A new ophichthid eel, Muraenichthys borealis, is described on the basis of ten specimens from the coast of Aomori Prefecture, the northernmost district of Honshu, Japan, This species is most closely related to M. gymnotus in morphometric characters and vertebral counts, but clearly differs from it in having a prominent median toothed groove on the ventral side of the snout and biserial prevomerine teeth.

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Laemonema yuvto sp.nov. is described from a single specimen 191mm SL from the Sala y Gomez Ridge. Although this species is similar to L. robustum and L. filodorsale in most proportions of head and body, it differs from both in having shorter second ray in first dorsal fin and more rays in second dorsal and anal fins. It also differs from L. robustum in maxillary not reaching the vertical from posterior margin of orbit and shorter pelvic fin, and from L. filodorsale in longer pelvics, fewer oblique rows of scales above lateral line and the absence of enlarged teeth in both jaws.

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Claspers of four species of freshwater stingrays, which belong to the genera Dasyatis (Dasyatidae), Paratrygon and Potamotrygon (Potamotrygonidae), are examined to reveal differences in the clasper structure among these genera. The relationships of freshwater stingrays are discussed based on our examination of the clasper structures as well as that reported in recent literature for two other genera of freshwater stingrays, Himantura (Dasyatidae) and Plesiotrygon (Potamotrygonidae).

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The larval development of Tribolodon hakonensis is described, and its sequence is characterized by six intervals of morphological, functional and behavioral development. The larval development of this species is a roughly double-folded process consisting of feeding and swimming functions, developments of which begin independently. A comparison with other related species of different reproductive and larval life styles reveals that the development of only one function, such as feeding-related development, may be shifted in adapting and regulating their sequence of intervals to the natural environments. Then the path through the development, i.e. the sequence of intervals, can vary according to different reproductive and larval life styles. For example, Abramis, a phyto-lithophils open substratum spawner, and Carassius, a phytophils open substratum spawner, develop feeding-related functions, absorb yolk and start to feed before notochord flexion. In the case of an ostracophils brood hider, Rhodeus reserves rich yolk and does not feed until it metamorphoses to a juvenile, although it develops feeding-related characters just after notochord flexion as in the case of T. hakonensis. On the other hand, T. hakonensis is a lithophils open substratum spawner and the larval adaptation of this species is characterized by its rich supply of yolk persisting beyond the start of notochord flexion. It starts to feed after notochord flexion with a short mixed endo-and exogeneous feeding period. This is probably closely related not only to the reproductive style but also to the scarcity of food for the larvae of this species.

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Embryonic, larval and juvenile development of the atherinid fish, Atherion elymus, was described on the basis of a series of laboratory-reared specimens. The eggs were almost spherical in shape, measuring 0.90-1.05 mm in diameter, with numerous chorionic filaments. Hatching occurred between 13 and 17 days after spawning at water temperatures of 20.5-21.4°C. Newly hatched larvae measured 3.95 4.70mm NL and had 4+37 myomeres. Flexion of the notochord started at 7.0-7.5mm NL. Aggregate numbers of all fin rays were completed at 10.7-11.5 mm SL, when the larvae reached the juvenile stage. Squamation was almost completed at 18.5-20mm SL. The larvae of this species can be distinguished from those of Hypoatherina tsurugae and H. bleekeri by having a few melanophores just before the tip of the notochord both dorsally and ventrally, and having punctate melanophores on the lateral median.

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Reproduction of Centropyge ferrugatus was observed in the aquarium. Reproduction between the same parent fish was observed on at least 16 occasions during the period from April 26 to May 16, 1987. The fertilized eggs were spherical, pelagic and measured 0.67-0.70mm in diameter. Hatching took place from 16 hours 10 minutes after fertilization at 25.0-26.0°C. Newly hatched larvae, measuring 1.28-1.30mm in total length, had a large ellipsoid yolk sac whose front tip clearly protruded beyond the snout of the larva. The larvae were maintained for five days after hatching and about ten of them reached the post-larval stage, measuring 2.43-2.50mm in total length. Larval characteristics are reviewed and a brief comparison is made with other studies of angelfish.

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Genetic variations in Nibea mitsukurii, N. albiflora and Pennahia argentata from different localities were assayed electrophoretically. The genetic variability in N. mitsukurii was relatively high. According to the chi-square values for heterogeneity between two localities and genetic distance (D) values, N. albiflora from the Ariake Sea and the Inland Sea or the East China Sea (D=0.0092 in average), and N. misukurii, from Tosa Bay vs. Atsumi Bay (D=0.0067) were considered to be independent subpopulations. The D value in N. albiflora from the Inland Sea vs. the East China Sea was quite small (D=0.0010). In P. argentata populations, the D values were also small. Further, the relationship between genetic and geographic distances observed in the three species were discussed. P. argentata showed a positive relationship between these two factors as compared to N. mitsukurii or N. albiflora. It seemed that the lower level of genetic divergence might be due to the frequent gene flow within the large-scale and wide distributional range of the population.

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The distribution and ultrastructure of mitochondria-rich cells in the inner ears of goldfish (Carassius auratus) and tilapia (Oreochromis niloticus) were examined by light and transmission electron microscopes. The mitochondria-rich cells were found in patches in the ampullae of three semicircular canals, sinus superior, utriculus and sacculus in both species. The cells were also found in the transverse canal in goldfish and the lagena in tilapia. They were absent in the goldfish lagena. The cells were characterized by a large number of mitochondria and an associated network of the smooth endoplasmic reticulum. Fenestrated capillaries were distributed in the connective tissue beneath the patches of the mitochondria-rich cells. The distribution and fine structure of these cells suggested their involvement in the ionic control of endolymph.

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A definite rhythm was observed in the bimodal oxygen uptake of the air-breathing siluroid fish, Clarias batrachus. The total oxygen uptake was at its peak (222.3±20.25 mlO₂·kg^-1·h^-1) during dawn (04-06h), whereas the minimum oxygen uptake (63.68±5.14mlO₂·kg^-1·h^-1) was recorded in the midday hours (12-14h). It seems that the rhythmic fluctuations in the metabolism of C. batrachus are related to the diurnal fluctuations of dissolved oxygen and free carbon dioxide in the swamps where this fish normally inhabits.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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