Effect of ration and seawater transfer on food consumption and growth of Atlantic salmon (Salmo salar) smolts

In Atlantic salmon smelts, fed at ration levels of 0.5, 1.0, and 3.0% body weight . day(-1), growth performance in fresh water was not a significant determinant of subsequent seawater growth (P > 0.05). X-radiography was used to measure food consumption rates of individual fish. Consumption rates of fish fed low and intermediate rations were similar in fresh water and seawater (P > 0.05). However, consumption rates for fish fed a high ration level were two times greater in seawater than in fresh water (P < 0.05), possibly owing to higher temperatures. Specific growth rates were generally negative in the period immediately following transfer to seawater and food consumption rates were lower than in fresh water for fish on high ration levels. Specific growth rates increased with increasing ration level in both fresh water and seawater. A linear regression model gave the best description for the relationship between individual specific growth rates and food consumption for all ration groups in both fresh water and seawater. Slopes and intercepts for the low ration groups in fresh water were similar to values for the same fish in seawater (P > 0.05). The intermediate and high ration groups had steeper slopes in seawater than in fresh water (P < 0.001).