Trunk Canal (Lateral Line)

　Two character states of the trunk canal were identified: complete and incomplete (Table 1). A complete trunk canal was found in all Tanakia species except T. tanago and all Acheilognathus species except A. typus. An incomplete trunk canal was found in T. tanago, A. typus, and all Rhodeus species.

　The Degree of completeness of the trunk canal (TRC) was determined by a pored scale count of the TRC vs. scale count in a longitudinal scale row. The number of scales in a longitudinal scale row ranged from 32 to 63, of which 0-38 had pores, in all bitterlings examined: 56 to 63 in A. typus and 32 to 38 in all other bitterlings. Scales of A. typus were smaller and more numerous than those of other bitterlings. In bitterlings with an incomplete TRC, the number of pored scales was 5-20 (e.g., 15+5 or 15+2+3 in case of 20) in T. tanago, 7-14 in A. typus, and 0-8 in 11 species/subspecies of Rhodeus: 2-7 in R. o. ocellatus, 0-5 in R. o. kurumeus, 3-5 in both R. a. atremius and R. fangi, 4-5 in both R. a. suigensis and R. notatus, 3 in R. sinensis, 4-6 in R. s. sericeus, 2-4 in R. s. amarus, 5-7 in R. haradai, and 5-8 in R. spinalis. One special case was found in T. tanago, in which a trunk canal was separated into 1 to 3 parts by interruption at various sites (Fig. 12C).

　As A. typus (scales, 56-63) was distinct ('Type B') in having more scales in a longitudinal scale row than those in other bitterlings (scales, 32-38), its pored scale count could not easily be compared with that in other species. Thus, except for A. typus, the TRC of all other bitterlings could be divided into 3 types: 'Type A', a complete TRC; 'Type C', an interrupted incomplete TRC found only in T. tanago; and 'Type D', a reduced incomplete TRC as found in all Rhodeus species (Fig. 12).

Fig.12
Fig.12.
Four types of the trunk canal in the Acheilognathinae. A, complete-canal type. B, reduced incomplete-canal in small scales type in Acheilognathus typus. C, interrupted incomplete-canal type in Tanakia tanago. D, reduced incomplete-canal in large scales type in all Rhodeus species. Arrows in dashed line show evolution by peadomorphosis. (See p. 19 for explanation.)