The Fish Destroyer! Mosquitofish as a Biotic Resistance to Invasion

Peninsular Florida is a hotspot for freshwater fish invasions with 34 reproducing, introduced species. One characteristic of nearly all of these successful invaders is a maximum total length (TL) >150 mm. Why have small-bodied invaders been unsuccessful? One hypothesis is that native communities resist invasion. Recent research suggests that the small (< 50 mm TL), eastern mosquitofish Gambusia holbrooki has an important role in community resistance to invasion in Florida. The noted ichthyologist George Sprague Myers was prescient of this concept when he dubbed the mosquitofish “The Fish Destroyer” in 1965. Research around the world has repeatedly shown large impacts of introduced mosquitofish on native small-bodied fishes. As native species, they also interact strongly with non-native fishes. Mosquitofish prey on larval fish but also kill and consume fishes larger than themselves. Moreover, they are aggressive competitors, biting caudal fins and harassing other species. These agonistic behaviors influence survival, habitat use, and behavior of other small fishes. Habitat mediates interactions between mosquitofish and other species, with hydrology and structural complexity being important. Mosquitofish may exclude small-bodied, non-native fishes from structurally complex refuge habitat such as aquatic macrophytes, making these fishes more vulnerable to predators like largemouth bass Micropterus salmoides, a non-additive, multiple predator effect. Morphology plays a role in the interaction of mosquitofish and non-native fishes, but behavior, particularly behavioral plasticity and ability to use context-appropriate behavior, is vital in influencing the ability of small-bodied, non-native fishes to survive with mosquitofish. Continued research on mosquitofish in experimental tank and pond settings; with African jewelfish Hemichromis letourneuxi, the sole widespread, small-bodied, established invader; and in those few, localized habitats where small-bodied, non-native fishes are reproducing will produce greater insights into a relatively little-studied aspect of invasion ecology, the influence of resident predators/aggressive competitors on invasion success.