TANK CULTURE OF TIL.^PIA 



25 



FiGiRE 4. — Filter and pump on a raceway tank. 



The general arrantrement of the assault-boat 

 tanks and the redwood tanks is shown in figure 5. 



STOCKING THE BROOD TANKS 



One of the first problems to be considered in 

 the operation of the j)ilot plant was what sex 

 ratio should be used when stocking the tanks. 

 Chen (1953: p. 6), working on tilajjia in Taiwan, 

 stated that the proper sex ratio for propagation 

 purposes is one male to a female. Other investi- 

 gators, however, reported that in mouth brood- 

 ers, which group includes T. mossambica, the 

 female visits the spawning grounds only briefly 

 to extrude her ova and collect the fertilized eggs, 

 and then moves away or often is chased away 

 by the male. The male remains on the spawning 

 ground to guard the nest and immediately begins 

 to court other females. He is, thus, available for 

 and presumably capable of fertilizing ova from 

 a succession of ripe females (Baerends and 

 Baerends-Van Roon, 10,50; Lowe, 19.55). Lowe 

 (p. 48), with respect to the mouth brooders, 

 concluded that as male fish can continue ferti- 

 lizing over a long period, the number of eggs ferti- 



FlouRE 5. — Tilapia tanks at the Kewali) plant after a heavy rain. 



619359 O — 62- 



