Introduction: Seasonal and tidal variations in nutrient concentration and water quality were investigated in the western Sundarbans of Bangladesh during the post-monsoon, winter and monsoon seasons during 2010-2011. Methods: Water collected from the surface, middle and bottom layers at six locations of the Kholpetua-Arpangashia river system during high and low tides was analyzed for temperature, salinity, pH, dissolved oxygen (DO), total dissolved solids (TDS), electrical conductivity (EC) and dissolved nutrients (NO 3-N, PO 4-P, SO 4 and NH 3-N). Results: The study revealed that nutrient concentrations were influenced by seasonal changes. Mean nutrient levels during post-monsoon, winter and monsoon seasons, respectively, were in the following ranges

European flat oyster (Ostrea edulis) production has suffered a severe decline due to bonamiosis. The responsible parasite enters in oyster haemocytes, causing an acute inflammatory response frequently leading to death. We used an immune-enriched oligo-microarray to understand the haemocyte response to Bonamia ostreae by comparing expression profiles between naïve (NS) and long-term affected (AS) populations along a time series (1 d, 30 d, 90 d). AS showed a much higher response just after challenge, which might be indicative of selection for resistance. No regulated genes were detected at 30 d in both populations while a notable reactivation was observed at 90 d, suggesting parasite latency during infection. Genes related to extracellular matrix and protease inhibitors, up-regulated in AS, and those related to histones, down-regulated in NS, might play an important role along the infection. Twenty-four candidate genes related to resistance should be further validated for selection programs aimed to control bonamiosis.

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