Acclimation of European seabass (Dicentrarchus labrax) to freshwater and determination of its optimal feeding rates in freshwater

The study is composed by two sections: In the 1st and 2nd experiments. of the Ist Section, it was shown that European sea bass, in two different sizes (1.70±0.26 ve 25.58±1.58 g), could be successfully acclimated from seawater to freshwater by short (2days) or long (lOdays) acclimation methods. Without acclimation, direct transfer resulted in cessation of feeding and heavy fish mortality. During the short acclimation period, survival was not adversely affected, but feeding activities were negatively influenced. No fish mortality occurred during the long acclimation method and that fish feeding activity index was also similar to that of the control group. Different acclimation methods were investigated in the 3rd experiment in order to acclimate the European sea bass with the least possible stress from seawater to freshwater. During the acclimation to the Seyhan Dam Lake water, the effects of salt and/or vitamin supplemented diets on survival and blood parameters (Na+, K+, CI", and haematocrite concentration) of fish, which had been grown on a normal or salt supplemented diet in well water for 1 month prior to the onset of the experiment, were studied and the results were discussed. It was clearly determined that the 7-day acclimation protocol was appropriate and that the fish must not be directly stocked into the lake water without acclimation. Three feeding experiments were carried out in the 2nd section. In the 1st experiment, 5 feeding rates (2.0, 2.5, 3.0, 3.5 and 4.0% body weight/day (BW/day)) were tested for 50 days to find optimal feeding rate for the sea bass (32 g) acclimated to freshwater. Highest growth and food conversion efficiency (FCE) were found in the group fed 3.0% BW/day feeding rate. Specific growth rate (SGR) showed an increase up to 3.0% BW/day, but declined above that feeding rate (3.5-4.0% BW/day). Throughout the experiment, condition factor (CF), viscera lipid, protein and dry matter contents increased with the increase in feeding rates (p<0.05), however, no significant difference was apparent in hepatosomatic index (HSI), viscerosomatik index (VSI), fillet rate (FR), fillet protein, lipid, dry matter or ash contents among the treatments (p>0.05). In the 2nd experiment, which lasted 60 days, the fish (2.62 g) were fed on 5 feeding rates (2.0, 2.5, 3.0, 3.5, 4.0% BW/day and ad libitum) in order to asses optimal feeding rates in both freshwater and sea water. Data of SGR and FCE have shown that optimal feeding rate was 3.5-4.0% BW/day in either water media. Fish fillet protein, ash and CF were similar (p>0.05), whereas, FR, HSI and VSI, lipid and dry matter were all significantly rose with increasing feeding rate in both groups (p<0.05). The effects of 6 different diets (control, 1, 3, 5, 7 and 9%) supplemented with salt (NaCl) on growth, FCE and fillet composition of fish (4.87 g) were studied for 50 days in the 3rd experiment. The fish fed with added salt had 20.76% more weight gain as compared to that in the control group (p<0.05). SGR was 1.78%/day in the control group whilst this was 2.12-2.23%/day in the groups fed with salt added diet (p<0.05). Highest FCE was obtained in the group fed with 1-7% salt in their diets (p<0.05). An increase in the salt level did not affect meat protein, dry matter or ash content, but raised the lipid level by 1-7% in meat of the fish. Keywords: Dicentrarchus labrax, Freshwater, Feeding rate, Fillet Composition, Dietary Salt II