Bass Breathing, Oxygen & Knowing Where to Cast


Bass Breathing – Understanding the Role of Dissolved Oxygen

Surely you’ve heard the old adage stating that 20 percent of the water holds 80 percent of the fish.  While this is quite an oversimplification, the crux of it is true – most of the fish in a given body of water hang out in a relatively small portion of that water.

A variety of conditions cause the fish to cluster in various places, rather than spreading themselves throughout the water evenly (something scientists call a “non-random distribution”).  For example, temperature, current, substrate, predators and illumination may cause fish to prefer one part of the pond to another.

Most bass anglers consider these factors and use them to their advantage.  For example, because bass avoid bright sunlight, wise anglers target shady banks, dense weeds or deep water on sunny days.  Other anglers may study bait fish behavior to find bass. However, one thing that isn’t often considered is the role of dissolved oxygen.  This may not seem like the kind of thing you can judge just by looking, but knowing which clues to look for can tell you where the dissolved oxygen is, adding another tool to your kit.

Oxygen and Water

Oxygen enters a body of water in three primary ways:

  1. Atmospheric oxygen diffuses through the water-air interface.
  2. Plants produce oxygen through the process of photosynthesis.
  3. Groundwater can carry oxygen and then release it into a lake, river or pond.

Once in the water, the oxygen tends to spread out, but not uniformly.  At the same time, fish, bacteria and other organisms, consume this oxygen, but again, not uniformly.

Ultimately, this means that some places will have more or less dissolved oxygen – usually measured in parts per million – than others do.  Bass often take advantages of these varying oxygen levels, and stack up in areas where conditions are ideal.

Bass Breathing Oxygen Requirements

Different species of fish tolerate differing levels of dissolved oxygen; for example, bluegill require less dissolved oxygen than largemouth bass or channel cats do, but they require more than cold-water fish, like rainbow trout do.  Unfortunately for bass, they lack the anatomical and behavioral traits that allow some other species to adapt to very low oxygen levels, so they must find suitable waters or perish.

In concrete terms, bass require about 5 parts of dissolved oxygen per million parts of water (ppm) to survive, but they prefer 8 to 12 ppm.   When the dissolved oxygen levels in a given area fall to the lower end of this range, bass usually head elsewhere.

Patterns of Oxygen Distribution

In some respects, this pattern of oxygen distribution varies in similar ways from one water body to the next.  For example, the colder portions of the water often (but not always) hold more oxygen than warm areas do.  Additionally, turbulent areas, such as where feeder creeks pour into the main lake or a fountain sprays water across the surface, have higher levels of dissolved oxygen than the surrounding area.

Because aquatic plants produce and consume oxygen, areas with abundant plant life may be rich in oxygen at one time, and low in oxygen at another.  Often, the levels of dissolved oxygen vary over the course of the day.  During the daytime, when photosynthesis occurs, the oxygen levels reach their peak.  After the sun goes down and photosynthesis stops for the night, the oxygen levels begin to tumble, reaching their lowest point around dawn.

If you want to take your fishing to the next level, consider purchasing a dissolved oxygen meter and putting it through its paces.  Finding areas with high levels of dissolved oxygen does not guarantee that you will find the fish, but by ignoring those parts of the lake without enough dissolved oxygen to support bass breathing, you can certainly improve your chances.