Lipid composition and partitioning of deepwater chondrichthyans: inferences of feeding ecology and distribution

The composition of lipids and fatty acids was determined for the livers, muscle, pancreas, kidney and stomach fluids of deepwater chondrichthyan species (including 11 squaliformes, 3 chimaeriformes, 1 hexanchiforme and 3 carcharhiniformes) caught as bycatch from continental waters off south-eastern Australia. The lipid class, fatty acid and fatty alcohol composition differed markedly in each tissue and in each species. The lipid and fatty acid composition of large, lipid-rich (38–70% wet weight, ww) livers demonstrated the multifunctional role of this organ in: lipid distribution, storage and biosynthesis, and buoyancy regulation. In the liver, the importance of certain lipids (including squalene, diacylglyceryl ethers, triacylglycerols and to a lesser extent wax esters) as mediators of buoyancy varied according to lifestyle and habitat. Less variability was observed in the muscle profiles, characterized by low lipid content (<1.0% ww) and high relative levels of polar lipids (>70%). The lipid and fatty acid profiles of the kidney and pancreas showed the highest intraspecific variability, suggesting these organs also have complex roles in lipid storage and metabolism. Overall intra- and interspecific differences in the tissue fatty acid profiles could be related to differences in a number of factors including phylogeny, habitat (depth), buoyancy regulation and diet and presumably also reflect different ecological roles. The lipid and fatty acid profiles are the first published for Rhinochimaera pacifica, Chimaera lignaria and Figaro boardmani and the first to demonstrate interspecific variation in lipid profiles of various tissues of deepwater chondrichthyans. The application of multivariate analysis to lipid class and fatty acid tissue profiles in chondrichthyans inferred dietary differences and metabolic preferences between species and habitats. These results have important implications for the future use of fatty acids as dietary tracers in chondrichthyan research.