9492 - Laserfiche WebLink

Home Browse Search

Comparative Summary The diagnostic criteria that follow are included in the computer-interactive key, but are provided here, along with the descriptive species accounts here and in Snyder and Muth (1990), to help confirm identities determined through the key or for use as an alternative to the key. Since extremes in character states beyond those reported here are likely to occur, identifications should be based on as many criteria as possible. Size relative to state of development. - Flannelmouth sucker eggs are the largest of UeRB suckers (3.8-3.9 rnrn diameter versus 3.3-3.5 for bluehead sucker and 2.3-3.3 for the others) and larvae hatching from them are usually much larger as well. This relative size difference is characteristic of tlannelmouth sucker throughout its early development (Table I). In contrast, razorback, mountain, and some white and longnose sucker eggs are notably smaller (2.3-2.8 rnrn diameter) than other species and their recently hatched proto larvae and recently transformed meso larvae tend to be correspondingly small. These species also complete yolk absorption at a much smaller size, usually by 12 rnrn SL; tlannelmouth sucker larvae finish their yolk at 15 rnrn SL (occasionally 16 rnrn SL). Size relative to state of development for all species but tlannelmouth sucker is nearly the same by the beginning of the metalarval phase. In general, fin development proceeds fastest (at smaller sizes) for white sucker and slowest (at larger sizes) for tlannelmouth sucker. However, pelvic fins develop earliest in longnose sucker. White and Utah suckers acquire the adult complement of all fin rays, lose their preanal finfolds, and become juveniles at the smallest sizes (19-20 rnrn SL) whereas transformation to the juvenile period for some razorback sucker occurs at sizes nearly as large as for tlannelmouth sucker (22-23 and 23-24 rnrn SL, respectively). Gut folding or coiling proceeds at a faster rate for most bluehead sucker than for other species and at a much slower rate for nearly all tlannelmouth sucker. Although gut folding begins only a little later in razorback larvae than in bluehead larvae, it slows during the metalarval phase. As a result, the upper end of the size range for razorback sucker at transition to gut phase 4 overlaps the lower end of the range for tlannelmouth sucker. The size at first appearance of the full series of lateral scales roughly correlates with scale size. The full lateral series of scales appears as early as 24 rnrn SL for Utah sucker and 29 rnrn SL for white sucker, both of which have large scales. But it appears no earlier than 39 rnrn SL for tlannelmouth sucker which has very fme scales. Meristies and morphometries. - Some character differences determined by comparison of species account summaries of meristics and morphometrics are not included in Tables 2 and 3 because corresponding data for an adjacent phase indicate that the differences might not hold up if additional specimens in the size range of concern are analyzed. When comparing morphometric characters, be aware that some characters, especially depth and width at origin or dorsal fm (OD), are affected by the amount of yolk in early larvae and by health or condition in later larvae and juveniles. Juvenile morphometric data might not be applicable to specimens much greater than 40 rnrn SL. The more useful meristics are counts of lateral line (or series) scales for juveniles in which scales are sufficiently formed; principal dorsal fm rays (and corresponding pterygiophores) and vertebrae for late posttlexion mesolarvae, metalarvae, and juveniles; and myomeres, both total and to the posterior margin of the vent (often referred to as preanal myomeres), for all larval 23