Turbidity-induced changes in feeding strategies of fish in estuaries

ENGLISH ABSTRACT: The aim of this study was to determine the effect of turbidity on the feeding strategies of fish in estuaries. Three species representing different feeding guilds were selected for the investigation. These were Elops machnata (representative piscivore), Pomadasys commefsonnii (a macrobenthivore) and Athefina breviceps (a planktivore). The stomach contents of these fish were examined from a clear and a turbid estuary and some experimental work was carried out on A. brevic8ps to test the hypothesis that turbidity affects feeding behaviour. Turbidity was found to have no effect on size selection of prey, but feeding rate, particularly of visual predators, was reduced at higher turbidity levels. This was caused by a decrease in the reactive distance of the fish. It would appear that in order to optimize the aquisition of food under different turbidity conditions fishes have the ability to change their feeding strategies. Visual predators are more affected by turbidity than are macrobenthic feeders. *********** AFRIKAANSE OPSOMMING: Die doeI van hierdie ondersoek was om die invloed van watertroebelheid op die voedingstrategie van vis in getyriviere te ondersoek. Drie spesies met verskillende voedingsgewoontes is gekies vir die ondersoek, naamlik E/ops machnata (verteenwoordigende visvreter), Pomadasys commefsonnii (makrobentiese vreter) en Athefina bfeviceps (planktonvreter). Die maaginhoud van hierdie vissoorte vanaf 'n helder en 'n baie troebel getyrivier is ondersoek en ontleed. Sekere eksperimentele werk is ook onderneem om die hipotese te toets dat watertroebelheid 'n verandering in die vreetgewoontes van vis teweeg bring. Die resultate het gewys dat troebelheid geen effek het op die grootte van die prooi wat geselekteer word, maar dat voedingskoers verlaag, hoofsaaklik by visuele roofvisse as gevolg van 'n afname in die reaktiewe afstand van die vis. Visuele roofvisse word tot 'n groter mate as makrobentiese vreters deur watertroebelheid geaffekteer.