Ken Maeda

Diel and Seasonal Occurrence Patterns of Drifting Fish Larvae in the Teima Stream, Okinawa Island.

Abstract: Drifting fish larvae were collected with a plankton net in the lower reaches of a freshwater area of the Teima Stream, Okinawa Island, Japan, during 24 hr periods each month from June 1998 to October 1999 (except July 1998). Newly hatched larvae of several gobioid and two pipefish species were collected, and their morphology was described. The larval occurrences suggested that most species spawn mainly from spring to fall, with some Rhinogobius species spawning in winter. Larvae of all fishes occurred predominantly during hours after dusk diroughout the year. It is suggested that larvae of amphidromous fishes spawned in freshwater streams on Okinawa Island begin to drift soon after hatching at dusk and complete their exit from freshwater areas into the estuary and sea by midnight.

Recruitment of amphidromous sleepers Eleotris acanthopoma, Eleotris melanosoma, and Eleotris fusca into the Teima River, Okinawa Island

Recruitment courses of three amphidromous sleeper species, Eleotris acanthopoma, E. melanosoma, and E. fusca, were investigated at the surf zone adjacent to the river mouth and at five stations in the Teima River on Okinawa Island, Japan. All three species occurred at the surf zone as pelagic larvae with transparent and compressed body, a conspicuous air bladder, and an emarginated caudal fin. Eleotris fusca (16.0–19.6 mm in standard length: SL) sometimes possessed a vestige of the larval chin barbel and were larger than E. acanthopoma (9.7–13.2 mm SL) and E. melanosoma (11.2–12.8 mm SL). The pelagic larvae were also collected during full tide from the lower reaches of the tidally influenced area of the river. The pelagic larvae may be carried in and out of the estuary with some tidal fluxes, and they may settle when they reach the upper tidally influenced area where the salinity becomes extremely low. Body width and pigmentation of newly settled larvae increased. E. fusca was considered to migrate upstream to the freshwater area against the flow of the river just after reaching the settled stage. After settlement, all three species became completely pigmented, the caudal fin became round in shape, and the fin ray counts became complete with growth. Also, E. acanthopoma dispersed widely to the lower part of the tidally influenced area or to the lower reaches of the freshwater area, E. melanosoma dispersed to the lower part of the tidally influenced area, and E. fusca dispersed upstream.

Instream distributions and feeding habits of two species of sleeper, Eleotris acanthopoma and Eleotris fusca, in the Teima River, Okinawa Island

The instream distributions and feeding habits of two species of sleeper, Eleotris acanthopoma and E. fusca, were studied in the Teima River on Okinawa Island, southern Japan. Both adult fishes inhabited the river, but their distribution patterns were found to be different. The distribution of E. acanthopoma was from the tidally influenced area to the lower part of the freshwater area, whereas E. fusca was distributed almost entirely in the freshwater area. They were found to coexist at the upper limit of the tidally influenced area and the lower part of the freshwater area. Their feeding habits were clearly different, although both species were carnivorous. Eleotris acanthopoma fed mainly on crabs in the tidally influenced area and on aquatic snails in the freshwater area, where they coexist with E. fusca. In contrast, E. fusca fed mainly on shrimps in the freshwater area. Their coexistence may result from the difference in their feeding habits.

Reproductive Biology and Early Development of Two Species of Sleeper, Eleotris acanthopoma and Eleotris fusca (Teleostei: Eleotridae)

ABSTRACT Reproductive biology and early development of two species of sleepers, Eleotris acanthopoma Bleeker, 1853, and E. fusca (Forster, 1801), were investigated in streams on Okinawa Island in southern Japan. Gonadal examination and morphology of the genital papillae indicated that E. acanthopoma matured at a smaller body size (ca. 28 mm in standard length) than E. fusca (ca. 50 mm). Mature ovaries were composed of oocytes that could be categorized into two size classes. Larger females of both species had several hundred thousand developed oocytes in the larger size class and may spawn them at one or several consecutive spawning events. Egg masses of both species were found in habitats typically occupied by adults and were deposited, often sparsely, on the underside of objects. Form of the egg masses and morphology of eggs and newly hatched larvae of both species were almost identical. Eggs were a nearly spherical pyriform in shape, with the widest diameters measuring approximately 0.4 mm. Newly hatched larvae were very small (1.0–1.4 mm in notochord length) and undeveloped. The mouth opened and the eyes became pigmented 3 days after hatching, and all of their yolk was consumed 4 days after hatching. Reproductive strategies of both species were characterized by high fecundity through production of small eggs and small newly hatched larvae, with high fecundity likely to mitigate the presumed increased risk associated with widespread larval dispersal.

Comparative larval development of three amphidromous Rhinogobius species, making reference to their habitat preferences and migration biology

Eggs and larvae of three amphidromous species of Rhinogobius goby (Rhinogobius brunneus, Rhinogobius sp. MO and Rhinogobius sp. CB) from Okinawa Island, Japan, were reared under uniform conditions to describe and compare their larval development. Although the larval morphologies of the three species were very similar, some differences were observed in the timing of ontogenetic events among them. R. brunneus had the largest yolk and saved it for a longer period of time, whereas Rhinogobius sp. MO had the smallest yolk, which was exhausted earlier. The period until yolk exhaustion is thought to restrict the distance that migrating larvae can drift, which determines the specific adult distribution. Each of these two amphidromous species are close relatives of different fluvial resident species. Evolution of the fluvial residents could be explained by different scenarios based on the larval traits of R. brunneus and Rhinogobius sp. MO. Rhinogobius sp. CB hatched at a smaller size and grew slower than the other two species. No fluvial species have derived from Rhinogobius sp. CB. One possible explanation is that the smaller and slower-growing larvae of Rhinogobius sp. CB find it more difficult to remain within streams.

Newly Collected Specimens of the Sleeper Eleotris acanthopoma (Teleostei: Eleotridae) from French Polynesia Indicate a Wide and Panmictic Distribution in the West and South Pacific

Abstract: The morphology of Eleotris acanthopoma collected from Moorea in French Polynesia is described. This is the first record of this species from French Polynesia, greatly expanding the known range, which was previously only considered to extend from southern Japan to New Caledonia. Nucleotide sequences of the mitochondrial ND5 gene of several Eleotris species and related genera indicate that E. acanthopoma from Moorea belongs to the same lineage as E. acanthopoma from Japan and the Philippines. Despite being separated by a distance of approximately 10,000 km, two of the specimens from Moorea and one from the Philippines had identical nucleotide sequences. Results of this study indicate that extensive dispersal occurs during the pelagic larval stage of this species.

Downstream migration of newly-hatched ayu ( Plecoglossus altivelis ) in the Tien Yen River of northern Vietnam

The ayu (Plecoglossus altivelis) is an annual, amphidromous, plecoglossid fish, distributed in Vietnam, China, Taiwan, Korea, and Japan. To date, ayu have been found only in two rivers in northern Vietnam, where little is known about their life history. The Tien Yen River is believed to be the most southwestern habitat for this species. To determine whether newly hatched ayu larvae drift and to understand their downstream migration, intensive surveys were conducted in the Tien Yen River from October to March of 2013–2016. In total, 529 drifting ayu larvae were collected from four of six sampling stations along the river. Thus, ayu reproduction has been confirmed in this river for the first time, where only adult fish had been found previously. However, we did not successfully collect larvae in the eastern branch of the river, which has a hydroelectric dam, suggesting that ayu do not inhabit this branch or else do not reproduce there. The presence of drifting larvae in the western branch from mid-December to late January implies that they spawn from late November to mid-January. Drifting larvae were captured primarily at night, but peak occurrences varied depending upon the day and the sampling station. With the range of body sizes and variable diel abundance patterns, ayu in the Tien Yen River probably employ multiple spawning grounds. This study provides fundamental life history data for the vulnerable ayu populations in northern Vietnam.

Review of Schismatogobius (Gobiidae) from Japan, with the description of a new species

Three species of Schismatogobius de Beaufort 1912, distinguished by their morphology and mitochondrial DNA sequences, were found in freshwater streams in the Ryukyu Archipelago, Japan. Although two species were previously known from Japan (S. roxasi Herre 1936 and S. ampluvinculus Chen, Shao, and Fang 1995), the taxonomy needs to be revised. To identify these species, the holotype morphology of S. marmoratus (Peters 1868), S. bruynisi de Beaufort 1912, and S. roxasi, originally described from the Philippines and Indonesia, were examined and re-described here, because relatively little information about their diagnostic characters was provided in the original descriptions. The three Japanese species were identified as S. ampluvinculus, S. marmoratus, and a new species. They were distinguished from each other and from their congeners by the banding pattern of the body, markings on the pectoral fins, pigment patterns on the ventral surface of the head and pelvic fin, body depth at the pelvic-fin origin, pre-anal length, and pectoral-fin ray counts. Although the new species had been regarded as S. roxasi in previous publications, we show that it is actually not S. roxasi and that it also differs from all other nominal species of Schismatogobius. This is described as a new species, S. ninja. Additionally, this is the first record of S. marmoratus from Japan.

A new species of the genus Stiphodon from Palawan, Philippines (Gobiidae: Sicydiinae)

Palawan is an island in the western Philippines, and the freshwater fish fauna of this island has received limited research attention. In the present study, a new goby species, Stiphodon palawanensis, is described on the basis of 57 specimens collected from freshwater streams on the island. This species can be distinguished from its congeners by having nine segmented rays in the second dorsal fin, 15 rays in the pectoral fin, a pointed first dorsal fin in males, premaxilla with 45-71 tricuspid teeth, the nape and posterior half of the occipital region covered by cycloid scales, 9-11 dusky transverse bars laterally on the trunk and tail, a line of black blotches (in male) or a black band (in female) on the distal part of the second dorsal fin, and the first dorsal and pectoral fins lacking distinctive markings. The new species has been found only on the Sulu Sea side of central Palawan. Three congeners, S. percnopterygionus, S. atropurpureus, and S. pulchellus have also been recorded from Palawan.