Effects of Ram-Air Ventilation during Transportation on Water Quality and Physiology of Fingerling Walleyes

Abstract

Ram-air ventilation (RAV) of the airspace in a fish hauling tank is achieved by equipping the tank with both forward-facing and rear-facing air scoops. To evaluate the benefits of RAV, we data-logged values every 5-min for dissolved oxygen (O₂), pH, and temperature in hauling tanks with and without (control) RAV during a 6-h haul. Levels of CO₂ were estimated from the pH–alkalinity relationship. To determine if RAV reduced hauling stress experienced by fingerling walleyes Stizostedion vitreum after a 6-h transport, blood samples were taken for measurement of physiological stress indicators, blood gases, and for assessment of acid–base status. Blood samples were collected before loading (preload), after loading (postload), and at the end of a 6-h trip (posthaul). The mean CO₂ for the trip was substantially lower and the pH was higher in water of tanks equipped with RAV compared with water of the control tanks. At posthaul, blood pCO₂ (partial pressure of CO₂ in the blood) in fish from RAV tanks was substantially lower than blood pCO₂ levels in fish from the control tanks. At posthaul, blood HCO₃ ⁻ concentrations were 1.5 times higher in fish from the control tanks compared with fish from the RAV tanks, which indicates a homeostatic compensation for high pCO₂. At postload and posthaul, levels of two indicators of stress (plasma cortisol and blood glucose) were substantially higher in fish from control tanks than in fish from RAV-equipped tanks. Equipping transport tanks with RAV improved water quality, and reduced physiological stress by venting CO₂ from the airspace above the water.