Wax esters versus triacylglycerols in myctophid fishes from the Southern Ocean

Abstract

Five species of myctophid fishes were collected by trawl from the Elephant Island region of the Antarctic Peninsula between 60°30′–62°S and 55°–61°30′W. Two species, Gymnoscopelus braueri and Krefftichthyes anderssoni were lipid-rich (406–456 mg g⁻¹ dry weight whole fish) with wax esters (WE) the major lipid class. In three species, G. opisthopterus, G. nicholsi, and Electrona carlsbergii, triacylglycerols (TAG) were the major lipid. All fish had oily bones, with values up to 471 mg g⁻¹ dry weight in the vertebral centra of K. anderssoni. The principal fatty acids of the TAG-rich myctophids included the monoenes 18:1(n-9) and 20:1. There were lower levels of 16:0 and 18:0 saturated fatty acids. Polyunsaturated fatty acids (PUFA) were present at higher abundance in the TAG-rich E. carlsbergii and G. opisthopterus, with lower levels in G. nicholsi. In comparison, the WE-dominated species contained lower levels of PUFA than in the TAG-rich species. The principal fatty acids of the WE-rich myctophids included the monoenes 18:1(n-9), 16:1(n-7), and 18:1(n-7), with lower levels of the saturated acids 16:0 and 18:0. Fatty alcohols were dominated by 16:0 and 14:0 and the monounsaturated 18:1(n-9) with 16:1(n-7), 18:1(n-7), and 20:1(n-9). Based on the fatty acid profiles, the diet of G. opishtopterus and G. nicholsi, previously thought to be mainly Euphausia superba, is suggested to include copepods and other zooplankton with only a minor krill component, possibly consisting of other species than E. superba.