Fish Ecology and Fisheries - Freshwater Ecology: Concepts and Environmental Applications - page 436

Eutrophic

Percids,
e.g., Walleye,
yellow perch,
Northern pike.

Centrarchids
Ictalurlids
e.g., catfish,
basses, bluegill

Mesotrophic

Salmonid,
with hypolimnetic
r efuge

Oligotrophic

Cold Cool Warm

FIGURE 21.6 Conceptual illustration of fishery types in temperate lakes with summer strat-
ification as a function of temperature and trophic status.

centrations of wax esters are an excellent food source for fish species with
high lipid requirements.
Fishes that live in warmer waters may require lipids with a higher melt-
ing point. Herbivorous fishes (such as grass carp) can have special enzymes,
extra long guts, or gut bacteria that allow them to use low food quality
plant materials more efficiently as a source of carbohydrate. If one type of
food is of a high quality, it can partially compensate for lower quality food.
For example, catfish can use cellulose as a carbon source almost as effi-
ciently as starch, if a high proportion of protein is present in their diet (Fig.
21.7). Less is known about the roles of vitamins and minerals in fish diets
(Pitcher and Hart, 1982).

1.5 Cellulose

Sucrose
Dextrose
Starch

1.3

1.1

0.9

0.7

0.5

0.3

20 40 60

% protein

FIGURE 21.7 Growth of channel catfish (Ictalurus punctatus) on four carbohydrate sources
as a function of protein content of food (data from Simco and Cross, 1966).