The growth, survival and maturation of induced triploids were compared with diploid control for 31 months after hatching in hirame Paralichthys olivaceus.
The growth of triploids was lower in the early stage after the hatching than diploids, but there are no differences in other stages. The survival rate of triploids was conspicuously lower in two stages, namely the early stage after hatching and the stage startingto feed the frozen fish. No retarding period of the growth was observed even in the spawning season in diploids which grew continuously as same as triploids. The gonadosomatis index of females continued to increase throughout the experimental term in both diploids and triploids, but increasing rate of triploid females was extremely low. Theprogress of gonadosomatic index of male was almost same as diploids. It was concluded that triploids were completely sterile in both sexes from the histological and the scanning electron microscopical observation and the mating test.

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Morphological development of the oriental goby, Acanthogobius flavimanus reared from eggs to juveniles in the laboratory at Sagami Bay, Japan is described. During mid February ovarian maturation is successfully induced by injection of the LH-releasing hormone of Gonadotropin. The dose of the hormone was 5IU/g body weight and was injected 4 times at an interval of one day for ovulation at water temperature of 12 to15°C. Artificial fertilization was accomplished on the first of March, 1985. The numberof ripe eggs removed artificially was about 25, 000. The eggs immediately after insemination are spherical in shape, measuring 0.99-1.10 mm in diameter. They have a bundle ofadhesive filaments at their basal end and a cluster of small oil globules. The egg membrane elongates to form a perivitelline space when the inflation ceases about 30 minutes after insemination. The eggs alter ellipsoid shape and measure about 3.93 mm on the long axis. Hatching began about 18 days after insemination at water temperature of 15.0-15.4°C. Soon before hatching, embryos fold down the tail at the basal end region of eggshell. The newly hatched larvae are 4.13-4.86 mm in total length (TL), with 31 (13+18) myomeres. The larvae usually lay on their body on the bottom of the aquarium. Many melanophores and guanophores are distributed on eye cups, gas bladder, intestine and in the caudal region. Complex of pigments form a band in the caudal region, but the band is never connected with the pigments on intestine. This character is not shared with larvae of A. hasta and A. lactipes. Seven days after hatching the yolk was completely absorbed and the larvae attained a total length of 5.73-6.10 mm.The larvae swim actively in the aquarium and start to practice feeding on the rotifer. Twenty days after hatching, the larvae averaged 9.01 mm in TL and the caudal notochord flex at 45°. Rudimental second dorsal, anal, caudal and ventral fins are also formed. The larvae attained 11.00-15.00 mm in TL, thirty five after hatching, are found to transit the bottom-life and first dorsal and ventral fins are completely formed. During the late postlarval stage, the fish is nervously to develop the free neuromast on the skin surface. The larvae reached the juvenile stage at 45-50 days after hatching and attained 13.85-24.90 mm in TL. At this period all scales appeared on the body. A clear black spot on the first dorsal fin is characteristic at the immature stage of the fish. The larvae and juveniles were reared by feeding them with the rotifers, Artemia nauplii, krill meat and lugworm meat for one year. The growth of larvae and juveniles in 1985 is expressed by the following equations.
Y₁=4.697×1.034^x (0≤X≤45)
Y₂=0.716X-14.123 (46≤X≤170)
Y₃=160.18lnX-715.90 (171≤X≤330)
where Y is the total length (mm) and X is number of days after hatching. The fish grew to 189.55-232.70 mm in TL and became mature in one year. Most of the individuals attained gonadal maturation and died after spawning.

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Nitrogen in the feed ingested by fish is balanced quantitatively by growth in body nitrogen, excreted nitrogen and nitrogen in egested faeces. Judging from growth efficiency of fish, a large proportion of the ingested nitrogen is removed to the rearing water in various forms of nitrogen as metabolic waste and egested faeces. It may be considered, therefore, that abundant nitrogen as food has a harmful influence upon the aquatic environment in the rearing tank.
This paper describes the nitrogen flow in the tank from the viewpoint of the nitrogen budget. Every item in the budget was estimated independently and measured as directly as possible.
The nitrogen load as feed into the tank is 0.282 g-N/l during 44 days of the rearing period. This nitrogen load converts to 0.123 g-N/l or 43.6% of DON, 0.028 g-N/l or 9.9% of PON, 0.027 g-N/l or 9.6% of DIN, 0.097 g-N/l or 34.4% of growth and 0.007 g-N/l or 2.5% of other. Total organic nitrogen concentration (DON+PON) increases at the rate of about 50% of the nitrogen load.

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In autumn 1987, a mortality of freshwater-reared coho salmon (Oncorhynchus kisutch; 6 months old and about 100 g body weight) had occured at Touhoku district in Japan. The water temperatures of culture ponds were 9-15°C and about 12°C at the peak of mortality. Oral administration of oxytetracycline resulted in a failure, so that the mortality reached 5.6% for three months. The moribund fishes showed external signs or internal signs such as eroded fins and white spot lesions in the liver. Characteristic histopathological changes, multiple foci of severe necrosis, were observed in liver sections.
In the bacteriological approaches on seven fishes, Flexibacter columnaris infection and Renibacterium salmoninarum infection were observed on all fishes and on one fish, respectively.
On the other hand, we succeeded in isolating viral agent from the diseased fishes using RTG-2 at 15°C. RTG-2 infected with the virus showed cytopathic effect characterized by syncytia without inclusion bodies. The maximum titer of the cell culture was approximately 10⁶ TCID₅₀/ml. The virus was acid, heat and ether labile. Replication of the virus was inhibited by IUdR. Hexagonal nucleocapsids, observed in nuclei and cytoplasm, measured of 85-95 nm in diameter and enveloped virions on cell surface about 160 nm. These features indicated that the virus was herpesvirus. The virus was neutralized by rabbit anti-OMV (Oncorhynchus Masou Virus) serum, but not by anti-Herpesvirus salmonis serum.
The pathogenicity and oncogenicity of the virus were not examined, however, this is the first report of herpesvirus isolation from a natural epizootic of coho salmon.Further biochemical and serological examinations are needed to clarify the relationships between the virus and other salmonid herpesvirus, so we provisionally called the virus herpesvirus strain OK of coho salmon.
These results suggested that the mortality of this case was caused by herpesvirus disease, columnaris disease and bacterial kidney disease.

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