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Factors affecting swimbladder volume in rainbow trout (Salmo gairdneri) held in gas suppersaturated water Shrimpton, James Mark


I examined the response of the rainbow trout. CSalmo gairdneriJ swimbladder bo gas supersaturated water. Cannulas positioned in the swimbladder of fish were connected to a pressure transducer, facilitating direct measurement of swimbladder pressure. Fish held in supersaturated water showed an increase in swimbladder pressure. The response showed a strong dependence on the total gas pressure and the oxygen partial pressure of the water. The minimum level of gas supersaturation observed to cause this response was a ΔP of 27 mmHg CPO₂ = 160 mmHg). Swimbladder pressure increased until gas was forced out the pneumatic duct. The pneumatic duct release pressure is size dependent, with greater pressure required to expel swimbladder gas in smaller fish. The expansion of the swimbladder due to increased pressure causes a decrease in density. The buoyant force created by decreased density is greatest for fish below 10g. These fish seek depth to compensate for swimbladder overinflation.

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