The Biology and Culture of Tilapias

Feeding, Digestion and Growth--Qualitative Considerations

Department of Biological Sciences

Michigan Technological University

Houghton, Michigan 49931

U.S.A.

BOWEN, S.H. 1982. Feeding, digestion and growth-qualitative considerations,

p. 141-156. In R.S.V. Pullin and R.H. Lowe-McConnell (eds.) The biology

and culture of tilapias. ICLARM Conference Proceedings 7, 432 p. Inter-

national Center for Living Aquatic Resources Management, Manila, Phil-

ippines.

Tilapias feed as herbivores and detritivores. Food particle size is reduced

in the pharyngeal mill which facilitates peristaltic mixing and increases

surface area for exposure to digestive fluids in the gut. Gastric acid secreted

to pH values < 2.0 lyses cell walls and cell membranes of bacteria and algae.

Subsequent intestinal digestion occurs gradually as the food passes down the

extremely long intestine. In addition to microorganisms, detritus is digested

and is a maior nutritional resource for detritivorous tilapias. Whole diet

assimilation efficiencies are lower for tilapias than for carnivorous fishes.

Food quality appears to limit the growth of tilapias in natural populations.

The limited data available indicate that within a given water body, tilapias

select precisely the food that will maximize growth. The combined abilities

for cell wall lysis and selective feeding suggest that tilapias hold considerable

promise for low technology, protein efficient aquaculture.

Introduction

Animal growth rate is determined through the combined effects of food
quantity and food quality. The quantity of food consumed is regdated
through appetite to satisfy the animal's energy requirements (Rozin and
Mayer 1961, 1964). Limited food availability that does not allow full
appetite satisfaction results in growth rates below the maximum potential.
Food quality depends on the composition of the diet, and the extent to
which the components are digested and assimilated. Quality is rarely a
limiting factor in the growth of carnivores since their diet is consistently of
very high quality, but the quality of diets consumed by herbivores and
detritivores is extremely variable and plays a major role in control of growth
at these trophic levels. This contribution reviews recent scientific research on
aspects of the diet, digestion, assimilation and growth of the tilapias (family
Cichlidae; genera Tilapia and Sarotherodon), which are herbivorous and
detritivorous, to assess our current understanding of how food quality
influences the growth of these animals in natural populations.