Salinity ranges of some southern African fish species occurring in estuaries

Abstract

The recorded salinity ranges of 96 fish species occurring in southern African estuaries are documented. Factors influencing the tolerance of fishes to low and high salinity regimes are discussed, with most species tolerant of low rather than high salinity conditions. This is important since most systems are subject to periodic freshwater flooding, especially during summer. The penetration of freshwater teleosts and elasmobranchs into estuaries is examined and the occurrence of marine fishes in rivers documented. Mortalities arising from salinity extremes in southern African estuaries are discussed, with temperature a key factor initiating such fish kills. Only eight fish species have been recorded spawning in estuaries although the fry of many species are attracted to estuarine waters. It is concluded that a small percentage of southern African fishes have succeeded in utilizing estuaries and this may be attributed to the paucity of strong osmoregulators.