/The Conscientious Aquarist

Chemical Communication in Fishes

Bob Fenner

(semi-editorial comment:) This piece and two following on Pheromonal Behavior Effects and Growth Inhibiting Substance(s) of Fishes are intended as companion articles to the magnum dopus, A Review of Literature on Hormonal Manipulation of Fishes as an Aquacultural Technique (FAMA 6/92). These are on-going attempts at bringing to our aquarist/hobbyist some more baseline knowing of physiology as it relates to practical keeping and breeding.

The auspicious Paul Speice(ous) provided the muse again in reminding this humble writer of the need for re-re-reminding the uninitiated of the value of frequent partial water change as a primary function of sound system management. If you can get your hands on the industry pub. Pet Product News, vol.5 no. 9, Sept. 92, "The Aging Aquarium" (Fancy Publications Inc., P.O. Box 6050, Mission Viejo, CA 92690-6050, 714-855-8822, Fax 714-855-3045, free to the trade), do so. So, ahem, on with it!

Let's review a bit: this periodical is aimed at enhancing/reinforcing our experience-enjoyment of ornamental aquatics, any and all fields/ways of knowing aquatics directly contributes to this ends. Hence my argument for technical understanding; science/engineering.

The scientific (testable, falsifiable hypothetical) study of life is termed Biology. Within this body of tentative facts, ideas, methods, attitudes and techniques is a sub-field of study called Physiology; scientific study of metabolic function. Even within this area are specialities of interest. One is called Endocrinology ("inside""cry""study"); the scientific study/practice involving the physiology of hormones (internal chemical messengers).

This and the next couple of articles discuss topics in a related category exocrinology, the science of chemicals that are "cried outside". These are simple to complex compounds, some of tremendous importance to us as aquariculturists, profoundly affecting growth, reproduction, color, immune systems (generally all aspects of health). These externally released chemical messengers are variously classified as eliciting behavior of the same species (pheromones, "Fair Oh Moans") and other than the releasor's species (allomones, "allo" like aloe vera).

In this offering we'll journey together on the issue of chemical communication in fishes, what it is, why you might/should be interested, and what you will want to do to optimize your situations. The following articles are more specific, concerning Growth Inhibiting Substance(s) affects, and Alarm Substance studies.

Chemical Communcation in General:

It makes sense that substances released by aquatic organisms migh serve to regulate, instigate and moderate the behavior of the same and other species. Not to be too reductionistic, but, as you know, 1) "water is the universal solvent" with more things being more soluble in it than any other material; 2) even with our senses of olfaction/gustation, nothing happens until whatever stuff dissolves into our fluids (mainly water) and gets into our systems' via aqueous solution. Many fishes have good vision and many do not. Same thing with hearing (remember this). Other senses have/are becoming evidently very important. The low frequency vibration sense of the lateralis systems and electromagnetic perception of cartilaginous (sharks, rays, skates, chimaeras) among other groups through the so-called pit organs, the Ampullae of Lorenzini are two of my favorite examples, that have become very highly attuned. External chemical sense is likewise been demonstrated to be extremely sensitive in some species.

Though most scientific studies have centered on work with sticklebacks, salmonids, american catfishes (ameiurids/"ictalurids") and sunfishes, there is growing awareness of how important chemical communication is among pet-fish. Especially the families grouped within the Superorder Ostariophysi, the catfishes, minnows and their relatives (barbs, danios, rasboras, koi and goldfish, loaches, hillstream fishes like chinese algae eaters), Characoids (tetras, hatchetfish, pencilfish,...), including many important captive hobbyist species, have a proven highly sophisticated chemical signaling system for clueing their school mates of present danger.

What Are They:

Everything from metabolites like ammonia to simple amino acids to oligo to polypeptides (few to several amino acids branched together), short-chain (8-12 carbon) fatty acids, and more have been detected to have discernible effects on the behavior and physiology of fishes. These are produced within the host fish's body and released through excretion, secretion and rupture of the body wall via the gills, skin slime, urine, feces, or trauma.

Site of Reception:

Is mainly olfactory. Most fish nostrils are used for smell, not breathing. Also, olfaction in some fishes is not just in the nostrils, but the mouth and body surface.

Experiments with eels have shown them to register response to as low as ten to the minus eighth (10-8) concentration of some chemicals. That's getting down to about one molecule in their nose period!

Importance to the Fish and To Us:

Since the fifties, we have known that chemical communication functions in attraction and recognition of individuals, the opposite sex offspring or parents. Chemical communication maintains hierarchies, flight, schools, especially at night and guiding migrating fishes.

Interesting experiments can/have been done with american bullhead catfishes and cichlids using diluted water from alpha/beta individuals, ablation and training/discrimination work showing that individuals and groups within a species do recognize each other and respond, at times overtly, to the chemical presence of conspecifics (members of the same species).

For hobbyists, it is of iminent importance to know and use this information for optimizing results. It turns out, you probably know the gist of what to do. Absolutely clean (e.g. sterile, or chemically inert) conditions are not practical or generally desired. That is to say, that some of this "chemical soup" we've been referring to is beneficial, but not too much, or too selective. The universal rule is once again FREQUENT PARTIAL WATER CHANGES. Different rules of thumb apply depending on size of the system, filtration, feeding, et cetera rei, but do them! At least semi-religiously vent a percentage of the systems water and solids and replace with new.

I'd like to make mention of the importance of plant hormones (phytohormones), and yes, even invertebrates, in the overall health/balance of a system. The closer you look, the more there seems to be.

Closing:

The three most important set of factors affecting fish growth and reproduction are light, temperature and metabolite build-up. Perhaps this last group should be re-described as the presence/absence of chemicals from all sources affecting the physiology of the target organisms, including chemical communication compounds.

Biblio. & Further Reading:

Atema, J., Todd, J.H., Bardach, J.; 1969 Olfactory and behavior sophistication in fish. In Olfaction and Taste III (ed. by Pfaffman, C.) pp 241-251. The Rockefeller Univ. Press, N.Y. Also II: 647-663.

Shorey, H.H.; 1976. Animal Communciation by Pheromones. N.Y. Academic Press.

Suzuki, N. and Tucker, D; 1971. Olfactory receptor responses to skin extracts in the catfish, Ictalurus catus (Linn.). Proc. Fedn. Am. Socs. Exp. Biol.30(2):552 abstr.

Wollman, J. & S. Gordon; 1975; Chemical Communication, III. Vertebrates. Chemistry 48(5):6-11.

Wilson, Edward .O.; 1963. Pheromones. Scientific American, May 1963. The granddaddy original popular/encompassing work on the topic. Go to the large library of your choice and copy or you can get a reprint via W.H. Freeman and Co., 660 Market St., San Francisco 4, CA. great stuff.

Wilson, E.O.; 1970; Chemical Communication Within Animal Species. In Chemical Ecology, B. Sandheimer & J.B. Simeone (ed.s). N.Y. Acad. Press.

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