First record of predation by the alien invasive freshwater fish Micropterus salmoides L. (Centrarchidae) on migrating estuarine fishes in South Africa

Abstract

This study presents results from stomach content analysis of 123 largemouth bass, Micropterus salmoides, sampled at the mouth of the fishway leading into a 3 m high  weir at the tidal limit of the Kowie River, Eastern Cape Province (33°32’39”S, 26°46’ 52.3”E). Stomach contents from small (120–240 mm fork length, FL) and large  (250–440mmFL) fish were analysed separately. Fish were the dominant prey item in small bass, followed by terrestrial insects and Potamonautes sp. In large bass, Potamonautes sp. dominated the stomach contents, while fish were less dominant and other prey items were considered incidental. Estuarine fish species, Monodactylus falciformis, and two species of the family Mugilidae, Mugil cephalus and Myxus  capensis, were the most common fish prey in both size classes of M. salmoides. These results are the first evidence of the alien M. salmoides preying on these three  indigenous estuarine species during their migration into fresh water.

Key words: predation, fishway, migration, Monodactylus falciformis, Mugilidae, Micropterus salmoides.