Vibrio is a very diverse genus that is responsible for different human and animal diseases. The accurate identification of Vibrio at the species level is important to assess the risks related to public health and diseases caused by aquatic organisms. The ecology of Vibrio spp., together with their genetic background, represents an important key for species discrimination and evolution. Thus, analyses of population structure and ecology association are necessary for reliable characterization of bacteria and to investigate whether bacterial species are going through adaptation processes. In this study, a population of Vibrionaceae was isolated from shellfish of the Venice lagoon and analyzed in depth to study its structure and distribution in the environment. A multilocus sequence analysis (MLSA) was developed on the basis of four housekeeping genes. Both molecular and biochemical approaches were used for species characterization, and the results were compared to assess the consistency of the two methods. In addition, strain ecology and the association between genetic information and environment were investigated through statistical models. The phylogenetic and population analyses achieved good species clustering, while biochemical identification was demonstrated to be imprecise. In addition, this study provided a fine-scale overview of the distribution of Vibrio spp. in the Venice lagoon, and the results highlighted a preferential association of the species toward specific ecological variables. These findings support the use of MLSA for taxonomic studies and demonstrate the need to consider environmental information to obtain broader and more accurate bacterial characterization. Vibrio spp. are Gram-negative halophilic bacteria belonging to the class Gammaproteobacteria. Vibrio is one of the most studied and diverse genera of microorganisms found in aquatic ecosystems and comprises the major culturable bacteria in marine and estuarine environments (1). According to the Association of Vibrio Biologists (AViB; http://www2.ioc.fiocruz.br/vibrio/AVib /species.html), there are 99 accepted or proposed Vibrio species, although the recent description of new species has led to a constantly changing taxonomy. Vibrio spp. are frequently isolated from fish, fish products, and edible shellfish, and a large number of species are pathogenic to different hosts. Some species, such as V. cholerae, V. parahaemolyticus, and V. vulnificus, cause serious food-borne gastroenteritis in humans. Other species, such as V. anguillarum and V. salmonicida, are pathogenic for fish; V. splendidus-related species are pathogenic for bivalves, and V. harveyi and V. campbellii are pathogenic for shrimps (1, 2, 3). Recently, Austin suggested a classification of zoonotic Vibrio in two classes named "higher-risk" vibrios (V. cholerae, V. parahaemolyticus, and V. vulnificus) and "lower-risk" vibrios (V. alginolyticus, V. fluvialis, V. furnissii, V. harveyi, and V. mimicus) (4). Bivalve mollusks such as clams and mussels represent products of great econ...

Acute hepatopancreatic necrosis disease (AHPND) of shrimps is a bacterial disease, first appeared in China in 2009 and causes mortality up to 100 % which usually occurs early (within approximately first 35 days) after stocking shrimp fry of black tiger shrimp, Penaeus monodon (Fabricius) and white leg shrimp, Litopenaeus vannamei (Boone). The purpose of this study was to isolate and identify the pathogenic strain of V. parahaemolyticus causing AHPND in cultured shrimps (P. monodon) using molecular techniques. After a disease outbreak in April 2017, shrimp samples were collected from three different locations of south-west shrimp farming region of Bangladesh viz. Satkhira, Khulna and Bagerhat districts. In this study, three selective media were used for primary isolation of V. parahaemolyticus. Among 28 primary isolates, representative14isolates were checked for the species-specific detection of V. parahaemolyticus using ldh primers and all of them were found to be positive. The isolates were further characterized to check their AHPND positivity using AP3 and AP4 primers. Four isolates showed positive results for both AP3 and AP4 which indicated that the isolates were AHPND positive. This study also report that all AHPND positive strains showed sensitivity to the antibiotics Tetracycline and Nalidixic Acid. The results of this study will help the farmers and policy makers to make plan to protect shrimps from AHPND and thereby sustain the shrimp farming in Bangladesh.

CitationSarder H, Khan T, Saha ML, Punom NJ, Mandal SC and Rahman MS (2016) Prevalence and antibiotic susceptibility of Aeromonas hydrophila isolated from freshwater fishes. Journal of Fisheries 4(3): 411-419. DOI: 10.17017/jfish.v4i3.2016.177 Abstract Aeromonas hydrophila is an opportunistic microorganism. It is a secondary biological agent that contributes to the occurrence of fish diseases and its deterioration. This research was undertaken to determine the prevalence of A. hydrophila in some freshwater fishes collected from three different fish markets of Dhaka City and to test their antibiotic susceptibility. Total bacterial count and total aeromonas on different aeromonas selective media were enumerated using serial dilution technique. Bacterial isolates were characterized to identify A. hydrophila using biochemical tests and with comparison to reference strain (ATCC 7966). The lowest Aeromonas count was detected to be 2.83±0.40×10 2 cfu/g in Anabas testudineus and the highest was 1.03±0.153×10 3 cfu/g in Oreochromis mossambicus. On market basis highest aeromonas count was found in Anando Bazar (8.10±1.09×10 2 cfu/g) and lowest in Hatirpool Bazar (5.63±0.90×10 2 cfu/g) with no significant difference. Maximum susceptibility to amikacin and gentamicin was observed whereas all of the isolates were found resistant to a commonly used antibiotic amoxycillin. The obtained results point that antimicrobial susceptibility was more or less similar regardless of the origin of the samples collected. All the fishes investigated in this study contained A. hydrophila in their different organs.

The effects of three wetting media (cattle blood, rice gruel and subsurface clean water) of the culture media ingredients (a mixture of mustard oil cake, soybean meal and mud) on the yield and amino acid composition of tubificid worms cultured on a pilot scale in a fish farm for 42 days were evaluated. The worm yields were in the order: cattle blood wetted media (683.68 ± 3.86 mg/cm 2 ), rice gruel (615.63 ± 3.66 mg/cm 2 ), water (584. 38 ± 1.41 mg/cm 2 ). Lysine, arginine and leucine were the most prevalent of the eight essential amino acids in worms cultured in the media wetted in cattle blood medium. The results suggested that a mixture of 40% mustard oil cake, 30% soybean meal and 30% mud can be used for the commercial culture of tubificid worms as live fish food. The tubificid worms showed high level of amino acids suitable for fish that require a high content of dietary amino acids.

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Presence of Vibrio spp., one of the deadliest fish and shrimp pathogens in aquaculture facilities worldwide for which hatchery owners often suffer hectic economic losses, were identified in shrimp and tilapia hatcheries of Cox’s Bazar and Mymensingh, Bangladesh. Thirty seven Vibrio isolates, selected on the basis of their morphological dissimilarities in thiosulphate citrate bile salt sucrose agar (TCBS) plate, were subjected to amplified 16S ribosomal DNA restriction analysis (ARDRA) by using AluI restriction enzyme following their DNA extraction and amplification of 16S rRNA (1450 bp). From this analysis, representative isolates of 8 ARDRA groups, named as ARH 1 to ARH 8, of different band patterns were sequenced and identified as Vibrio alginolyticus, Aeromonas veronii, A. hydrophila, Vibrio vulnificus, V. cholerae, Edwardsiella hoshinae, Bacillus methylotrophicus and Aeromonas veronii, respectively. Vibrio species identified in this study are pathogenic for human and aquatic organisms, and were found only in shrimp hatchery with the dominance of V. alginolyticus. Findings of this study indicate the poor quality of water treatment and management of the hatchery. It was also observed that all the three Vibrio species were present in the Artemia rearing tank which indicates the possible source of pathogens. Dhaka Univ. J. Biol. Sci. 26(1): 45-58, 2017 (January)

The Optimum harvest suitable for sustainable yield of tubificid worms without affecting the future yield for a period of 60 days was determined. The media ingredients used to culture the worms were 20% wheat bran, 30% soybean meal, 20% mustard oil cake, 20% cow dung and 10% sand. A harvest level of 50 mg/cm 2 (maximum yield; 518.93 ± 14.36 mg/cm 2 ) at ten days interval starting from 30 days of worms' inoculation was found suitable for sustainable yield in the later sampling durations. Results of this study have implications in increasing fish yield by producing reliable and sustainable yield of fish live foods tubificid worms.

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