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

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

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

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

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)

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

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)

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)

Cod eggs

Copper rockfish larvae at first feeding

Canary rockfish larvae with feed in gutsix weeks after first feeding stage

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

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

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

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)

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

Vitamin requirements of salmon and growing chickens (IU or mg/kg dry diet)

Vitamin Salmon/trout ChickensVitamin 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

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

Proximatecategory Percent

Moisture 28-30Crude protein 34Fat 17Ash 5

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)

Qualitative dietaryarginine requirement(Halver)

Relationship between thiamin intake and liver thiamin concentration

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 eggs

pigments

• NOTE: Other minerals are probably essential but can be obtained from rearing water

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.

Ascorbic acid requirements of salmonids

Requirement* Comments

15-20 ppm Prevents deficiency signs250-500 ppm Supports maximum wound

healing activity1000-2500 ppm Supports maximum disease

resistance 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

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

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

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

Changes in protein and fat levels in trout feeds

0

10

20

30

40

50

1970 1980 1990 2000 2006

ProteinDigestible ProteinFat

Changes in protein and fat levels in salmon feeds

0

10

20

30

40

50

60

1960s 1970s 1980s 1990s 2000

ProteinDigestible ProteinFat

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

The authoritative text for all fish nutritionists