The Cutting Edge

Fish senses

It’s More than Sight and Smell

By Eric West

Sometime back we reviewed several studies related to fish senses. How do fish senses work and what are they? What unknown factors cause fish senses to go off and how do they react?

Keep in mind fish senses, whether physical or biological, are likely similar across multiple species. What goes on in Bass, Yellow Perch or Fatheads may also exist in other pond fish species.

One of those issues is spawning suppression i.e., little to no spawning/recruitment? We do not see this as often, but it does happen and can unbalance populations quickly if not addressed. The question asked is, “What is causing this problem?” The fish are in good condition and the water is fine–why are there no little fish?

There were no cold snaps or large-scale water changes so what happened? Several studies use the term “physical and biological factors.” What possible factors are those and how do they arise?

One such study titled: Factors Influencing Nest Survival in Florida Bass by Z. Slagle and S. L. Shaw in  Transactions of the American Fisheries Society 146:696–702, 2017 Volume 146, 2017 - Issue 4 ) (© American Fisheries Society 2017) gives insight on differences in Bass spawning. The survival of both Largemouth and Smallmouth bass offspring can depend on a number of physical and biological factors, including the size and age of the guarding male, bed fishing pressure, and environmental changes during the nesting period.

Many nest attempts fail, and hatchling abandonment is common due to storms, sudden temperature changes, angling, and nest predation. If the male bass abandons the brood (or is fished or runoff off the nest), the brood is unlikely to survive long.

Another older study, Behavioral Suppression of Spawning in Largemouth Bass by Interspecific Competition for Space Within Spawning Areas by Stephen Lee Smith in Transactions of the American Fisheries Society 1976, No. 6 pg. 682 notes the inconsistencies in prior studies on this exact question. The results from these studies were mixed, with some indicating an excretion and build-up of a hormone-like repressive factor by overcrowded sunfish and forage species. Others found a link to physical factors such as aggressive interaction with forage species, primarily affecting the male bass. That was effective in suppressing the spawning behavior sequence even before nest building.

These are the probable “physical and biological factors” to spawning suppression. The sight of swarms of harassing forage species and chemical suppression factors released by them can suppress bass reproduction. Further, it appears this situation is more common in highly fertile waters. Bass failed to produce offspring in several eutrophic Florida lakes which boast large populations of sunfishes. It was further determined that reproductive failure was due to a refusal of the adult population to spawn and characterized in the female by retention of enlarged, ripened ovaries long past the spawning period. Further, that condition could be replicated in hatchery ponds and attributed the reproductive suppression to the excretion and build-up of a hormone-like repressive factor by overcrowded sunfish and forage species. Others documented similar reproductive failures at high population densities of the blue tilapia but did not set out the mechanism of the repression.

Another senses issue involves growth rates and is discussed in, Chemicals Released by Predation Increase the Growth Rate of Yellow Perch, Perca flavescens by T. P. Barry, G. K. Dehnert, P. D. Hoppe and P. W. Sorensen, Journal of Fish Biology (2017). doi:10.1111/jfb.13475, online wileyonlinelibrary.com, where water-soluble factors associated with walleye predation on either yellow perch or fathead minnows markedly increased the early growth rate of Yellow Perch. The findings suggest that Yellow Perch possess an inducible growth-promoting mechanism regulated by water-born chemicals. Note the “water born chemicals” which can be sensed by the fish.

Yet another study addresses predator recognition and is titled, Population Differences in Responses of Fathead Minnows (Pimephafes promefas) to Visual and Chemical Stimuli from Predators by Alicia Mathis, Douglas P. Chivers and R. Jan Smith in Ethology 93, 31-40. This study demonstrates that fathead minnows recognize pike as a potential predator from a two-tiered predator recognition system that incorporates both visual and chemical cues.

Here, two populations that vary in exposure to pike predation under natural conditions show corresponding variation in their ability to recognize pike as a potential predator. Chemical cues may be of particular importance in the identification of a predator such as the northern pike that is often well hidden in the weeds.

Here, the authors note that reliance solely on visual cues may be of limited utility under conditions in which visibility is poor (e.g., in muddy streams) or when predators are hidden.

Because of the concealed nature of pike under natural conditions, predator detection by nonvisual cues may be of critical importance to the survival of potential prey.

This study demonstrates that fathead minnows from a population that is accustomed to living with northern pike are better able to recognize pike as potential predators than are minnows from a population that is unaccustomed to living around pike. These results are consistent with the results of other studies of small fishes that have reported differential predator recognition abilities between those habituated to predators and those which are unaware.

In other studies, it has been documented that fish caught and released emit a warning signal chemical which other fish notice and they quickly quit biting. In addition, other works show that male Bluegill can chemically identify (smell) and distinguish their fry from those of others. So, we know through more recent studies that fish readily produce and use chemical signals for various purposes.

There is still a very lot we must learn about fish senses. But for those stocking fish into lakes with existing predators investigate (see the Pond Boss Forum) habituating those stocker fish for much better survival.