Mortality of Rainbow Trout Due to Ingestion of Fire Ants in the Peruvian Andes

AUTHOR(S): Robert J. Eakins, Dean G. Fitzgerald, Alan J. Burt, Dennis G. Farara, Guillermo Tello

CITATION:

Eakins, R.J., D.G. Fitzgerald*, A.J. Burt, D.G. Farara and G. Tello. 2006. Mortality of rainbow trout due to ingestion of fire ants in the Peruvian Andes.

Poster presented at the 136th American Fisheries Society Annual Meeting, September 10-14, 2006, Lake Placid, New York.

ABSTRACT:

Mountain streams of the Peruvian Andes have low fish species diversity, and also generally have low productivity. Rainbow Trout (Oncoryhncus mykiss), which were introduced to these coldwater streams, have become an important supplement to indigenous peoples diets.

The protection of these aquatic resources is a high priority for local inhabitants. Two separate kills of Rainbow Trout were reported (~1000 fish in total) downstream of a copper mine. An investigation was promptly undertaken by the mine. Due the existence of an established environmental effects monitoring program, it was possible to quickly rule out the mine as the cause of the fish kills. Total evidence from this study identified selective mortality through natural causes. Examination of the gut contents of the dead Rainbow Trout revealed the presence of nonnative fire ants (Solenopsis invicta) which are known to be toxic to fish. The fire ants construct mounds along the streambanks, and winged ants were apparently washed into the stream following rain events, leading to predation by adult Rainbow Trout. By contrast, young-of-the-year Rainbow Trout and native sucker-mouth catfish (Astroblepus spp.) that consume primarily smaller benthic-oriented prey, avoided the same fate.

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