A Thesis submitted in partial fulfilment of the requirements of the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1989

Tilapia , although popular for its favorable characteristics, high yield and high market demand , faces t he problem of intensive production, especially in pond breeding condition. To overcome this, artificial incubation is being tried in some places. One such system has been developed in AIT, where an incubation system has grave l pre-filter and slow-sand filtration units. But the eficiency and capacity of t he fry nursing system under intensive nursing has not yet been done . The present study intends to fill this gap . The present study was carried out on just-hatched and on swim-up fry of Oreochromis niloticus under intensive nursing within a re- circulated system in aluminum trays (2 . 4 litre capacity). The system has no water filtration facility . Feeding was maintained ad-libitum on yolk sac fry and at 20%, 30% and 40% BW/day on swim- up fry. Feeding frequency was maintained at 5 times a day. Both the experiments were conducted using randomized design. From t he period of just-hatched to swim- up, t he optimum flow rate for the system would lie between 3 and 5 litre/minute. But in view of the limitation of the system capacity, 3 litre/minute flow rate is considered the best to estimate system capacity in respect of fry growth and survival. Of artificial versus natural hatched fry results show that artificially hatched fry perform slightly better than naturally hatched fry in survival, Specific Growth Rate, Percent Weight Gain and Daily Weight Gain. For early nursing a feeding level of 40% body weight per day is found to be the optimum one for swim-up fry. In yolk-sac fry survival and growth parameters maintain a positive relationship with density in lower flow rates and inverse at higher flow rates, in swim-up fry the relationship is inverse. Mean observed mortality percent of swim-up fry is positively related to density and inversely to feeding l evel, and is enhanced by an infection of Trichodina spp . Cannibalism accounted for a mortality rate of 0 . 47- 9 . 60% of the original density and is inversely related to feeding level.