Fat deposition and flesh quality in seawater reared, triploid brown trout (Salmo trutta) as affected by dietary fat levels and starvation

Three isoproteic (crude protein content: 56%) diets with different fat leve ls (11%, 20%, and 26%) were fed to triplicate groups of triploid brown trou t (initial average body weight of 1.5 kg), reared in seawater. At the end o f 3 months of feeding, fish fed the high-fat (HF) diet were split into two groups: a triplicate group of fish received the low-fat diet and another tr iplicate group was kept unfed for a further 2-month period. Fish initially fed the low-fat diet during the first period were continued to be fed the s ame diet. Fish fed the medium-fat (MF) diet during period 1 were eliminated for period 2. At the end of each period, comparative whole body analyses, sensory and instrumental (texture and colour) analyses were made on fresh a nd smoked fillets. During the first period, increasing dietary fat level ha d no significant effect on growth or feed utilisation, but increased whole body (14.6% to 17.9%, on wet weight basis) and muscle (8.3% to 11.0%) fat c ontent. During the second period, the fish fed the low-fat diet had similar growth performance irrespective of previous nutritional history, whereas s tarvation led to significant loss of weight and fillet yield. Whole body fa t content did not differ between groups (around 15%) at the end of period 2 . In fish initially fed the HF diet, both starvation and feeding a low-fat diet led to a reduction in muscle lipid content. Sensory analyses revealed few differences between treatments, in terms of visual colour aspects, for both cooked and smoked fillets at the end of period 1. A positive relations hip between instrumental colour analyses (L*, a*, b* values) and dietary fa t levels was observed, but no difference was observed for instrumental text ure measurements. At the end of period 2, a significant increase in paramet ers of colour was observed in unfed fish. Although both feed withdrawal and feeding a low-fat diet 2 months before slaughtering led to a reduction in fat content, starvation had the disadvantage of leading to significant weig ht loss. (C) 2001 Elsevier Science B.V. All rights reserved.