Apparently, the only sure biological fact is that adult bass that have recently fed heavily and are digesting food tend to be inactive or neutral regardless of any environmental factor, including barometric conditions. The length of time since many of the bass in an area fed heavily and the time required to digest that meal are perhaps the most important clues to when a significant proportion of any bass population will next become active.

We found it interesting that in Texas in midsummer we experienced daily barometric pressure changes, due to the sun’s warming effects, that sometimes exceeded pressure changes associated with fronts. Each day, as the sun warmed the land and water, pressure dropped. Each morning, pressure was high due to the all-night cooling.

Mornings tended to be clear or with short-lived low clouds, while afternoons generally brought increasing high cloudiness. We didn’t find bass more active or less active in typical morning highs or late afternoon lows. Yet frontal passages and associated conditions, including overcast skies, wind, rain, and temperature changes, often seemed to turn bass on. Apparently, heavy cloud cover and low-light conditions affected bass activity, not air pressure changes alone.

Effects of Air Pressure On Fish

Air pressure and associated temperatures and moisture contents are major factors creating clouds and weather. Changes in pressure often are indicative of coming changes in weather and sky conditions. But when the possibility that air pressure alone controls fish behavior is considered, distinct limitations appear. A fish with a gas bladder needs only to swim up or down a foot or two to experience as great or greater a pressure change than that created by all but the largest natural pressure changes—typhoons and hurricanes.

A fish might notice that it’s floating or sinking a few inches in response to a change in air pressure, but it experiences larger pressure changes as it changes depth a few feet while hunting prey or moving to a new location. Black bass and other fish with closed gas bladders use their bladders to achieve neutral density and hold at constant depths. This weightlessness conserves energy by reducing their need to swim.

If air pressure or depth changes, a fish with a gas bladder slowly and naturally adapts bladder pressure to reestablish equilibrium. Depth adjustment of a few inches easily re-establishes balance and makes it unlikely that bass sense pressure changes for long periods. Depth changes likely override the perception of small changes in air pressure.

Biologists never have identified physical mechanisms or sensory systems that would specifically allow fish suspended at neutral density to sense relatively small changes in water pressure associated with air pressure shifts. But biologists have long postulated that clouds, waves, and changes in lighting affect hunting success by predators, by favoring species with eyes sensitive to low light levels.

We await any scientific information or interpretation that better explains the relationship between gamefish behavior and changes in air pressure, when isolated from the confounding effects of weather conditions. Until a biologically reasonable mechanism is proposed, we think it’s more reasonable and likely more accurate to consider weather and sky conditions rather than barometric pressure in explaining fish activity and inactivity.

*Ralph Manns, Rockwall, Texas, is a fishery scientist and angling authority who has contributed features and columns to In-Fisherman for almost two decades.