Effect of introduced mosquitofish on pacific treefrogs and the role of alternative prey

Mosquitofish (Gambusia affinis) are distributed by, many mosquito control p rograms because of their. broad habitat tolerance and because they are cons idered by some to be effective mosquito predators. As a result, mosquitofis h have become established as an exotic species in numerous perennial stream s in the Santa Monica Mountains within the last 10-15 years Previous studie s have found that mosquitofish prey heavily on California newt (Taricha tor osa) larvae that inhabit mountain streams. We found Pacific treefrog (Hyla regilla) tadpoles in the stomachs of 65% of stream-caught mosquitofish. In both laboratory, and field experiments, we found that mosquitofish preyed h eavily on treefrog tadpoles even when high densities of mosquito larvae wer e presented as alternative prey. Thus, despite apparent high densities of P acific treefrog populations, our experiments suggest that introduced mosqui tofish may negatively affect stream-breeding H. regilla in the Santa Monica Mountains.