The comparative study of endemic cottoid fishes (Cottidae, Comephoridae) and their adaptation to pelagic habitat in Lake Baikal

Abstract

This article describes the adaptive processes in the evolution of bladderless fish from benthic to secondary pelagic habitation in both Lake Baikal and the Antarctic eco-systems. It demonstrates how lipids play a major role in the achievement of neutral buoyancy by the endemic Baikalian species, genus Cottocomephorus (Cottidae family), and Comephorus (Comephoridae family), similar to the Antarctic secondary pelagic species of the Notothenioidei suborder. In addition, it also describes how the skeletons of these species became lighter due to bone mass reduction and lower mineralization; and how fin surface area became larger than that of the rest of the body in order for these secondary pelagic fish to attain appropriate balance and floatation.