Fishes in Ditches: Ongoing non-native fish research in the Tampa Bay area

By: Katie Lawson
PhD Student

University of Florida

The Tampa Bay area is home to many ornamental aquaculture facilities. While these farms maintain excellent compliance with the Best Management Practices required for licensure by the Florida Department of Agriculture and Consumer Services (Tuckett et al. 2016), fish do occasionally escape (Tuckett et al. in press). The county ditches of the Tampa Bay area are not the most glamourous habitats to sample, but we have learned and seen some interesting things while studying them. Although we have seen a variety of ornamental fishes in ditches on and around farms, very few of those species are found farther away from farm effluents. Non-native fishes we have commonly found in ditches farther away from farms include green swordtail Xiphophorus hellerii, southern platyfish Xiphophorus maculatus, pike killifish Belonesox belizanus, Jack Dempsey Rocio octofasciata, and African jewel cichlid Hemichromis letourneuxi.

Clockwise from top left: Green Swordtail Southern Platyfish, African Jewel Cichlid, Jack Dempsey, Pike Killifish
All pictures courtesy of TAL staff

Of these five species, African jewelfish and pike killifish are widespread in the Tampa Bay area across a variety of habitats. Green swordtails, southern platyfish, and Jack Dempsey all have a similar pattern of distribution in the area. They are found primarily in ditches, and their populations are disjunct and localized in areas where there is a current or historic farm. Some of these populations appear to be self-sustaining yet unlikely to spread, while others appear to be reliant on new propagules for persistence. Jack Dempsey are particularly interesting because small populations have popped up around the state, but ultimately declined to extirpation. The mechanism behind these declines is still unknown, however it is possible the same trend will be observed in the current populations within the Tampa bay region.

Ditch fish assemblages in the area are dominated by poeciliids, both non-native and native. Native mosquitofish Gambusia holbrooki dominate these assemblages and are known to be very aggressive toward non-native small-bodied fishes like the swordtail and platyfish. This aggressive behavior is possibly a strong biotic filter prohibiting spread and success of these non-natives. As one would expect, swordtails and platyfish tend to be more abundant in areas with lower mosquitofish densities. The pike killifish has also been observed in many ditches around the Tampa Bay area, although it is also in a variety of larger water bodies such as the Alafia and Little Manatee Rivers. Pike killifish are unique poeciliids with a relatively large body size, and are predatory from birth. They seem to favor preying on mosquitofish over non-native swordtails and at one site in particular, both pike killifish and green swordtails were more abundant than mosquitofish. This suggests facilitation of green swordtail persistence by the pike killifish’s predation on the aggressive mosquitofish. All of these interactions are currently being researched at the University of Florida’s Tropical Aquaculture Laboratory in experiments led by Dr. Quenton Tuckett. While not many people think about the fish assemblages of central Florida’s ditches, there are some fascinating patterns and interactions we are learning. These provide valuable insights relating to community assembly theory and biotic resistance, the invasion process, and potential impacts by non-natives.

References:

Tuckett, Q.M., J.L. Ritch, K.M. Lawson, and J.E. Hill. 2016a. Implementation of best management practices for Florida ornamental aquaculture with an emphasis on non-native species. North American Journal of Aquaculture, 78: 113-124.

Tuckett, Q.M., J.L. Ritch, K.M. Lawson, and J.E. Hill. 2016b. Landscape-scale survey of non-native fishes near ornamental aquaculture facilities in Florida, USA. Biological Invasions. DOI 10.1007/s10530-016-1275-2