Larval rearing of an Asian catfish Pangasius hypophthalmus (Siluroidei, Pangasiidae): Analysis of precocious mortality and proposition of appropriatetreatments

Both in Indonesia and Vietnam, larval rearing of Pangasius hypophthalmus re mains problematic due to the variable and generally low survival rates obta ined. The first week represents the most critical period for these larvae a nd up to now, cannibalistic behaviour was considered as the main cause of m ortality. Ln the present study, two experiments were carried out in order t o better understand the evolution and causes of mortality of P. hypophthalm us larvae from hatching up to 8 d of age and to find measures to improve su rvival rates. The first experiment was designed to evaluate the importance of cannibalism and differences in mortality when larvae from two different females were reared either in groups of 30 individuals or in isolated condi tion (30 larvae reared separately). In both cases, the culture was carried out either with or without antibiotic. The aim of the second experiment was to test oxytetracycline and different disinfectants (chloramine-T, formali n and 'formalin + malachite green oxalate') at different dosages in order t o prevent bacterial outbreaks in the culture. The results indicated that th e survival rates of P. hypophthalmus larvae was dependent on the initial qu ality of larvae or eggs and that larval mortality was more a consequence of pathogenic infection than a direct effect of cannibalism. The present stud y demonstrated that the survival rates of larvae were systematically improv ed when rearing was carried out in water containing antibiotic (oxytetracyc line at a dose of 5 to 20 mg.L-1). Survival rate and final mean body weight of larvae as high as those obtained using antibiotic were also reached wit h applications of disinfectants such as chloramine-T and formalin. The use of these disinfectants is recommended for commercial P. hypophthalmus hatch eries. (C) Ifremer/Elsevier, Paris.