Requirement And Regulation Of Arachidonic Acid In Young Cobia (Rachycentron Canadum)

Nine (9) groups of young cobia (Rachycentron canadum) (age: 70 days, body length: 13.41±0.12cm, body weight: 12.90±0.17g) with triplicate each were fed for 4 weeks in laboratory (sea-water temperature: 28-31.5℃, salinity: 27-33‰) using a control diets (D-C group) and eight (8) experimental diets (D1-8) with different levels of AA and various ratios of DHA/EPA/AA to study the dietary effects in young cobia during August 29th to September 28th , 2006.Two (2) groups of young cobia (age: 94 days, body length: 14.04±0.08cm, body weight: 17.84±0.13g) with triplicates each were fed for 16 days in the same above laboratory conditions using a control diet (D-C) and above eighth diet (named D-T) and then starved for 6 days to study the dietary and starved effects on the growth, survival, protein, fatty acids, the composition and ratio of RNA and DNA in young cobia during October 2nd to September 23rd in 2006 ,.The experimental results are as follows:(1) No significantly effect (P>0.05) of different levels of AA, various ratios of DHA/EPA/AA and starvation was found on the growth of young cobia in the AA experiment. The optimal amount of AA and optimal ratio of DHA/EPA /AA were 1.01% and 2.20/1/0.16, respectively. Six-day starvation caused the decline of growth in young cobia, but not significantly different (P>0.05).(2) The water composition in the young cobia was the highest, while the crude fat the lowest at the end of AA and starvational experiments.The water composition in the young cobia at the end of AA experiment was higher than week 0, however, it was not significant (P>0.05) except the young cobia fed D-7 (P<0.05); the crude fat composition was significantly lower than week 0 (P<0.05); except those fed D-C , D-1 and D-6, the crude protein in AA experimental young cobia was lower than week 0, but only the young cobia fed D-3 was significantly lower (P<0.05).Comparing to the crude protein, the crude fat was preferentially utilized as energy sources in young cobia, in the starvational experiment.(3) The fatty acid composition of the muscle, liver and serum in the young cobia was significantly affected by diet. Highly unfatty acids (HUFA) in the diet were selectively used and deposited .(4)AA biosynthetic pathway might exist in the young cobia because of the increatment of AA in both AA and starvation experiments.(5) The fact that the ratio of RNA/DNA in the muscle of young cobia was significantly correlated with its weight implied that the ratio of RNA/DNA could be used as an index of the fish growth.