Ammonia excretion at different life stages of silver catfish/excrecao de amonia em diferentes estagios de vida do jundia

This study examined ammonia excretion at different life stages (eggs, larvae and juveniles) in silver catfish (Rhamdia quelen) and determined the influence of fasting time on ammonia excretion. Eggs and larvae were collected from incubators at different times after fecundation and placed in chambers. Juveniles were separated into two weight classes (2-50 g and 150-320 g) and placed in individual chambers after feeding. Water was collected from each chamber to determine ammonia excretion. Ammonia excretion by the eggs was low, but when hatching began approximately 28h after fecundation, excretion increased until 48h after fecundation. In fasting silver catfish juveniles, there was a significant negative correlation between ammonia excretion and weight. Moreover, ammonia excretion decreased significantly after 12 and 48h of fasting (compared to 6h fasting) in the smallest and largest specimens, respectively. Consequently, during incubation of silver catfish eggs, water renovation must be increased at hatching time to avoid a build-up in the concentration of ammonia. In addition, as ammonia excretion in this species increases after feeding, feed must be discontinued when ammonia levels in the tanks are high to avoid a further increase of this metabolite and consequent mortality of silver catfish. Keywords: eggs, fasting time, nitrogenous compound, larvae. Verificou-se a excrecao de amonia em diferentes estagios de vida (ovos, larvas e juvenis) e determinou-se a influencia do tempo de jejum na excrecao de amonia no jundia, Rhamdia quelen. Ovos e larvas foram coletados das incubadoras em diferentes tempos apos a fecundacao e colocados em recipientes. Juvenis foram separados em duas classes de peso (2-50 e 150-320 g) e apos a alimentacao foram colocados em recipientes individuais. As aguas foram coletadas de cada recipiente para determinacao da excrecao de amonia. A excrecao de amonia pelos ovos foi baixa, mas iniciada a eclosao--28h apos a fecundacao, ela aumentou ate as 48h. Nos juvenis em jejum, houve significativa correlacao negativa entre a excrecao de amonia e o peso. Alem disso, a excrecao de amonia diminuiu significativamente apos 12 e 48h de jejum nos especimes menores e maiores, respectivamente. Portanto, a renovacao da agua deve ser aumentada no momento da eclosao dos ovos de jundia para evitar aumento da concentracao de amonia. Como nessa especie a excrecao de amonia aumenta apos a alimentacao, quando os niveis nos tanques forem elevados a alimentaca