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This study was undertaken to clarify the downstream drifting of Macrobrachium larvae in the Shimanto River by 24-hour sampling. Stage I zoeae accounted for most larvae collected in fresh and brackish waters. M. formosense and M. japonicum dominated in brackish and fresh waters, respectively, while M. nipponense occurred only in brackish waters. The amount of yolk droplets of M. formosense and M. japonicum reduced over time in freshwater. However, no larvae that had completely used up their yolks were observed. Even though M. japonicum larvae drifted from farther upstream than those of M. formosense, they had a higher residual amount of yolk droplets. Therefore, long-distance and long-time drifting in M. japonicum may be enabled by delaying the absorption rate of droplets. [ABSTRACT FROM AUTHOR]

In early life history, the clupeoid fishes, Ilisha elongata (Pristigasteridae) and Sardinella zunasi (Clupeidae) have similar spawning seasons and nurseries from spring to summer in the Ariake Sound, Shimabara Bay, Japan. Surveys conducted using larva nets and a beam trawl in July showed that the horizontal egg and larva distributions of I. elongata and S. zunasi both overlapped considerably in the inner estuaries; however, I. elongata settled in the estuaries while S. zunasi retained a pelagic distribution. A comparison of the vertical distributions of the two species in the estuary showed that I. elongata larvae were dispersed from the surface to near-bottom layers during the flood tide, and moved downwards to avoid being swept out of the estuary after the high tide, while S. zunasi larvae remained spread throughout the water column in all tidal phases. The findings suggest the existence of niche segregation during the pelagic larval period in the two species. Thus, by examining differences in larval mouth sizes, which are much larger in I. elongata than in S. zunasi, it appears that prey preference varies between the two species, prey specialization occurs, and there is no niche competition between the two species. [ABSTRACT FROM AUTHOR]

The ontogeny of Ilisha elongata was reviewed, and their early distribution was examined because information on the early life history of this species is limited. Revision in ontogeny revealed several unique characteristics to this species, such as two chorions in the egg and a more anterior pelvic bud (fin) position. These characteristics contrast strikingly with the clupeid fishes, suggesting that this species belongs to the Pristigasteridae and not to the Clupeidae. Data from ichthyoplankton collected in March, May, July and November suggest that I. elongata spawned just off river mouths in summer and attained peak spawning in June. The larvae with elliptical eyes migrated inside the rivers, where the waters were more turbid. Thus, the spawning and nursery grounds of I. elongata almost entirely overlapped with those of the clupeid Sardinella zunasi both temporally and spatially, which may result in larval competition between the two species. [ABSTRACT FROM AUTHOR]

The vertical distribution of eggs and larvae of Maurolicus japonicus were described based on discrete depth oblique tows of a larva net seasonally collected during both day- and nighttimes at a 130 m-depth station near the continental shelf of Tosa Bay. The abundance and diel differences in the vertical distribution of eggs and larvae in relation to physical properties of the water column were also examined. Both eggs and larvae occurred only in spring and neither occurred in other seasons. In spring, water temperature, salinity and specific gravity were less stratified in the water column with a modest upwelling to ca. 100 m-depth, around which the seasonal temperature hardly changed. Unlike the Japan Sea, with a year-round reproduction of M. japonicus, the limited occurrence of eggs and larvae in Tosa Bay was likely related to upwelling in April. Eggs were twice as abundant at night- than daytime, suggesting that this species spawns at night. Most of the eggs were in A and B-stages and aggregated at 30-70 m depth during both the day and night. Larvae that were mainly in preflexion without yolk and flexion stages, were found in the 110-70 m and 130-90 m depth layers during day- and nighttimes, respectively. Earlier larval stages were dispersed abundantly from 130-m to the surface during daytime, with little correspondence to light attenuation or chlorophyll-a concentrations. Compared to the Japan Sea, Tosa Bay yielded various mesopelagic fish species that inhabit and breed in the mesopelagic zone, so that the reproductive niche would be temporally and spatially limited for M. japonicus. [ABSTRACT FROM AUTHOR]

A total of 40 robust tonguefish (Cynoglossus robustus) larvae [2.1-10.2 mm body length (BL)] collected from Osaka Bay, eastern Seto Inland Sea were investigated. Those larvae that were smaller than 4 mm BL possessed a single filament-like elongate fin ray emitting from the most anterior dorsal fin. In larvae of between 4 and 5 mm BL we subsequently observed a second short fin ray, next to the first one. At the preflexion stage, 6.5-7 mm BL, the longer of the elongated fin rays extended to about 60% of BL and the shorter one extended to approximately 30-40% of the length of the longer one. These specimens did not develop transverse bands of melanophores laterally on their tails. These characteristics are the same as those presented in hatchery-reared larvae of the same tonguefish. Osaka Bay is also home to larvae from C. interruptus and C. joyneri, both with double elongated dorsal fin rays. These larvae can be easily distinguished from larval C. robustus by counting the myomeres, dorsal and anal fin rays, and by observing the pigmentation pattern on the tail. [ABSTRACT FROM AUTHOR]