Related FAQs: Marine Fishes Related Articles: /A Diversity of Fishes A Diversity of Fishes
Bob Fenner	Mixed school of Grunts, family Haemulidae

The diversity of fishes is astounding. Living fishes comprise three of the seven classes of vertebrates. The other four extant classes, the amphibians, reptiles, birds and mammals number less in total than the 25,000 or so scientifically described fish species. The non-fish Classes are collectively separated into the Tetrapods, "four legs".

The Seven Living Classes of Vertebrates:

Agnatha ("Lacking jaws") The jawless fishes, lampreys & hagfishes

Chondrichthyes ("Cartilaginous fishes") Sharks, rays, skates & chimaeras

Osteichthyes ("Bony Fishes") All the >25,000 rest

Amphibia ("Both types of life") Frogs, Toads, Salamanders, Newts, Caecilians

Reptilia (Greek for "To crawl") Lizards, snakes, crocodilians, turtles, tortoises, terrapins and the styling Tuatara

Aves: The Birds

Mammalia ("Latin, first declension noun, mamma, mammae fem.,"breast") in reference to their nurturing young with milk

If you can use a taxonomic category, like Classes, as a yardstick (index) for diversity, you could liken the total differences among living fishes to that between humans and a newt.

A Fish Is A Fish Is A Fish?: Casual observation yields this knowledge: a fish is not a fish is not a fish... (Until you've tasted Hamms?) Ask yourself, my fellow pet-fish ichthyologists; why is there less known about fishes than any other Class of vertebrates? Maybe I've coined a term: species-centricity. Like ethnocentricity, an emotional attitude that one's own (terrestrial) species is superior. We're land-lubbers, so aquatic types are less interesting and worthy? No way! Well, doggone it here goes:

From the abysmal depths of the seas to above timberlines, below freezing to 109 degree F. From one third inch to forty five plus feet, 2-3 gram to some twenty tons; highly varied in color, luminescent, drab, chameleon-like, in and out of water, swimming, walking, flying, gliding...breathing in and out of water...blind, bi-focaled...planktivorous, vegetarian, scale eating, eye biting, piscivorous, some with built-in fishing rods...free-living, commensal, mutualistic, parasitic...burrowing like moles, hibernating...tasty, edible, toxic and venomous. Fishes, yeah. By some measures fishes possess the most acute vision, best olfactory (taste & smell) sense, vibration sense, electric sense, orientation sense

What is a fish? This may seem an obvious dumb question, but try to answer it. Fish respire by gills. Not all. You're familiar with labyrinth fishes (Anabantoids, Gouramis et al.), lungfishes, Callichthyid catfishes and many other south American family examples that are to some degree obligatory to facultative aerial respirators. Many of these fishes have only vestigial gills and would actually "drown" if kept underwater!

Fish live in the water. Oh really? What about the comical Periophthalmids, the mudskippers, or the climbing "perch" Anabas?

Many fishes aestivate or otherwise "wait-out" a portion of their life history virtually without water. Lungfishes and many of the egg-laying toothed carps, Cyprinodontidae (Killifishes), are notable examples.

Fish have scales. Oh yeah; you better look around. All the true eels, order Anquilliformes, are scaleless as are many "naked" and "armored" catfish families... All the jawless fishes, class Agnatha, the lamprey and hagfish species as well.

Okay wise guy, how about fins? The "typical" fish has two sets of paired fins, pectorals and pelvics and three unpaired, dorsal, caudal and anal; but, alas, there are fishes that lack some or all of these.

They're cold-blooded. Not exactly. Mackerel sharks, family Isuridae (e.g. Makos) and several tunas, family Scombridae are at least partially homeothermic.

They utilize a gas bladder for buoyancy control. How about the darters, family Etheostomidae, several of the flatfishes, order Plectognathiformes?

Besides, many other non-fish have scales, fins, gills...!

One last try, they're all slimy. Ah, now you're getting closer. The characteristics that saliently distinguish fishes are more easily described internally. Like all vertebrates they have a dorsal stiffening rod, a cartilaginous notochord in primitive forms appearing more bony or ossified as a "back bone" in higher/advanced species. Scientific characteristics discriminating fishes from other , so-called "higher" vertebrates include other morphological (structural), embryological, physiological and other differences that more accurately define fishes for what they are not. We'll actually leave off with any further discussion at this point concerning what makes a fish a fish and nothing but a fish and pick it up later in a survey of fish higher taxonomy (classification).

Next: The Greatest Story Ever Told:...or, my stab at making taxonomy understandable.

Bigger PIX: The images in this table are linked to large (desktop size) copies. Click on "framed" images to go to the larger size.

Pempheris vanicolensis Bali 2014

Verticals (Full/Cover Page Sizes Available)

Parapriacanthus ransonetti SIP 2, RA,  P. guentheri RS

Verticals (Full/Cover Page Sizes Available)

Calamus calamus BAH

Chirolophis decoratus, Warbonnet; family Stichaeidae. Here at the Ripley's Aq. in Toronto, Canada. 2015

Enoplosus armatus (White 1790), Oldwife. Endemic to S. Australia. Here at the Shedd Aq., Chicago. 2015

Tilodon sexfasciatus, the Moonlighter; a Kyphosid endemic to S. Australia.  Here at the Shedd Aq., Chicago. 2015

 

 

Further Reading:

Greenwood, Humphrey P., Donn E. Rosen, Stanley H. Weitzman & George S. Myers. Phyletic Studies of Fishes With A Provisional Classification of Living Forms. Bulletin of the American Museum of Nat. Hist. Vol 131: Art. 4. New York: 1966, 68.

Herald, Earl S. Living Fishes of the World. Doubleday. 1967.

Marshall, N. B. The Life of Fishes. Universe Books, NY 1972.

Nelson, Joseph S. Fishes of the World. Wiley-Interscience. 1976.

Schultz, Leonard P. The Ways of Fishes. Van Nostrand. 1948.