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<br />Other Countable Structures <br /> <br />Other structures that may be treated <br />meristically (and in some cases morphologi- <br />cally) include branchiostegals, gill rakers, <br />pharyngeal teeth, and scales. Branchiostegals <br />form early in larval development, but counts <br />are usually constant within major taxon <br />groups. Within the order Cypriniformes, all <br />members of superfamily Cyprinoidea, which <br />includes Cyprinidae and Catostomidae, have <br />three branchiostegals (McAllister 1968). Due <br />to later development, small size or internal <br />location, the other characters are seldom <br />used to diagnosis fIsh larvae. Gill rakers <br />form gradually in postflexion mesolarvae or <br />metalarvae with numbers increasing through- <br />out much of the early portion of the juvenile <br />period. The adult complement of gill rakers <br />on the fIrst gill arch is not achieved in many <br />Catostominae until they reach about 70 mm <br />standard length (Smith 1966). Pharyngeal <br />teeth form relatively early but may not be <br />sufficiently well developed to be readily <br />removed and observed until late in the larval <br />period or early in the juvenile period. <br />Detailed study of gill rakers and pharyngeal <br />teeth might reveal some useful diagnostic <br />qualities, including size, shape, and number. <br />However, most specimens are more easily <br />identified using external characters. Scales <br />typically become apparent late in the larval <br />period or early in the juvenile period. First <br />scales on cypriniforms typically appear mid- <br />laterally on the posterior half of the body and <br />from there spread anteriorly, dorsally, and <br />ventrally toward adult coverage. Scales of <br />large-scaled species are sometimes suffIciently <br />obvious by late in the metalarval phase to <br />distinguish certain species or genera. <br /> <br />Morphology <br /> <br />The shape or form of larvae and specific <br />anatomical structures (e.g., gut, air bladder, <br />yolk sac, and mouth) change as fIsh grow and <br />provide some of the most obvious characters <br />for identifIcation, particularly at family and <br />~ubf~ily levels. Within genera, morpholog- <br />ICal differences among species are usually <br />much more subtle, but may still be of diag- <br />nostic value. Much shape or form-related <br />i?formation can be quantified via propor- <br />tional measurements or morphometrics. <br /> <br />Morphometric data emphasize the rela- <br />tive position and relative size of various body <br /> <br />components and dimensions and may be criti- <br />cal to species identification. Such measure- <br />ments may be allometric, changing in propor- <br />tion as the fIsh grow; thus morphometric data <br />should be related to size, at least for proto- <br />larvae and mesolarvae. Some morphometric <br />data, particularly body depths and widths, <br />may be directly affected by the condition of <br />individual specimens and volume and form of <br />food items in their digestive tracts. The <br />source of specimens and the preservative in <br />which they are stored also may affect mor- <br />phometric data. Some measures in wild fIsh <br />may differ from those of laboratory reared <br />specimens (e.g., rm lengths). Shrinkage and <br />deformation are notably greater in alcohol <br />than in formalin preservatives. <br /> <br />Morphometric data in this guide are <br />reported as percentages of standard length. <br />Use of standard length avoids the allometric <br />influence of caudal rm growth included in <br />percentages based on total length. As <br />explained later (Methods), data can be easily <br />converted to percent total length for compar- <br />ison with other works. Prior to hypural plate <br />formation and completion of notochord flex- <br />ion (protolarvae and flexion mesolarvae), <br />standard length is the length from snout to <br />posterior end of the notochord (notochord <br />length). Thereafter, it is the length from <br />anterior margin of the snout to most poster- <br />ior margin of the hypural plates (usually the <br />superior plate or hypurals). Use of noto- <br />chord length for protolarvae and early meso- <br />larvae gives the appearance of greater allo- <br />metric growth differences than may really <br />exist, at least in comparison with subsequent <br />measures based on posterior margin of the <br />hypural plates. This undesirable effect is a <br />result of upward bending or flexing of the <br />notochord and the switch from use of end of <br />the notochord to posterior margin of the <br />hypurals as the basis for length measurement. <br />These factors must be taken into account <br />when reviewing morphometric data herein. <br /> <br />In contrast to procedures recommended <br />by Hubbs and Lagler (1958) for larger juven- <br />iles and adults, measurements of body length <br />and various parts thereof for fIsh larvae are <br />generally taken along lines parallel to the <br />horizontal axis of the fIsh. Exceptions are fIn <br />lengths, which in studies conducted for this <br />manual were measured from origin of the fIn <br />base to most distal margin of the rm rays. <br />Typical measures include total, standard, <br /> <br />12 <br />