There have been relatively few studies on the diseases of molluscs in the Asian region, and those that have been carried out are often difficult to access. Therefore, our current knowledge of mollusc diseases in Asia is, at best, fragmentary. Despite this, serious viral diseases have been reported from hard clams (Meretrix lusoria) in Taiwan, flat oysters (Ostrea angasi, Tiostrea chilensis) and rock oysters (Saccostrea glomerata) in Australia and New Zealand, pearl oysters (Pinctada fucata martensii) in Japan, abalone (Nordotis discus discus) in Japan, pearl mussels (Hyriopsis cumingi) in China, and mussels (Perna canaliculus) and scallops (Pecten novaezelandiae) in New Zealand. Prokaryote infections (Rickettsiales-like organisms, Vibrio spp., Nocardia crassostreae), and fungal infections (Steinhausia mytilovum) have also been reported. Several serious and potentially serious protist infections (Haplosporidium spp., Bonamia sp., Mikrocytos roughleyi, an unidentified haplosporidian, Marteilia spp., Marteilioides spp., Perkinsus olseni) also occur in the region. It is concluded that as more research is carried out on the parasites and diseases of Asian molluscs, other undescribed serious pathogens will be encountered.

In Thailand, farming the giant freshwater prawn, Macrobrachium rosenbergii, is a viable aquaculture industry. In 1995-96, giant freshwater prawns collected from grow out ponds located in Supanburi Province, Thailand showed severe branchiostegite melanization associated with poor growth and high cumulative mortality in affected ponds. The objective this study was to report the histopathological features of branchiostegite melanization and associated lesions in affected giant freshwater prawns. The gross lesions displayed by the collected prawns were bilateral branchiostegite melanization in the medial surfaces with normal underlying gill lamellae. Histopathological examination revealed a massive number of sporonts in the gill tissue causing a hyperinfection. Enlargement of the sporonts occurred in the gills. High magnification using a light microscope revealed massive round microsporidia-like spores in the sporonts measuring 1-2 m in diameter. The muscles of collected prawns were normal showing no signs of opaque cottony or milky white coloration. The hepatopancreas, however, were yellow in color. Positive Giemsa and PAS stained spores were found in hemocytes and cytoplasm of hepatopancreas cells. Because these results do not include electron-micrographic data, more observation is needed before the spores can be identified as microsporidia.

The number of diseases affecting cultivated penaeid shrimp has increased steadily with expansion and intensification of large-scale commercial cultivation. In the 1990s the most serious losses have occurred from the emergence of new viral pathogens, like white spot virus (WSV) in Asia and Taura syndrome virus (TSV) in the Americas. These initially endemic diseases have quickly become global, probably via infected carriers, including aquaculture stocks. The most alarming of the newly emerging viruses are those like spawner mortality virus (SMV) that produce no pathognomonic lesions and require sophisticated molecular diagnostic techniques for detection. This requirement severely limits the prospects for successful control and it provides a high incentive for the development of more field friendly detection methods. In the coming years, more viral pathogens will undoubtedly be found, especially as cultivation expands geographically and non-native species are used for rearing. To lower risks of disastrous viral epizootics, we should be more cautious with the international movement of living shrimp for aquaculture. We should also lower risks by realistically assessing and limiting other possible modes of pathogen transfer, without unreasonably interfering with international trade. In comparison to viruses, bacteria constitute a much less serious threat to shrimp farmers because most can be controlled by appropriate pond management techniques and because proper chemotherapy is possible in the event of management failure. In spite of this, new pathogens are still being described and too little is known about them. Particularly threatening are new intracellular forms (e.g., molecutes) that may often be overlooked because they cannot be detected in the absence of sophisticated molecular techniques. Even for more traditional pathogens like Vibrio species, we still do not understand why some strains are lethal and others are not. However, some progress is beginning to be made regarding the toxins from Vibrio harveyi and V. penaeicida, the genes controlling toxin production and the possible transfer of these genes amongst strains by bacteriophages. Much remains to be done. To date, fungi and parasites come far behind the viruses and bacteria in the ranking of pathogens that threaten farmed shrimp. However, the example of crayfish plague suggests that this may not always be the case. Control of all these diseases requires a level of understanding that we still lack, not only for the pathogens, but also for the shrimp host. Admirable progress is being made with respect to crayfish cellular defence mechanisms based on pattern recognition proteins targeted against bacterial and fungal cell wall components. Cultivated shrimp species seem to have similar defence systems, but work on them is uneven and much still remains to be confirmed or characterised. In contrast to bacteria, our knowledge of the shrimp response to viral pathogens is almost totally lacking and this is a serious shortcoming given the staggering losses the viruses have caused. We must accelerate investigations at the molecular level for both the host shrimp and its pathogens in order to rationally assess and improve the benefits of proposed therapies and preventative measures for disease. This work must go hand in hand with a concerted effort to develop certified domesticated shrimp stocks and secure, but affordable, cultivation systems.

Penaeus monodon postlarvae (stage 10) were reared with Artemia nauplii enriched with 50,100 and 150 mg/l (ppm) of L-ascorbyl-dipotassium-2- sulfate dihydrate for 5 days. Postlarvae in the control group were given non-enriched Artemia nauplii. Responses of postlarvae to toxic (ammonia and methyl parathion exposure) and stressful (salinity and dissolved oxygen stress) conditions, as well as their resistance to challenge with Vibrio harveyi, were compared. Acute toxicity tests using ammonia and methyl parathion revealed better tolerance of postlarvae given enriched Artemia at 100 and 150 ppm L-ascorbyl-dipotassium-2- sulfate dihydrate for 5 days. Transfer of postlarvae from 30 to 0 ppt water caused 100% mortality in all groups after 2 hr of transfer, but postlarvae that were transferred from 30 to 5 ppt showed significantly different mortality rates after 48 hr. Postlarvae that were given enriched Artemia had lower mortality compared with the control. In the oxygen depletion experiment, mortality rates were significantly different between enriched and non-enriched postlarvae. However, on the fourth day, all enriched and control shrimp died. Challenge with pathogenic Vibrio harveyi by bath challenge for 7 days showed significantly different mortality rates among postlarval groups. Postlarvae given 100 and 150 ppm L-ascorbyl-dipotassium-2- sulfate dihydrate for 5 days had lower mortality. Results from this study indicate the benefits of L-ascorbyl-dipotassium-2-sulfate dihydrate enrichment through Artemia in improving the survival of P. monodon postlarvae against some stressful conditions and bacterial challenge.

Vibriosis is one of the most serious problems in the shrimp culture industry worldwide. Antibiotic treatment is becoming less and less effective, as new strains of pathogens evolve, which are resistant to commonly used antibiotics. Use of probiotics is an alternative method for controlling bacteria in shrimp culture. In this experiment, lactic acid bacteria (Peddiococcus sp, Lactobacillus sp, and L. acidophilus) and marine bacteria (Alteromonas sp. and Vibrio alginolyticus) were mixed with pellet feed and used to feed juvenile shrimp. The growth and survival rate of the shrimp were monitored during the experiment. After feeding the shrimp for 60 days, all the surviving shrimp were bath-challenged with Vibrio harveyi (10⁵-10⁶ CFU/ml) for 7 days. Mortality of the shrimp was recorded. The result shows that the total biomass and survival rate of the shrimp fed with probiotics were significantly higher than the control group (p<0.05). However, there were no significant differences in the mean growth rate of shrimp between treatments. The results of the challenge test shows that the groups fed with lactic acid bacteria had the highest survival rates (Peddiococcus sp., 86.4%; Lactobacillus sp., 90.5% and L. acidophilus, 93.8%), followed by the treatments fed with marine bacteria (Alteromonas sp, 74.6% and Vibrio alginolyticus, 61.8%) and the control treatment had the lowest survival rate (59%).

A taxonomic relationship of thirty one Vietnamese bacterial isolates from different fish and shellfish together with twenty two reference strains was investigated by Euclidean distance with unweighted average linkage clustering. Comparison based on fourty seven phenotypic characters showed that these isolates mainly clustered in six groups of which four were equated with the well known Vibrio species, V. alginolyticus, V. harveyi, V. cholerae and V. mimicus. For the remaining two groups comprising twelve isolates, it was more difficult to establish any relationship with known species when compared with reference strains. Strains were also subjected to rRNA gene restriction pattern analysis (ribotyping), using Mlu I as restriction enzyme. Eleven ribotypes were detected among the Vietnamese isolates. Similarity of ribotyping patterns between strains supported the phenotypic identification. Twenty-eight strains were found to carry at least one plasmid and 12 different sized plasmids were detected ranging from less than 2 to 140 kb. The two Vibrio spp. groups performed high phenotypic and genotypic similarity within each group but were only remotely related with the reference strains. The evidence suggest that these strains may represent new Vibrio species.

The prevalence and geographic distribution of Yellow head virus (YHV) in cultured Penaeus monodon in the Philippines was documented by Western blot assay. Fifty-three out of 219 samples (24.2%) were found to be positive for YHV infection. Among the ten provincial sampling sites, selected shrimp farms from Misamis Occidental had the highest prevalence of infection with 66.7% followed by South Cotabato, Negros Occidental and Capiz with 43.7%, 35.4% and 33.3% respectively. Selected shrimp farms in Agusan del Norte and Bohol were also positive for YHV infection at lower prevalence. Samples from Bataan, Batangas, Cebu and Misamis Oriental were all negative for YHV infection. The prevalence of YHV in the different life stages of shrimp was also determined. Post larval stage had the highest prevalence of infection with 54.5% followed by the juvenile stage with 40.8% and adult stage with 16.9%. Infectivity studies resulted to 60% cumulative mortality 17 days post-infection in juvenile shrimp and 50% cumulative mortality 19 days postinfection in adult shrimp. YHV infection was further confirmed by electron microscopical examination, histopathological examination and in vitro infectivity assay.

White spot syndrome virus (WSSV) is a relatively new agent causing a zoonotic disease in shrimp. Taxonomically this virus is presently an orphaned, floating virus species. WSSV has a unique virion morphology, genome structure, gene content and a distant phylogenetic relationship with other large DNA viruses on the basis of a few conserved genes. The virus lacks overall gene homology with members of the baculovirus genera Nucleopolyhedrovirus and Granulovirus and has a discriminate size of the virion structural proteins. We here propose that WSSV is a representative of a new genus characterized by viruses with an appendage at one end of the virion. For this genus we coin the name whispovirus to accommodate WSSV and related viruses.

Aquaculture is one of the fastest growing food production industries globally (Natale et al., 2011), and it is expected to exceed the production of other animal production industries such as beef, pork, or poultry in the next decade (OECD and FAO, 2012). In the Philippines, aquaculture contributes significantly to food security, employment for the poor, women, youth, and foreign exchange earnings (FAO, 2019; Sekhar and Ortiz, 2006). The Philippines is the 11th top aquaculture producing country in the world; it ranked third, fifth, and ninth in seaweeds, finfish, and marine crustacean productions, respectively (FAO, 2018). However, unsustainable aquaculture practices in the country “contributed to nutrient loading, threatening environmental harm” (FAO, 2018). The majority of countries in the world, including the Philippines, are experiencing environmental problems due to unsustainable aquaculture practices. Thus, to address these problems and further develop aquaculture, research was actively done by the government, academic, and research institutions. According to Superio et al. (2019) research plays a major role in development, and commonly, the results were published for public consumption. However, some fisheries and aquaculture researches were unpublished and of limited distribution because a high proportion of fisheries information was published as grey literature (Parker et al., 2010). Notably, FAO (2009) found that fisheries information in developing countries was published in grey literature due to the stringent criteria of the editorial boards of Western peer-reviewed journals, while in Africa, an estimated 70 percent of fisheries information is published as grey literature.

Two separate feeding experiments determined taurine requirement levels in diets for growth of two sizes of snubnose silver pompano. The first experiment was conducted for 14 weeks using pompano with average weight of 0.4 ± 0.01 g. Experimental diets were isonitrogenic, isolipidic and isoenergetic. Inclusion of 0.346% taurine in diet served as control, while five diets were with graded taurine levels at 0.5 (0.846%), 1.0 (1.346%), 1.5 (1.846%), 2.0 (2.346%) and 2.5 (2.846%) %. Three hundred and sixty pompano fishes were randomly distributed to experimental tanks (250-L, 15 fish per tank) in quadruplicate. Pompano fed diets with 1.0% taurine had significantly higher (\(p\) < .05) specific growth rate, per cent body weight gain (PWG) and feed utilization efficiency. The second experiment was conducted for 17 weeks using 104 ± 1.82 g pompano. Similar treatments were used except for diets with 0.5% and 2.5% taurine. Fifteen pompano were stocked in floating net cages in triplicate. Quadratic regression analysis of PWG and taurine levels revealed that pompano weighing 0.4 g required 1.55 g taurine 100 g^-1 diet (0.352 g taurine 100 g^-1 protein) while larger-sized pompano weighing 104 g required 0.937 g taurine 100 g^-1 diet (0.213 g taurine 100g^-1 protein).