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Fish Nutrition Research Differences and similarities with livestock nutrition and what the future holds. Part I.
Ronald W. Hardy, DirectorAquaculture Research InstituteUniversity of Idaho University
of Idaho
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Topics to cover
• Differences between fish and livestock
• Brief history of fish nutrition
• Brief overview of evolution of fish feed manufacturing
• Today’s hot topics in fish nutrition
– Replacement of marine protein and oils
– Effects of nutrition on food quality and fish health
– Microparticulate feeds for small fish larvae at first feeding
• Opportunities presented by developments in molecular biology
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Fish Facts
• Fish evolved in a very diverse environment, and 20,000 species exploit every possible niche
• Currently, there are ~140 species fish being farmed
• First publication on fish farming was 2500 BC
• In 2005, 43% of all fish consumed globally was produced by farming
• Aquaculture production growing at 9-10% annually, fastest sector of animal production
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Differences among farmed fish species
• Marine, brackish and freshwater fish
– Differences in osmotic cost to maintain homeostasis
• Coldwater and warmwater fish
– O2 content in water, plus availability of natural food in ponds compared trout raceways or marine net-pens
– metabolic rate and temperature tolerances
– membrane fluidity that influences fatty acid requirements
• Fish and crustaceans (shrimp, crabs)
– Huge differences in mechanisms of locating feed
– Shrimp are external masticators, fish gulp feed
– Differences in digestive physiology
– Feeds must be water-stable for slow eaters like shrimp
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Fish vs. livestock and poultry
• Major differences associated with aquatic existence– Fish maintain neutral buoyancy and do not need skeletal
and muscular systems to oppose gravity
– Fish excrete ammonia
– Fish are cold-blooded
• Other differences– Fish exhibit indeterminate growth
– Huge differences in digestive system among farmed fish
• Fish are monogastric, but…
– Gastric stomached fish (carnivores like salmon/trout)
– Agastric (carp)
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Fish vs. livestock and poultry:differences associated with aquatic existence
• Fish exist in neutral gravity, no need for heavy skeleton– Dietary calcium and phosphorus needs are lower
– Energy expenditures for locomotion are lower
• Fish excrete ammonia via the gills– Lower metabolic cost than excreting urea or uric acid
– Higher caloric energy yield from metabolism of amino acids
• Fish are cold-blooded– Upside: no need to stay warm
– Downside: rates of metabolism, digestion, etc. decrease in cooler water, plus membrane fluidity must change
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Fish vs. livestock and poultry:differences in physiology
• Many fish exhibit indeterminate growth
–Growth continues after first maturation and spawning
–Hypertrophy and hyperplasia (make new muscle cells)
• Fish are monogastric (few herbivorous fish)
–Some fish have an acid stomach
–Other start with an acid stomach, then lose it as fingerlings
–Some are stomach-less (agastric)
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Fish vs. livestock and poultry:differences at start of exogenous feeding
• Some fish spawn large eggs
– Salmon & trout (2000-15,000 eggs/female)
– Incubation requires 50-100 days depending on water temperature
– First feeding fry are 200-400 mg and can be fed small, particulate feed
• Many fish spawn very small eggs
– Most marine species (> 1 million small eggs per female)
– Incubation requires 3-7 days
– First feeding fry are very small and must be fed live-feed through metamorphosis or until reach a decent size
– It is very challenging to provide adequate nutrition via live feed• Right live feed at the right time• Correct nutritional content of live prey ( need PUFA enrichment)
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Cod eggs
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Copper rockfish larvae at first feeding
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Canary rockfish larvae with feed in gutsix weeks after first feeding stage
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Fish vs. livestock and poultry:other nutritional differences
• Fish nutritional requirements
– Ascorbic acid
–Polyunsaturated fatty acids (PUFAs)
–Many minerals obtained via the water
• Carnivorous species have a limited ability to utilize or metabolize starch–They evolved using protein and lipid for metabolic
energy
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Efficiency of fish compared to livestock
• FCR values less than 1.0 for fish
• FCR values 1.6-1.8 for chickens
• FCR values 8-10 for cattle
• Yield of high-quality protein from salmonids is 55%
• Total yield from poultry or cattle is lower and quality varies with cut
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Brief history of fish nutrition
• Prior to 1950s: –empirical feed formulation research with a variety of ingredients
–Nutritional diseases quite prevalent
–Little solid information on nutritional requirements
• 1950s and 60s:
–“Golden age” due to development of semi-purified diet that allowed single nutrients to be deleted and added back (Halver’s PhD work)
–Vitamin and amino acid requirements of salmon and trout were discovered
–Common nutritional diseases eliminated
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Brief history of fish nutrition• 1970s :
–Essential nutrient list expanded to other species
–Refinement of nutrient requirement estimates using new approaches to assess nutritional adequacy
• 1980s and 90s: Aquaculture production takes off–Need for economical and efficient grow-out feeds
–New species including those with larval stages
–Low-pollution feeds (low-phosphorus, highly digestible)
• 2000 until now –Main story is alternative protein and lipid sources
–Sub-plot is supplements to enhance disease resistance, provide “semi-essential nutrients” and to produce healthful products (low in POPs, high in omega-3 fatty acids)
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Dietary nutrient requirements:Pioneering fish nutrition research
• Development of semi-purified diet (1953) that supported normal growth
• Establishment of quantitative dietary requirements of vitamins & amino acids (1960s)– USFWS Western Fish Nutrition Laboratory
• John Halver & colleagues
• Pacific salmon were focus, hatchery support
• all work was conducted with fry & fingerlings
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Vitamin requirements of salmon and growing chickens (IU or mg/kg dry diet)
Vitamin Salmon/trout Chickens
Vitamin A 2500 1500Vitamin D 2400 200Vitamin E 50 16Vitamin K unknown 0.5Thiamin 1 1.3 Riboflavin 7 3.6Pyridoxine 6 3.0 Pantothenic acid 20 10Niacin 10 11 Biotin 0.15 0.10Folic acid 2 0.25Vitamin B12 0.01 0.003Ascorbic acid 50 not requiredCholine 800 500myo-Inositol 300 not required
*values in yellow are lower for chickens
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Semi-purified diet for salmonids
Ingredient Percent in diet
Vitamin-free casein 40.0Gelatin 8.0Dextrin 10.0Wheat starch 10.0Carboxymethylcellulose 1.3Alpha-cellulose 6.0Mineral mixture 4.0Vitamin mixture 3.0Amino acid mixture 2.0Choline chloride (70% liquid) 0.3Herring oil 17.0
Proximate
category Percent
Moisture 28-30
Crude protein 34
Fat 17
Ash 5
Proximate
category Percent
Moisture 28-30
Crude protein 34
Fat 17
Ash 5
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Determining nutrient requirements in fish
• Feed semi-purified diet, adding back graded levels of single essential nutrient
• measure response variables
– growth, feed conversion ratio, survival (1950’s)
– tissue nutrient levels, assuming that they plateau at requirement level (1950’s through today)
– measure activity of enzymes that require essential nutrient as co-factor (same assumption, 1980’s)
– measure excretion of nutrient or metabolites (1990’s)
– Nutrigenomics (study of effects of nutrients on gene expression and single gene products in tissues)
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Qualitative dietaryarginine requirement(Halver)
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Relationship between thiamin intake and liver thiamin concentration
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Nutrient requirements of salmonids
• Protein Ten essential amino acids
• Lipids Omega-3 fatty acids (1% of diet)
• Energy Supplied mainly from lipids and protein
• Vitamins 15 essential vitamins
• Minerals 10 minerals shown to be essential
• Carotenoid Needed for viable eggspigments
• NOTE: Other minerals are probably essential but can be obtained from rearing water
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Criteria or method used to establish a dietary vitamin requirement affects value
• Response variable– absence of deficiency sign (minimum level)– tissue saturation or plasma level– enzyme activity
• Statistical evaluation– broken-line (Almquist plot)– curve-fitting and models
• fit curves but are they biologically relevant?• do we chose 95% or 100% response as requirement?
• Real-world environmental conditions – crowding, water quality, pathogen load etc.
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Ascorbic acid requirements of salmonids
Requirement* Comments
15-20 ppm Prevents deficiency signs
250-500 ppm Supports maximum woundhealing activity
1000-2500 ppm Supports maximum diseaseresistance in laboratorychallenges
>2500 ppm Maximum tissue storage levelsand max. immune response
* When included in purified diet, with ideal conditions and no oxidation of vitamin C
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Mineral requirements of fish
Macrominerals (g/kg diet) Microminerals (mg/kg diet)
(trace elements)
Calcium IronPhosphorus* Manganese*Sodium CopperPotassium* Zinc*Chlorine CobaltMagnesium* Selenium*Sulfur Iodine*
Molybdenum* Required in the diet, but not always supplemented in practical feeds
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Carotenoid pigments in farmed salmon and trout feeds
Synthesized products Carophyll red Carophyll pink Natural products Krill meal Phaffia yeast Marine algae Crustacean waste (crab, shrimp, crayfish)
Note: astaxanthin shown to be essential nutrient for salmon to produce viable offspring
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Nutrient requirements – Halver’s contribution
• Complete estimates of nutrient requirements only done for juvenile Pacific salmon and rainbow trout
• Halver’s work never duplicated for Atlantic salmon
–Dietary requirements still based on Pacific salmon work
• Atlantic salmon production
– >1,200,000 metric tons
– ~2,000,000 metric tons of salmon and trout feed per year
• The nutritional information upon which this industry is based is that of Halver and his colleagues
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Changes in protein and fat levels in trout feeds
0
10
20
30
40
50
1970 1980 1990 2000 2006
Protein
Digestible Protein
Fat
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Changes in protein and fat levels in salmon feeds
0
10
20
30
40
50
60
1960s 1970s 1980s 1990s 2000
Protein
Digestible Protein
Fat
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Changes in feed conversion ratios for salmon and trout
0
0.5
1
1.5
2
2.5
1970 1975 1980 1985 1990 1995 2000
SalmonTrout
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The authoritative text for all fish nutritionists