An experimental study of the effects of predatory fish on macroinvertebrates in a Hong Kong stream

Abstract

Predation upon macroinvertebrates by loach Oreonectes platycephalus (Cobitidae) was studied. Taxa were influenced differently, with mayflies decreasing by a factor of two while the more mobile shrimps (Atyidae) were unaffected. Chironomid abundance (largely Chironominae) was unaffected by predator density and increased in week four. Detritus acted as a confounding variable at this time. While invertebrates were more abundant in cages lacking fish, there were no fewer invertebrates in cages with two fish than with one fish. This may indicate the presence of secure refuges among substrates in the cages. No significant effects of predators on relative prey abundance or species richness were detected. -from Author