Water temperature differentially affects the feed transit time through stomach and intestine in Cobia fry

Abstract

Efficient macronutrients digestion depends on the time the feed is available for hydrolysis within the different sections of the digestive tract under the appropriate digestive enzymes. In fish, feed transit rates usually are estimated from gut filling or evacuation after a unique meal. Nevertheless, food residence time within the gut is dependent on the feeding frequency, as well as on the environmental conditions. In this study we have analyzed the transit rate in the stomach and intestine in early juveniles of cobia (Rachycentron canadum) under routine feeding and at two different temperatures. 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 16:00 h) with a diet containing 47% protein and 10% lipid. The diet included yttrium (Y) as marker only in the morning meal. At the end of the experiment, fish were sampled every 4 hours and Y-content in the stomach and intestine was analyzed by ICP-mass spectrometry. Total gut content at each sampling time was estimated from the weight of the stomach and intestine, and the transit rate from the difference of Y content between successive sampling. In juvenile cobia, mass and volume of the stomach are much higher than in the rest of the intestine. The feed transit rate in the stomach was notably faster at 34 than at 30 °C during the first eight hours post-feeding; afterwards the rate was similar at both temperatures. Contrarily, no differences were found in the intestine, but transit rate declined drastically to residual values 12 h post-feeding. The increased temperature induced a change of filling pattern and a decrease of food residence time in the stomach.