Abstract The geographical distribution patterns of two closely-related wrasses, Pseudolabrus eoethinus and P sieboldi, on the Pacific and Sea of Japan coasts of southern Japan were examined. Relative frequencies of the two species were sur-veyed in 53 localities (six bordering the Sea of Japan), based on 586 specimens, 91 photographs and a total of 724 minutes of diving observations. Although the distri-butions of the two species broadly overlapped, P. eoethinus was exclusively distrib-uted along the southernmost parts of the peninsulas projecting into the Pacific Ocean, such as Kii Peninsula and Izu Peninsula, except in some protected areas (e.g. around the Koza River mouth near southernmost Kii Peninsula and within the Shimoda City harbor, southernmost Izu Peninsula). On the other hand, P. sieboldi was exclusively distributed in the innermost parts of bays opening to the Pacific (e.g. Sagami and Osaka Bays), and in the Seto Inland Sea and Sea of Japan. These geographical distribution patterns of the two species suggested that P. eoethinus preferred relatively warm, saline waters strongly influenced by the Kuroshio Cur-rent, whereas P. sieboldi preferred relatively cold, less saline waters not or only weakly influenced by the current. It was inferred that the two closely-related wrasses were able to coexist partly by differences in their preferred habitats.
Abstract The freshwater fish fauna on the southern islands of Japan is largely composed of peripheral and diadromous fishes, with few genuinely freshwater species. Although paddy water systems are known to provide important habitats for the latter in Japan, the utilization patterns by such on the southern islands are poorly understood. A paddy water system on Iriomote Island, where traditional style rice farming is maintained, was investigated so as to evaluate its function as a habitat for insular freshwater fishes. A total of 24 species were found, including 6 brackish, 3 peripheral, 12 amphidromous, 2 catadromous species, plus Gambusia ajfinis, the only genuine, and freshwater fish, which had been introduced. Of the 12 amphidromous species, five belonged to Eleotridae, including the endangered species Hypseleotris cyprinoids, the remainder being gobies. Based on binary data (presence/absence of dominant fishes), logistic regression analyses were conducted to construct predictable models. Dominant fish occurrence was explained by sig-nificant environmental conditions, that were expressed as principal components. Openness, species' richness, impoundment, stony substrate, deep water column and brackish water were all factors primarily preferred by particular fish groups, the paddy water system on Iriomote Island supplying several types of habitat avail-able for insular diadromous fishes. In particular, the lack of hazards along the mi-gratory course was a significant habitat factor for fishes with less upstream-migra-tory ability, such as eleotrids.
Abstract Growth and microhabitat characteristics, including distance from bank, water velocity, water depth and distance from river substrates at focal points of un-deryearlings of sympatric honmasu salmon Oncorhynchus masou, which is consid-ered as a hybrid of masu salmon O. m. masou, red-spotted masu salmon 0. m. ishikawai and biwa salmon O. m. subsp., and brown trout Salmo trutta were inves-tigated from early June to mid September in 1996 in the Toyamasawa River, dis-charging into Lake Chuzenji, central Japan. Both fork length and body weight of honmasu salmon were greater than those of brown trout throughout the study pe-riod. Honmasu salmon focal points were located further from the bank, in faster water velocity, and were deeper and further from the substrate than those of brown trout in each study month, except for distance from the bank after August. Com-parison of focal point environments for honmasu salmon and brown trout of equal size classes (fork length 5 mm intervals) showed that the former took positions fur-ther from the substrate. However, no significant differences were apparent in other environmental factors between the two species. The results indicated that minimal differences existed in habitat selection between honmasu salmon and brown trout for the same body sizes, suggesting that competition for microhabitats between un-deryearlings of honmasu salmon and brown trout was reduced by their different body sizes resulting from different hatching periods.
Abstract A swimming, pelagic, giant (63.0mm SL) postlarva of Laeops nigro-maculatus was collected from the sea surface off the coast of Shirahama, Wakayama Prefecture, southern Japan. The postlarva is identified as a member of Laeops because it possesses such features as: an elongated second dorsal fin ray, dorsal and anal fins much elongated, an extra-ilial portion of the liver and intestine greatly produced from the abdominal cavity and supported by the posterior process of the pelvic bone, and no teeth in both jaws on the left side. The postlarva is iden-tified as Laeops nigromaculatus based on meristic features. This report represents the first description of a postlarva of this species based on a specimen in good con-dition. An earlier, incomplete description of a larval stage of this species was based on a badly-damaged specimen. Possibly the present postlarva was trans-ported into coastal waters due to strong onshore winds, and once arriving there succumbed to the effects of these colder, coastal waters.
Abstract The habitat utilization by Halichoeres tenuispinnis and Stethojulis in-terrupta terina (Labridae) on a rocky reef at Izu Ocean Park, the east coast of Izu Peninsula, Japan is described. A total of 17 labrid species was observed by monthly observations from August, 2000 to August, 2001. H. tenuispinnis and S. i. terina were abundant, comprising 54% and 23% of the 3, 464 labrid sightings, re-spectively. Both species occurred equally over areas of boulders, rocky flat, rocky slope, rocky-sand and sand. However, observations on feeding behavior revealed significant differences between the species in their utilization of microhabitats on each bottom condition.
Abstract Fine structures on the egg membranes of alfonsino (Beryx splendens) were examined under SEM to assist in egg identification. Alfonsino, spawn small spherical eggs, which have needle/petal-like projections over the entire egg surface (chorion). The projections of unfertilized eggs occurred at a density of 4.9 per 100μm2, the length of each “petal” being from 0.3 to 4.9μm, whereas those of fertilized eggs occurred at reduced densities (0.9 per 100 μm2) with shorter “petals”, from 0.6 to 3.4μm in length. These structures may play an important role in the attachment of the eggs to one another, and may improve fertilization effi-ciency during spawning.
Abstract Two females and a male of chum salmon Oncorhynchus keta (600-808 mm in fork length) were collected from near shore regions and a river in the west coast of Kagoshima Prefecture, southern Japan, in November 1991, October 1993 and November 2002. The specimens, 3-5 years of age, showed nuptial col-orations with matured gonads. This study represents the southernmost record of chum salmon collected in Japan.
Abstract The distribution pattern of a Japanese spinous loach, Cobitis takat-suensis, was surveyed along the tributaries of four water systems (Shigenobu, Hiji, Iwamatsu and Shimanto Rivers) in Ehime Prefecture, in order to clarify the present status of the species. Local populations were found in only 18% of 259 surveyed areas (28% of 86 tributaries). The species occurred between 50-380 meters alti-tude, except in the Iwamatsu River in which lower stretches were inhabited. On-corhynchus masou ishikawae, Phoxinus oxycephalus jouyi, Zacco temminckii, Rhinogobius flumineus and R. sp.LD, which prefer mountain streams, were often found co-existing with C. takatsuensis. Judging from river basin scale and fish density, the Iwamatsu River populations were considered to be in the most critical state. Ongoing monitoring of habitat conditions, including water temperature and gravel bed status, is essential for future conservation of this endangered species.
Abstract Three specimens of a small-fin wrasse, collected at Kerama Islands and Chi-bishi, off Naha, Okinawa Island, Japan, were identified as Pseudojuloides sev-ernsi Bellwood and Randall, 2000 on the basis of the following characters: slender body, small caudal fin, single pair of canine-like teeth anteriorly on jaws followed by incisor-like teeth, IX 11 dorsal fin rays, 13 pectoral fin rays, terminal phase with a large blue-margined black patch covering posterodorsal region of head and an-terodorsal one-third of body, and initial phase with a white line extending along upper jaw and passing below orbit to rear orbital margin. The specimens constitute the first confirmed record of the species from Japan, although a number of under-water photographs of P severnsi have been taken at Ie-jima Island (Okinawa), Kashiwa-jima Island (Kochi) and Izu-oshima Island (Tokyo), the last-mentioned locality being the northernmost recorded for the species.
Abstract We conducted underwater observations on courtship and spawning be-haviors of the tetrarogidid fish, Hypodytes rubripinnis in Kyushu Island, Japan. The reproductive behavior and seasonal changes of gonad somatic index on col-lected specimens showed that spawning occurred from late April to early August. Individuals of various sizes in both sexes reproduced in the study area. About 90 min before sunset, a male courted a female actively with several patterns of be-haviors such as male's lying by a female in a side-by-side position, display of his lateral side around a female, and male's riding on a female back. Finally, the pair swam toward 20 to 100 cm above the bottom to release gametes. Spawning time was around sunset. The average egg number in each spawning was about 1600. Upward rush of the pair to the middle water occurred very quickly. Frequent sneaking behavior by another male was also observed.