A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science, School of Environment, Resources and Development

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

Nursing methods of juveniles fish in nylon hapas in pond was conducted both on-campus trials in AIT a n d on-farm trials in Udonthani Province , N.E. Thailand. The first experiment on-campus compared nursing juveniles in 4 0 m2 nylon hapas 2 stocking densities of common carp ( Cyp.ri1111s carpio ) , 7 5 a nd 1 50 /m 2, a nd polyculture with MT - treated tilapia ( Oreochromis niloticus ) at 75 /m2 each . Th e second trial determined both the appropriate stocking density of common carp fry i n polyculture with MT- treated tilapia in 5.4 m2 nylon hapas at 150 and 300 /m2, and the appropriate ratio of MT-treated tilapia and common carp at 1:1 , 2:1 , and 4:1 respectively. On-farm trials were conducted in Kumpawapi district, Udonthani Province to develop appropriate methods of nursing juvenile fish in nylon hapas for s mall- scale farmers. The first experiment, showed t h at t h e growth of MT- treated tilapia increased very fast, from an initial weight of 0.19 g to 12 . 89 g within 13 weeks , but s lowly for common carp . The final size of commo n carp fingerling showed highly significant differences between ( P<0.01 ) treatment. The highest mean individual weigh t was obtained from low stocking density ( 3. 26 g ) , followed by polyculture (2.65 g ) and high density monoculture (2.13 g ) respectively. I n the second experiment , a high stocking density of MT - treated tilapia and common carp showed significantly (P<0. 01 ) lower growth t h an a J. ow stocking, but there ratio h ad no significant effect. Juveniles nursed on farms, in a variety of polycultures , showed very fast growth and high survival in all cases . Concentration of dissolved oxygen and the presense or absense of fish outside the hapas may have affected growth and survival of fish fingerlings especially common carp.