Dietary composition of Gambusia affinis (Family Poeciliidae) populations in the northern Waikato region of New Zealand

Invertebrates were collected and identified from the stomach contents of eight mosquitofish (Gambusia affinis) populations in the northern Waikato region of New Zealand at 3-month intervals from December 1994 to September 1995. To investigate temporal and spatial patterns in dietary composition a novel analysis programme was created that used Cower's similarity coefficient. The analysis found differences in diet among months, lakes, and three size groups of mosquitofish (less than or equal to 15, 15-25, and greater than or equal to 25 mm). Smaller mosquitofish fed mostly on zooplankton whereas larger G. affinis ate greater quantities of terrestrial fauna and large invertebrates. These differences are probably correlated with gape size and visual acuity, although ecological factors may also be important.