Studies were made on the distribution of phenoloxidase (PO) activity in the blood of kuruma prawn, Penaeus japonicus. PO activity was higher in the sonicated hemocytes than in the plasma. The optimum temperature for the PO activity was 40°C. EDTA lowered the relative activity of PO to 50%, and higher temperature than 60°C or HEPES of higher molarities than 0.5 M completely inhibited the PO activity. Phenylmethylsulfonyl fluoride (5 mM) or diethyldithiocarbamate (5 mM) markedly inhibited the PO activity, suggesting that the serine protease and copper enzyme are involved in the enzyme cascade of prophenoloxidase-activating system.
The present paper describes the detection of striped jack nervous necrosis virus (SJNNV), the causative agent of viral nervous necrosis, in eggs, larvae, and brood stocks of hatchery-reared and captured striped jack Pseudocaranx dentex by indirect ELISA. An appropriate condition for the ELISA was determined using purified SJNNV and the detection limit of virus antigens was approximately 5 ng/well. All samples of larvae supposed to be affected with the disease were proved positive for the presence of SJNNV antigens in this ELISA test. The viral antigens were also detected in some samples of fertilized eggs and ovaries of spawners but not in the testis or brain. Thus, it was indicated that spawners were an inoculum source of this viral disease in striped jack.
A caligid copepod was collected from the body surface of striped jack, Pseudocaranx dentex cultured in net cages in western Japan. It is identified as Caligus longipedis Bassett-Smith, 1898. Adults as well as all the developmental stages are described; morphologically they are divided into 2 nauplius, 1 copepodid, 4 chalimus, 1 preadult and 1 adult stages. Newly hatched nauplii moulted two times into copepodids in about 19 h at 22.5±2.0°C. Copepodids survived in sea water 7 days at most at 20°C. Chalimus larvae were found on the fins and body surface of fish. When free-swimming larvae were exposed to uninfected fish, they were transformed into adults on Day 10 (10 days after exposure to uninfected fish), and possessed egg sacs on Day 12 at 21.2±0.6°C. Nauplii were recovered from the rearing water on Day 13. It is thus estimated that the life cycle was completed in about 2 weeks.
Since 1986 mass mortalities attributable to erythrocytic inclusion body syndrome (EIBS) have occurred in juvenile coho salmon (Oncorhynchus kisutch) reared in freshwater in Japan during May to July every year. The manifest sign of the diseased fish was severe anemia. Fish affected with fungi and/or with damage in snout increased in number as mortality rose. Erythrocytic inclusion bodies contained enveloped viral particles 70-80 nm in diameter and similar in morphology to the EIBS virus were found in the erythrocytes of the diseased fish and the syndrome was induced by artificial infection with the blood homogenates from the diseased fish, and hence the disease was diagnosed as EIBS. Survivors of the disease were resistant to artificial infection with EIBS. This is a first report of the occurrence of a natural infection of EIBS in juvenile coho salmon in freshwater in Japan.
Acquired resistance to erythrocytic inclusion body syndrome (EIBS) was investigated in coho salmon (Oncorhynchus kisutch). Fish which were experimentally infected with EIBS and maintained at 15°C for 242 days were challenged by EIBS virus and kept at 8°C. The fish survived the challenge, though they showed a slight decrease in Ht values which recovered presently. This result indicates that acquired resistance to EISB continues at least as 242 days. Follow-up examination of coho salmon which survived EIBS in freshwater farm ponds revealed that they maintained acquired resistance after being transferred to marine farms.
Three morphologically distinct populations of hemocytes (hyaline, semigranular and granular cells) were isolated from the blood of the kuruma prawn, Penaeus japonicus, by Percoll continuous gradient centrifugation. All three types of hemocytes ingested glutaraldehydefixed sheep red blood cells (SRBCf), and the phagocytic activity of semigranular cells and granular cells was significantly higher than that of hyaline cells. Phagocytosis of SRBCf by the hemocytes was greatly enhanced by the opsonization of SRBCf with kuruma prawn serum (KPS), but this opsonic activity of KPS was inhibited by N-acetylglucosamine (GlcNAc). Lectin was eluted from KPS-opsonized SRBCf using 100 mM GlcNAc solution. The lectin which showed a strong opsonic activity had a molecular weight of 330 kDa and consisted of identical subunits of 33 kDa. The opsonic activity of the lectin was inhibited by GlcNAc, but not by heating (60°C, 15 min) nor by EDTA treatment. We therefore conclude that the opsonic activity of KPS on phagocytosis is dependent on the lectin in the serum.
A one-year field survey on the presence of Vibrio sp. PJ, the causative agent of vibriosis in kuruma prawn (Penaeus japonicus), was carried out in prawn farms in Hiroshima and Yamaguchi Prefectures by a conventional bacterial culture method. The result revealed that the pathogen has already been widely distributed in the prawn culture environment. The population of the pathogen increased both in prawns and in their environment with a rise in water temperature. Indirect fluorescent antibody technique (IFAT) was applied to smear specimens of the lymphoid organ of both experimentally and naturally infected kuruma prawns. This method was found effective as a rapid and reliable diagnostic method for the present disease, though the sensitivity was slightly lower than that of the culture method.
Several bacterial strains were isolated in France from diseased European eels (Anguilla anguilla) reared in freshwater. The resemblance of these isolates to the known eel pathogen Pseudomonas anguilliseptica led to the comparative study of two of them with the type strain NCIMB 1949T and with four reference strains from different geographical origins. Morphological, physiological and biochemical characteristics of the seven strains proved to be very similar. DNA base composition was in the same range (60 to 62 mol % G+C) for the four strains tested. Comparison of the DNA by the S1 nuclease DNA-DNA hybridization method showed that the seven strains formed a tight genomic species with DNA relatedness above 85 %. This is the first identification of this fish pathogen in France. As its pathogenicity for salmonids has been demonstrated in Finland, this bacterium may prove a potential hazard, not only for the small eel farming industry in France, but also for the trout and salmon farming which is of much greater economical significance in this country.