Rapid cold-induced changes of fatty acids and intestinal histology in tilapia (Oreochromis niloticus) 100% fed rapeseed oil and fish oil diets

The present study aimed at evaluating the effects of rapid cold-induced changes of fatty acid and intestinal histology of Nile tilapia (Oreochromis niloticus) fed with rapeseed (RO) and fish oil diet (FO). Fish (18.5±0.6 g) were transferred into two thermo-controlled recirculation systems (control and cold-induced) connected to 6 tanks/each RAS. The control group was maintained at 26 °C consistent with the original temperature. After conditioning period, temperature of the cold-induced group water temperature was decreased by 0.3 °C every 24 h over a 3-day period to a cold-induced temperature of 20 °C and this group fish was held at this temperature for one week. After cold period, fish were acclimated again to 26 °C within 3 days and were at this temperature for two weeks. Each experimental diet was fed daily to fish two times daily (3% body weight d-1). There were no adverse affect on growth and survival during conditioning and cold-induced period in fish fed both FO and RO diet. Growth differences across the treatment were not different. Fish in all groups reserved DHA in their tissues. However, after that period fish increased utilization of the MUFA, specifically oleic acid. Typically, intestine of fish fed RO showed supranuclear accumulation of various-sized lipid droplets in the apical part of the enterocyte while fish fed FO showed more ordered lipid droplets distributed among the enterocyte under cold condition.