The aim of the present study was to determine the effects of waterborne un-ionized ammonia (NH3) on the survival and growth of silver catfish (Rhamdia quelen). Juveniles were exposed to 0.10, 0.22, and 0.42mg L-1 NH3 at pH 8.2 for 45 days. After 15 days, a significant mortality rate (33%) was observed in the fish exposed to 0.42mg L-1 NH3. After 20 days, 23% and 43% mortality (both significant) was observed in fish exposed to 0.22 and 0.42mg L-1 NH3, respectively. A significant negative relationship between survival, length, daily weight gain, standard growth rate, and biomass of juveniles of silver catfish per tank with waterborne NH3 levels was found at the end of the experiment. The resulting survival and waterborne NH3 relationship indicated that, to avoid any mortality of silver catfish, the maximum level of chronic NH3 exposure at pH 8.2 would be 0.01mg L-1.
fish culture; nitrogenous compounds; weight gain
