Trunk Canal (Lateral Line)

　As shown in Table 1, a complete TRC was found in all Tanakia species except T. tanago and all Acheilognathus species except A. typus, while an incomplete TRC was observed in T. tanago, A. typus, and all Rhodeus species. Polarity of the TRC is from the complete to the incomplete state (Webb, 1989a, 1989b). Among all bitterlings, four types of TRC were identified (Fig. 12): a complete TRC type (Fig. 12A) is plesiomorphic; a reduced incomplete TRC as found in all Rhodeus species (Fig. 12D), apomorphic; an incomplete TRC combined with small scales as only found in A. typus (Fig. 12B), autapomorphic; and an interrupted incomplete TRC (Fig. 12C) as found in only T. tanago, also autapomorphic. Tanaka (1909) reported 9-25 pored scales in T. tanago. An incomplete trunk canal corresponds to a structure at juvenile stage in cyprinids having a complete trunk canal (Disler, 1971; Webb, 1989a, 1989b). Therefore, each of these three incomplete TRC states might have been derived independently from the complete TRC state by peadomorphosis (Figs. 12 and 13).

　For identification of acheilognathine genera, an incomplete TRC has been considered to be an autapomorphy of Rhodeus by many ichthyologists (e.g., Choi et al., 1990; Lin, 1998). R. oryzae Jordan & Seale, 1906 was erected based on an incomplete TRC. Choi et al. (1990) placed a Korean bitterling, Pseudoperilampus hondae Jordan & Metz, 1913 in the genus Rhodeus. However, an incomplete TRC is not an autapomorphy of the genus Rhodeus. As shown in Table 2, an incomplete TRC is found in not only the Acheilognathinae, but also many other cyprinid subfamilies. As for R. oryzae, Arai & Akai (1988) reported that R. oryzae was a juvenile Tanakia limbata (Temminck & Schlegel, 1846), an adult of which has a complete TRC (Fig. 14). It was also proposed that P. hondae did not belong to Rhodeus but to Acheilognathus based on numbers of the dorsal and anal fin-rays as well as a long incomplete TRC, which consisted of 25 pored scales (Arai et al., 2001).

Fig.14
Fig.14.
Morphogenesis of the trunk canal in Tanakia limbata. ◇, NSMTP 29821, fish used for development experiment, 65 days after hatching; △, NSMT-P SK 4717, from Kumamoto Prefecture; ○, NSMT-P 21695, from Fukuoka Prefecture; ●, SU (Stanford University) 9258, paratypes of Rhodeus oryzae, from Kawatana, Nagasaki Prefecture, Japan. (From Arai & Akai, 1988)