Fish Science
Skin Senses: Touch and pH Sensitivity

Photo: Berkley Doc Jones has learned a lot by trying to touch bass.

What do we sense through our skin? We have a sense of touch, we can feel temperature – anything else?

A bass can sense touch/pressure and temperature through its skin as we can. Then it one-ups us with the ability to detect pH, or the level of acidity or alkalinity of the water it swims in.

How does it use these senses to survive, and how can we catch more bass by knowing about it?

Today we'll look at touch and pH-sensing in bass. We'll cover temperature in the next article.

This information is based on the book "Knowing Bass" by Dr. Keith "Doc" Jones, Berkley's king of science about all things fishy.

Comfortable Bass = Active Bass

The senses we've already discussed in previous articles – sight, hearing, vibration detection, taste, smell – all monitor many environmental cues for bass. Jones contends that "another set of senses affects bass fishing success every bit as much as the eyes, ears, nose, mouth and lateral lines." These are the somatic senses, or sensations of the skin.

How the bass senses and responds to water temperature (and its corresponding effect on oxygen content) and pH influence where it goes and how it acts when it gets there.

Water is rarely uniformly mixed. There are pH, temperature, clarity and other gradients, occurring not just as horizontal layers but from area to area. Inflows, plant growth, sunlight exposure, wind exposure, bottom composition and other influences all contribute to this mix.

In his book, Jones has a chart that depicts the preferred and total ranges of several water quality parameters for bass. Some highlights include:

> Temperature – Bass prefer 80 to 90 degrees F, but can tolerate near-freezing to 97 degrees F.

> pH – They prefer 7.4 to 8.1, but can tolerate 4 to 10. In pH world, 7 is neutral, lower is more acid, higher is more basic.

> Oxygen: Bass like greater than 5 parts per million (ppm), but can tolerate 1.5 to 24 ppm.

(The book also has a cool table on the preferred ranges for several prey fish.)

Jones notes that since all physical variables are linked together, the angler shouldn't consider one to be more important than another. Instead, the total microenvironment of each area should be considered in the hunt for active bass.

'The average mouth retention time for a hard-plastic crankbait body is a quarter of a second. Softbait retention times average several times as long.'

The Skinny on Skin Sense

So how does skin help a bass feel out its environment?

Bass have somatic sensors only on the outside of their skin (while we humans have those and inner receptors). They have many free nerve-ending sensors that form a mesh of nerve fibers which essentially cover its surface and intertwines its muscles and many internal organs. These nerve fibers feed to the spine, and in the case of the four main stems serving the head, to the brain directly.

Touch
Bass are very touch- and pressure-sensitive. Evidence suggests the mouth lining is extremely so, allowing the fish to gauge the hardness of an object in a split-second.

"The average retention time for a hard-plastic crankbait body is 0.25 second," writes Jones. "Softbait retention times average several times as long."

pH
Bass try to avoid steep gradients of acid. If a strong acid is added to a bass in a tank, it evokes a strong escape response. A weak acid may arouse their curiosity. Thus they are observed to be keenly aware of their pH environment.

The skin nerves very likely help them in this function, but likely other chemoreceptors – taste and smell – participate as well.

Jones explains that dissolved carbon dioxide in the water will vary with acid or base changes, spiking with an abrupt acidic influx – and fish can taste the CO2.

While a bass cannot regulate its temperature other than by changing locations, it can regulate its internal pH, or relative alkalinity, by changing its breathing. "A higher ventilation rate removes more carbon dioxide from their blood, thereby raising blood pH," Jones points out.

This self-regulation allows bass to operate with more freedom in waters of varying pH than it can with temperature. And larger bass are much more tolerant of acidic water than juveniles.

Take-Away Points

> Bass will hold soft baits much longer than hard baits.

> Decaying vegetation produce acidic compounds like tannic acid that are repulsive to bass. Bottom waters are generally lower in pH than surface waters.

> Photosynthesis by algae, aquatic plants and phytoplankton drive the pH up (away from acidic readings).

Notable

> Hard water carries high levels of salts and can withstand much greater additions or deletions of acid without a change in pH. Most natural waters are hard enough to resist major changes in pH, a few in the U.S. and Canada have almost no natural buffering capacity.

> Pages 229-230 in Jones' book contain a list of 16 points to ponder (related to temperature and pH) when looking for active bass. Get it! Read it! The book is "Knowing Bass, The Scientific Approach to Catching More Fish," and is available at amazon.com, Barnes and Noble and other booksellers.