Chapter 16 Diet and Energy Flow

Importance of fish diet (3)

Growth and production of fish typically measure the success of a fishery and is directly related to nutrient and quantity of food

Dietary info is important to identify constraints to fish growth and guiding management decision

Food habits and trophic status is important in evaluating the competition between exotic species and endemic fishes

Sampling diet considerations (1)

less stressful sampling methods are preferred to prevent stomach content regurgitation

Stressful sample methods (4)

Electrofishing

Gillnets

Rotenone

Deep water collections

Less stressful methods

seine

cast net

short time gill nets

Loss of gut contents considerations (3)

Large piscivores tend to have higher regurgitation rate than small fish

regurgitation higher in warm temperature

fish may regurgitate in holding tanks and/or big fish eat small fish

Effects on gut contents considerations (3)

digestion rates increase with water temp

prey items will have different digestion rates

life stages of prey have different digestion rates, larval fish digest very quickly

Sampling the prey (4 things)

quantitative diets provide info about choice but little about prey quality or density

knowledge of density, locations, and species composition can provide additional insights

prey availability can change due to diet cycle, season, or size of prey

insights on diet important before attempting to sample prey items

Removal of gut contents (5 things)

Complete removal of the gut is the only way to ensure entire diet sample

gastric lavage most productive method

clear tubing can flush, grab, and view prey items

water syringe

low pressure pump causing regurgitation

Gut handling and preservation (3 things)

appropriate labels

can be stored in whirlpaks, ziplock, or bottle

preservation may be required

Gut preservation methods (4)

10% formalin

45-70% alcohol

freezing

ice (short term)

Quantification of diet (4 things)

frequency of occurrence

percent comp can be calculated based on prey item number or weight

composition by weight can be wet or dry

dry weights more precise than wet weights