Physiological and behavioural effects of simulated tide conditions on toadfish males
The choice of where to build a nest is influenced both by the needs of the offspring and the costs that parents experience when nesting at a certain location. Some fishes, including the plainfin midshipman (Porichthys notatus) fish, nest and rear their young in a particularly extreme and abiotically dynamic environment – the rocky intertidal zone. Nesting in intertidal zones may speed up the development of plainfin midshipman eggs, but exposes parents to frequent bouts of aquatic hypoxia and air exposure when the tides recede. We investigated the physiological costs and mitigating strategies demonstrated by guarder plainfin midshipman males in response to normoxic water, water with declining oxygen levels, or air exposure for six hours. We also tested for physiological and behavioural strategies that could mitigate these costs. Air exposed fish showed the greatest physiological disturbance based on plasma and tissue metabolites, although glycogen content did not vary in any tissue with exposure. Male plainfin midshipman may draw upon O2 stores from their swim bladders during bouts of environmental hypoxia, as we found that swim bladder oxygen content decreased during air exposure. In a second experiment, we found that plainfin midshipman males performed surface respiration more frequently when exposed to hypoxia than when exposed to normoxia. Our results illustrate the costs of nesting intertidally, but these fish rely on a suite of physiological and behavioural coping mechanisms that mitigate some of the costs of providing parental care in a fluctuating and harsh breeding environment.