Osmoregulation in three species of Ambassidae (Osteichthyes: Perciformes) from estuaries in Natal

Abstract

Whole blood osmotic regulation was evaluated in three co-ocurring, estuarine species of Ambassis exposed to ambient salinities from fresh water. Blood molality of all three species, acclimated to fresh water, showed significant increases over the range of ambient salinities. Histological investigation of Ambassis kidneys indicated that all three species have structurally advanced kidneys of the mesonephric type common to most teleosts which spend a proportion of their lives in a hyposmotic medium. Osmotic regulatory characteristics of Ambassis species are discussed in relation to their distribution in estuaries.