Fishes: The Animal Answer Guide

1. Introducing Fishes

What are fishes? While probably everyone thinks they know what a fish is, it turns out to be very difficult to actually define “fish” because of the vast diversity of different species of fishes. Recognizing this diversity, one can define a fish as an aquatic vertebrate that breathes with gills and has limbs in the shape of fins. Several other groups of aquatic animals, such as shellfish (clams and oysters), whales, cuttlefish (squids) and fossil ichthyosaurs (reptiles) are sometimes mistakenly considered to be “fishes” but clearly do not fit the definition. Unlike familiar groups of vertebrates such as birds and mammals that can trace their roots back to some common ancestor, fishes include a tremendous diversity of groups with different ancestries. Hence our definition encompasses lancelets, hagfishes, lampreys, sharks, lungfishes, and bony fishes, each evolving from a different ancestral group. What is the plural of fish? The word “fish” is singular and plural for a single species: one Green Sunfish, two Green Sunfish. Ichthyologists (people who study fishes) use “fishes” to refer to more than one species, four different species of sunfishes, fishes of the Gulf of Maine. When ichthyologists use the common rather than the scientific (Latin) name of a specific fish species, they capitalize the name. Capitalizing common names avoids the problem of understanding a phrase like “green sunfish.” Does this mean a sunfish that is green or does it refer to the Green Sunfish, Lepomis cyanellus? This “rule” about capitalization only applies to discussing a single species. For example, salmon species Chapter 1 Introducing Fishes 1 2 Fishes: The Animal Answer Guide along the U.S. west coast are referred to as Pacific salmons (lowercase s), but each species is capitalized (Chinook Salmon, Sockeye Salmon). How many kinds of fishes are there? There are three major groups of fishes: about 115 species of jawless fishes (Agnatha, lampreys and hagfishes), almost 1,300 species of cartilaginous fishes (Chondrichthyes, sharks, skates and rays, and chimaeras), and the remaining 31,000-plus species, the bony fishes (Teleostomi) on which this book will focus (and to which are added more than 200 newly discovered species each year). Bony fishes differ from jawless fishes in possessing true jaws and from both other groups in having a bony instead of a cartilaginous skeleton. Why are fishes important? Fishes are most important to people as food. Many families of fishes contain species that form valuable commercial fisheries, such as the Clupeidae (herrings), Engraulidae (anchovies), Salmonidae (salmons), Gadidae (cods), Serranidae (sea basses), Xiphiidae (Swordfish), Scombridae (mackerels and tunas), Pleuronectidae and other families of flatfishes. Other families contain species of great interest to marine sportfishers, such as Coryphaenidae (dolphinfishes or mahi mahis), Istiophoridae (marlins and spearfishes), and Scombridae (tunas), or to freshwater sportfishers, such as Salmonidae (trouts and salmons), Esocidae (pike and pickerels), and Centrarchidae (black basses and sunfishes). Other fishes are important in the pet trade. These include freshwater fishes such as the Cyprinidae (barbs, goldfish, and other minnows), Characiformes (several families of tetras and relatives, mostly from South Amer- “Fish” versus “fishes”: Ichthyologists refer to one species using the singular “fish,” regardless of the number of individuals (left). When more than one species is discussed, the correct term is “fishes” (right). From Helfman et al. 2009; used with permission of Wiley-Blackwell 3 Introducing Fishes ica), Siluriformes (several families of catfishes from South America, Africa, and Asia), Cichlidae (cichlids), and Anabantoidei (Siamese fighting fish and gouramis); and marine fishes such as Pomacentridae (damselfishes), Acanthuridae (tangs, surgeonfishes), Labridae (wrasses), Gobiidae (gobies), and Scorpaenidae (lionfishes). Because of their small size, ease of care, rapid growth, and short generation time, fishes such as the Zebrafish (Danio rerio, Cyprinidae) and the Medaka (Oryzias latipes, Adrianichthyidae) are becoming increasingly important in studies of toxicology, pharmacology, neurobiology, and medical research. Even the gas bladders of some fishes have uses. These organs, also called swim bladders, help fishes maintain buoyancy (see “What is a gas bladder?” in chapter 2). Those from fishes such as sturgeons (Acipenseridae) have been used to prepare isinglass, a whitish, semitransparent, very pure gelatin valued as a clarifying agent and as a component of glue and jellies. Gas bladders from other fishes, such as drums (Sciaenidae), are used in soups. Perhaps the strangest use of fishes is for pedicures, using small fishes to nibble away flakes of dead skin from peoples’ feet. The use of fish to treat skin conditions is popular in Turkey where...