Ecological significance of cold shock: reflex action impairment in bonefish

Bonefish, Florida Sportsman

Fast moving weather fronts or upwelling events can rapidly drop water temperature in sub-tropical areas. Effects of cold shock were studied in bonefish by Szekeres et al. 2014. Fish at 25^oC were exposed to either 18^oC or 11^oC for 2 hours. Ventilation rate and reflex actions were monitored throughout the cold shock. Five reflex actions were tested before and after cold shock, including equilibrium, body flex, vestibular-ocular response, tail grab, and head complex (Brownscombe et al. 2013). Given that the focus of this study was on sub-lethal effects, cold shock exposure was terminated if the fish lost equilibrium. Blood plasma and swimming ability, defined as line crossings and time to loss of equilibrium associated with chasing were also sampled during the experiments.

The authors found that “Behavioral responses of bonefish to cold shock were generally characterized by decreased ventilation rates for the 7°C below ambient treatment with little reflex impairment, and extreme behavioral and reflex impairment in the 14°C below ambient treatment. Fish in the latter treatment exhibited varying periods of hyperactivity followed by impaired or no swimming ability, reduced responsiveness, and the loss of equilibrium, which are all common traits of cold shock exposures.” Experiments with bonefish exposed to the 14°C below ambient temperature were terminated after 30 minutes, as fish lost equilibrium.

Importantly, the authors found “Despite the fact that bonefish in the 14°C below ambient treatment had almost complete reflex impairment during the exposure and sustained high blood lactate concentrations than other treatments, post-exposure swimming abilities were similar to handled control fish. This suggests that although fish become highly behaviorally impaired at colder temperatures, if they are able to escape to more suitable conditions, swimming abilities quickly return and they are unlikely to experience further fitness consequences due to behavioral impairment (e.g. higher predation risk).” 

There “are many facets that have yet to be explored as this research was the first attempt to understand the sub-lethal consequences of cold shock on these sub-tropical fish species. Our research only considered swimming ability as a proxy to understand predation risk in the wild. Future research may focus on determining whether the fish experience compromised disease resistance, poor foraging decisions, changes to fecundity or altered developmental stages. The combination of a changing climate and the economic importance of bonefish throughout the Caribbean warrant more research to be conducted on this species and their responses to an array of changes to ambient conditions.”