An experimental analysis of foraging and aggressive behavior between mosquitofish and bluegill

Background/Question/Methods

Mosquitofish (Gambusia affinis) have been introduced worldwide and are found in small ponds in Ohio.  Mosquitofish may occupy the same niche and share common prey with native bluegill sunfish (Lepomis macrochirus) especially juveniles living in the littoral zone.  Research has shown that invasive species can influence the foraging efficiency of native species due to competition as well as aggression between the two species.  Studies also show that mosquitofish can display aggressive behaviors toward each other, which may influence their foraging success.  We experimentally tested for foraging and aggressive behaviors between an invasive species, mosquitofish, and a native species, bluegill.  Individual bluegill, female mosquitofish, and male mosquitofish were used in eight treatment combinations: each alone, bluegill with female, bluegill with male, male with male, female with female, and male with female mosquitofish.  Fish behaviors in the presence of food were filmed, and we then quantified feeding and foraging attempts.  In particular we determined handling time as the seconds between grasping the food and swallowing it, feeding time as the seconds between orienting toward a food item and swallowing it, and proportion of time spent on foraging activities during the observation period.

Results/Conclusions

Fish spent the same proportion of time on foraging activities regardless of fish treatment, however the time spent on specific foraging activities sometimes differed among treatments.  Male mosquitofish spent more time successfully handling food when paired with a same-sex partner or when alone than when paired with a female mosquitofish or a bluegill.  The feeding time by female mosquitofish was significantly reduced when the female was paired with a male mosquitofish or a bluegill.  On average, bluegill spent significantly more time feeding when paired with male mosquitofish, than when alone.  Our findings from these head-to-head interactions suggest that for mosquitofish, the presence of bluegill or a conspecific of the opposite sex reduces time spent on individual foraging activities.  For bluegill, feeding time seems to be enhanced by the presence of male mosquitofish.  Thus, for native bluegill living in small ponds, the presence of male moquitofish may not negatively influence their foraging activities as long as food is abundant.  However, the presence of bluegill or members of the opposite sex may negatively impact the foraging activities of mosquitofish.