The Biology and Culture of Tilapias

come out. This simple device could have advantages over more sophisticated

automatic and demand feeders. Dr. Philippart stated that in experimental

tank trials in Belgium, tilapias in excess of 200 g fed five or six timeslday

grew better than those fed more frequently, e.g., twicelhour. It was agreed

that juvenile fish require more frequent feeding than larger fish: usually

about 10 feedslday.

It was agreed that there is very little information available on the nutri-

tional requirements of tilapia broodstock. There is, for example, no informa-

tion on the effects of nutrition on fecundity in tilapias apart from general

observations that well-fed fish have higher counts of oocytes at all stages

than poorly-fed fish. Prof. Roberts reported work at Stirling University

which indicates that the dietary protein requirements of broodfish are

significantly lower than those of immature fish in the most active phase of

somatic growth. The quality of protein required for broodstock diets is,

however, very high. Earthworms are an excellent protein source. For a

number of species, it has been shown that broodstock can be spawned

at approximately monthly intervals for as much as 18 months given good

nutrition. Also, for S. mossambicus in tanks, all the animal protein, for

example fish meal, in the diet can be replaced with high quality algal protein.

For spawning ponds, however, broodstock pelleted diets should contain

animal protein.

Dr. Guerrero reported that a commercial animal feed company in the

Philippines is developing a diet for S. niloticus broodstock. The starting

point for this is a salmonid-type diet with high energy content and 25%

protein, at least half of which is animal protein, largely from fish meal.

The natural foods present in spawning ponds are a very important part of

broodstock nutrition.

To summarize on nutrition, it is clear that vastly different approaches

are needed to optimize the nutrition of tilapias in extensive and intensive

culture systems. The feeding niches in extensive systems need fuller definition,

particularly the microbial ecology of detrital aggregates, while for intensive

culture, least cost formulation of complete diets is still awaited for most

culture situations.

Seed Supply

In spawning tanks, the territorial aggression of males is the major factor
limiting stocking density. In Israel, however, as Mr. Mires pointed out, mixed