Comparative morphological analysis of four populations of the grayling Thymallus tugarinae from the Amur River basin (Khabarovsk region)
Recently 4 forms of graylings are known in the Amur basin, with specific differences, and the grayling Thymallus tugarinae is one of them. The data on comparative morphology of this species populations in 4 tributaries of the lower Amur are analyzed. Two small rivers (Tarakanovka, Gera) and two large rivers (Khor, Anuy) are explored. Fish was caught by casting net (mesh size 5 mm, average opening area 3 m2). In total, 27 specimens were sampled from the Tarakanovka, 24 - from the Gera, 30 - from the Anuy, and 22 - from the Khor. The samples were fixed by 4 % formaldehyde, and than morphological analysis was conducted according to Pravdin (1966) technique of measurement applied to salmonids. Fish age was determined by scale with using binocular microscope MBS-10 (zoom 2x8). Statistical analysis was made according to Student t-criterion. Morphological differences were statistically significant with significance p = 0.001. In total, 33 plastic parameters were analyzed for 6 pairs of samples. Length of the head and paired fins had statistically significant differences for 5 pairs of samples; length of the dorsal fin, length of the upper and lower caudal lobe, depth of the head in occipital area, and longitudinal diameter of the eye had statistically significant differences for 4 pairs of samples; antedorsal distance, depth of posterior part of the dorsal fin, depth of the anal fin, width of the forehead, and length of the maximal gill raker had statistically significant differences for 3 pairs of samples; the body length to the end of scale cover, anteanal distance, postdorsal distance, distance between the insertions of pectoral and ventral fins, depth of anterior part of the dorsal fin, postorbital distance, and length of the lower jaw had statistically significant differences for 2 pairs of samples; distance between the insertions of anterior margins of ventral and anal fins, anteventral distance, length of the anal fin, the minimal depth of the body, and depth of the head in orbital area had statistically significant differences for 1 pair of samples; and other 7 parameters (maximal depth of the body, length of the caudal peduncle, length of the middle caudal rays, length and width of the upper jaw, length of middle part of the head, and length of the snout) had no statistically significant difference for any pair of samples. Level of the grayling meristic features in analyzed samples was lower than the differences of plastic parameters. Only one comparative pair (graylings from the Tarakanovka and the Khors) was characterized by statistically significant difference for two parameters - number of perforated scales in the lateral line and number of the gill rakers. The parameters of fin and head of grayling were the most variable, and the body proportions were the least variable. The analyzed samples of grayling could be divided onto two groups: the fish from small rivers and the fish from large rivers. The graylings caught in small rivers had less differences between each other than the fish from the Khor and Anuy.