Effects of Feeding Frequency and Handling on Growth and Mortality of Cultured Walking Catfish Clarias fuscus

Two experiments were conducted to study the effects of feeding freqnency on growth, and of handling stress on growth and mortality, in intensive tank culture of the walking catfish Clunas fuscus. In the first experiment, fish were grown from an initial weight of 37 g for 34 d. A fixed ration of 3.0% body weight per day was divided into either 1, 2, or 3 feedings per day, and fish were either handled weekly or left unhandled for the entire experiment. Fish given 3 feedings per day experienced 19% faster growth (P < 0.05) than fish given the same ration in a single feeding per day. These differences in growth reflect differences in assimilation efficiency, assuming dl other metabolic costs were constant among treatments. Handling of individuals caused decreased growth however, there was no effect on mortality. In the second experiment, fish were grown from an initial weight of 78 g for 29 d. Fish were fed either 1 or 2 satiation feedings per day and were either handled weekly or left unhandled for the entire experiment. Fish fed 2 satiation feedings per day experienced 47% faster growth (P < 0.05) than fish fed 1 satiation feeding per day, which was assumed to reflect a higher level of food consumption. No effect of handling on either growth or mortality was observed for fish in experiment 2. Multiple meals per day also reduced depensatory growth among individuals in both experiments. When supplemental feed is administered in fish culture, the primary objective is to maximize growth per unit feed. Given an adequate protein intake, fish growth is related to the amount of energy assimilated, which in turn depends upon two important variablesvoluntary food consumption and assimilation efficiency (Webb 1978; Brett 1979; Diana et al. 1988). Assimilation efficiency is the fraction of ingested food which is absorbed. Feeding frequency is an important factor affecting both voluntary food consumption and assimilation efficiency (Brett 197 1 ; Windell 1978). It is essential to understand the effects of feeding frequency on consumption and assimilation in order to optimize feeding practices in a culture system. Many studies of feeding frequency in fish have employed satiation feeding in the laboratory, where increased growth occurred in response to increased food consumption that occurred with higher meal frequency Corresponding author. (Andrews and Page 1975; Hogendoom 198 1 ; Marian et al. 198 1; Sampath 1984). Differences in assimilation efficiency or nitrogen excretion rates that occurred with higher meal frequency could be detected by differences in feed conversion. During the above laboratory studies, it was possible to accurately quantify food consumption, since feeding rate was closely monitored and corrected for uneaten feed. Food application rate does not necessarily equal food consumption rate in larger scale commercial systems, since a significant and unknown portion of administered food may not be eaten (Yamada 1985). This study of fish feeding frequency employed a two-stage method that was more applicable for commercial-type systems (Grayton and Beamish 1977). Absolute ration size was fixed at a level below satiation in the first set of experiments, and we assumed complete ingestion of the ration and a constant energy expenditure due to metabolism at this fixed ration. If these assumptions are met, differences observed in growth for experiment 1 (when meal freQ Copyrieht by the World Aquaculture Society 1994