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14 METHODS AND MATERIALS space (Loos and Fuiman 1977). Cyprinid eggs, except as noted above, are typically 1.0 - 2.0 mm in diameter, while catostomid eggs are typically 2.5 - 3.5 mm in diameter except in the subfamily Ictiobinae and tribe Erimyzantini in which eggs measure around 2.0 mm. Cyprinid eggs are deposited in a variety of ways from broadcast with no parental care to attachment in masses under submerged rocks or other objects with intimate parental care. Catostomid eggs are broadcast with no parental care. METHODS & MATERIALS Most of the specimens studied were collected from the Yampa, White, Colorado and Gunnison Rivers in Colorado from 1976 through 1979 as part of Bureau of Land Management and Colorado Division of Wildlife Surveys (Carlson et al. 1979, Prewitt et al. 1978, Wick et al. 1979, and Wick et al. 1980). Unrecognized larval specimens were originally segregated into like groups. Continua were then established with identifiable juveniles. Once dis- tinguishing characters were determined for the various species, most larvae and early juveniles were assem- bled into developmental study series based on size. Several series of specimens were reared from artifi- cially-fertilized eggs during the spring and summer of 1978 through 1981, and from collected larvae during the summer of 1977. Additional specimens or series were loaned or donated by outside sources (see Acknowledgments). Most of the collected and reared specimens were killed and fixed in 10% formalin, then stored in 3% buffered formalin. Some borrowed specimens were stored in ethyl or isopropyl alcohol. Figure 4 illustrates the various measurements, fin ray counts, and myomere counts that were made on at least two or three specimens, if available, in each l-mm total-length (TL) interval throughout the larval period of each species. One or more specimens in each 3- to 4-mm interval were similarly processed thereafter to a length of about 50 mm TL. Juveniles for each species, for which specimens were available, were cleared with trypsin, potassium hydroxide, and glycerin and stained with Alizarin Red (modifications of methods by Taylor 1967) to enable the recording of internal meristics such as vertebra counts and verify fin meristics. Specimens were studied under low power stereo-zoom microscopes with measuring eyepiece reticles and various combinations of reflected, trans- mitted and polarized light. Magnification was adjusted before each series of measurements to cali- brate the scale in the eyepiece against a stage micrometer for direct measurement. Measurements were made to the nearest tenth of a millimeter and occa- sionally to half that unit. Remeasurement of selected specimens by a second observer indicated that most measurements are repeatable to within 0.1 mm. Most measurements are reported as a percentage of standard length but are" readily converted to percent total length by dividing the length of interest, in terms of SL, by total length, in terms of SL, and multiply- ing by 100. Drawings, including dorsal, lateral and ventral views were prepared for a recently transformed and later stage of each larval phase available and for the juvenile period. Enlarged photographs were traced to assure accurate body proportions. Various struc- tures were checked and additional detail was added to the drawings while the specimens were examined under a microscope. Final drawings were idealized (e.g., closed or frayed fins opened and smoothed and curved bodies straightened). If necessary, melanophore dis- tribution was modified to represent a more typical pattern. RESULTS The remainder of these "contributions to a guide" consists of three parts: a preliminary key to the metalarvae, the species accounts, and a pair of com- parative summary tables. U~fortun~tely, i~for'!1ation on the development of certaln specles remalns lncom- plete and many characters exhibit a l~rge degree of overlap among the various species considered. Accord- ingly, it might not always be possible to trace the identity of a specimen to the species level with the degree of confidence desired. Still, with the infor: mation provided, the vast majority of collected specl- mens can be accurately identified. The key is not absolute and does not cover all contingencies, but it should prove to be satisfactory for determining the identity of most metalarvae. . In many instances, the key will also work for earlY.Juve- niles. Specimens with atypical morphometry or fln ray or myomere counts might not key-out properly. Upon reaching a conclusion via the key, the identity should bevarified with the data and illustrations provided in the species accounts. Median fin ray counts given in the key are for the principal rays only. Most species accounts consist of a page of tabu- lated data and two pages of illustrations. Some accounts currently consist of only one or the other. A few species have not been sufficiently studied or the information adequately assembled to provide either tabulated data or illustrations. Previously published illustrations are used where originals are not yet available. Most of the developmental studies upon which this material is based are still underway. The planned guide will include detailed coverage of additional species; the addition of background information, verbal descriptions and commentary, graphed morpho- metric length data, and more original illustrations to the species accounts; a summary table of repro- ductive information; and refinement to the metalarvae key and the addition of keys to the protolarvae and mesolarvae. Users of the key, species accounts and summary tables are asked to make known any errors, problems, or suggestions for improvement.