A fish recompression tool comprises an elongate body having and internal airtight chamber, an attachment member, a locking member, a piston, and a spring within the airtight chamber that engages the piston. The attachment member may switch between open and closed configurations, such that a fish is attached to the device in the closed configuration. The attachment member configuration is controlled by the locking member, such that a locked configuration corresponds to a closed configuration. The attachment member switches to the open configuration when the piston moves in response to reaching a water depth that results in the external pressure surrounding the airtight chamber being sufficiently greater than the internal pressure within the airtight chamber and the spring force on the piston. In preferred embodiments, a plug attaches to an open ended elongate body and may be moved to set different unlocking requirements (i.e. different release depths).
