TANK CULTURE OF TILAPIA 



27 



Table 2. — Guaranteed analyses (percent) of ingredients in 

 the feeds used at the pilot plant and the Kewalo plant 



Table 4. — Amount {in pounds) of the feeds used at the 

 Kewalo plant 



' Not lesii than, 

 a Not more than. 



The brood stock at both plants was fed once 

 a day, usuall}' at midday. There were periods 

 during the operation of both plants when the 

 adults did not feed readily, and during these 

 times smaller portions were supplied to the fish. 

 This apparent lack of interest in feeding is prob- 

 ably associated with the mouth-brooding habit of 

 the female. 



The amounts of the various kinds of feed that 

 were supplied to the adults and young during op- 

 eration of the pilot plant and the Kewalo plant 

 are given in tables 3 and 4. The fry were usually 

 fed twice a day during weekdays, once in the 

 morning and once just after midday, and once a 



Table .3. — Amount (in pounds) of the feeds used at the 

 pilot plant 



day on weekends. The amount of feed given to 

 the young varied with the number and size of fry 

 and juveniles. 



FRY PRODUCTION 



T. mossambica reportedly first spawns at the 

 age of 2 to 3 months and at a length of 8 to 9 centi- 

 meters. The frequency of spawning varies consid- 

 erably, depending on environmental factors, and 

 ranges from 6 to 16 times a year (Chen, 1953; 

 Panikkar and Tampi, 1954; Chimits, 1955). 

 Chen reported that a spawning fish of about 8 cm. 

 in length pi-oduces from 100 to 150 ova at each 

 spawning, although at the first spawning it may 

 produce less than 100 ova. He stated further that 

 the number of ova spawned increases with succes- 

 sive spawnings, so that a fish more than 6 months 

 of age may produce in excess of 1,000 ova per 

 spawning. 



The developmental period of tlie ova is likewise 

 variable but, generally, tlie ova hatch after 2 to 5 

 days and the young are carried in the mouth of 

 the female for another 5 to 8 days before they are 

 released (Chen, 1953; Panikkar and Tampi, 1954; 

 Chimits, 1955). 



From the time of the initial stocking at the pilot 

 plant, careful daily observations were made on 

 each tank to determine if young were being pro- 

 duced. As no signs of young fish were seen for 

 about 6 weeks, the three tanks were partiallj' 

 drained and cleaned on November 28-29, 1956. 

 Before the water level was restored in each tank, 

 the detritus on the bottom of the tank was ex- 



