Effect of rearing temperature on the digestive function in Cobia fry

Abstract

Water temperature is a key factor affecting metabolic rates and therefore fish feeding physiology and behavior. These effects have a special significance in the scenario of the global warming. In this study we have examined effects of an increased water temperature on the daily pattern of gastrointestinal pH, enzymatic proteolytic digestive activity and the food transit time in early juveniles of cobia (Rachycentron canadum), a candidate species for aquaculture in tropical and subtropical waters. Juveniles (3.7±0.4 g wet BW) were randomly distributed to 6 experimental 200-L tanks (60 fish tank-1) and reared at two temperatures (30 and 34 °C) in recirculation systems for six weeks. Fish were fed twice a day (8:00 and 16:00h) with an experimental diet containing 47% protein and 10% lipid. At the end of the experiment, fish were sampled every 4 hours to obtain daily patterns of processes related to digestive activity. Cobia reared at 30oC grew faster and with higher FCR than those at elevated temperature (34oC). The fish reared at high temperature had lower intestinal luminal pH but similar gastric pH. Overall the pepsin activity during the complete daily cycle, but it was significantly different from the fish maintained at 30oC only at 8 hours post-feeding. Similarly, the trypsin activity was not significantly affected by the water temperature but tended to be higher at 34°C during the first hours postfeeding. The transit rate was notably faster 34°C in the stomach but similar in the intestine. These results indicate that the slight increase of proteolytic activity that was observed at 34°C cannot compensate for the faster gut transit rate. The reduced time the dietary proteins are available for hydrolysis can explain the lower growth observed at this temperature.