Studies on nutritive value of dietary lipids in fish-XXXII. Essential fatty acids of grass carp Ctenopharyngodon idella.

Two feeding experiments were conducted to detect any essential fatty acids (EFA) deficiency and clarify EFA requirement of grass carp Ctenopharyngodon idella by feeding diets containing various fatty acids. The fish fed diet without EFA (fat-free and 12:0 alone diets) showed high percentages of vertebral column curvature (VCC) which exhibited an upward displacement of the column at the region of the 12-15th vertebrae from the caudal end, indicating lordsis. At a 1% level of dietary n-6 or n-3 fatty acids, the diet containing 18:3n-3 performed better than that containing 18:2n-6. However, a higher percentage of the VCC was still observed in the fish fed the 1% 18:3n-3 diet, sug-gesting that 18:3n-3 inspite of its positive role on growth, could not prevent the occurrence of VCC. On the other hand, the addition of 1% 18:2n-6 to the diet completely prevented the appearance of the VCC. The highest weight gain and feed efficiency were observed in the fish fed the diet con-taining pollock liver oil plus corn oil or soybean oil mixture. Next in performance came the fish fed both 1% 18:2n-6 and 1% 18:2n-3 or 0.5% n-3HUFA diets. The ratios of 20:3n-9 to 22:6n-3 and 20:3n-9 to 20:4n-6 in polar lipid fractions of hepatopancreas showed less than 0.4 and 0.6 when fish fed the diet containing both 1% n-6 and 0.5 or 1% n-3 fatty acids. This experiment clearly indicated that VCC is one of the EFA-deficiency symptoms, and also suggested that the requirement of grass carp for dietary n-6 and n-3 fatty acids is found to be 1% and 0.5-1%, respectively.