Campbell (pers. comm.), experimenting empirically with S. niloticus
and a 25% protein feed, reached the conclusion that DFR's should be adjusted
with size as follows: fry/fingerlings less than 25 g, 10 to 8% B; 25 to 150 g, 6
reducing to 4% B; 150 to 200 g, 3% B; and over 200 g, 2% B. He has even
reduced the DFR to 1% B for fish larger than 200 g to increase the efficiency
of pelleted feeds. Taking a more scientific approach, Mklard and Philippart
(1980) estimated the optimum DFR for S. niloticus in tanks and cages using
a 46% protein commercial feed at 27 to 31°C. Table 10 summarizes their
recommendations. In the Philippines, Guerrero (1980a) has also proposed a
progressive reduction of DFR with increasing size for S. niloticus: from 5% B
(fish less than 50 g) to 4% B (50 to 100 g) and 3% B for larger fish. These are
smaller DFRs than those in Table 10 and also refer to lower protein feeds.
Table 10. Recommended daily feeding rates (DFR) expressed as percentage fish biomass
(% B) for Sarotherodon niloticus in tanks and cages at 27 to 31°C, fed a 46% protein
commercial fish food (after Me'lard and Philippart 1980).
Mean fish weight (g) DFR (% B)0 to 5 30 reducing to 20
5 to 20 14 reducing to 12
20 to 40 7 reducing to 6.5
40 to 100 6 reducing to 4.5
100 to 200 4 reducing to 2
200 to 300 1.8 reducing to 1.5When fixing the DFR for a particular operation, one should also take
into account the natural productivity of the environment. In Alabama,
S. aureus were fed 40% protein floating pellets (DFR, 3% B) for 10 weeks in
0.25 m3 cages placed in fertilized ponds (Armbrester 1972). Although the
feeding efficiency was very good in presence of moderate algal blooms
(Net FCR = 1.1 to 1.5), it decreased considerably in ponds with dense
algal blooms (Net FCR = 3.3 to 6.3). This was attributed to the abundant
availability of natural food.
The methods used to distribute feed to caged tilapias may greatly in-
fluence the results. This depends on numerous factors including digestive
physiology and feeding behavior relative to fish size; the shape and size of
the cage; the water circulation through the cage and the stocking density.
There are three major variables: feeding frequency, feed presentation and
distribution methods.
Increasing feeding frequency by dividing the DFR into several meals
may allow increased DFRs and give improved production and feeding
efficiency. Although no scientific evidence exists to support such practices,
in one commercial cage farm S. niloticus are fed their DFR as five meals
(Campbell pers. comm.).