Nutritional and Physiological Strategies for Sustainable Aquaculture: Challenges in Nutrition Christopher Kohler and Craig Kasper Fisheries and Illinois Aquaculture Center Southern Illinois University Carbondale

What is fish nutrition? “Nutrition is the process by which an “Nutrition is the process by which an organism ingests, assimilates and utilizes organism ingests, assimilates and utilizes various nutrients and converts them into various nutrients and converts them into body tissues and/or activities.” body tissues and/or activities.” –Robinson et al –Robinson et al. 2001

Diversity of Species Over 20,000 spp. (marine, freshwater, diadromous)Over 20,000 spp. (marine, freshwater, diadromous) All trophic levels above autotrophicAll trophic levels above autotrophic Zooplankton first food:Zooplankton first food: 60% crude protein 60% crude protein 15% lipid 15% lipid Broodstock need dietary HUFA’sBroodstock need dietary HUFA’s

Diversity of GI Tract: Carnivores: large stomach, short intestineCarnivores: large stomach, short intestine hybrid striped bass salmonids hybrid striped bass salmonids Omnivores: moderate size stomach & intestineOmnivores: moderate size stomach & intestine channel catfish channel catfish Herbivores: small stomachs,Herbivores: small stomachs, long intestine long intestine tilapia grass carp tilapia grass carp Trituration and digestionTrituration and digestion processes also vary processes also vary

Fish are more efficient in protein synthesisFish are more efficient in protein synthesis -catfish, 0.84 g wt/g diet -catfish, 0.84 g wt/g diet -chickens, 0.48 g wt/g diet Nitrogenous wastes excreted through gills (~85%)Nitrogenous wastes excreted through gills (~85%) Little energy to maintain body temperatureLittle energy to maintain body temperature fish (3%) vs. mammals (30%) fish (3%) vs. mammals (30%) Less energy needed to maintain positionLess energy needed to maintain position Bioenergetics: Fish vs. Warm-blooded Animals

Fish require high protein/low energy diets, yet require substantially less protein than their forage base doesFish require high protein/low energy diets, yet require substantially less protein than their forage base does Fish seem to require dietary ω -3 fatty acidsFish seem to require dietary ω -3 fatty acids Fish can absorb some minerals from waterFish can absorb some minerals from water Most fish can’t synthesize ascorbic acidMost fish can’t synthesize ascorbic acid Nutrient Requirements

Protein Protein is the main nutrientProtein is the main nutrient in fish feeds (28-55%) in fish feeds (28-55%) Size dependent requirementsSize dependent requirements Fry > Fingerlings > Stockers Fry > Fingerlings > Stockers > Adults/Brood stock > Adults/Brood stock

Protein Challenges Reduction of fish meal is a primary goal/challengeReduction of fish meal is a primary goal/challenge –Why the need? Competition for usage (swine, poultry, etc.) Variable nutrient composition (AA’s and FA’s) (AA’s and FA’s) Finite resource Expensive

Fish Meal Usage 30 MMT

Protein Challenges Plant feedstuffs generally low protein/high carb.Plant feedstuffs generally low protein/high carb. soybean meal: good protein & amino acid profile soybean meal: good protein & amino acid profile Plant feedstuffs contain “antinutritional” factorsPlant feedstuffs contain “antinutritional” factors such as phytic acid, trypsin inhibitors, lectins, etc. such as phytic acid, trypsin inhibitors, lectins, etc. - may render protein and minerals unavailable - may render protein and minerals unavailable -decreases weight gain -decreases weight gain -increases phosphorus into effluents -increases phosphorus into effluents

Protein Challenges Plant usage increases fecal outputPlant usage increases fecal output Plant based diets = amino acid deficienciesPlant based diets = amino acid deficiencies eg. lysine & methionine eg. lysine & methionine Supplementation increases diet costSupplementation increases diet cost

Carbohydrates Some fish can tolerate high carbohydrate feedsSome fish can tolerate high carbohydrate feeds tilapia carp catfish pacu tilapia carp catfish pacu Spares protein for muscle synthesisSpares protein for muscle synthesis Inexpensive energy sourceInexpensive energy source Many sources:Many sources: wheat corn wheat corn yucca plantain yucca plantain

Carbohydrate Challenges Not required, excess will decrease protein gainNot required, excess will decrease protein gain (Carnivorous fish have been on the Atkins diet for eons.) (Carnivorous fish have been on the Atkins diet for eons.) Fish have poor control over blood glucoseFish have poor control over blood glucose –post prandial levels rise rapidly, yet take hours to decline, may effect liver health –reduced growth in largemouth bass fed diets containing 13% carbohydrate

Lipids Fish require 4-16% dietary fatFish require 4-16% dietary fat -Requirement is also size dependent -Requirement is also size dependent Main energy source of feedsMain energy source of feeds Spares protein for growthSpares protein for growth Certain fatty acids required:Certain fatty acids required: 18:2n-6 (Linoleic), 18:2n-6 (Linoleic), 18:3n-3 (Linolenic) = freshwater fish 18:3n-3 (Linolenic) = freshwater fish 20:4n-6 (Arac. acid) = healthy immune response 20:4n-6 (Arac. acid) = healthy immune response 20:5n-3 (EPA); 22:6n-3 (DHA) = saltwater fish 20:5n-3 (EPA); 22:6n-3 (DHA) = saltwater fish

Lipid Challenges Too much, or wrong ratio, decreases growth, degrades liver & decreases cold toleranceToo much, or wrong ratio, decreases growth, degrades liver & decreases cold tolerance When reducing animal products in feeds, fattyWhen reducing animal products in feeds, fatty acid requirement is more difficult to achieve acid requirement is more difficult to achieve Moreover, plant-based ω -3 fatty acids are limited to 18-carbon chainsMoreover, plant-based ω -3 fatty acids are limited to 18-carbon chains Fish oil remains the bestFish oil remains the best source of EPA and DHA source of EPA and DHA

Fate of Nitrogen and Phosphorus from Feed Food 100% N 100% P Retained 30% N 32% P Dissolved 87% N 10-40% P Solids 13% N 60-90% P Effluent 70% N 68% P

New Topics Always emergent species to study:Cobia, Pacu, etc.Always emergent species to study:Cobia, Pacu, etc. Finishing dietsFinishing diets Alternative protein sourcesAlternative protein sources –canola protein concentrates –barley fractions –fermentation bi-products –microbial protein production (single-celled protein, SCP) (single-celled protein, SCP)

New Topics Many nutrient requirements still unknown for many species, particularly mineralsMany nutrient requirements still unknown for many species, particularly minerals Nutriceuticals-using fish as a delivery system for beneficial nutrientsNutriceuticals-using fish as a delivery system for beneficial nutrients EPA/DHA Antioxidants EPA/DHA Antioxidants