Studies on the Lipids of Micronektonic Fishes caught in Sagami and Suruga Bays, with Special Reference to Their Wax Esters

Abstract

Following to the previous studies on micronektonic fishes in Sagami and Suruga Bays, five species of micronektonic shrimps, Acanthephyra quadrispinosa (A), Sergestes prehensilis (B), Sergestes lucens (C), Gennadas sp. (D) and Bentheogennema borealis (E), belonging to the order Decapoda were investigated. Most of them were not previously analyzed. Four species except for C show brilliant-reddish-natural carapace color. They live in the meso- and bathypelagic zones and undertake diel vertical migration as the micronektonic fishes do. These specimens were collected from surface to about 2000m depths in Sagami and Suruga Bays by ORI-plankton net and Isaacs-Kidd midwater trawl at night.The lipid contents of the micronektonic shrimps on the wet weight basis were 1.7% in C, the least value of all, and about a few per cent in A and B, and over 10% in D and E. Their lipids had 17.9% wax esters in C, around 30% in A and B, and more than 60% in D and E. As the representative examples of micronektonic shrimps, A and E were chosen and their viscera, muscle and carapace lipids were analyzed. The viscera contained the highest amounts of lipids (32.0% in A and 61.2% in E), however, the wax ester contents were almost equal even in the different tissue lipids of same specy.The wax esters cover the range from C30 to C46 with exceptional C which has rather shorter range. The major esters are C34, C36, C38, C40, C42, and C44, and also a trace amounts of odd numbered esters exist. Since the acid moiety of wax esters is dominantly monoenoic and docosahexaenoic acids and the alcohol moiety consists mainly of C16 : 0, C20 : 1 and C22 : 1, the combined wax esters range rathers longer esters. The fatty acid composition of triglycerides shows less highly unsaturated fatty acids, while that of free fatty acids reveals rather larger amounts of them, and fur thermore that of phospholipids contains the largest amounts of docosahexaenoic acid (4749%).Finally the importance of such studies on the micronekton was discussed and emphasized from the stand-points of food hygiene as well as of exploitation of marine resources, because the micronektonic fishes and shrimps rich in the wax esters would be mixed in the capture as the fishing grounds extend from horizontal to vertical directions.