10 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Taule 11. — Amount {in pounds) and cost of feeds supplied tilapia fry, J95S 



Table 12. — Amount {in pounds) and cost of feeds sup- 

 plied tilapia fry, 1959 



1 nigh quantities fed bait-size fish carried over from 1958. 



of bait-size Hsh. The.se amounts do not include 

 natural foods occurring in the ponds, such as 

 green algae and mosquito and midge larvae, which 

 were consumed in some quantity by the young 

 fish. 



COLLECTING THE FRY 



Once production had started, a diligent effort 

 was made each day to remove all the young that 

 could be captured by dipnetting. A sorting de- 

 vice consisting of a large net mounted behind a 

 frame with grating of aluminum tubing, which 

 was to be pulled through the brood tanks, was 

 tried but did not prove feasible. The device was 

 effective in catching young fish but was judged 

 impractical because of the problem of removing 

 the young from the net and from the detritus 

 that was also collected. Since the young schooled 

 near the surface of the water, dipnetting with a 

 square-framed, 20 X 20-inch net "walked" along 

 the walls of the brood tanks was a simple and 



satisfactoiy method of collection (fig. 8). The 

 yoimg were transferred from the dipnet to a 

 bucket and then counted and released into the fi-y 

 tanks. Each fry tank was stocked with about 

 6,500 young, or 91 young per square foot of sur- 

 face area. Some effort was made to put fry of the 

 same size into each tank to reduce cannibalism. 

 The few young that escaped the daily dipnetting 

 were removed at intervals of 3 to 4 months when 

 we seined the ends of the brood tanks where the 

 juveniles tended to congregate. 



FiQUEE 8. — Dipnetting tilapia fry. 



