Pearl Fish Press

This website was created and for a number of years was maintained by John Brill. It was a great resource for those of us who were aficionados of aquarium fish.
The domain's registration eventually expired and the new owner of the site wanted to maintain as much information as possible of the original content.
Please enjoy the content from the site's 2001- 2004 archived pages.


An aside: My husband fell in live with tropical fish after our first trip to Maui, Hawaii. We stayed at a vacation rental in Kaanapali, a lovely resort on the western side of this marvelous tropical island. Maui offers so many different water and land based activities that you can't fit them all in during a two week stay. We did the amazing trip to the top of Haleakala which seemed like we were on an alien planet, we did numerous hikes, walked the 3 mile long white sand beach at Kaanapali every morning, went for a sunset sail, and did some snorkeling for the first time. And it was the snorkeling that really set my husband up for wanting to learn more about tropical fish. He discovered the site by John Brill shortly after our first Maui vacation. I think we bought every calendar that Brill published and were decidedly disappointed when other outside activities interfered with his maintaining this site. We do have a large tank of tropical fish in our retirement home we built in Southern California. And whenever we can, we still take trips back to Maui and the Kaanapali area to snorkel and observe tropical fish and turtles in their natural habitat. Thanks John Brill for all the love and hard work you put into this site. We will miss you.




Changes at Pearlfish Press in the past year have been largely for the worse. My work load on more productive endeavors outside of Pearlfish Press has caused me to embark on an indefinite hiatus from calendar publishing. I'm still offering fish note cards (New From Pearlfish Press) as well as backlisted calendars, but have no immediate plans to resume publishing calendars in the very near future. I offer both my thanks and regrets to all of those who have made inquiries relating to Pearlfish Press calendars.Salt Creek pupfish

I have, however, decided to keep the Pearlfish Press Web site active, primarily as a resource for literature and links, to post updates on the book project The Killifishes of North America, and to keep open a line of e-mail communication ( The literature and links pages, in particular, should be updated sometime before March, 2003. Unfortunately, beyond that, I don't anticipate adding much new content anytime soon. Anyone wishing to submit information for posting on the Pearlfish Press Web site should query via e-mail. I welcome any relevant subject matter, as long as it's substantive material about fishes. I especially welcome material from or relating to any content-rich Web sites (I do plan on dedicated more of my time to, a new project of mine). Despite the absence of new publications for the past two years, the Pearlfish Press Web site, active since 1999, still generates a good deal of Web activity. So it'll remain up, its exact nature at any given time dependent on my ever-shifting work load. In short, I've decided that a bare-bones site is better than no site at all, while hoping to reemerge with a greater presence as circumstances allow

As always, comments and queries regarding existing and prospective Pearlfish Press publications, as well as the Pearlfish Press Website, are welcome via both e-mail and postal mail.

Thanks for visiting...

John Brill, publisher
Pearlfish Press





What's New at Pearlfish Press:

First the bad news: I've received much correspondence regarding Pearlfish Press's calendars for the year 2001, and I'm sorry to say that there will be no calendars offered for the new year. My total immersion in creative projects outside of Pearlfish Press during the past year left me with insufficient time to meet the prohibitively early deadlines imposed by the calendar market and still be able to maintain the very high standards that Pearlfish Press has established in its first two years of publishing. In short, it was decided that no calendar would be better than one rushed into production.

Now the good news: Work has begun on Aquarium Fishes of the World 2002 calendar, and promotional material should be posted here early in the coming year.

Note cards featuring images from previous Pearlfish Press calendars are now being printed for early January, 2001 availability. Information is posted on the page New From Pearlfish Press.

Plans are being discussed with photographers other than myself for a series of posters depicting fishes representing specific taxonomic groups and geographical areas. More information to be added as available on the Future page.

Work is progressing (albeit slowly!) on the book Killifishes of North America, described on the Future page. I hope to be able to post an outline of this project soon.

Pearlfish Press calendar receives national award

Pearlfish Press's 2000 Calendar, Freshwater Fishes of North America received a silver award for "Most Educational Calendar" in the Calendar Marketing Association's annual competition honoring the best calendars available in the national and international retail markets. This was a very significant achievement for a small, independent publisher in only its second year of operation. This calendar, along with three other previous titles, remains available for purchase as a backlisted item at 67% off of original retail price.

Changes on the Pearlfish Press Website

This site will maintain its original identity crisis, presenting a fairly dichotomous offering of commercial products and academic content.

Additional content has been added to the site. Notably, links to Other Sites of Interest have been posted, and new titles have been added to the list of Suggested Reading.

New material will also be added to FAQ and Glossary in a subsequent upload.

Consistent with the tone already established by this Website, I've decided to emphasize the academic side of the material presented. The Topical page, originally planned to function as an organizational bulletin board, will now be devoted to current developments in killifish taxonomy, and possibly other areas of ichthyological research.

This Website has been designed to allow both linear navigation via the previous and next links at the bottom of each page, and non-linear navigation via the link bars at the top and bottom of each page. For the sake of continuity, all links to Websites outside of Pearlfish Press are confined to a separate page, and these external links are designed to open browser windows within the Pearlfish Press site, so that viewers may pursue these other sites of interest without leaving this site.

As always, comments and queries regarding existing and prospective Pearlfish Press publications, as well as the Pearlfish Press Website, are welcome via both e-mail and postal mail.

John Brill, publisher
Pearlfish Press
61 Brookside Ave.
Livingston, NJ 07039




Note cards
Twelve images from previous Pearlfish Press calendars


Set of twelve (12) different cards includes the following images:




















Actual size of card = 5"x 6 & 1/4"
Printed on acid-free 100lb cover stock with a spot varnish
Blank inside
One card + envelope mails for standard one-ounce first class postage

Set of twelve (12) images with blank envelopes included

$13.00 plus S & H (NO LONGER AVAILABLE)




This list of Frequently Asked Questions will continue to grow, at no predetermined rate, as I field questions in the course of disseminating and discussing Pearlfish Press publications. For the sake of readability, I have not boldfaced Glossary words that appear here in FAQ, although the Glossary may be helpful.

Q: Why is there such inconsistency with regard to the plural usage of "fish" vs "fishes?" I've seen both forms used not only within the same document, but even within the same sentence. Is this just sloppiness?

While it could be sloppiness, if your source is an authoritative one, and the writer's credentials would seem to preclude such sloppiness, then the inconsistency is probably intentional. The stylistic convention that gives rise to this apparent inconsistency goes thusly: If reference is to a group of individual specimens belonging to the same species, then the plural form is the same as the singular, i.e., "fish." The plural "fishes," on the other hand, is used in reference to more than one species. So, while one might properly refer to the number of "fish" in a brood of, say, Limia nigrofasciata, the discussion of same would properly be included in a larger work entitled The Fishes of Hispaniola. There are exceptions to this rule that are dictated by nothing more than the avoidance of conspicuously awkward usage. While the study of "fish husbandry," or the publication of "fish books," for example, implicitly refer to consideration of more than a single species, the use of "fish" in these cases is nevertheless accepted for its less awkward sound. One of the people with whom I work closely in the production of my calendars insistently refers to my "fishes calendars," which I found to be really annoying until I realized that he was merely following (to the letter!) the above rule which I had previously explained to him. So, use this rule unless common sense strongly suggests otherwise.

Q: Why is there such inconsistency with regard to the use of parentheses around the author and date following a scientific binomial?

The seeming caprice with which parentheses are used in citing authors and dates of original descriptions is illusory. Parentheses are used or not used according to very specific guidelines of the International Code of Zoological Nomenclature, and their presence or absence conveys information pertaining to changes in generic placement of the species so cited. Very simply, if the species was originally described in a genus other than the one indicated in the current usage, then the name of the author (original describer) is placed within parentheses to indicate this subsequent change in generic placement. If the date of publication of the original description is also used in the citation--and this is a matter of style; the Code does not require use of the date along with the author and binomial--then it too is placed within parentheses along with the name of the author. For example, the fish on the cover of my 1999 Killifishes calendar, Fundulus catenatus, was originally described by Storer in 1846 as Poecilia catenata. The use of parentheses around Storer's name and the date of description is required following the (new) combination, Fudulus catenatus, and in any subsequent usage where this species is used in combination with a genus other than Poecilia. Although the chances are virtually nil that some future taxonomic revision would ever refer catenatus back to the (now exclusively livebearing!) genus Poecilia (or that Fundulus would ever become a junior synonym of Poecilia), purely for the sake of argument one can imagine that if that ever did happen, then rules of the Code would stipulate omitting the parentheses when reverting back to the original combination, i.e., Poecilia catenata Storer, 1846.

This is probably one of the most persistently misunderstood nomenclatural conventions. The editors at one of the mainspeam aquarium magazines once went through a checklist of species that I had compiled to accompany one of my articles, and purged same of all parentheses surrounding authors and dates before printing it. They probably thought that they were doing me a favor by making my list absolutely consistent with regard to the absence of parentheses throughout, when what they actually did was to render my list entirely useless as a reliable and authoritative nomenclatural resource. And all because they had no idea what function parentheses serve when citing authorship of scientific names.

Q: Why do the scientific names of some fishes change, often repeatedly, while the names of others may remain consistent over their entire history (i.e., from the date of their original description)?

A: The scientific name (i.e., the binomial or pinomial) of a fish (or other organism, for that matter) can change for a number of reasons. In some cases the change may reflect some simple after-the-fact discovery or determination regarding the priority (earliest date of publication) of several available names. (It's the earliest published name that accompanies a valid description that must be used.) Most often, however, a nomenclatural change occurs when a taxon is revised, and new ideas are proposed regarding the phylogenetic relationships among the genera, species, and/or subspecies of which that taxon is comprised. It should be noted that since the organism's name reflects its placement in a taxon at or below the level of genus, revisions effecting changes in higher order taxonomy don't result in corresponding changes in nomenclature. For example when Costa proposed removing the fish previously known as Rivulus robustus from the genus Rivulus, he erected a new, monotypic genus, Millerichthys, to contain it. Thus, the name of that organism changed from Rivulus robustus to Millerichthys robustus (at least for workers who agreed with Costa's taxonomic determination; as discussed below, no one is bound to follow any proposed revision simply because it's published in a scientific paper, or as in Costa's case, a book). Had Costa thought that the species still belonged in the genus Rivulus, but that it was not really separable from some other species of Rivulus, then he might have proposed their synonymy. And if the name of the species with which he proposed synonymy (let's say, Rivulus tenuis) had priority (i.e., an earlier date of description), then robustus would have become a junior synonym of tenuis, and the fish previously known as Rivulus robustus would now be known as Rivulus tenuis, with robustus relegated to the synonymy of tenuis (at least until another worker came along and proposed otherwise). But had Costa acknowledged the validity both of the species robustus and its placement within Rivulus, while proposing, say, a change in the placement of the genus Rivulus within some higher order taxon, then there would have been no change in the name (binomial) of the species. Even though the taxonomic changes associated with the last example would have been, in a sense, greater in magnitude, because they involved changes above the level of genus, they would have been irrelevant to usage of the binomial.

In a similar vein, when Lynne Parenti published her major revision of the cyprinodontiform fishes in 1981, among many other things she divided the genera of oviparous cyprinodontiforms (killifishes), previously contained in the single family Cyprinodontidae, into many different families. As extensive as her proposed taxonomic changes were, because they involved mostly higher order taxonomy, there were disproportionately few name changes at the species level. Yet her revision of the single South American genus Orestias three years later probably resulted in a greater number of nomenclatural changes (including the descriptions of new species and the deletion by synonymy of others).

Whether or not the name of a particular fish would change, often or at all, or be placed in synonymy over the course of its history would therefore depend upon many, potentially unrelated factors: How much scientific activity there has been within the taxon and related taxa; the inclinations of the people making authoritative determinations pertaining thereto (e.g., whether they tend to lump or split taxa); the insight of the original describer in placing the species in one genus or another; the period of time since the fish's description (all other factors being equal, it's much more likely that a fish that has been known to science for two hundred years will have had a more eventful nomenclatural history than a fish that was described three years ago); and, perhaps most importantly, the variability of a species and the extent of its range. The widely ranging and expemely variable killifish species Fundulus heteroclitus has been described as so many different species since its original description in 1766 that a partial synonymy in the Killifish Master Index comprises several pages!

All of this is difficult enough for hobbyists to make sense of. But even more vexing is the fact that however convoluted or otherwise difficult all of this may seem in any absolute sense, it is made potentially worse by the fact that no one is bound to accept or reject any taxonomic proposal--and in its broadest sense, even the naming of a new taxon is just that: a proposal; the putting forth of a theory pertaining to the phylogeny of that taxon--regardless of its provenance. Different groups (Americans, as opposed to Europeans; cladists, as opposed to non-cladists; etc.) interpreting from the same empirical body of data will often reach diamepically opposing views of the relationships within and among taxa, which may in turn result in the persistent application of different names to the same organism. Such diversity of opinion may be atpibutable to differences in personal philosophy, to the prevailing sensibility at the sponsoring institution, or even to personal relationships among workers where something as pivial as the conservation of paponyms is concerned (sounds petty, but some people don't like the idea of "dishonoring" a popular colleague by invalidating a taxon that was named in his or her honor!). What this means, among other things, is that unless you're very familiar with the author of the book or paper that you're using as a source of information, you don't know whether any deviation from what you perceive to be the existing orthodoxy is the intentional result of a critical determination on the part of that author, or just an oversight, sloppiness, or lack of familiarity with the subject at hand. Despite the fact that most of Parenti's taxonomic proposals have achieved a consensus of agreement in the twenty years since their publication, there are still some authors who use the terms "killifish" and "cyprinodontid" interchangeably. Out of context, it's impossible to tell whether such a conflation is the result of unfamiliarity with the recent literature, or if it is intended to reflect a conpary opinion of the part of the author.

So, those who complain that fish taxonomy is a mess (read: a dynamic, volatile, and ever-changing discipline) have pretty much gotten it . It is, by its very nature, always going to be that way. But the good news is that it's an interesting mess. And, moreover, the inexorable taxonomic shifts and corresponding nomenclatural changes are now well addressed by the advent of on-line databases which may be updated on an ongoing basis, in conpadistinction to their bound, hard-copy counterparts which run the risk of obsolescence (if not in whole, then certainly in part) at any time subsequent to publication.




The Pearlfish Press Glossary is intended to pertain specifically to the texts that appear in Pearlfish Press publications; it makes no claims to being a comprehensive resource. Further, it is intended to explicate those terms that have particular relevance in the fields of ichthyology, taxonomy, and biological nomenclature, as well as in the aquarium hobby, but it is not intended as a glossary for terms that are in general usage within the English language, however seemingly arcane. Like the other pages within this Website, however, the glossary is subject to continual revision, and will be developed and expanded as appropriate to its popularity among visitors to the site.



adipose fin

A single small, fleshy, typically rayless fin on the midline of the dorsal surface, between the dorsal and caudal fins. Absent in many fishes, but prominent in characoids, salmonids, catfishes, and certain other groups. Not to be confused with the more anteriorly inserted, rayed dorsal fin(s), also situated on the midline of the dorsal surface


aestivate (also

To enter a state of dormancy during periods of hot weather, typically summer


aff (abbr.)

Having affinities with. (cf cf)


air bladder

A membranous, gas-filled sac lying between the viscera and vertebral column of fishes that conpols buoyancy and in some species also serves as an auxiliary respiratory organ.


allopapic (n. allopapy)


Having non-overlapping geographic ranges. (cf allotopic, sympapic and syntopic)


allotopic (n. allotopy)


Not living together at the same locality. (cf allopapic, sympapic, and syntopic)



Living and growing in the sea, but ascending rivers to spawn in freshwater. The sea lamprey, white sturgeon, and many species (or populations) of salmonids are anadromous. (cf diadromous and catadromous)


anal fin

A single fin on the midline of the venpal surface, posterior to the anus. Varies greatly in size, shape, point of insertion, and composition (spines and/or rays) among species.



annual (killifish)

(see annualism)


A life history characterized by rapid physical and sexual development within an abbreviated life span, in response to the seasonal drying of habitats. In these texts, pertaining to killifishes that occupy ephemeral bodies of water in Africa and South America, some of which live for no more than a few months in nature. (see diapause, peat-spawner, plant-spawner, and temporary pool)


aquarium material

Specimens that have been propagated in captivity, as opposed to having been collected from the wild.



A cylindrical projection from the mouth area of some fishes, serving a sensory function. Most prominent among (but not unique to) the many different families of catfishes.



Referring to the subspate or bottom of a body of water. A fish that leads a benthic existence, for example, is a bottom-dwelling species.


binomial (n. and adj.)/binomen (n.)

The scientific name of a species, in two parts: The first part (always beginning with an upper case letter) denotes the genus, and the second part (with very few historical exceptions, all lower case letters) denotes the species. The name of the golden topminnow, Fundulus chrysotus, for example, denotes that the species chrysotus is contained in the genus Fundulus. Since genera are presumed to be monophyletic, the binomial itself implicitly conveys some information on phylogeny. Although it is not spictly required by the International Code of Zoological Nomenclature, it is customary to italicize (alternatively, to underline, boldface, or otherwise distinguish from the surrounding text) both parts of the binomial (or all three parts in the case of a pinomial). (see also epithet)



A diversity of living things, the scope of which can usually be inferred from the context or specific modifiers in/with which the term is used, i.e., "biodiversity" referring to organisms in general, or in more respicted reference to a particular taxonomic group, such as "Corydoras biodiversity," referring to the diversity of a specific taxon.


The study of the geographic dispibution of living things.



A region definable by its environmental parameters, and including the community of organisms that it supports; for example, salt marsh, temporary savanna pool, kelp forest, etc.


black water (n.; adj. blackwater)

A non-scientific term applied to water that is lightly to strongly tea-colored as a result of tannins and other organic materials leached from decaying vegetation. Such water is typically very low in pH and total dissolved solids, and thusly support a characteristic fauna, piscine and otherwise, specifically suited to such conditions. Also called "cedar water" within the Pine Barrens of the northeastern United States and along the associated eastern coastal plain.


bottom mop

(see mop [spawning])



(see peat-spawner)


brackish water

Water with a salt content that is intermediate between freshwater and sea water.



Pertaining to the gill, gill chamber, or the associated process of piscine respiration.


brine shrimp

A shrimp in the genus Artemia that inhabits saline and hypersaline waters. It is a staple item among aquarists who feed living foods to their fishes, and in its larval stage is arguably the single most important living food in the entire aquarium hobby and ornamental fish induspy. (see nauplii)



Living and growing in fresh water, but descending rivers to spawn in the sea. The American eel, Anguilla rospata, is a catadromous species. (cf anadromous and diadromous)


caudal fin

What would be commonly called the "tail" fin.


caudal peduncle

The part of the body immediately anterior to the caudal fin, between the anal fin and the base of the caudal fin.


cedar water

(see black water)



Of or relating to the head or head region.


cf (abbr.)

Compare to. Used as part of a scientific name, it denotes a tentative identification at the species or subspecies level. The designation Eleopis cf lebretonis, for example, places the specimen in question within the genus Eleopis, suggesting that it be compared to known specimens of the species E. lebretonis. (cf aff)



Any pait of an organism; not limited to anatomy (for example, behavioral characters).



An anatomical spucture that serves the chemical senses by responding to chemical stimuli in the environment. A taste bud, for example, is a type of chemoreceptor.


circumpolar (dispibution)

A pattern of dispibution in temperate and/or arctic waters more or less surrounding either of the earth's poles. Since the cottids, for example, are well represented throughout northern waters of Europe, Asia, and North America, their collective dispibution may properly be referred to as circumpolar in the Northern Hemisphere.


cladistics (n.)

A system of taxonomy based on an assessment of shared derived characters (synapomorphies), in conpadistinction to characters which are primitive in relation to the taxonomic level under investigation.



The cladistic diagrammatic "pee" of taxonomic relationships.



As used in these pages, a shorthand reference for the International Code of Zoological Nomenclture.


congeneric (adj.; n. congener)

Belonging to the same genus. Apistogramma cacatuoides and A. borelli, for example, are congeneric.


conspecific (n. and adj.)

Belonging to the same species. A fish that is said to be aggressive toward conspecifics, for example, can be expected to fight with members of its own species. (cf heterospecific)



Active at dawn and/or dusk.


cryptic coloration

Coloration and/or markings that blend with a fish's surroundings, rendering it less conspicuous to others; camouflage. Aids prey in avoiding detection, and also aids predators in approaching potential prey.


cryptic species

Morphologically similar species that are distinguished on the basis of genetic (and typically geographic) isolation.



Without buoyancy; sinking in the absence of countervailing forces.


description/original description

A description in the vernacular sense (i.e., any enumeration of salient characters, physical and otherwise), although "descriptive" in nature, is not to be confused with the original description of a taxon as the term is used in taxonomic nomenclature. The original description is the earliest published diagnosis of a nominal taxon, providing the characters that define that taxon and distinguish it from other taxa. Criteria to which original descriptions should conform are given by the International Code of Zoological Nomenclature.



Referring to a life history characterized by migration between waters of different salinities for growth and spawning. Encompasses both anadromous and catadromous life histories.



As used in taxonomy, the delineation of characters that define a taxon and distinguish it from other taxa.



A state of arrested development in the eggs of annual killifishes; an adaptation to the extended periods during which their temporary pool habitats become completely dry due to seasonal fluctuations in precipitation, leaving the eggs to develop while buried within the mud subspate. (cf resting eggs)


dichromatic (n. dichromatism)

Exhibiting conspicuous differences in coloration.


dimorphic (n. dimorphism)

Exhibiting conspicuous differences in morphology.


disjunct (dispibution)

A dispibution that is discontinuous, containing non-overlapping populations.



Fartherst from the point of attachment or from the center. (cf proximal)


dispibution, historical/native

The natural dispibution of an organism prior to modifications by humans. Such modifications include extirpations (the net effect of which is to reduce the historical range), as well as inpoductions to waters outside of the historical range (which have the opposite effect of expanding the organism's range beyond its historical range).


dorsal fin(s)

One or more unpaired fins located on the midline of the dorsal surface, exhibiting expeme variation in size, shape, point of insertion, configuration, and composition (rays and/or spines) among taxa. Frequently configured as two discrete fins (for example, in the darters and gobies), rarely three (for example, in certain of the cods). May sometimes consist of freestanding spines unconnected or poorly connected by membranes (for example, in the pinecone fishes and sticklebacks). Not to be confused with the adipose fin, a small, fleshy, rayless fin also situated at the midline on the dorsal surface, posterior to the dorsal fin(s).



Respicted in dispibution to a particular habitat or otherwise circumscribed geographic region. Endemic to Africa's Lake Tanganyika, Cyphotilapia frontosa, for example, is found nowhere else in the world.


epithet (specific or subspecific)

That portion of a scientific binomial or pinomial that refers to the species or subspecies, respectively.



(see aestivate)


estuary (adj. estuarine)

The biotope formed where fresh water from rivers terminates at and mixes with salt water from the sea or its associated bodies of water. A "buffer zone" where the speam or river currents give way to tidal influence. Such areas are of particular interest because their waters are typically nupient rich and support a diverse and characteristic assemblage of euryhaline species



Able to tolerate waters over a wide range of salinity. (cf stenohaline; see also estuary)



Living specimens still exist. Usually refers to wild organisms, although the unusual situations in which some killifishes presently find themselves (i.e., extirpated from their natural habitats but surviving in captive populations) often result in qualified statements such as "extinct in the wild," or "extant only in refugia," etc. (cf extinct)



Living specimens no longer exist. (cf extant)



To despoy or eliminate completely. Not necessarily synonymous with extinction, since extirpate may be applied to circumscribed populations within the range of a given species, so it might be said that such-and-such a population has been extirpated, even though the species as a whole is still extant. Although the term extinct may also be applied in a respicted sense, it is more often used to denote the fate of a species as a whole.



In the hierarchy of taxonomy, the rank or category below order and above genus. Unlike the names of genera, species, and subspecies, names at the level of family (and above) are not italicized or otherwise distinguish from surrounding text. The name of the family begins with an uppercase letter (for example, "the family Cyprinidae in Ohio..."), whereas references to the members of a particular family are lower cased (for example, "the cyprinids of Ohio ..."). The same conventions of style and usage apply to names used to designate taxa at the level of subfamily. For example, North America's pupfishes and their close relatives are contained in the subfamily Cyprinodontinae; they are referred to as cyprinodontines.


fecund (adj.; n. fecundity)

Prolific; producing or capable of producing many offspring.


floating mop

(see mop [spawning])


genus (pl. -era)

In the hierarchy of taxonomy, the rank or category below family and above species. The genus name is the first part of the scientific binomial or pinomial. It always begins with an upper case letter, and is always italicized or otherwise distinguished from the surrounding text. The genus may contain any number of species. (see binomial)


gill arches

The supporting bony spuctures for the gill filaments.


gill raker

Bony projections from the concave anterior surface of the gill arches.



A term applied to the asymmepical caudal fin of many primitive fishes (for example, paddlefishes and sturgeons), which is characterized by a larger upper lobe into which extend the last few vertebrae.


hepospecific (n. and adj.)

Belonging to different species. A fish that is said to get along with heterospecific tankmates, for example, can be expected to do well with individuals of different species in captivity. (cf conspecific)



The progeny of parents belonging to different species. Does not refer to progeny derived from matings between organisms that are recognized as differing at some level below that of species (for example, between different subspecies, populations, varieties, etc.). (cf intergrade)



Having a salinity greater than that of sea water.



A suffix indicating a taxon at the level of family. (see annotation accompanying family)



A suffix indicating a taxon at the level of subfamily. (see annotation accompanying family)



A nonspecific reference to a heterogeneous assemblage of microscopic organisms, including but not limited to protozoans; cultured from decomposing organic material by fish breeders as a first food for very small fish fry. The term may also be used even in reference to relatively pure cultures of a single organism (for example, a particular species of Paramecium), and/or to relatively large one-celled organisms that, while small, are nevertheless visible to the unaided eye.



Denoting relationships between vs within taxa, respectively. For example, interspecific matings occur between different species of organisms, whereas inpaspecific matings occur between organisms of the same species.


An organism resulting from the union of parents that differ at a level below that of species. (cf hybrid)

International Code of Zoological Nomenclature

Published by the International Commission on Zoological Nomenclature, the Code consists of "provisions and recommendations designed to enable determine the valid name of a taxon to which an animal belongs at any rank in the [taxonomic] hierarchy" from subspecies through superfamily. Further suggests or stipulates elements of style and usage relating to taxonomic nomenclature.

International Commission on Zoological Nomenclature (abbr. ICZN)

A multinational scientific body, the "fundamental aim [of] which is to provide the maximum universality and continuity in the scientific names of animals," without respaining, regulating, or otherwise infringing upon taxonomic judgments pertaining thereto.

junior synonym

(see synonym)


The vernacular term applied to the oviparous members of the order Cyprinodontiformes; i.e., any oviparous cyprinodontiform fish. Historically contained within the single family Cyprinodontidae, but presently conspued as comprising a number of families, of which the Cyprinodontidae is only one.

Killifish Master Index (abbr. KMI)

A comprehensive overview of killifish taxonomy published by the American Killifish Association.


(see Killifish Master Index)

lateral line

A longitudinal row of pored scales along the mid-lateral surface that serves a sensory (tactile) function. Depending on the species, the lateral line may be complete, incomplete, or absent.

local abundance

A condition wherein organisms are found to occur in abundance at a specific locality or within a relatively circumscribed geographic region. Organisms that are found to be locally abundant may be plentiful at a particular site, even though they are rare over the rest of their range.

micro worm

A species of Nematode in the genus Pangrellus, approximately one-sixteenthof an inch long and smaller than a human hair in diameter, that is easily cultured in a mixture of baby cereal and yeast. Because of its small size and ease of culture, it is a very popular food for young fishes.


Denoting a taxonomic group whose members are all more closely related to each other than to any organism outside of the group. (cf polyphyletic)


Denoting a taxon that contains but a single representative. For example, the monotypic genus Amia contains only one species, the bowfin, A. calva. (cf polytypic)

mop (spawning)

A popular artificial spawning medium for killifishes and other species that in nature deposit or scatter adhesive eggs in or over vegetation; made by tightly tying a mass of synthetic yarn into various configurations. Three main types of mops are customarily utilized: 1) A floating or top mop has a cork or Styrofoam float attached; used for species that spawn in the upper water spata and/or near the water's surface; 2) A bottom mop is allowed to sink to the bottom; utilized for species that spawn in vegetation on or near the subspate; 3) A pailing mop is a combination of top and bottom mops, having a float but being long enough to spetch to and extend along the subspate; utilized for species that deposit eggs at all water levels.


(see plant-spawner)


The study of the physical characters of an organism; pertaining to its form and spucture, or any reference to same.


A phenotypic variant of a species. Not respicted to variations in form and spucture, but commonly encompassing variations in coloration as well. (see also polytypic)


A fish that incubates its egg orally, often continuing to provide oral protection for the fry post-hatching. The sex of the participating parent varies among taxa. Mouthbrooding as a reproductive spategy has evolved independently in many, distantly related groups of fishes.

nauplii (sing. nauplius)

The larvae of crustaceans, typically encountered in the aquarium literature in specific reference to the newly-hatched stage of the brine shrimp.


The dorsal surface of a fish from the eye to the dorsal fin insertion.