Influence of dietary fat level and increased adiposity on growth and fatdeposition in rainbow trout, Oncorhynchus mykiss (Walbaum)

摘要

Rainbow trout, Oncorhynchus mykiss (Walbaum), (initial weight approximate to 90 g) were fed diets differing in fat content (27.5% versus 12.6%) to examine the effects of dietary fat level on growth and fat deposition. During phase 1, which was run for 11 weeks, the fish were fed either a high- (27.5%) or low-fat (12.6%) diet. The fish were held at 14.5 degrees C under a 24 h:0 h light:dark photoperiod and were fed for 4 h each day during this phase. Subsequently, in phase 2, both diets were presented simultaneously, and the influence of adiposity on growth and fat deposition was examined in a growth trial which lasted for 8 months, There were no significant differences in body weights at the end of phase 1 (360.7 +/- 7.7 g versus 348.2 +/- 18.7 g for the fish on the high- and low-fat diets, respectively), but body composition was influenced by the fat content of the diet. The trout fed the high-fat diet had higher viscerosomatic indices (VSI: 11.7 +/- 2.0% versus 9.1 +/- 0.7%) and higher visceral fat contents (per cent fat: 38.0 +/- 6.7% versus 23.3 +/- 3.7%) than trout fed the low-fat diet, The percentage fat contents of the carcass (per cent fat: 12.4 +/- 1.0% versus 9.3 +/- 0.7%) and whole body (per cent fat: 15.4 +/- 1.6% versus 10.5 +/- 0.7%) were higher amongst the trout fed the high-fat diet, and these fish had a higher energy gain than those fish fed the low-fat diet. Differences in adiposity between the trout fed the high- and low-fat diets did not result in any differences in weight gain when the fish were provided with both diets simultaneously. During phase 2, the fish that had previously been fed the low-fat diet deposited more fat than those fed the high-fat diet during phase 1. The latter maintained whole body fat concentrations at approximate to 15% (phase 1: 15.4 +/- 1.6%; phase 2: 15.2 +/- 1.2%), whereas the fish that had been fed the low-fat diet increased their body fat concentration during phase 2 (phase 1: 10.5 +/- 0.7%; phase 2: 14.7 +/- 1.3%). Thus, there were no significant differences between groups in either body weight or proximate composition by the end of the experiment.