Natural History of Vertebrates Characters Used in Fish Identification 1-9-03 (modified 20050118) This lab is designed to familiarize the student with characters used in the identification of fishes. Only the most frequently encountered characters are mentioned here. Many other characters will be learned as the student finds a need for them when working with special groups. Do not allow specimens to dry out, especially the fins. Part I. Measurements. ( Fishes of Arkansas, by HW Robison and TM Buchanan 1984-- will be helpful.)(figure 73B) Standard length = distance from snout tip to structural base of caudal fin. Total length = distance fro anterior most projection of head to end on longest caudal ray. (Lobes of caudal fin should be squeezed together.) Body length = greatest depth of body not including fins or structures at fin bases. Head length = from the snout tip to the end of the opercular membrane. Snout length = from the mid-anterior snout tip to the boy anterior orbital rim. 1. Why do you think standard length is more frequently used in ichthyological work than total length?. 2. Measure and record the standard length and total length of the largest shiner.. 3. Measure and record the body depth, head length and snout length of the largest largemouth bass (Centrarchidae). Part II. Scalation (Figure 2.3). Three scale types are represented by the fishes we will examine: ganoid (Figure 2.3A), cycloid (Figure 2.3B), and ctenoid (Figure 2.3B). Ganoid scales are covered with an enamel-like substance and seldom overlap; cycloid scales are roughly circular, lack spines, but bear circuli and radii. Ctenoid scales are often quadrangular, bear circuli and radii and possess a posterior field with small spines. Examine a ganoid scale from a gar (Lepisosteidae), a cycloid scale from a shad (Clupeidae) and a ctenoid scale from a member of the family Centrarchidae. What type of scales are possessed by sturgeons (Acipenseridae) by suckers (Catostomidae), by cyprinids. Some fish lack scales, i.e., catfishes (Ictaluridae). Name two other families in which the member lack scales. ;. Various scale counts are often important in differentiating between species. Lateral line scales (Figure 73 B)= the number of scales along the lateral line beginning with the first scale in contact with the shoulder girdle and ending with the scale over the structural base of the caudal fin.
Scales above lateral line = the number of scales in a diagonal line downward and backward from the origin of the dorsal fin to, but not including the lateral line scale. Scales below lateral line = similar to above, but from the origin of the anal fin upwards and forwards. Scales around caudal peduncle = the number of scales around the most slender portion of the tail, counted in zigzag fashion. 1. What makes it difficult to count lateral lines scales on a creek chubsucker (Erimyzon oblongus)? 2. Make the above scale counts on a pirate perch (Aphredoderidae) and record your answers. Lateral line scales Scales above lateral line Scales below lateral line Scales around caudal peduncle Part III. Fins (Figure 73 A and B): Typical teleost fishes have three unpaired fins and two pairs of paired fins. The unpaired fins are the dorsal fin, the caudal fin, and the anal fin. The paired fins are the pectoral fins and the pelvic fins. The dorsal, anal, and paired fins may possess spines, soft rays or both. Spines are unbranched and may be stiff or soft and pliable. At times, the portion of the dorsal fin containing spines is widely separated from the portion containing rays, and it appears like there are two distinct dorsal fins. Another fin-like structure which occasionally occurs in fishes is the adipose fin (Figure 73 A). This fin is not supported by spines or rays but is merely a fleshy integumentary outgrowth. It is found, when present, mid-dorsally, behind the dorsal fin. 1. Compare the positions of the paired fins on a centrarchid with those on a minnow (Cyprinidae). How do they differ? 2. Count and record the number of spines on the dorsal, anal, and pectoral fins of a black crappie (Centrarchidae). Dorsal Anal Pectoral 3. Count and record the number of soft rays in the dorsal and anal fin of the brook silversides (Atherinidae). Dorsal Anal Pectoral 4. Of the following species, which possess an adipose fin: rainbow trout, chain pickerel, longear sunfish, and channel catfish? The caudal fin, which together with the posterior post anal portion of the body composes and tail of the fish, never possess spines but is entirely supported with soft rays. The caudal fin may be deeply forked, slightly forked (emarginate), rounded, squared off (truncate) or exhibit other types of margins.
Most of the fishes you will study possess a homocercal tail (Figure 74 A) in which the vertebrae end at the base of the caudal fin, the lobes of which are about equal. Some, such as the sturgeons and paddlefish, have a heterocercal tail (Figure 74 C) in which the vertebrae bend upward to enter the upper caudal lobe, which is larger than the lower. The gars and bowfin have an abbreviated heterocercal tail in which the vertebrae bend up, but the tail is nearly symmetrical externally. 1. Compare the channel catfish with the yellow bullhead. Which has an emarginate caudal fin? 2. Examine fishes which show the three basic tail types. Part IV. Coloration. Many species of fish possess very distinctive patterns and coloration. Unfortunately much of the color is lost in preservative, although the basic pattern often remains. 1. Compare the bluegill and the longear sunfish in coloration. Is there a difference in coloration? 2. Compare the pigmentation of two species of trout (Salmonidae). Is there a difference? 3. What conspicuous pigmentary characteristic is shared by the two shad, the bluegill, and the green sunfish?. 4. In most fishes, the venter is pigmented less heavily than the dorsum. This is counter shading and occurs in many animals. What is its function? Examine the hog sucker. What is unusual about its counter shading? Part V. Sexual Dimorphism: Most of the conspicuous differences between male and female fishes are pigmentary and are most conspicuous during the breeding season. These differences are lost in preservative. In live-bearing fishes males often have a copulatory organ by which they may be distinguished from females. Examine the copulatory structure (gonopodium) of the male mosquitofish. It is formed from the first few rays of the anal fin. Note its absence in the female. 1. Separate the male mosquito fishes from the females. What other sexual difference can be seen, aside from the gonopodium? Part VI. Special Characters 1. Barbels (Figure 73A). Barbels are fleshy filaments or projections usually present on some part of the head. The whiskers of catfish are barbels. They function as tactile structures and are found on fishes of many families and genera. 3
1. Examine the chin barbels of various catfish species. Can you differentiate between the black and yellow bullhead (Ictaluridae) on the basis of chin barbels? How? 3. Considering the function of barbels, can you make a general statement about the feeding habits of fishes that possess them?. Does a carp possess barbels? 2. Branchiostegal Rays (Figures 73D and 77C). These are bony flattened structures that support the membranes on the lower side of the head, just below the gill covers. Their number is often of taxonomic importance. 1. Count and record the number branchiostegal rays in the species of Esox (Esocidea). E. niger E. americanus. 3. Pseudobranchiae. Pseudobranchiae are gill-like structures on the inner surface of the gill cover (operculum), near the top. Mullets (Mugilidae) possess these structures. 4. Gill Rakers (Figure 76 A-D). These are slender rod-like to blunt knoblike projections along the anterior edges of the bony arches that support the gills. Their number and shape is often of use in differentiating similar species. Only those of the first (outermost) gill arch are counted. 1. Compare the gill raker counts of the shadow bass (Ambloplites) and the black crappie (Pomoxis) and record the differences.. 2. Compare the gill raker shape of Lepomis machrochirus and Lepomis megalotis (Centrarchidae) and record the differences. 5. Pharyngeal Teeth (Figure 78 A-C). These teeth are born on two bones in the throat (the modified 5 th gill arches). Their number and position are often of taxonomic importance, especially in the minnows. To examine the teeth on these bones, the operculum and outer gill arches must be pushed back and then the bone bearing the pharyngeal teeth must be removed with great care and carefully cleaned. The teeth must not be broken off during this process or erroneous counts will result. The pharyngeal bones are sickle shaped and bear one or two (three in the carp) rows of teeth. The teeth in each row are counted and given in a formula from left to right; thus, the formula of 1, 5-4, 2 indicates that the pharyngeal bone of the left side has one tooth in the outer row and five in the inner, whereas the right bone has four teeth in the inner row and two in the outer. (For the Cyprinidae, see also The Fishes of Missouri, by WL Pflieger, 1975). Select three species of minnows and record the pharyngeal teeth formulae: Species 1: ; formula Species 2: ; formula Species 3: ; formula 4
5