Ecology, Osmoregulation and Reproductive Biology of the White Steenbras, Lithognathus Lithognathus (Teleostei: Sparidae)

Abstract

AbstractOver a one-year period 437 steenbras, Lithognathus lithognathus, ranging from 8-39 cm fork length were sampled from the Heuningnes River Estuary. The length-weight relationship was linear and there was no fluctuation in the modal size range throughout the year. Steenbras up to the age of six years and over inhabited the estuary, adapting to large salinity fluctuations. Abundance of food items, mainly Crustacea and Annelida, and virtual absence of predators made the estuary an ideal nursery ground. Ectoparasitic infestation by leeches and copepods was moderately intense without causing any apparent deleterious effects.In a series of experiments designed to study osmoregulation in steenbras, it was found that haematocrits from fish sampled after 48 hours in freshwater were significantly (P<0,01) higher than the seawater controls. Two of the five protein fractions, however, as well as total protein, chloride, sodium, potassium and osmolality were all significantly (P<0,01) decreased in freshwater. St...