The Itasenpara bitterling Acheilognathus longipinnis is a small cyprinid fish belonging to the Acheilognathinae, a subfamily that has an unusual symbiotic spawning relationship with freshwater mussels. During the spawning period, mature males select a mussel to accommodate spawning of a female. Because females possess short ovipositors for inserting their eggs inside the suprabranchial cavity of the host mussel via the exhalant siphon, the pattern of mussel utilization by spawning Itasenpara bitterling was investigated in the Moo River and a conservation pond (Himi City, Toyama Prefecture, Japan), so as to clarify the most preferred mussel size. In the Moo River (lotic environment), Nodularia douglasiae nipponensis (38.8% of total 747 individuals) was the major host of A. longipinnis larvae, there being no obvious size preference, possibly because neither eggs nor larvae of A. longipinnis could be readily ejected from the host in the lotic environment. By contrast, in the conservation pond (lentic environment), where N. d. nipponensis (24.3% of total 136 individuals) was again the main host of A. longipinnis larvae, a tendency to prefer smaller-sized mussels was apparent, due to the ease of ejection of eggs and larvae of A. longipinnis from larger-sized hosts (shell length >66 mm) in the lentic environment. Accordingly, differences in host mussel suitability are suggested as being related to habitat differences.
To clarify the ichthyofauna of the Amami Island Ryukyu Archipelago, fish specimens from the region were examined in museums throughout Japan resulting in the discovery of a single specimen (75.9 mm standard length; SL) of the dwarf squirrelifish Sargocentron iota Randall, 1998 (Beryciformes, Holocentridae) in the Yokosuka City Museum. Collected from a deep (23m) dark recess in a rocky reef grotto at a rocky reef off Kakeroma Island. The specimen was characterized by XI, 13 dorsal-fin rays, IV, 9 anal-fin rays, 15 pectoral-fin rays, I, 7 pelvic-fin rays, 6 + 10 + 9 + 5 caudal-fin rays, 45 lateral-line scales, 3.5 scale rows between the mid base of the spinous dorsal fin and the lateral line, 9 scale rows between the lateral line and anal-fin origin, 4 oblique scale rows on the cheek, 5 + 10 gill rakers, 11 + 16 vertebrae, body depth 2.5 in SL, head length 2.7 in SL, head depth 3.6 in body depth, snout length less than half orbital diameter, upper-jaw length 2.6 in head length, fourth dorsal-spine longest, third dorsal-fin soft ray longest, a pair of retrorse spines on the edge of the premaxillary groove, a spine on the upper edge of the lacrimal absent, and a bright red body coloration when fresh. The longest anal-fin soft ray length of the Kakeroma Island specimen was slightly shorter than that of the type specimens of S. iota which is likely to be an individual or geographic variation. Although S. iota is distributed in the Indo-Pacific, it has been recorded only from the Hawaiian Islands and Palau within the North Pacific Ocean. Accordingly, the Kakeroma Island specimen represents the first record of S. iota from Japanese waters and the northernmost record for the species. The new standard Japanese name “Kogashira-ebisu” is proposed for the species.