Gastrointestinal evacuation time in European sea bass (Dicentrarchus labrax) fed diets containing mixture of vegetable oils at high temperature

The rate of gastric emptying is positively related with the return of appetite and food consumption in fish. Gastric evacuation is affected by various factors, including water temperature and diet composition. Thus, we hypothesized that increasing levels of vegetable oil could have effect gastrointestinal evacuation time (GET) at high temperature. Triplicate groups of European sea bass (initial 39.7 g) were fed three diets in which the added lipid was 100% fish oil (FO), 70% FO + 30% vegetable oil mix (15% canola:15% cottonseed oil;Miks-1) and 40% FO + 60% vegetable oil mix (30% canola:30% cottonseed oil; Miks-2) for a period of 120 days. Fish were held at optimum (24°C) and maximum (30°C) water temperature. At the end of experiment, fish were fasted for 72 h before being fed to make sure that gastrointestinal tract was empty. Six fish per treatment were sacrificed at 0, 8, 16, 24, 32 and 48 h after a single satiation feeding. The digestive tract was separated into three parts: stomach, foregut and hindgut. The mathematical models giving the best fit were found to tested diets being exponential for the stomach and linear for the foregut and the hindgut. The control diet (FO) required 9.0 h to evacuate half of the initial feed content in stomach, followed by Miks-1, 8.3 h and Miks-2 with 8.5 h at 24°C. However, GET for Kontrol, Miks-1 and Miks-2 were 7.97, 9.12 and 9.76 h at 30°C, respectively. While increasing levels of vegetable oil in the diet increased GET in stomach of fish held at 30°C, there was no dietary effect on GET at 24°C. The whole meal cleared from the foregut within 60.7-62.6 h for all dietary groups at 30°C. With regards to the effects of dietary vegetable oil level, it was found that while evacuation rates in foregut decreased in fish fed Miks-2 at 24°C, there was no significant dietary effect at 30°C. However, GET in hindgut was significantly higher in fish held at 30°C compared to fish held at 24°C. The GET computed for hindgut significantly longer in groups fed FO compared to the Miks-1 andMiks-2. The findings of this study suggest that 30% or 60% vegetable oil mixture could increase GET in the stomach; however, GET could decrease through digestive track for European sea bass fed with those diets at both temperature.