The importance of olfaction in spawning of medaka Oryzias latipes was established for the first time by observation of spawning behavior by fish subjected to an olfactory blockage. Experimental fish were prepared by (1) covering the nostrils on both sides (bilateral treatment), thereby excluding all olfactory stimuli, and (2) covering nostrils on one side only (unilateral treatment), thereby giving partial exclusion. A control group comprised untreated (intact). Experiments conducted for both males (bilateral male-intact female, unilateral male-intact female and intact male-intact female) and females (bilateral female-intact male, unilateral female-intact male and intact female-intact male) resulted in no spawning by intact females paired with bilateral males, whereas spawning occurred in intact females paired with both unilateral and intact males. Spawning also occurred when intact males were paired with intact, unilateral or bilateral females, indicating that olfactory stimuli were necessary for males to complete spawning, but not so for females. Spawning acts exhibited from pairing started by bilateral males-intact female pairs included “following” (initial act of following female), “positioning” (lateral courtship display), and “quick circle” (turning in front of female), but they did not include “contact” (bodies in contact posteriorly prior to gamete release), “wrapping” (male embracing female using their dorsal and anal fins during gamete release). On the other hand, intact and unilateral males participated in all of the above spawning acts, indicating that olfactory stimuli are indispensable for behavior concerning emitting semen.
A single specimen of an engraulid fish, Encrasicholina devisi (Whitley, 1940) as collected from Uchinoura Bay, Kagoshima Prefecture, southern Japan, in January 011. The previously reported northernmost record of the species being as Taiwan, the agoshima specimen is described here as the northernmost (and first Japanese) record nown of E. devisi. Although the species is similar to E. heteroloba in having the maxilla osteriorly reaching to the subopercle, differences between the species have been unclear, ue to a lack of detailed comparisons. Comparisons of E. devisi with E. heteroloba based n 29 and 32 specimens, respectively, from the Indo-West Pacific revealed the former to ave 3 unbranched rays in the dorsal and anal fins [vs. 2 or (rarely) 1 in E. heteroloba]. ncrasicholina devisi also differs from E. heteroloba in having relatively fewer gill rakers: 6–46 (mode 40) on the first gill arch [vs. 44–51 (46)], 30–37 (34) on the second gill rch [vs. 33–42 (38–40)], 15–22 (19) on the fourth gill arch [vs. 19–25 (21)] and 3–7 (6) n the posterior face of the third gill arch [vs. 5–8 (7)]. Morphometrically, E. devisi is eparable from E. heteroloba in head length [25.8–27.5% (mean 26.7%) of standard length s. 22.8–25.5% (24.3%)], first unbranched dorsal-fin ray length [0.4–1.8% (1.0%) vs. 4.1– .7% (5.6%)], second unbranched dorsal-fin ray length [5.3–7.5% (6.7%) vs. 12.3–15.2% 13.5%)], first unbranched anal-fin ray length [0.3–2.1% (1.0%) vs. 2.5–5.0% (3.6%)] and econd unbranched dorsal-fin ray length [2.3–4.9% (3.9%) vs. 7.3–11.0% (9.6%)], and in aving the third or fourth soft ray in the dorsal fin longest (vs. second to fourth), and third o fifth soft ray in the anal fin longest (vs. second or third).
Three specimens (191–247 mm in standard length) of a meso/bathy-pelagic ophidiid, Brotulotaenia nielseni Cohen, 1974, collected off Miyagi Prefecture and near the Ogasawara Islands, southern Japan, represent the first records of the genus Brotulotaenia from Japanese waters. Brotulotaenia nielseni, which can be distinguished from the other three species of the genus (B. brevicauda, B. crassa and B. nigra) on the basis of several meristic and proportional characters, including dorsal fin rays (85–101), total vertebrae (68–76) and preanal length (36.5–47.4% SL), was previously known from the western and mid (Hawaii) Pacific Ocean, and the western Indian Ocean.
Eight specimens (28.2–170.2 mm SL) of the non-indigenous bagrid catfish Pseudobagrus fulvidraco were collected from the Lake Kasumigaura system, Ibaraki Prefecture, central Japan, during December 2008 and November 2011. Three juvenile specimens of this invasive species indicated successful reproductive activity in the lake system. The species is known to have similar morphological and food habits to channel catfish Ictalurus punctatus, which has also invaded Lake Kasumiguara, causing damage to the ecosystem and problems for local fisheries. The establishment and future habitat expansion of P. fulvidraco would also cause serious ecological and economic problems.
To clarify the distribution during spawning and spawning habitat of Itasenpara bitterling (Acheilognathus longipinnis), one of the most endangered freshwater fish species in Japan, the habitats of mature individuals and freshwater mussels (Unio douglasiae nipponensis) were investigated in the Moo River (Himi City, Toyama Prefecture, Japan) in relation to environmental factors during the fall and winter seasons in 2010. Mussel density-influenced sex ratios of bitterling varied in the study area, males remaining in areas of high mussel density during spawning, while females frequented deeper feeding grounds until their eggs had matured.
Seven specimens (21.3–52.3 mm standard length) of the damselfish Stegastes insularis Allen and Emery, 1985, collected from Yoron-jima Island, the Amami Islands, Kagoshima Prefecture, Japan, are described in detail. A review of distributional records in Japanese waters, based on specimens, literature records, and underwater photographs, revealed the species to be distributed mainly in the Ogasawara, Izu and Ryukyu islands. On the basis of an underwater photograph, Kushimoto, Kii Peninsula, Wakayama Prefecture, is regarded as the northernmost record of the species, although it is not considered to reproduce in that area. The occurrence of S. insularis at Minamitori-shima Island appears to have resulted from dispersal from the northern Ogasawara Islands where the species commonly occurs. Known localities of the species, viz., Japan, Taiwan and Christmas Island, and the lack of records from Micronesia and Southeast Asia suggest that the population of Christmas Island is relictual.