The documentary that @Paul Robertsshared with us talked about the staging areas bass use during the pre-spawn, and it got me to wondering about something that I have only guessed at.   How long does it take a bass to adjust it's swim bladder so that it is buoyant at various depths?   For instance, let's say a bass is wintering in 20' of water, and spawns in 4' of water, how long would that take for the bass to add the volume necessary to be buoyant at 4'?   I know it takes some time, I just don't know if it is days or weeks.   Closed swim bladders (bass) don't change quickly like that of fish with an open bladder (goldfish, carp), but I don't know the rate.   

As far as I've been able to find, it's not known. Bass can move for short periods quite a vertical distance, although they would have to be sufficiently motivated. Telemetry generally shows little vertical movement, although smallmouth were shown to make substantial relatively short term vertical movements (up to 18ft) daily in one water body, presumably to feed.

 

Most observations are by anglers via sonar. From what I've been able to ferret out, movements of 10 vertical feet are not uncommon. But again, such fish would have to be sufficiently motivated; i.e. not conserving energy.

 

How long it takes to adjust is unknown for bass. There was some early work on yellow perch (which are known to show greater vertical movement than bass generally speaking, but are still physoclists) showed a certian level of acclimation over 24hrs. If you think about it, that's a long time considering that fish are so energy conservative.

It actually takes less gas volume or pressure to equalize neutral bouyancy at 4' of water verses 20'. LMB don't have air bladder valves to release the gas quickly, the gas is created and released via the digestive process. How long it takes depends on the vertical depth changes to achieve neutral bouyancy. When the basses bouyancy isn't neutral the bass needs to swim to maintain a specific depth until the air bladder adjust to the changed pressure. I am not sure how long this takes, it's days not hours. I am not a biologist don't recall reading how long the gas takes to increase or decrease volume.

Tom

Using perch as the basis for a guideline, Ralph Manns has stated 1 hr per each foot of depth. It does vary based on temperature though, and on their own, bass rarely make large scale depth changes for any length of time. They can make short feeding sorties without issue though. It is also easier for a bass to move shallower than it is to move deeper.