Effects of the extensive culture system as finishing production strategy on biometric and chemical parameters in rainbow trout

The effect of finishing extensive farming period, to reduce fat content and manipulate the fatty acid profile of fish muscle, was evaluated in rainbow trout. Fish were stocked in an artificial lake, in which fish were fed only on naturally available nutrients with no supply of artificial feed, for different lengths of time from 0 to 120 days. No weight loss was noted during the whole finishing period while total length increased from 228 ± 7 to 269 ± 3 mm and the condition factor decreased from 1.41 ± 0.04 to 0.89 ± 0.02. The total fat content of the fillets decreased considerably from 4.7 ± 0.6% at the beginning to 2.4 ± 0.4% and 0.7 ± 0.2% after 45 and 120 days respectively. Fillet fatty acid composition was affected by the time of stocking in the extensive farm. In contrast to the reduction in C18:ln-9, C18:2n-6, total monounsaturated fatty acid and total n-6 percent values, an increase in the C20:5n-3, C22:6n-3, total polyunsaturated fatty acid and total n-3 percent values was observed. It was shown that while other finishing strategies for salmonids have some disadvantages, the extensive culture system seems to be a potentially useful tool for increasing the general quality of the end product.