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Nutritional and Physiological Strategies for Sustainable Aquaculture: Challenges in Nutrition

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

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Nutritional and Physiological Strategies for Sustainable Aquaculture: Challenges in Nutrition

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

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

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

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

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

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

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

  8. Protein Challenges • Reduction 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) Finite resource Expensive

  9. Fish Meal Usage 30 MMT

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

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

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

  13. Carbohydrate Challenges • Not required, excess will decrease protein gain (Carnivorous fish have been on the Atkins diet for eons.) • Fish 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

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

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

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

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

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

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