Physiological and behavioural consequences of cold shock on bonefish (Albula vulpes) in The Bahamas

Abstract

The effects of cold shock on fish have rarely been assessed in sub-tropical regions despite the fact that such events can occur as a result of upwelling, storms, or other climactic events that are expected to increase as a result of global environmental change. Here, the sub-lethal physiological and behavioural consequences of cold shock on bonefish (Albula vulpes) were assessed using four treatment groups (control, handled control, 7°C below ambient, and 14°C below ambient conditions; n=8 fish/treatment). The control and handled control remained at ambient temperature (~24°C) while other treatments were exposed to a 2h cold shock. Handled controls were treated with the same handling procedures as cold shock treatments, while control fish were less disturbed. Ventilation rate and reflex indicators (e.g., equilibrium, response to stimuli) were recorded throughout the experiment, and swimming ability was evaluated 2h after cold shock exposure. A blood sample was taken after the cold shock exposure and 2h following the swimming assessment to quantify glucose and lactate concentrations, hematocrit and pH in whole blood, and cortisol titers from spun plasma. Bonefish exposed to 14°C below ambient temperature experienced elevated lactate concentrations and high reflex impairment, with the majority of fish losing equilibrium <30min into exposure. During cold shock exposure, ventilation rates were significantly lower in the 7°C below ambient treatment than in the handled control. After cold shock exposure, swimming ability decreased as the magnitude of cold shock increased, however, it was also depressed in the handled control relative to unhandled controls. Exposure to 14°C below ambient temperatures had significant physiological and behavioural impacts on bonefish, while 7°C below ambient had little effect. Abrupt declines in water temperature in shallow tropical or sub-tropical seas >7°C due to storm events or upwelling have the potential to cause physiological and behavioural impairment that could lead to mortality in this species.