Comparison of total lipids and fatty acids from liver, heart and abdominal muscle of scalloped (Sphyrna lewini) and smooth (Sphyrna zygaena) hammerhead sharks.

Bruce Clement Davidson,Wynand Nel,Afsha Rais,Vahid Namdarizandi,Scott Vizarra,Geremy Cliff

doi:10.1186/2193-1801-3-521

Abstract

Liver, heart and abdominal muscle samples from scalloped (Sphyrna lewini) and smooth (Sphyrna zygaena) hammerhead sharks were analysed to characterise their lipid and fatty acid profiles. Samples were compared both between and within species, but there were no significant differences in total lipids for either comparison, although much greater total amounts were found in the liver samples. Within the individual fatty acids, the only significant differences were greater amounts of 22:6n-3, total n-3 polyunsaturates and total polyunsaturates in smooth, when compared to scalloped, hammerhead liver. This may reflect the more wide spread distribution of this species into cooler waters. Within both species the liver levels of the same fatty acid fractions decreased from spring to summer, which may correlate with changes in fatty acid profile to adapt to any differences in amount or species of prey consumed, or other considerations, eg. buoyancy, however there was no data to clarify this.

Highlights

The Indian Ocean coastline of South Africa is home to many species of shark, and some of these have the reputation of being dangerous to humans (Cliff and Dudley 1992; Cliff and Wilson 1986)
Given the dearth of data on elasmobranchs from this region and as part of a large project to quantify the lipids of South African shark species, in this study we report the results of analyses of the fatty acids found in the total lipid fractions from the livers of two of the mid-sized shark species resident in South African coastal waters - the scalloped hammerhead (Sphyrna zygaena) and the smooth hammerhead (Sphyrna lewini)
The relatively high levels of liver total lipid and the highly unsaturated nature of the fatty acids are indicative of the central role of the liver in lipid metabolism in elasmobranchs

Summary

Introduction

The Indian Ocean coastline of South Africa is home to many species of shark, and some of these have the reputation of being dangerous to humans (Cliff and Dudley 1992; Cliff and Wilson 1986). The main mechanism employed to reduce the incidence of shark attack was the placing of nets off the coastline to catch large sharks (Cliff and Dudley 1992; Cliff and Wilson 1986). This practice has led to the development of a large database of the sharks most commonly found off the KwaZuluNatal (KZN) coast While in most other vertebrates ketones are produced as a response to reduced availability of dietary input (Newsholme and Leech 1983), in elasmobranchs they are produced under normal circumstances as a primary energy source for extra-hepatic tissues (Chamberlin and Ballantyne 1992; Moon and Mommsen 1987; Moyes et al 1990; Singer and Ballantyne 1989). In contrast they do not provide the primary energy source for the liver as the capacity for hepatic ketone oxidation has been shown to be limiting (Ballantyne and Moon 1985, 1986; Mommsen and Moon 1987; Moyes et al 1986)

Methods

Results

Conclusion