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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

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The Peacock eel, Macrognathus aculeatus is a near threatened highly valuable small indigenous species in Bangladesh. It is not only toothsome nutritive table fish but also notable aquarium species but still rely on natural stock. Keeping in mind the paucity of information on the biology which is crucial to develop artificial propagation and culture technique of this species, the present research was performed as an attempt to contribute to the information on the taxonomy and other biological aspects of M. aculeatus. Total 50 samples were collected from Khulna region during April to May 2014 to assay. The taxonomical study revealed that the total length, standard length, head length, eye diameter, pre and post orbital length; length of dorsal, anal and caudal fin; length of upper and lower jaw; body depth and width, distance between dorsal fin to caudal fin ranged from 17.00-21.00, 15.00-19.00, 0. The mean values of hepatosomatic and alimentosomatic indices persuaded greater liver activity and feeding intensity in M. aculeatus. Moreover, stomach content depicted that the diet of peacock eel composed of small fish species, small prawn, prawn larvae, earthworm, water strider, insects pupae, Metaphire posthuma, Caenorhabditis, sand and mud for instance, which in brief expressed that M. aculeatus is omnivorous in its feeding habits. Indeed, this preliminary research outcome would be utile for the species identification, seed production, developing culture technologies as well as biodiversity conservation of this near threatened fish species.

Mangrove provides a unique ecological environment for diverse communities and Sundarbans is a rapidly changing ecosystem due to various anthropogenic activities. In order to assess the spatial and temporal variation of total Nitrogen and total Phosphorus concentration in Major River Systems of Sundarbans, a study was carried out from September, 2010 to February, 2011. Fourteen sampling location from major River systems were chosen. During post monsoon and winter seasons the range of total Phosphorus (0.326~0.409 mg/L and 0.091~0.371 mg/L respectively) and total nitrogen (2.52~3.50 mg/L and 3.43~5.25 mg/L respectively) were observed in Rupsha-Passur River system. On the other hand the range of total Phosphorus (0.475~0.144 mg/L and 0.060~0.113 mg/L respectively) and total nitrogen (2.31~3.61 mg/L and 3.22~5.95 mg/L respectively) were found in Arpangashia-Malancha River system during post monsoon and winter seasons. The nutrients of water of Baleswar-Bhola River system during rainy and dry seasons were found in the range of total Phosphorus (0.106~0.364 mg/L and 0.053~0.075 mg/L respectively) and total nitrogen (2.59~3.57 mg/L and 2.87~5.60 mg/L respectively). Total Nitrogen and total phosphorus levels were relatively higher than the EPA standards for surface water during the two seasons. The Dynamic nutrients level observed in the study area may have severe consequences on the in-dwelling aquatic flora and fauna.

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.

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