The influence of turbidity on juvenile marine fishes in estuaries. Part 2. Laboratory studies, comparisons with field data and conclusions

The turbidity preferences of juveniles of 10 marine species common in estuaries of southeastern Africa were investigated in an experimental turbidity gradient. The tests allowed the elimination of all environmental factors except turbidity. Liza dumerilii (Steindachner), was found to be a clear-water species (< 10 NTU); L. macrolepis (Smith), Rhabdosargus sarba (Forsskal), Gerres filamentosus Cuvier, and Valamugil buchanani (Bleeker), preferred “clear to partially turbid” water (< 50 NTU); Monodactylus argenteus (L.) preferred intermediate turbidities (10–80 NTU); and the remaining four, Rhabdosargus holubi (Steindachner), Acanthopagrus berda (Forsskal), Pomadasys commersonni (Lacépède) and Terapon jarbua (Forsskal), were indifferent to turbidity. Statistical analysis of laboratory and field data revealed significant correlations. The results of these are discussed in relation to fish distribution patterns, ecology, and the importance of turbidity to juvenile marine fishes in estuaries.