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Predation on native tadpoles by non-native fishes in South Florida

Introductions of non-native fishes have been implicated as one of the major causes of amphibian population declines (Kats and Ferrer, 2003). In south Florida, there is little information on the interactions between amphibians and non-native fishes, even though over half of the fish fauna is non-native (Courtenay, 1997). While many non-native fishes in South Florida are predatory to some degree (Hogg, 1976; Loftus and Kushlan, 1987), information about predation on tadpoles is scarce. The purpose of this project is to determine whether selected species of non-native fishes currently established in Everglades National Park will consume native tadpoles.

Mayan cichlid Cichlasoma urophthalmus

African jewelfish Hemichromis letourneuxi

Black acara Cichlasoma bimaculatum

Non-native fishes to be studied include Cichlasoma urophthalmus, Hemichromis letourneuxi and C. bimaculatum. These species were chosen because they are established in Everglades National Park and display carnivorous or omnivorous habits. Tadpole species most likely to be used are Hyla cinerea and Rana sphenacephela. If these species are unavailable, we will substitute Acris gryllus, Bufo terristris or Pseudacris nigrita. These species were chosen because they are common throughout Everglades National Park, especially in seasonally inundated marshes and solution holes, and they breed in water bodies inhabited by fish.

Experimental Methods

In this experiment, each non-native fish species will be tested with three prey treatments: tadpoles alone, Gambusia alone or tadpoles and Gambusia combined. Fish will be allocated to one of these three treatments; no fish will be used more than once. Prey will be introduced into the experimental aquaria 24 hrs before the experiment, to allow them time to equilibrate. Predators will be starved 24 hrs before the experiment to be sure they are all at the same hunger level. The purpose of this series of experiments is to examine the susceptibility of each tadpole species and the Gambusia to a chosen predatory fish when presented alone (e.g., only one prey type per each individual predator) and together (i.e., to test whether the predator exhibits a preference for either prey species).

Extremely fast digestion of tadpoles in fish guts is one hypothesis that may explain the lack of tadpoles in the diet studies of non-native fishes. Therefore, we aim to determine the rate at which tadpoles are digested by three non-native fishes: C. urophthalmus, H. letourneuxi and C. bimaculatum. To do this, we will feed tadpoles to each species of fish, record when the fish consumes the tadpole, then sacrifice the fish at preselected intervals to determine the state of decomposition of the tadpole.

Results

This study is currently underway. Please check back for results in summer 2008.

References

Courtenay, W.R., Jr., 1997, Nonindigenous Fishes, in Simberloff, D., Schmitz, D.C., and Brown, T.C., eds., Strangers in paradise: Impact and management of nonindigenous species in Florida: Washington, D.C., Island Press, chap. 7, p. 109-122.

Hogg, R.G., 1976, Ecology of fishes of the family Cichlidae introduced into the fresh waters of Dade County, Florida: University of Miami, Ph.D. dissertation.

Kats, L.B., and Ferrer, R.P., 2003, Alien predators and amphibian declines: Review of two decades of science and the transition to conservation: Diversity and Distributions, v. 9, p. 99-110.

Loftus, W.F., and Kushlan, J.A., 1987, Freshwater fishes of southern Florida: Gainesville, Bulletin of the Florida State Museum of Biological Science, v. 31, no. 4, p. 147-344.

For more information, contact:

Denise R. Gregoire or Jacqueline N. Langston
U.S. Geological Survey
7920 NW 71st Street
Gainesville, FL 32653
(352) 264.3527; 264.3530
dgregoire@usgs.gov;jlangston@usgs.gov

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