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Fish Nutrition ResearchFish Nutrition Research Differences and similarities with livestock nutrition and what the ft hld P tIIfuture holds. Part II.

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Published by , 2016-01-16 01:42:03

Fish Nutrition ResearchFish Nutrition Research

Fish Nutrition ResearchFish Nutrition Research Differences and similarities with livestock nutrition and what the ft hld P tIIfuture holds. Part II.

Fish Nutrition Research

Differences and similarities with
livestock nutrition and what the
future holds. Part II.

Ronald W. Hardy, Director

Aquaculture Research Institute

University of Idaho University

of Idaho

Current areas of emphasis in fish
nutrition research

• Replacing marine protein and oil
• Effects of nutrition on food quality and

fish health

• Developing micro-particulate feeds for
small larvae at first feeding

• How can these areas be investigated
using new genomic tools?

Replacing marine protein and oil

• Rapid growth of aquaculture over the past 15 years is

due to:

– Industry growth in developed species
–expanded production of new species
–Switch from extensive to intensive production of pond fish

through higher feed inputs in SE Asia and China

• Proportion of annual global production of fish meal and

fish oil used by aquaculture has tripled

• Production of fish meal and oil cannot increase except

in Alaska by increased recovery of processing waste

• Only way to meet expected demand for protein and oil in

aquafeeds is to find alternatives to fish meal and oil

World fish meal use in livestock and
fish feeds in 1994, 2000 & 2006

60 Poultry
50 Swine
40 Aquaculture
30 Other
20
10

0

1994 2000 2006

World fish feed production
1995, 2000, and 2010 (predicted)

30,000,000 1995
25,000,000 2000
20,000,000 2010
15,000,000
10,000,000 Catfish Marine Cyprinids

5,000,000
0

Salmonids Shrimp

Summary of demand

• Average annual production of fish meal will be

equal to demand in fish feed by:

– 2015 at current incorporation levels in fish feeds

– But, if global production of fish meal decreases due to El

Nino or wild stock collapses, demand may equal supply
as soon as 2010

• More likely scenario

– Global production is adequate until at least 2020

if percentage use in fish feeds decreases

– Fish meal will no longer be used as the main

protein source, but rather as a feed supplement

• Palatability of plant-based feeds
• Source of taurine, carnitine, and other compounds
• Essential amino acid balance in plant-based feeds

Can carnivorous fish be
converted to a vegetarian diet?

• Trout fed a fish meal-free diet grow about

7% slower and are 10% less efficient

• We cannot formulate a fish meal-free diet

without adding several limiting amino acids
or adding rendered animal products

• Basing veggie trout feeds on plant protein

concentrate increases fiber (phytate) in diet,
thereby contributing to pollution

Similarities to past situation in
poultry feeds

• In USA, poultry feeds are based on soybean meal

and corn

• In 1970s, however, poultry performance could not be

sustained without 3-5% fish meal in the formulation

• Research over decades showed that fish meal

contained various micronutrients, mainly ultra-trace
elements, that were essential to chickens

• When these were supplemented, fish meal could be

eliminated from poultry feeds

Poultry feed analogy is not perfect

• Ultra-trace mineral aspect may not

be relevant to aquatic animals

• More likely the growth factors in

fish meal are related to:
–Amino acid imbalances
–Palatability
–Bioactive compounds in fish meal and plant

proteins

Challenges in feed formulation-1

• Replacing fish meal with plant proteins

–Corn or wheat gluten, soybean meal, soy

protein concentrate, canola protein concentrate

• Emphasis is on maintaining digestible

protein and limiting amino acid levels

• Fish meal contains bioactive compounds

–Gonads, nucleotides, others

• Oilseed meals contain bioactive compounds

– phytoestrogens and other compounds

Challenges in feed formulation-2

• Replacing fish oil with plant oils

–Canola, soy, flaxseed and others

• Fatty acid profiles of fish reflect dietary fatty

acid intake

• Fish oil contains bioactive fatty acids

–Long-chain omega-3s

• Plant oils contain relatively high amounts of

linoleic acid (C18:2, n-6)

–Interferes with omega-3s
–Can lead to production of inflammatory factors

Nutritional pathologies caused by
changing feed formulations

• Fin erosion

• Skeletal deformities

– Phosphorus deficiency, but

complicated etiology with ascorbic
acid or other factor possibly
involved

• Enteritis in distal intestine

– soybean meal and salmonids

Effect of diet on fin erosion of
rainbow trout

Standard Experimental
fish-meal based feed krill meal based feed

Atlantic salmon with jaw deformity
(Screamer)

“Screamer” at harvest

Skeletal deformities in Atlantic salmon

Normal Atlantic
rainbow salmon
trout screamer

Phosphorus
deficient
rainbow
trout

Skeletal deformities

• Deformities in farmed Atlantic salmon

– Behind head (chicken head)
– Mid-dorsal area (humpy)
– Caudal area (stumpy)

• Fish look normal at seawater transfer, but develop spinal

deformities during grow-out and are downgraded at harvest

• Examination of fry and fingerlings prior to seawater transfer

shows abnormal vertebra

– Abnormalities not grossly apparent, but seen in X-ray imaging

• Cause is thought to be inadequate mineralization (low dietary P

with other factors involved) at juvenile stage, followed by injury
during seawater transfer and size-grading

Skeletal deformities in Atlantic salmon

Example of problems with plant
proteins: soybean meal and enteritis

• Morphological abnormalities of intestinal villi

• Appearance related to dietary soybean meal

level and duration of feeding

• Can be induced in Atlantic salmon and

rainbow trout, but not in Atlantic cod

• Causative factors unknown but not present in

soy protein concentrate

SBM-induced enteritis- Distal intestine histology

STOMACH PROXIMAL
SECTION

PYLORIC DISTAL
SECTION SECTION

Soybean meal-induced enteritis after 24 weeks

Control vs. 40% SBM diet

Control diet: No SBM. 40% SBM diet: Villi are
Photo showing normal villi swollen and those in the
of distal intestine (X 75) center fused. Note
numerous large apical
vacuoles(X 75)

Summary of results in our laboratory

• Trout growth performance

• higher on diets containing 20% soybean meal than 40%

soybean meal

• Expression of immune factors

• Tumor necrosis factor (TNF) expression elevated in fish fed

40% soybean meal

• No differences in IL-8 or CD-8 expression

• Soybean meal-induced enteritis

– No evidence in any treatment after 12 weeks growth trial
– No evidence in Control fish (0% SBM) after 24 weeks
– Very low incidence in 20% SBM after 24 weeks
– High incidence in 40% SBM after 24 weeks

Chapter 10: Nutritional Pathology

Note to Dr. Roberts:

Chapter will need to
be expanded to
address new
pathological
conditions caused
by feed imbalances

Marine fish larval feeds

• Four problems with microparticulate feeds

– Larval fish cannot swim to catch feed
– Larval fish often do not recognize feeds as food
– Very small feed particles are susceptible to nutrient

leaching

– Larval fish do not have fully developed digestive

systems, so special forms of protein are required

Early fish larvae

Copepod: live prey for larval fish

Marine fish larval feeds

• Larval fish cannot swim to catch feed
• Larval fish often do not recognize

feeds as food

• One solution: add little glass balls to
increase pellet buoyancy and reflect
certain wavelengths of light that the
fish can detect

Making microparticulate feeds float and visible to larvae
by imbedding very small glass balls in the feed

Halibut larvae with microparticulate
feed (containing glass balls) in gut

Marine fish larval feeds

• Very small feed particles are

susceptible to nutrient leaching

Regular feed Coated feed

Marine fish larval feeds

Larval fish do not have fully developed
digestive systems, so special forms of
protein are required

• Line of research: Look at gene expression

of digestive enzymes and transporter
proteins in gut of developing larvae

– Pep1: peptide transporter expressed early in marine

larvae

• Develop diets containing amino acids and

peptides rather than intact proteins

Omega-3 fatty acid levels in farmed
fish

Problem: How to maintain omega-3 fatty
acid levels in fillets when plant oils are
used in the feed??

• Line of research: Use diets that
contain fish oil at the end of the grow-
out period

• Genomic research: Look at expression
levels of fatty acid desaturase enzymes

Fillet eicosapentenoic acid (EPA) composition

mg EPA 100/g edible tissue 500

Canola to menhaden oil

400 Menhaden to canola oil

300

200 *

100

0

Initial 6 weeks
* Denotes significant differences within dietary groups over time (One factor

ANOVA, P<0.05).

Diet history: Previously fed oil source for 17 weeks then switched

Initial weight 807g. At the completion of the experiment fish had attained an
average weight of 1118 g fish-1 with an SGR of 0.905 and an FCR of 1.17.

Fillet n3/n6 fatty acid ratio

Ratio of n3/n6 fatty acids 4.0

* Canola to menhaden oil

Menhaden to canola oil

3.0

2.0

*

1.0

0.0 6 weeks
Initial

* Denotes significant differences within dietary groups over time (One factor
ANOVA, P<0.05).

D-6 fatty acid desaturase expression

d6FAD-MGB Expression 1.0E+09 Canola to menhaden oil *
8.0E+08 Menhaden to canola oil 6 weeks
6.0E+08
4.0E+08 *
2.0E+08
0.0E+00 Initial

Genomics in fish nutrition research

• Nutritional genomics (nutrigenomics)

involves measuring expression of genes that
respond to different dietary factors

– Digestion, nutrient transport, metabolism, nutrient

partitioning, protein synthesis, protein turnover, and
so on respond to nutritional inputs

– Studying expression of regulatory genes in various

pathways will provide insight into physiological
processes

• Nutrigenomics is relevant to growth, immune

function, reproduction, and just about
everything

Genomic tools

• Micro-arrays
– Zebrafish array (genome fully sequenced)
– GRASP chip for salmonids

• RT-PCR
• Proteomics

Problem with existing microarrays

Have to sort through up to 25,000 genes to connect the dots in
metabolic pathways of interest, plus not all genes of interest
exist on available arrays

Strategy to utilize genomics and
proteomics in fish nutrition

• Conduct feeding studies

• Measure physiological responses and correlate these

with changes in gene expression using existing micro-
arrays

• Identify genes of interest, e.g., key regulatory genes

• Create groupings (panels) of key regulatory genes in

specific pathways of interest

• Incorporate panels into mini-arrays that allow us to

design precise, targeted experiments to test specific
hypotheses

Mini-arrays solve the problem of
gene expression overload

• Mini-arrays measure gene expression in key

regulatory or rate-limiting enzymes that are up or
down regulated in specific metabolic pathways

• Additional panels being developed by others can be

added to expand to stress, effects of pollutants,
intestinal enzyme expression

• Mini-arrays will simplify nutritional studies in fish

compared to using global microarrays

Food restriction in zebrafish
(why we need mini-arrays)

Microarrays ALDOLASE FRUCTOSE-1,6-
BIPHOSPHATASE
(gluconeogenesis)

Genes Brain Liver PYRUVATE
5 KINASE

genes 1041

genes MALATE
DEHYDROGENASE
(glucogenesis)

In LiverSUCCINATE

DEHYDROGENASE

Persistent organic pollutants (POPs)

• PCBs, dioxin, etc. were present in fish oil and the residual oil in

fish meal

• Wild fish from Baltic and North Sea are known to have much

higher concentrations of POPs than products from the Pacific

• Industry now removes POPs by extracting residual oil from meal

with isohexane, then treating with activated carbon (same for oil)

• After treatment, meals and oils are below EU and EPA action

limits

• Farmed salmon have lower POP levels than wild salmon,

especially those from Washington State

• All salmon have lower POP levels than English muffins

Farmed fish and contaminants

Farming fish is really the only hope to produce
fish with reduced levels of POPs

– Dietary inputs can be managed
– High percentage of diet is plant protein in

contrast to diet of wild fish which cannot be
controlled


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