BACKGROUND:The purpose of this study was to evaluate ecological function of small-scale pond and movement characteristics of mudfish (Misgurnus mizolepis) during midsummer drainage period. METHODS AND RESULTS:In situ experiments were performed in the paddy field with mudfish under the condition of midsummer drainage from 13 July to 29 July 2010. The mudfish used in this experiment is approximately 1,000 individuals with a cut tail. Mudfishs were released in the rice field before midsummer drainage and caught again in the small-scale pond and the paddy field after midsummer drainage. Results showed that the abundance of mudfish was higher in drainage canal than small-scale pond at the early stage of midsummer drainage, because flow was formed toward the drainage canal. In that time, 3% of the total marked mudfish were captured at outlet of drainage canal. As the paddy was drying, 5% of total marked mudfish moved to the small-scale pond during midsummer drainage period. Contrary to the general hypothesis, the marked mudfish was not found in holes in paddy field.of total caught in the small-scale pond ingested mainly animal prey, and it's frequency of empcy stomach was 10%.oOn

Red sea bream iridoviral disease (RSIVD) causes serious economic losses in the aquaculture industry. In this paper, we evaluated RSIV kinetics in rock bream under various rearing water temperatures and different RSIV inoculation concentrations. High viral copy numbers (approximately 103.7–106.7 RSIV genome copies/L/g) were observed during the period of active fish mortality after RSIV infection at all concentrations in the tanks (25 °C and 20 °C). In the group injected with 104 RSIV genome copies/fish, RSIV was not detected at 21–30 days post-infection (dpi) in the rearing seawater. In rock bream infected at 15 °C and subjected to increasing water temperature (1 °C/d until 25 °C) 3 days later, the virus replication rate and number of viral copies shed into the rearing seawater increased. With the decrease in temperature (1 °C/d) from 25 to 15 °C after the infection, the virus replicated rapidly and was released at high loads on the initial 3–5 dpi, whereas the number of viral copies in the fish and seawater decreased after 14 dpi. These results indicate that the number of viral copies shed into the rearing seawater varies depending on the RSIV infection level in rock bream.

Grouper is one of the favorite sea food resources in Southeast Asia. However, the outbreaks of the viral nervous necrosis (VNN) disease due to nervous necrosis virus (NNV) infection have caused mass mortality of grouper larvae. Many aqua-farms have suffered substantial financial loss due to the occurrence of VNN. To better understand the infection mechanism of NNV, we performed the transcriptome analysis of sevenband grouper brain tissue, the main target of NNV infection. After artificial NNV challenge, transcriptome of brain tissues of sevenband grouper was subjected to next generation sequencing (NGS) using an Illumina Hi-seq 2500 system. Both mRNAs from pooled samples of mock and NNV-infected sevenband grouper brains were sequenced. Clean reads of mock and NNV-infected samples were de novo assembled and obtained 104,348 unigenes. In addition, 628 differentially expressed genes (DEGs) in response to NNV infection were identified. This result could provide critical information not only for the identification of genes involved in NNV infection, but for the understanding of the response of sevenband groupers to NNV infection.

White spot syndrome virus (WSSV) is the most problematic pathogen in crustaceans. In this study, we investigated the horizontal transmission model of WSSV based on the correlation between the disease severity grade and viral shedding rate and determined the minimum infective dose of WSSV via the waterborne route. Intramuscular injection challenges at different doses and water temperatures revealed that the thresholds of viral shedding and mortality were G1 (3.1 × 103 copies/mg) and G2 (8.5 × 104 copies/mg), respectively. Furthermore, a positive linear correlation was observed between viral copies of pleopods and viral shedding rate (y = 0.7076x + 1.414; p < 0.001). Minimum infective doses of WSSV were determined via an immersion challenge. Infection was observed within 1, 3, and 7 d in 105-, 103-, and 101 copies/mL of seawater, respectively. In the cohabitation challenge, infection was observed within six days with viral loads of 101 to 102 copies/mL of seawater, which further increased in the recipient group. Our results indicate a positive correlation between disease severity grade and viral shedding rate of infected shrimp and suggest that the waterborne transmission of WSSV depends on the viral load and exposure period.

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