Fish rearing tanks are each stocked, at 6 week intervals with 800, 30-gram (1 oz.) male tilapia. Projected harvest size is 450-gram (1 lb.). Density is a major limiting factor that determines the stocking rate in the rearing tank. Mortalities increase (from zero to two or three per day) during the final weeks of production. Mortalities are due to crowding and increased abrasions with other fish and the tank walls as water quality, oxygen levels and feeding rate are all maintained. Bacterial septicemia was symptomatic of these conditions and a probable cause of the mortalities. Our initial stocking rate of 1000 fish has been reduced to 800 per tank and mortalities have ceased. Individual harvest size was also low at the high stocking rate. Female tilapia should not be stocked as they do not grow as fast as males.
The fish are stocked into the 4 rearing tanks at six week intervals. This staggered stocking allows for a regular supply of market sized tilapia. The grow-out period for the tilapia is 24 weeks. At system startup one tank is stocked. Six weeks later a second tank is stocked, followed at 12 weeks by the stocking of the third tank and at week 18 by stocking the fourth tank. On week 24 the first tank stocked is harvested and restocked with new fingerlings. Every six weeks after the first harvest, one rearing tank is harvested and restocked.
Fish feeding practices