The Biology and Culture of Tilapias

possible explanation is that the tilapia cannot crush the hard grain of sorghum
as well as can the common carp. The latter have molar-like pharyngeal teeth
suitable for such a task.
Stickney and Simmons (1977) incorporated dried poultry waste into
pelleted trout feed and fed this to S. aureus.
yd 30%, a considerable negative effect o
was noticed, Supplementary feeding with a pr
yields very considerably. Huet (1970) suggests that yields of tilavias with
supplementary feeding can be increased 2- to 10-fold over yields from non-fed
ponds. The effect of supplementary feed is emphasized at higher stocking
densities. Lovshin et al. (1977) conducted a feeding experiment at two
stocking densities (5,600 and 8,9601ha) with all-male hybrid tilapia (S.
niloticus x S. hornorum). They fed a mixture of 50% wheat chaff and 50%
castor bean meal. The diet contained 25% protein and was fed at 3% of body
weight. Taking the net yield in the control ponds as 100% (= 288 kglha at
5,600 fish/ha and 179 kg/ha at 8,960 fishha) the following increased yields
were found: at 5,6OO/ha with organic fertilizer, 265% and with supplementary
feeding, 326%; at 8,9601ha with organic fertilizer, 518% and with supple-
mentary feeding, 938%.
The FCR can serve, to a certain extent, as an indicator of the nutritional
value of a feed, although feed conversion is also affected by other factors
such as the physiological state of the fish, environmental conditions, the
amount of available natural food and the amount of feed consumed. Balarin
and Hatton (1979) give a feed conversion table for various supplementary
feedstuffs. The following FCR values for S. niloticus will illustrate their wide
variability with different feeds: groundnut cake, 3.6; cottonseed cake, 4.8;
pelleted chicken feed + 10% fresh fish equivalent, 1.8 to 6.5 ;brewery waste,
12.6; cottonseed crush, 18.9.
Natural food in ponds contains about 55% protein on a dry weight basis
and can therefore be supplemented, to a certain extent, by carbohydrate-rich
feeds sdh as rice bran. Tilapias seem to utilize such carbohydrates well. E.M.
Cuz (pers. comm.) conducted experiments in the Philippines to determine
the effect of feeding rice bran and copra meal on the production of S.
niloticus and common carp. The addition of these feedstuffs increased the
yield of the tilapia by about 50% over that of fertilized ponds with no
supplementary feeding.
With increased standing crops, the quality and quantity of dietary protein
become more important. Inclusion of protein in diet of S. niloticus reduced
feed conversion considerably (de Kimpe 1971). In Israel it has been observed
that feeding pellets of 25% protein, which include 10 to 15% fishmeal, has
a pronounced effect on the growth of tilapia hybrids (S. niloticus x S.
aureus), especially at high densities (Piperno 1970a, 1970b; Marek 1970).
Not many systematic studies have been done on rates of feeding. Since
natural food constitutes an important part of the nutrition of tilapias,
the amount of supplementary feed given is usually lower than that for
common carp. Shell (1967) shows that the best FCR for protein-rich pellets
(Auburn No. 2) by S. mossambicus was when fed at a rate of about 2% of its
body weight per day. For S. niloticus the best was obtained at 4% of body
weight per day. Marek (1975) developed a feeding chart for tilapias in Israel