Attraction and Consumption of Crayfish by Centrachids

Abstract

Fish attractants are a small but stable component of the U.S. recreational fishing industry, generating $28.1 billion in 1985. Subsequently, fish attractant manufacturers compete for a share of the market, introducing new products annually. Although dilute concentrations of scent have been shown to influence fish behavior, there is little published information regarding the effectiveness of today's marketable products. As a demand for commercial attractants utilizing crayfish scent increases, the need to document crayfish attracting capabilities through fish behavioral research becomes more pertinent. To date, there are few fish attractant products on the market that utilize softshell crayfish, creating an identifiable marketing niche for:crayfish products. Commercial products utilizing Minnesota's abundant crayfish population would further develop Minnesota's crayfish industry, and assist local businesses in competing in the fish attractant market. The mechanism of odor detection in fish is well known. It is also well established that many fish species can detect odors with concentrations in the parts per billion or even parts per trillion. Taste and odor detection in fish is difficult to separate because both senses detect molecules dissolved in water. Odor has been described as distant chemoreception, while taste is nearby or contact chemoreception. Taste detection of molecules dissolved in water can be as sensitive or even be more sensitive than the sense of smell. The spectrum and minimum concentration detected by both olfaction and taste varies greatly between species. A variety of fish behaviors are influenced by odor. These behaviors include: 1) homing migrations, 2) feeding, 3) reproduction, 4) fright reactions, and 5) schooling. Feeding behavior is influenced by both olfaction and taste. The odors most frequently identified as eliciting fish behavior responses have been amino acids and bile acids. Several individual amino acids and combinations of amino acids have been found to elicit olfactory-mediated feeding responses in fish. Other compounds and some amino acid-like components have also been shown to elicit feeding responses. It is generally believed that scent which elicits the greatest response will most often contain mixtures of compounds rather than single substances. Studies attempting to correlate feeding behavior response to olfactory stimuli are limited and have not been conducted on primary U.S. recreational fish species. Two methods have been used to evaluate olfactory responses in fish: 1) behavioral studies, and 2) electrophysiological response of anesthetized fish. Electrophysiological studies are similarly limited in scope and are not necessarily suitable predictors of feeding behavior since they only detect physiological stimulation and not instinctive foraging activity. Soft crayfish are more desirable than hard shell crayfish for use as angling bait, presumably because a perception exists that soft crayfish are a more effective in catching fish. Glycine betaine (found in marine invertebrates and elasmobranch fish, but not in teleost fish) increases the attractiveness of amino acids combinations. Based on reports describing the effectiveness of live and dead crayfish as bait to attract marine crustaceans, it is possible that crayfish possess the amino acid combinations that would attract popular recreational species. While many species universally respond positively to certain amino acids, even closely related species can vary significantly in their response. Crayfish are readily consumed by a variety of fish species including smallmouth bass, largemouth bass, walleye, yellow perch, catfish and others. Major physiological changes occur as crayfish grow. The transformation results in individuals shedding a hard exoskeleton. Following the molt, crayfish are soft, have limited coordination, and are completely vulnerable to predators or other crayfish. As a result, they secure secluded locations to molt and allow the new shell to harden. Since crayfish are vulnerable during the time immediately post molt, it is likely that they would be especially attractive to fish. An odor that is unique to this highly vulnerable life stage may be more attractive than odors from a hard shell crayfish.