REARING TILAPIA FOR TUNA BAIT 

 Table 13. — Monthly prodiictiwi of young tilapm in hrood-tanks A ami B, J9oS 



11 



1 Tank A contained 750 females during the January-September period and 689 females during October-December. 

 ' Tank B contained 750 females during January-September period and 736 females during October-December. 



PRODUCTION OF YOUNG 



The monthly fry production is given in table 13 

 for 1958 and in table 14 for 1959. These data are 

 based on gross production and do not indicate 

 losses from disease, cannibalism, or other factors. 

 There was marked seasonal variation with the 

 peak production in 1958 occurring in July and in 

 1959 in May. 



There was an important difference in the pro- 

 duction of the two brood tanks in 1958 that may 

 have been related to the position of the inlets and 

 drains, the direction of the prevailing winds, ami 

 the resultant circulation of the water within the 

 tanks. Tank A, with the drain on the upwind side, 

 was generally cleaner and more productive than 

 tank B, which had the drain on the downwind 

 side. In 1959 a drain was installed on the upwind 

 end of tank B and the water was somewhat cleaner 

 than in tlie previous year. 



Production was higher in 1959 than in 1958 an<l 

 there was little difference l)etween the two tanks. 

 Factors operating in 1959 which may have con- 

 tributed to the higher production that year were — 



1. Improved drainage in brood-tank B. 



•2. Larger bottom area (4.21 sq. ft. versus 3.37 

 in 1958) allotted to each male. 



3. Aeration of the brood tanks. 



4. Water filtered and recirculated in brood- 

 tank A. 



5. Slightly higher water temperatures. Since 

 both brood tanks were heated slightlj' and there 

 were no control tanks, it is difficult to evaluate the 

 results. "We can .state, however, that water tem- 

 peratures rose following installation of the heat- 

 ing cables (figs. 4 and 5) and that production in- 

 creased over that of the previous year. 



6. Increased oxygen coi^tent in brood tanks. 



7. Higher grade of feed fed adults. 



> Based on 600 females In each brood tank throughout the year. 



