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Southeast Ecological Science Center


 Effects of predatory fish on Rana capito
and Rana sphenocephala larvae

Denise R. Gregoire
Florida Integrated Science Center, USGS, Gainesville, Florida

Presented at the Joint Meeting of Ichthyologists and Herpetologists
the week of July 10, 2006 in New Orleans, Louisiana.


Southern Leopard Frogs Rana sphenocephala and Gopher Frogs R. capito are two species of anurans found in the southeastern United States whose larvae are very similar morphologically. Leopard Frogs are habitat generalists occurring in virtually all aquatic habitats within their geographic range, whereas Gopher Frogs are a species of conservation concern and only breed in semi-permanent fishless ponds. The introduction of predatory fish into historically fishless breeding sites has been suggested as a cause of Gopher Frog population declines.

Tadpole image mapGopher Frog (Rana capito) - click to enlargeLeopard Frog (Rana sphenocephala) - click to enlarge


The purpose of this study was to evaluate the effect of predatory fish on the survival and behavior of Leopard Frog and Gopher Frog tadpoles.


Leopard Frog and Gopher Frog tadpoles were reared from egg masses collected from a semi-permanent fishless pond on the Ordway-Swisher Biological Station in Putnam Co. Florida. The three species of fish used were warmouth sunfish (Lepomis gulosus), banded sunfish (Enneacanthus obesus) and the eastern mosquitofish (Gambusia holbrooki). All are commonly found in Leopard Frog breeding sites.

I conducted a randomized factorial experiment to examine the survival rate and behavior of the tadpoles when exposed to predatory fish. All possible combinations of the two tadpole species (Leopard Frog and Gopher Frog) and four predator treatments (warmouth, banded sunfish, mosquitofish and no predator) were represented. Each treatment was replicated five times.

Forty aquaria (50 x 25 x 30cm) were filled with well water. Two artificial refuges constructed from mesh screening were added to each tank to create cover for the animals. Each tank contained 30 tadpoles (total length 14.65 + 1.90 mm) of either species, and one predator according to the treatment.

Lab aquaria w/ artificial refuges - click to enlarge

Observation of tadpole hiding behavior (number of tadpoles underneath or inside a mesh refuge) were recorded periodically during the experiment. The experiment was terminated before any treatments reached 100% mortality. Surviving tadpoles were removed, counted and examined for injuries.

I also conducted choice experiments to examine tadpole survival when both species were simultaneously exposed to a predator. The choice experiments consisted of two treatments: predator (warmouth or banded sunfish) and no predator. Aquaria were set up the same as in the first experiment. 15 tadpoles (total length 22.94 + 3.20 mm) from each species were added to each tank along with one predator.


Tadpole Survival

Tadpole Survival - click to enlarge

Tadpole Injuries

Tadpole Injuries - click to enlarge

Tadpole Hiding Behavior

Tadpole Hiding Behavior - click to enlarge


Survival Rate

Tadpole survival was significantly affected by predator treatment (ANOVA, F3,24 = 16.07, P <0.01). Survival of both tadpole species was lower with warmouth than with either banded sunfish or mosquitofish.

Injury Rate

Mosquitofish inflicted more injuries than any other predator (ANOVA, F3,24 = 7.87, P = 0.01), and injured significantly more Gopher Frog than Leopard Frog tadpoles (ANOVA, F3,24 = 4.0, P = 0.02).

Hiding behavior

In all predator treatments, Gopher Frog tadpoles hid significantly more than Leopard Frog tadpoles (ANOVA F3,24 = 20.31, P < 0.01). Both species showed an increase in hiding behavior when exposed to warmouth and mosquitofish. (ANOVA F3,24 = 3.0, P = 0.05)

Choice Experiments

Warmouth consumed significantly more Gopher Frog than Leopard Frog tadpoles. (Paired t-test, t = -3.05, df = 7, p=0.02). Mean number of Leopard Frog survivors with warmouth was 11.0 + 3.01 compared with only 7.75 + 2.62 Gopher Frogs. Alternatively, survival of Gopher Frogs with mosquitofish did not differ significantly from Leopard Frog survival. (Paired t-test t = -0.41, df = 7, p=0.70).


Predator image mapBanded sunfish (Enneacanthus obesus) - click to enlargeEastern mosquitofish (Gambusia holbrooki) - click to enlargeWarmouth sunfish (Lepomis gulosus) - click to enlarge


  • Warmouth consumed more tadpoles than the other predators and, when given the choice, ate more Gopher Frogs than Leopard Frogs.
  • Mosquitofish did not affect tadpole survival, but inflicted injuries to more Gopher Frog tadpoles than Leopard Frog tadpoles.
  • Banded sunfish did not affect survival or induce hiding behavior in either tadpole species.
  • Both tadpole species hide when in the presence of warmouth and mosquitofish. A higher proportion of Gopher Frogs sought refuge than Leopard Frogs.
  • Predatory fish had significant negative effects on Gopher Frog tadpoles. Gopher Frog tadpoles experienced lower survival and higher rates of injury than Leopard Frog tadpoles, and also increased hiding behavior.
  • Introduction of fish, including small fish such as mosquitofish, into previously fishless Gopher Frog breeding ponds will have detrimental effects on Gopher Frogs.

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