lake or reservoir with fish pens and cages installed. Confer with the farm technician
regarding the species of fish being cultured in the pens and cages. Likewise, try to obtain
information on the sizes of the fingerlings of these species. Using these information, make a
tabulation of size of mesh nets appropriate per each species. Use the pattern below:

Species of fingerling Size of fingerlings Mesh net size

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