No abstract

White spot disease (WSD) is at present the most serious viral disease affecting cultivated shrimp species globally. The causative agent, white spot syndrome virus (WSSV), is extremely virulent, has a wide host range and can also be transmitted from broodstock to their offspring. The shrimp postlarvae (PL) act as asymptomatic, latent carriers of the virus, and stocking of WSSV-infected PL has been reported as a risk factor for WSD outbreaks in culture ponds. However, there is no population-based study on WSSV prevalence in PL of shrimp. The present manuscript documents the approaches and the results in the estimation of prevalence of WSSV in PL populations of Penaeus monodon at the time of stocking. A maximum of 300 PL from each of the 73 batches of PL stocked at various farms in the west coast of India during September 1999 to January 2000 were tested for the presence of WSSV by 2-step nested PCR. Thirty-six (49%) of the 73 batches tested positive for WSSV either by 1-step alone (3 batches) or after 2-step nested PCR (33 batches). Sub-samples of 5 PL each or 1 PL each tested to quantify the proportion of infected PL within batches showed that WSSV prevalence was very high in 1-step PCR-positive batches and low in 2-step PCR-positive batches. The study also showed that appropriate sampling and sample size were major factors in determining the prevalence of WSSV in PL populations, underlining the need for testing large samples of PL to reduce errors from falsely negative results. KEY WORDS: WSSV · PCR · Penaeus monodon · Postlarvae · Prevalence · Aquatic epidemiologyResale or republication not permitted without written consent of the publisher

Coastal aquaculture in Aceh was severely affected by the Asian Tsunami in December 2004. Capacity building among stakeholders was one of the key activities implemented by various agencies during the post‐tsunami aquaculture rehabilitation and subsequent development phase. The main objective was improving production efficiencies and farmer incomes. This article describes the process of implementation of the approach and crop outcomes until the end of 2009. In 2009, 1135 farmers and their 1296 ponds were ‘organized’ in 27 clusters across 84 villages of three districts to implement better management practices (BMP). Interventions reduced the prevalence of shrimp disease outbreaks significantly in participating ponds (22.45%) compared with non‐participating ponds (62.64%). Among the normal harvested ponds, though there was no significant improvement in shrimp yield but costs of shrimp production were significantly reduced by 12.1% and benefit cost ratio was significantly increased by 0.523 points in normal harvested participating ponds compared with normal harvested non‐participating ponds. Multivariable logistic regression analysis with 27 independent variables including a set of BMP showed that many factors were significantly associated with the normal harvests, improved yield and profits. The study shows that simple management improvements can reduce risks and improve economic returns.

This paper describes the utility of dead shrimp samples in epidemiological investigations of the white spot syndrome virus (WSSV) and chronic bacterial infections. A longitudinal observational study was undertaken in shrimp farms in Kundapur, Karnataka, India, from September 1999 to April 2000 to identify risk factors associated with outbreaks of white spot disease (WSD) in cultured Penaeus monodon. As a part of the larger study, farmers were trained to collect and preserve dead and moribund shrimp (when observed) during the production cycle. At the end of the production cycle, 73 samples from 50 ponds had been collected for histopathology and 55 samples from 44 ponds for PCR. Intranuclear viral inclusion bodies diagnostic of WSSV infection were detected in dead samples from 32 ponds (64%). Samples of dead shrimp from 18 ponds (36%) showed no histopathological evidence of WSSV infection. However, of these, samples from 13 ponds (26%) showed clear evidence of shell, oral, enteric and systemic chronic inflammatory lesions (CIL) in the form of haemocytic nodules, typical of bacterial infection. Samples from 5 ponds (10%) were negative for both WSSV and CIL. Samples from 8 ponds had dual WSSV and CIL, although both WSSV and CIL were only observed in the same shrimp from 1 pond. Useful information was obtained from these shrimp despite the presence of post-mortem changes. Samples from 19 ponds (43%) tested positive for WSSV by 1-step PCR and samples from an additional 10 ponds (22.7%) were positive by 2-step nested PCR. Samples from 15 ponds (34.1%) were negative for WSSV by 2-step nested PCR. There was moderate to substantial agreement between PCR and histopathology in the diagnosis of WSSV infection in dead shrimp. WSSV infection in dead shrimp was significantly associated with crop failures as defined by a shorter length of the production cycle (< 90 d) and lower average weight at harvest (< 22 g). WSSV infection was also associated with lower survival (< 50%), but this was not significant. Ponds with CIL did not experience any crop failures, and the presence of CIL was significantly associated with successful crops. The study demonstrates that samples of dead shrimp can provide useful information for disease surveillance and epidemiological investigations of WSSV and chronic bacterial infections.

A longitudinal study was conducted from January to August 2005 in small-holder black tiger shrimp (Penaeus monodon) ponds in the West Godavari District of Andhra Pradesh, India (16°25′ N, 81°19′ E). The study involved 457 ponds owned by low-income farmers participating in a better management practice (BMP) programme. Disease outbreaks occurred in 16.6% of ponds. There was significant spatial clustering of disease outbreaks with 31 (40.8%) of the 76 recorded disease outbreaks occurring in a single village block. Bivariate analysis indicated a 1.6-fold higher likelihood of disease outbreaks from nursery-stocked ponds but this was not significant in multivariate analysis due to the confounding effect of pond location. There was evidence of increasing prevalence of WSSV infection during grow-out. WSSV was detected in 5.9% of 119 batches of postlarvae tested at stocking, 38.2% of 34 juvenile batches collected at the time of transfer to grow-out ponds, and 47.0% of 336 pond stock tested at normal harvest or crop failure. WSSV was detected in 43 of 59 (72.9%) disease outbreak ponds tested and 115 of 277 (41.5%) non-outbreak ponds tested. Heavy WSSV infection was detected at harvest in 116 of the 336 (34.5%) of the ponds tested, including 78 ponds for which no outbreak was recorded. Duration of crop was recorded for 431 ponds with a mean of 117.0 days and a range of 20 to 176 days. Median duration was significantly shorter for disease outbreak ponds (68.5 days) compared to nonoutbreak ponds (119.0 days). Duration of crop also varied according to WSSV detection levels at harvest, with median duration for ponds classified as heavy WSSV infection (108.5 days) significantly shorter than for ponds classified as either light WSSV infection (116.0 days) or WSSV-negative (116.5 days). The study indicated a high risk of WSSV infection during grow-out but a relatively low incidence of disease despite a high prevalence of heavy WSSV infection in non-outbreak ponds.Crown