Crab farmers will be happier, and the environment hopefully better, with recent improvements at the mangrove crab hatchery of SEAFDEC/AQD in Iloilo, Philippines. Crablets used in the farming of the prized mangrove crabs, Scylla serrata, are usually collected from the wild and increasing demand has threatened their natural population. However, Huervana recently revealed that simple tweaks in protocols at the SEAFDEC/AQD hatchery have led to a significant boost in their crablet production, with survival increasing twofold.

This report was prepared by the 18th Asia Regional Advisory Group on Aquatic Animal Health (AG) that met at Bangkok, Thailand on 18-19 November 2019. The group discussed OIE standards and global issues, review of regional disease status, reports on the aquatic animal health programmes of partner agencies, and disease reporting.

From a survey of wild, adult Penaeus monodon of potential broodstock size from the Indian Ocean in April 2018, we obtained positive nested RT-PCR test results for infectious myonecrosis virus (IMNV) and positive nested PCR test results for DIV1. As a confirmatory step, a second round of nested PCR tests was carried out using new, in-house primers designed from regions of the respective viral genomes distant from the target regions used in the first round of tests. These results suggested the possibility that the grossly normal, PCR-positive captured P. monodon specimens might be infected with the respective viruses at the carrier level. If so, they might serve as potential vehicles for introduction of IMNV and/or DIV1 into crustacean culture systems, especially if they were used in hatcheries for production of PL for distribution to shrimp farmers without proper precautions in place.

We carried out laboratory injection challenges that employed extracts prepared from shrimp naturally-infected with decapod iridovirus 1 (DIV1). We found that diseased shrimp from the injection trials showed pathognomonic lesions for DIV1 in the hematopoietic tissue that matched those reported for DIV1 in P. vannamei from China (Qiu et al. 2017. Scientific Reports. 7). In addition, we also found distinctive lesions in the lymphoid organ that could be used as an additional indicator in confirming diagnosis of DIV1 disease. Also, the lesions from shrimp challenged with the 10x dilution were more severe than those from 100x dilution, and for some shrimp in the 100x dilution, the lesions were very clear in the LO but absent in the HPT. Altogether, the results suggested that histology of the HPT and LO could be used together to help in the diagnosis of DIV1 in conjunction with RT-PCR, amplicon sequencing and in situ hybridization (ISH) analysis. This is particularly important in confirming the presence of virulent isolates of DIV1 in new geographical locations.

In this issue:

Mahseer sanctuaries of Meghalaya: A conservation and recreational perspective; Impacts of climate change on aquaculture in Vietnam: A review of local knowledge; Simple means of water aeration adopted by progressive fish breeders in West Bengal, India; Breeding striped snakehead (Channa striata) using the concrete tank method in the Cangkringan Area, Special Region of Yogyakarta; NACA Newsletter.