Transcript Nutritional and Physiological Strategies for Sustainable Aquaculture

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
organism ingests, assimilates and utilizes
various nutrients and converts them into
body tissues and/or activities.”
–Robinson et al. 2001
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
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
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
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
Protein
• Protein is the main nutrient
in fish feeds (28-55%)
• Size dependent requirements
Fry > Fingerlings > Stockers
> Adults/Brood stock
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
Fish Meal Usage
30 MMT
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
20
17
29
55
48
17
23
1988
1998
24
35
2000
Others
Swine
Poultry
Aqua
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
Protein Challenges
• Plant usage increases fecal output
• Plant based diets = amino acid deficiencies
eg. lysine & methionine
• Supplementation increases diet cost
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
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
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
18:3n-3
20:4n-6
20:5n-3
(Linoleic),
(Linolenic) = freshwater fish
(Arac. acid) = healthy immune response
(EPA); 22:6n-3 (DHA) = saltwater fish
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
Fate of Nitrogen and Phosphorus from Feed
Retained
30% N
32% P
Solids
13% N
60-90% P
Food
100% N
100% P
Effluent
70% N
68% P
Dissolved
87% N
10-40% P
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)
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