Salinity Tolerance of Hemichromis letourneuxi
The African jewelfish, Hemichromis letourneuxi, has been established in canals surrounding the Miami area since the 1960s. With changes in water delivery to the park, the species has recently (2000) entered Everglades National Park and expanded its range westward through Big Cypress National Preserve. Simultaneously, African jewelfish from a separate introduction along the southwestern Florida coast have moved both southeasterly into the western Big Cypress ecosystem and northward into the Caloosahatchee estuary. Before this study, the salinity tolerance of the species was unknown. We conducted an experiment to test the salinity tolerance of the species to assist in determining whether it could expand its range into brackish and/or saline waters.
Laboratory setup showing boxes used to
house fish during the experiment.
Fish were housed separately in plastic experimental aquaria that were plumbed with airstones. All fish began the experiment in water at 0 ppt (well water). Individuals were assigned to one of nine target salinities (0, 10, 20, 30, 40, 50, 60, 70 and 80 ppt). Eight replicate fish were tested for each treatment. Fish were fed (flake food), and their water changed twice weekly. To bring fish to their target salinities, we increased the salinity of the water by 5 ppt twice per week (for a total increase of 10 ppt per week). We maintained fish at their target salinities for at least 30 days before terminating the experiment.
Hemichromis letourneuxi was remarkably tolerant of salinity, easily handling concentrations up to 50 ppt with 100% survival. Most fish grew during the experiment; the mean difference in wet mass (final minus initial) was 0.26 g (+ 0.46 SD). The difference between beginning and ending wet mass did not vary as a function of salinity for from 0 and 60 ppt (one-way ANOVA, df = 6, F = 1.307, P = 0.270).
Survival of H. letourneuxi for 30-day period over a range of salinities.
Mass gain during the experiment (ending mass - beginning mass)
for H. letourneuxi over a range of salinities. The dark line is the
median; the box bounds 50% of the data; whiskers denote data
limits and the asterisks represent outliers.
Acknowledgments
This study was funded by the U.S. Fish and Wildlife Service and the U.S. Geological Survey, Invasive Species program. Denise Gregoire provided expert assistance in the field and laboratory. Shane Ruessler and Bob Lewis provided technical assistance in the laboratory. This study was completed under IACUC approval USGS/FISC 2006-03 and Everglades National Park permit EVER-2007-SCI-0014. Buck Albert assisted with photography.
For more information, contact:
Jacqueline N. Langston or Pamela J. Schofield, Ph.D.
U.S. Geological Survey
Florida Integrated Science Center
7920 NW 71st Street, Gainesville, FL 32653
(352) 264-3527; 264-3530
jlangston@usgs.gov; pschofield@usgs.gov
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