Voluntary intake of diets with varying digestible energy contents and energy sources, by juvenile rainbow trout Oncorhynchus mykiss, using self-feeders

Abstract

A feeding trial using self-feeders was conducted to examine the ability of juvenile rainbow trout Oncorhynchus mykiss to voluntarily control their dietary intake of energy. A low-energy (LE) diet and three high-energy (HE) diets containing additional amounts of either protein (fish meal and casein, HP), fat (fish oil, HF) or digestible carbohydrate (dextrin, HC) to the LE diet, were prepared. Each diet was fed by self-feeders to four groups of 10 fish (initial weight: 85 g/fish) stocked in 60 L tanks under the following conditions for 8 weeks: photoperiod 14L:10D, water temperature 16°C, and reward level 0.25 g/activation. Percentage weight gain of the LE diet group was not different (P>0.05) from the three HE diet groups, but that of the HF diet group was significantly lower (P<0.05) than the HP and the HC diet groups. Feed efficiency of the HP and the HC groups was significantly higher than the LE group. Voluntary dry feed intake (per cent body weight per day, % BW/day) and gross energy intake (kJ/kg BW/day) tended to be high in the LE group and low in the HF group; however, digestible energy (DE) intake was not different among treatments. These findings indicate that rainbow trout voluntarily control DE intake per unit body weight irrespective of dietary energy content and energy source.