Various aspects of temperature have differing effects on the potential distribution of an invasive fish

Background/Question/Methods

Invasive species are among the top three greatest threats to global biodiversity, yet our understanding of the characteristics that make a species a good invader or a habitat more susceptible to invasion is limited.  Understanding these mechanisms can aid in predicting areas with a high invasion risk.  Cuatro Ciénegas, in Coahuila, Mexico is an oasis in the Chihuahua desert and an endemic hotspot.  A common aquarium trade fish, the West African jewel cichlid (Hemichromis guttat), was introduced in 1995 and is a potential competitor of two endemic, threatened fishes, the Cuatro Ciénegas cichlid (Herichthys minckleyi) and two-line pupfish (Cyprinodon bifasciatus).  H. guttatus is present in large numbers in parts of the valley, and this presence has been correlated to temperature and vegetation.  In this study, we aim to determine which aspects of temperature (maximum/minimum tolerance, preference, and/or optimal temperature for growth) are most important for H. guttatus establishment and spread.  Laboratory experiments were performed to determine the physiological thermal limits (using the critical thermal maximum and minimum methodology) and temperature preference (in a horizontal temperature gradient).  Optimal growth temperature will be determined by raising fry at different temperatures and comparing their growth.

Results/Conclusions

Hemichromis guttatus has a temperature tolerance range of 14-40 °C.  The temperature of water bodies in the valley lie within this range year round with the exception of a few downstream locations during the coldest part of the winter.  Thus, it does not appear that physiological limitations are the major force determining H. guttatus distribution.  Preliminary analysis of the temperature preference experiment data suggests a preferred temperature of 25 °C for H. guttatus.  Preference for this intermediate temperature could, thus, be implicated as a potential mechanism controlling H. guttatus distribution in the valley.  Determining the optimal temperature for growth will shed more light on the role that temperature plays in determining this fish’s presence and absence in certain locations in the valley.