Effects of long term feeding diets differing in protein source and pre-slaughter starvation on biometry, qualitative traits and liver IGF-I expression in large rainbow trout

The effects of feeding two complete extruded diets differing in protein source (fish meal-FM vs. vegetable proteins-VP) over 30 weeks and subsequent 30 days of starvation on biometry, fillet composition and liver IGF-I mRNNA were studied in large rainbow trout. At the end of the feeding period, the dietary protein source little affected major biometry traits, dressing out yields and overall adiposity (P>0.05) but fish given the VP diet resulted in higher content of PUFA n-6 fatty acids in muscle (0.46 vs. 0.22 g/100g fillet, P<0.05). Regardless of the previous diet, 30 days of starvation resulted in increased carcass yield (P<0.05), in a slight reduction in adiposity (P>0.05) and of all fatty acids in fillet (P<0.05), except DHA. Liver IGF-I mRNNA content was little affected by the test diet and starvation.