The Biology and Culture of Tilapias

(Figure 1). Digestion of protein is complete in the first quarter. This com-
ponent of the diet is thought to be microbial protein present in living cells
and protein that may be associated with detritus. The results indicate that
microbial cells lysed in the stomach are digested immediately in the intestine
while those not lysed are not digested at any point. Very different results
were obtained for total amino acids (Figure 2). This class of compounds is
comprised of amino acids bound into the complex chemical milieu of
the detritus in addition to amino acids that make up microbial proteins.
Whether detrital amino acids are single amino acids, oligopeptides or poly-
peptides is not yet known. As a group, the total amino acids are digested
gradually as food passes down the intestine and .maximum digestion is not
achieved until the end of the digestive tract.

I

Protein

protein

Digestive tract segment

Figure 1. Comparisons of samples from the stomach (S) and the four quarters of the

digestive tract of Sarotherodon mossambicus from Lake Valencia, Venezuela, to show the

course of digestion. Means * 95% confidence limits, n = 55 (after Bowen 1980).