Starvation prior to slaughter in Atlantic salmon ( Salmo salar) : I. Effects on weight loss, body shape, slaughter- and fillet-yield, proximate and fatty acid composition

Abstract

During an 86-day winter period, triplicate groups of 20 Atlantic salmon weighing ca. 5 kg were fed a high-energy diet and subsequently starved for 0, 3, 7, 14, 30, 58 and 86 days prior to slaughter. Length, whole body and organ weights were recorded. Gutted fish were subjected to evaluation of visual fatness and X-ray computer tomography evaluation of body shape and visual fat deposits. Proximate and fatty acid analyses were performed on liver, viscera, and different fillet segments. Starvation for 86 days resulted in an 11.3% weight loss, whereas fish fed during the same period showed a 26.3% weight gain. The rate of weight loss was diminished with increasing starvation time. A systematic leaner body shape was documented by decreases in visual fatness score, condition factor and in the ratios of the cross-sectional height, width and area to fork length with increasing starvation time. Slaughter yield increased systematically up to 30 days of starvation, whereas fillet yield decreased after 58 and 86 days starvation. Fillet fat content was slightly lower after 58 and 86 days of starvation compared with normally fed fish. Predicted visual fat deposits (by X-ray tomography) were not significantly affected by starvation time. Independent of starvation time, a high variation in fat content was found among different fillet segments. The fillet protein content was higher in fed fish (0 days starvation) than in fish starved for 86 days. Some significant, but marginal differences in the fatty acid composition of muscle, belly flap and liver between fed and starved fish were observed. Both protein and fat were important sources of energy during starvation. Fillet was used most, followed by viscera and liver. Long-term starvation at winter temperatures seem to produce only marginal changes in body composition of big Atlantic salmon, but rather a shrinkage of the total body mass as illustrated by weight loss, less fillet-yield and a leaner body shape in starved fish.