Chemical compositions of commercial cobia feeds in Taiwan and the effects of the practical finisher diets on the fish meat quality.

Abstract

The chemical compositions of fifteen commercial feeds of cobia (Rachycentron canadum) from six feed manufacturers were analyzed. The effect of two diets designated as A (low protein: 46.3%, low fat: 16.8%) and B (high protein: 48.6%, high fat: 19.9%) on the chemical compositions and meat quality of the fish raised in a practical commercial production scale were also investigated. The commercial cobia feeds had different sizes and shapes according to the culturing stages of the fish. The moisture contents of the feeds ranged from 3.56% to 9.91%, ash 9.40% to 13.32%, protein 41.15% to 50.86%, fat 10.85% to 21.34%, and carbohydrate 15.24% to 24.32%. The major fatty acids were C16:0 and C18:1n-9. The levels of n-3 polyunsaturated fatty acids including EPA and DHA were also high (ranged from 6.05% to 14.22% and from 4.42% to 14.81%, respectively); suggesting that the feeds contained good levels of fish oil. When two finisher diets were fed to two groups of cobia for two months to grow the fish to their marketable size (5~6 kg/fish), the protein, fat, ATP-related compounds, free amino acids and anserine in both dorsal (D) and ventral (V) meats of the fish tended to increase with a raise of 2.37% protein plus a raise of 3.14% fat in the diets. The fatty acid profiles of D and V meats from A and B groups were relatively similar to those of the two diets. The predominant fatty acids were C16:0, C18:1n-9, C16:1n-7, EPA and DHA. However, n-6/n-3 ratios in both D and V meats changed from 0.51 or 0.50 to 0.66 or 0.69 with the raise of protein and fat levels in the diets.