The giant freshwater prawn (Macrobrachium rosenbengii) is one of the indigenous prawns found in many parts of the country. Locally known as ulang, it is a hardy species that is easily farmed. On the average, farmed ulang weighs from 30 to 100 grams, which translates to 10 to 25 pieces per kilo. This is very much comparable to the medium to large or jumbo sizes of brackishwater tiger shrimps or sugpo. In the wild, ulang grow as much as 500 g and sells at 300 to 350 pesos/kg ($1=P55.50), however, the quantity harvested is limited and is dependent on its seasonality. Despite the development of both hatchery and grow-out technologies for ulang, there is really no significant commercial production in the country yet, except in BFAR-operated hatcheries in Muñoz and in Dagupan. To date, the only private ulang hatchery is MBL Farms producing up to 150,000 PL or post-larvae per run (45 days), although there are entrepreneurs trained in Muñoz who are also operating small backyard hatcheries for prawns. With the emerging global market on this giant freshwater prawn coupled with improved technologies, it is but imperative to speed up the development of the industry in the country. However, the industry is faced with problems and constraints that include: • insufficient breeders • insufficient supply of post-larvae or PL for stocking • limited market supply • limited funds for interested stakeholders • insufficient information • inadequate promotion of technology transfer • very few skilled and/or trained technicians • research and development of ulang hatchery and grow-out are still wanting new technologies

Research and commercial production of the freshwater prawn, Macrobrachium sp., in the Philippines are yet not well-developed. Although studies on Macrobrachium sp. (or ulang as it is locally known), started at the Binangonan Freshwater Station (BFS) of SEAFDEC/AQD in the mid-1980s, research efforts were discontinued soon thereafter because of: (a) inadequate technical skills; (b) problems with larval rearing and the domestication of wild stocks; and (c) the Macrobrachium sp. is being considered in the Philippines as a low priority species in contrast to commercially important freshwater commodities like tilapia and milkfish. That was two decades ago and in retrospect, researches continued and the freshwater prawn in the Philippines could have been successfully domesticated and current problems concerning the limited aquaculture production of genetically depauperate non-indigenous stocks could have been resolved. With the renewed interest in the culture of alternative species like the freshwater prawn, researchers at the Binangonan Freshwater Station (BFS) started to conduct some studies on the refinement of breeding, larval rearing and culture of Macrobrachium rosenbergii since 2003.

One way of increasing the production of freshwater prawn is through a genetic improvement program. The GI Macro seeds (Genetically Improved Macrobrachium rosenbergii) that Indonesia developed have been released to farmers since 2001. However, producing 50 g prawns have become difficult with survival rate of as low as 40% after 9-11 months of culture. Thus, the program to improve growth rate and increase the edible portion of the prawn was conducted. Giant freshwater prawn is an important commodity that is successfully cultured in Indonesia. Its culture has been developed in several areas of West Java, i.e., Ciamis (Tambaksari, Pamarican and Kalipucang) and Tasikmalaya. The Indonesian Government has developed a hatchery in Jogjakarta province (Central Java), while the private sector control about seven hatcheries. In East Java, freshwater prawn is cultured in brackishwater ponds. Freshwater prawn culture has also spread to some areas of Bali Island, e.g., in Gianyar, Klungkung, Buleleng and Tabanan. Indonesia has been recognized as the center of origin of the giant freshwater prawn because about 19 identified species are found in almost all islands of the country (Holthuis, 1980). However, this genetic resource is not yet fully used in freshwater prawn culture. Although freshwater prawn culture has been widely developed in Indonesia, some problems have been encountered, e.g., declining growth rate, disease, and the small edible portion (abdominal muscle). In recent years, the Government of Indonesia has stressed the need to increase the production of freshwater prawn. One way to increase production is through the genetic improvement program. In 2001, the GI Macro (Genetically Improved Macrobrachium rosenbergii), strain of freshwater prawn has been developed and released to farmers.

This is the first report of the isolation and characterization of a fish virus from the Philippines. The virus was isolated using snakehead spleen cells (SHS) from severely lesioned epizootic ulcerative syndrome (EUS)-affected snakehead Ophicephalus striatus from Laguna de Bay, in January 1991. The virus induced cytopathic effects (CPE) in SHS cells yielding a titer of 3.02 x 106 TCID50 ml-1 at 25°C within 2 to 3 d. Other susceptible cell lines included bluegill fry (BF-2), catfish spleen (CFS) and channel catfish ovary (CCO) cells. Replication in chinook salmon embryo cells (CHSE-214) was minimal while Epithelioma papulosum cyprini cells (EPC) and rainbow trout gonad cells (RTG 2) were refractory. Temperatures of 15 to 25°C were optimum for virus replication but the virus did not replicate at 37°C. The virus can be stored at -10 and 8°C for 30 and 10 d, respectively, without significant loss of infectivity. Viral replication was logarithmic with a 2 h lag phase; viral assembly in the host cells occurred in 4 h and release of virus occurred 8 h after viral infection. A 1-log difference in TCID50 titer between the cell-free virus and the total virus was noted. Freezing and thawing the virus caused a half-log drop in titer. Viral exposure to chloroform or heating to 56°C for 30 min inactivated the virus. Exposure to pH 3 medium for 30 min resulted in a more than 100 fold loss of viral infectivity. The 5-iododeoxyuridine (IUdR) did not affect virus replication, indicating a RNA genome. Neutralization tests using the Philippine virus, the ulcerative disease rhabdovirus (UDRV) and the infectious hematopoietic necrosis virus (IHNV) polyvalent antisera showed slight cross-reaction between the Philippine virus antiserum and UDRV but established no serological relationship with SHRV and IHN virus. Transmission electron microscopy (TEM) of SHS cells infected with the virus showed virus particles with typical bullet morphology and an estimated size of 65 x 175 nm. The Philippine virus was therefore a rhabdovirus, but the present study did not establish its role in the epizootiology of EUS.

Hepatopancreatic parvovirus (HPV) was detected in samples of Penaeus monodon postlarvae (PL-13, PL-18, PL-19, PL-26) from 2 hatcheries in 2 provinces (Samar and Iloilo) in the Philippines. The percentage of infection was 20 to 100% in postlarvae obtained from the hatchery in Samar in August 2001. Postlarvae from the hatchery in Iloilo, sampled in October and November 2001, had 70 to 99% HPV infection. Wet mounts of squashed hepatopancreatic tissue stained with malachite green (wet-mount technique) and histopathology revealed the presence of large, usually single, basophilic intranuclear inclusion bodies in the distal tubules, which led to displacement of the nucleoli. Light microscopy showed ovoid to spherical inclusion bodies, 5 to 11 µm in diameter. Transmission electron microscopy revealed that the inclusion bodies were composed of electron-dense granular material and virions. The virions appeared roughly spherical and averaged 18 to 22 nm in diameter. An experiment was undertaken to induce HPV infection by feeding P. monodon postlarvae with virus-infected postlarvae. P. monodon postlarvae (PL-16), initially determined as free from HPV, were found HPV-positive 24 h after being fed with infected material. The percentage of infection ranged from 30% at Day 1 post-infection (p.i.) to 100% at Day 7 p.i. determined by the wet-mount technique and by histopathology. This is the first report of a successful horizontal transmission of HPV in P. monodon postlarvae.

Giant freshwater prawn (Macrobrachum rosenbergii) is one of the most important economic species in Thailand as well as in many Southeast Asian countries. It is highly demanded as food for the Thais that lead to its gradual over-catching from the natural waters every year. Thus, domestication experiments on the Macrobrachium have been conducted by the Department of Fisheries since 1956 to increase prawn production (Sidthimunka and Bhukaswan, 1982). This resulted in the nationwide extension of its culture technology to a number of commercial giant freshwater prawn culture companies. Now this species has become one of the economic commodities in the country’s aquaculture industry. Recently, statistics report showed that the total prawn culture in 2002 increased by 38% from the year 1996, while the total value in the same year increased by 89% from the year 1996. The statistics also showed that in 1996 and 2002, the total production were 7200 and 10,000 mt, respectively, valued at 596.3 and 1,117.6 million Thai Baht, respectively (Department of Fisheries and Suwannatos, 2003). The market price per kg of freshwater prawn, which varies according to the prawn sizes, has been increasing since 1989. In 1997, the large, medium and small sizes increased by 76%, 123% and 81% from those in year 1989, respectively.