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

This study evaluates the effect of probiotics, Zymetin, on the immune efficiency of Macrobrachium rosenbergii juvenile against pathogenic Vibrio spp. and Aeromonas spp. The experiment was conducted in glass aquaria with same level of feeding under different treatments, that is, negative control (Cn), positive control with Vibrio spp. (Cv) and Aeromonas spp. (Ca), prawn juveniles fed with probiotics (Zymetin) at 5 g/kg of feed but without pathogen (T1), probiotic fed prawn challenged with Vibrio spp. (T2) and Aeromonas spp. (T3). The results demonstrated that T1 showed higher survival rate, total haemocyte count, non-granular haemocyte count, phagocytic activity, and clearance efficiency compared to other treatment groups. In contrast, decreased number of small and large granular haemocyte was observed in T1.Despite that, THC was found to be significantly different (p < 0.05) among all the controls and lowest was in Cv, followed by Ca. Besides, phagocytic activity and clearance efficiency against Vibrio spp. and Aeromonas spp. decreased significantly in Cn, Ca, and Cv fed M. rosenbergii juvenile, while the values were found to be higher in T1 followed by T2 and T3, in that order. In addition, the challenge test showed an increasing trend of total and beneficial bacterial density as well as declining trend of some harmful bacteria in the water and gut of prawn in all the groups tested (p < 0.05). K E Y W O R D Sclearance efficiency, Macrobrachium rosenbergii, phagocytic activity, probiotics wileyonlinelibrary.com/journal/are Aquaculture Research. 2019;50:644-657. 2 | MATERIALS AND METHODS 2.1 | Pathogen isolation, culture, and biochemical confirmation Before conducting the challenge test, the pathogenic bacteria (i.e., Vibrio spp. and Aeromonas spp.) were isolated from four diseased prawns which displayed typical symptoms of inactivity, poor growth leading to weight loss, anorexia, and frequent mortality. All the diseased GFP were collected from the farmer's pond of Dumuria, Khulna, Bangladesh. Infected prawns were brought to the Fish Pathology Laboratory of Fisheries and Marine Resource Technology AZAD ET AL.| 645

The blue mussel (Mytilus edulis) is known as a robust bivalve species, although its larviculture appears to be highly susceptible to diseases. In this study, we isolated 17 strains from induced mortality events in healthy wild-caught blue mussel adults and demonstrated that they caused between 17% and 98% mortality in blue mussel larvae in a newly developed, highly controlled immersion challenge test model. Eight of the isolates belong to the Splendidus clade of vibrios, while the other isolates belong to the genus Photobacterium. The genomes of the most virulent Vibrio isolate and the most virulent Photobacterium isolate were sequenced and contained several genes encoding factors that have previously been linked to virulence towards bivalves. In vitro tests confirmed that all 17 isolates were positive for these virulence factors. The sequenced genomes also contained a remarkably high number of multidrug resistance genes. We therefore assessed the sensitivity of all isolates to a broad range of antibiotics and found that there were indeed many strong positive correlations between the sensitivities of the isolates to different antibiotics. Our data provide an ecological insight into mass mortality in blue mussels as they indicate that wild mussels contain a reservoir of pathogenic bacteria.

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Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

The present study was conducted to evaluate the effects of C/N ratio on the volume of floc formation as well as on the load of several potential microbes of the fresh water prawn (Macrobrachium rosenbergii) culture tanks. The experiment was designed with three different C/N ratios viz. 10:1, 15:1, and 20:1 as T1, T2 and T3 were applied with a control (C) at laboratory condition. It was observed that C/N ratio 15:1 (12.22 ± 1.08 ml/L) and 20:1 (15.33 ± 1.37 ml/L) gave higher floc development compared to control C (5.22 ± 0.62 ml/L) and T1 (7.22 ± .46 ml/L) (P<0.05). The loads of Enterococcus spp.was found to be highest in T2, followed by T1, C and T3 (P<0.05). Higher Lactobacilllus spp. load was found in T1 and T2 compared to T3 and C, which indicates that growth of Lactobacillus spp. require a fair range of carbon source. No Salmonella spp. was found in any treatment. The present findings indicate that C/N ratio 15:1 could be applied in sustainable freshwater prawn culture.