In aquaculture, vaccination is one of the approaches for disease prevention and control. The aim of the present study was to determine the efficacy of a VP28 double stranded RNA (VP28 dsRNA) and recombinant VP28 protein (rVP28) administered together as an antiviral treatment against WSSV. Double-stranded RNA was produced in RNAsedeficient Escherichia coli HT115 following published methods. To determine the appropriate dose, different concentrations of dsRNA ranging between 0.2 μg and 20 μg, were either injected intramuscularly or delivered orally to the shrimp via the feed ration. Thereafter, the shrimp were challenged with WSSV either by injection (LD₅₀=10^-7 dilution of the gill tissue filtrate) or bath immersion (LD₅₀=10^-4 dilution of the filtrate) in glass aquaria and transferred to fiberglass tanks for daily monitoring and recording of mortalities. Results showed significant differences in survival between PBS and the 0.2, 10, and 20 μg dsRNA/shrimp doses. Time to 100 % mortality significantly differed among the treatments with the control reaching mortality earlier (day 4) while shrimp injected with 0.2 and 10 μg dsRNA succumbed to WSSV much later on days 9–12. Different frequencies of dsRNA administration were also tested. The best result obtained was a dose of 20 μg/shrimp administered 4 times over 28 days (2 times before and 2 times during challenge for a total 80 μg/shrimp). Finally, VP28 dsRNA was combined with rVP28 at ratios of 1:1, 1:2, 1:3, 3:1, and 2:1, entrapped in chitosan microparticles and delivered per os via the feed according to the dose and frequency as previously determined. Following bath exposure challenge with WSSV, the best survival obtained in trials 1 and 2 was 40 % and 43 % at 1:3 VP28 dsRNA to rVP28 ratio.

The growth efficiency, productivity and economic viability of Indian white shrimp (Penaeus indicus) fed with diet containing 40% (CP_high) and 34% (CP_low) crude protein (CP) levels were determined in a 90-day grow-out culture trial. Growth parameters including average body weight (ABW), specific growth rate (SGR), survival and feed conversion ratio (FCR) were not statistically different. CP_low had lower overall shrimp production (797.53 kg/ha, DOC 90), but was not significantly different from CP_high (843.78 kg/ha, DOC 90). The mean values for the water parameters of both treatments, such as DO, pH, salinity, temperature, TAN, NO₂-N, NO₃-N and PO₄-P, also showed no significant differences. However, the TAN values of CP_high were consistently higher from day of culture (DOC) 63 and increased significantly (p = .048) at DOC 90. Furthermore, the total bacterial and Vibrio counts in both treatments were not significant throughout the culture period. The economic analysis revealed that CP_low obtained higher net profits (6093 USD/ha/year), return on investment (72%) and discounted benefit–cost ratio (1.73). The current study found that feeding a low protein diet to P. indicus is economically viable and profitable and results in improved growth efficiency and productivity while also improving water quality and lowering nitrogen discharge.

We developed a triply nested, high-resolution (1/50°) ocean model to reproduce tides and tidal currents under realistic oceanographic conditions, mainly on the Pacific shelf around Hokkaido, Japan. The model reproduced observed properties of tides and tidal currents reasonably well. Dominant diurnal tidal currents were simulated and accounted for mainly by propagation of coastal-trapped waves (CTWs) of the first mode. The first-mode CTWs were generated mainly around the Four Islands, which are located to the east of Hokkaido, where the massive energy of gravity waves was scattered to CTWs. After leaving the forcing area around the islands, diurnal CTWs propagated along the Hokkaido coast to Cape Erimo. Around the cape, CTWs were also excited via scattering of gravity waves and superposed with first-mode CTWs propagating from the Four Islands. The K₁ (O₁) currents associated with the CTWs weakened (strengthened) around and west of the cape because of out-of-phase (in-phase) superposition. The K₁ currents therefore ended up being smaller than the O₁ currents by one order of magnitude. Moreover, the first-mode CTWs generated around the Four Islands were attenuated along the propagation route through complicated processes. The unsteadiness of the K₁ and O₁ currents related to their 13.67-day beats therefore increased gradually along the propagation route. The unsteadiness on the shelf west of the cape was further enhanced by superposition with CTWs forced around the cape, which were occasionally unstable.

Philippine fishery statistics classified fish production into 3 major production sources: commercial, municipal and aquaculture. Of these, only commercial fisheries and aquaculture have shown positive growth; municipal fisheries has been declining since 1992, with the inland sector being the most affected. Alternative ways to lighten the current fish supply crises are considered. It is believed that a sustainable option is to raise more fish, rather than merely hunt for them. An examination is made of available resources, including physical, technical and financial, which would enable increased production. Particular reference is made to increased tilapia production, but milkfish, carps, groupers and seabass are also considered.

In September 1996, a disease outbreak was reported in one turtle farm in the New Territories, Hong Kong. Soft-shelled turtle (Trionyx sinensis) cultured in tanks showed white spots on their body surface and carapace resulting in gradual, but high levels of mortalities. Microscopic examination of the affected tissues revealed the involvement of thick, non-septate fungal mycelia. A fastgrowing straminipilous oomycete was isolated from the infected animals and identified as Achlya sp. Physiological studies on vegetative growth and sporulation were undertaken and results showed that the isolate could grow from pH 4 to 10 with maximum growth at pH 5 to 9. Growth was also observed at 0-20 salinities, at temperatures of 10-35°C, with an optimum at 0 salinity (distilled water) at 30-35°C. Abundant zoosporangia were produced and primary zoospores released at 0-5 , but secondary zoospores were only released in freshwater (0 ). A wide temperature range was observed for sporulation (10-40°C) with optimum at 15-35°C. This is the first report of a fungal infection in tank-cultured soft-shelled turtle in Hong Kong.

We tracked the spawning habitat use of two native stream gobies (Rhinogobius fluviatilis and Rhinogobius nagoyae) before and during the invasion of a non-native goby (Rhinogobius sp. OR) and after its disappearance in the Tani River, Japan. Throughout the three phases, the majority of the two native gobies showed high preference and use for the habitat with medium-fast current velocity and coarse substrates as spawning sites. When the non-native Rhinogobius sp. OR invaded, the majority of them also preferred and used the same habitat as spawning sites, and the spawning habitat use of the three Rhinogobius species substantially overlapped. These results suggest that the invasion by the non-native goby did not significantly change the spawning habitat use of the two native gobies. However, the similar habitat requirement among the three Rhinogobius species may cause competition for the spawning habitat when the availability of their favorite habitat is greatly restricted. The non-native Rhinogobius sp. OR could utilize the spawning space on the undersurface of nest stones more efficiently than the two native gobies. Therefore, in the non-native Rhinogobius sp. OR, the size of nest stones is unlikely to be a limiting factor for reproductive success. Such ecological characteristics on nest stone use may enable Rhinogobius sp. OR to easily acquire nest stones with less competition in the spawning habitat where they coexist, which have also helped Rhinogobius sp. OR to extend its distribution area.

A new frog disease occurred in frog culture farms located in Central Thailand since early 1998. The disease affects 20-100% of the frog population in affected farms. Diseased adult frogs usually exhibit ulcerative lesions on the dorsal part of the body and legs with moderate mortality (20-50%). Some frogs had red lips, ulcerated mouths and rostrums. Diseased tadpoles and small frogs appeared weak with systemic inflammation. Mortality ranged from 50-100%. Histopathological changes observed include cutaneous ulceration and systemic inflammation with exuberant hematopoiesis. No bacteria could be isolated from the kidney, spleen and liver of frogs at the early stage of the disease. Viral investigation was, therefore, conducted. Seventy virus isolates were obtained from 107 diseased frogs collected from 8 provinces using the Epithelioma papulosum cyprini (EPC) cell line at 25°C. One virus isolate (AV9803) was partially characterized. The virions were enveloped, possessed genomic DNA and hexagonal nucleocapsid morphology, and were ~128 nm in diameter. The virus completely lost infectivity when incubated at 56°C for 30 min, in organic solvent or buffer pH 3. These findings indicate that this frog virus belongs to the family Iridoviridae. DNAs of 8 virus isolates from different provinces were extracted and compared using polymerase chain reaction or PCR. Similar sized PCR products were obtained using primers that were specific to different parts of a major capsid protein gene of Ranavirus type genus FV3. Over 99% nucleotide homology was observed between one sequenced PCR product of AV9803 and the sequence of FV3. These findings suggest that a single virus species was isolated which is most likely a strain of Ranavirus. This virus strain is temporally designated as Rana tigrina ranavirus (RTRV) . The RTRV seems to be associated with cutaneous ulceration. Further infection experiments and electron micrograph examinations in the diseased frog need to be done to confirm the causative agent.

An interview-based questionnaire survey of one fish farmer and one fisherman randomly selected in each of the 64 districts of Bangladesh was carried out to study prevalence of EUS, and risk factors associated with EUS outbreaks. The survey was carried out during the EUS season, November 1998 to March 1999. At each site, 100 fish were examined for lesions, and one fish of each species with lesions was sampled for histological diagnosis. A fish farm or wild fishery was classified as affected with EUS if one or more fish of any species had a positive diagnosis based on the presence of characteristic mycotic granulomas in histological sections. Univariate analyses were used to examine the association between EUS occurrence and putative risk factors using crude relative risk (RR) as the measure. Out of 64 districts, fish with lesions were recorded from fish farms in 32 districts and 30 were confirmed EUS positive, and from wild fisheries 52 districts demonstrated lesions and 49 were confirmed as EUS-positive. In total, 6434 wild fish and 6401-farmed fish were examined, and average prevalence of lesions was calculated as 16.0% and 15.5% respectively. Although disease was more widespread in the wild fisheries, the percentage fish with lesions was generally higher at farm sites (8-45%) than wild fisheries (3-32%). A total of 471 fish with lesions was sampled for histology from the 84 affected sites and 80% of these were diagnosed as EUS-positive. Thirty-one species of fish were confirmed as being EUS-positive out of 47 recorded with lesions. Combining data on affected species from both farmed and wild fisheries sites, the highest prevalences of EUS were recorded in Channa marulius (30%); Glossogobius sp. (25%); Cirrhinus mrigala (24%); Channa striata (22%); Channa punctata (21%); and Anabas testudineus (20%); and the lowest prevalence was in Lepidocephalus guntea (3%). Data showed that there is a significantly higher relative risk of EUS occurring in farmed fish when wild fish are present in the pond; pond embankments are not high enough to prevent in-coming flood water; ponds are connected to natural waters; ponds are not dried or limed prior to stocking; ponds are not limed post-stocking; and pond water colour is black or clear (as opposed to red or green). Of the wild-caught fish, those sampled from haors had a significantly higher relative risk of getting EUS. Fish from rivers and flood plains were at a lower risk of EUS infection.

A new aquabirnavirus (BSNV, blotched snakehead virus) was isolated from a persistently infected warmwater fish cell line (BSN) developed from blotched snakehead (Channa lucius). Four polypeptides of molecular mass 112 (polyprotein, PP), 91 (VP1), 44 (VP2) and 37 (VP3) kDa have been identified in BSNV. The reciprocal cross-neutralisation studies involving BSNV and four classical strains of infectious pancreatic necrosis virus (IPNV), strains WB, Sp, Ab and TV-1, revealed that BSNV antiserum was capable of neutralising only homologous virus while no cross reaction was evident against the other viruses. In order to further study and compare the antigenic properties of the virion structural proteins of BSNV and IPNV strain Sp, Western blot analysis of separated viral proteins was conducted using antisera against BSNV and IPNV Sp. The analysis indicated that VP2 protein (44 kDa) of BSNV alone was recognised by homologous antiserum while antiserum against IPNV Sp did not recognise any BSNV polypeptides. This, combined with weak recognition of the structural protein VP2 of IPNV Sp and SGV using BSNV antiserum showed that VP2 is probably the only protein expressed on the virion surface and this protein carries neutralisation epitopes in BSNV.

A Japanese flounder Paralichthys olivaceus cDNA library was constructed from leukocytes that had been previously infected with hirame rhabdovirus (HRV). Eight hundred ninety six independent clones were isolated from which 1,237 sequence reads were obtained. These sequences consist of a total of 925,169 base pairs with an average sequence length of 758 base pairs. Six hundred three (67.3%) of the clones showed significant similarity to previously reported genes. These identified clones were derived from 350 distinct genes, in which 52 clones were considered as putative biodefense and immune-related genes. Forty-one of 52 putative biodefense and immune-related genes, including several clusters of differentiation (CDs), interleukin receptor, TNF receptor, and transcription factors, have not been previously reported in cDNA copies of fish genes.