The effects of acidosis on visual function in fishes

<p dir="ltr">The intense physical activity associated with capture by fishing causes a range of metabolic changes and physiological stressors in fishes. When fight time is prolonged, as is common with larger fish species such as mako sharks, tiger sharks, and marlin, the physiological challenge can result in profound changes to the chemistry of the blood and other body fluids, making them much more acidic than normal. These metabolic perturbations may have a significant impact on the survival prospects of a fish if subsequently released. Although the relationship between capture stress and blood acidosis has been studied extensively in fish, the adverse effects of acidosis on sensory function are poorly understood. In particular, the high metabolic demands of the retina, which is part of the central nervous system, means that vision is likely to be one of the primary neural systems affected, and this may be problematic given that most fishes rely heavily on vision for survival. To assess the impacts of capture-induced acidosis on visual function, I first compared the effects of capture on the pH and lactate concentration in the blood and vitreous, the clear fluid in the eye of all vertebrates that abuts the retina, in a range of teleost and elasmobranch fishes. Overall, I found that the pH and lactate concentration in the vitreous are correlated with those of the blood, and likely reflects the state of the retina following capture. Next, I conducted behavioural experiments in sharks to investigate whether changes in blood pH are correlated with the ability to visually navigate around obstacles. Immediately following release there were significantly more collisions with obstacles as blood pH decreased, and the effects on visual navigation persisted for at least 15 minutes after release. While an increase in collisions may have been due to other factors, such as disorientation, fatigue, and muscle soreness, it is also possible that some of the reduced performance is explained by impacts of acidosis on visual function. To explore this possibility, I used electroretinography to assess gross retinal function in response to changes in vitreous pH and blood pH and show that acidification reduces the overall sensitivity of the fish retina. This research highlights the potential effects of acidosis on visual function in fish and makes an important contribution to our understanding on the adverse effects of capture stress in post-released species.</p>