What happens to a walleye pulled up from deep water?

The walleye's swim bladder is physoclistous — a closed system with no duct to burp gas through — so it can only shed pressure slowly through the bloodstream. Hauled up quickly from 10 m (33 ft) or more, the expanding gas has nowhere to go: the bladder balloons, compressing organs, sometimes pushing the stomach into the throat, popping eyes outward, and leaving the fish floating helplessly on release. This is barotrauma, and it scales with depth — fish from 5–8 m (16–26 ft) usually manage, fish from 12 m+ (39 ft+) often cannot. The practical rule is to decide before you drop: fishing deep schools is a harvest decision, not a catch-and-release one.

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