Comparison of fatty acid composition of muscle, liver, mature oocytes, and diets of wild and captive Macquarie perch, Macquaria australasica, broodfish

Abstract

Macquarie perch, an Australian native freshwater species, does not respond to hypophysation when caught from the wild, spawned and subsequently held in captivity. In this paper, the fatty acid composition of the liver, mature oocytes, muscle and diets of wild and tank-reared fish are compared. The fatty acid profiles of the two groups of fish were closely related to their diets, and of the fatty acid profiles, those of the liver showed the least variation between years. The most significant differences in the fatty acid profiles of the two groups were observed in the liver, in which tank-reared fish had more monoenes, largely 16:1 n − 7, but less n − 6 fatty acids and a higher n − 3 to n − 6 ratio than did wild fish. Muscle differed from other tissues in that 16:0 and 16:1 n − 7 acids were present in greater amounts than 22:6 n − 3 and did not show a consistent variation between wild and tank-reared fish. In the mature oocytes of wild fish polyunsaturated fatty acids were present in consistent amounts between years. The mature oocytes of tank-reared fish had lower levels of n − 6 fatty acids and as a result these oocytes had significantly higher n − 3 to n − 6 ratios compared with those of wild fish. Principal component analysis indicated that the fatty acid composition of all three tissues was clearly separable in the two groups of fish. It is hypothesised that the low levels of n − 6 fatty acids, in particular 20:4 n − 6, in the diet of tank-reared Macquarie perch, may be responsible for the lack of response to hypophysation techniques in these fish, owing to the lack of precursors for the synthesis of prostaglandins. It is also suggested that Macquarie perch, like its marine relatives, is incapable of de novo synthesis of the highly unsaturated fatty acids of the n − 3 and n − 6 series and has to rely on its diet for these fatty acids.