Vibrio cholerae, a bacterium autochthonous to the aquatic environment, is the causative agent of cholera, a severe watery, life-threatening diarrheal disease occurring predominantly in developing countries. V. cholerae, including both serogroups O1 and O139, is found in association with crustacean zooplankton, mainly copepods, and notably in ponds, rivers, and estuarine systems globally. The incidence of cholera and occurrence of pathogenic V. cholerae strains with zooplankton were studied in two areas of Bangladesh: Bakerganj and Mathbaria. Chitinous zooplankton communities of several bodies of water were analyzed in order to understand the interaction of the zooplankton population composition with the population dynamics of pathogenic V. cholerae and incidence of cholera. Two dominant zooplankton groups were found to be consistently associated with detection of V. cholerae and/or occurrence of cholera cases, namely, rotifers and cladocerans, in addition to copepods. Local differences indicate there are subtle ecological factors that can influence interactions between V. cholerae, its plankton hosts, and the incidence of cholera.Vibrio cholerae, the causative agent of cholera, is native to the aquatic environment. Cholera, the disease caused by V. cholerae, is endemic in regions of the world where inadequate sanitary practices and consumption of contaminated water and food are common. More than 200 serotypes of V. cholerae have been identified, of which several can cause mild to serious gastroenteritis and even local outbreaks of diarrheal illnesses with cholera-like symptoms. Toxigenic strains of V. cholerae serogroups O1 and O139 have been identified with cholera epidemics and pandemics (4, 24).V. cholerae O1 and O139 are commensal to crustacean zooplankton, notably copepods, which are present both in their gut and in biofilms on their chitinous surfaces (15, 28). Furthermore, V. cholerae is present throughout the year in and on its zooplankton host (13), and V. cholerae serogroup O1 has been shown to attach preferentially to zooplankton, but also to some species of phytoplankton in Bangladesh waters (33). Its commensal existence provides protection from grazing by heterotrophic nanoflagellates (23) and also from toxic chemicals, including those used to disinfect drinking water, such as alum and chlorine (6). V. cholerae, like all Vibrio species, produces chitinase(s) (12), with chitin serving as a nutrient source (25, 27). In a recent study, Kirschner et al. (21) demonstrated that association with zooplankton is important for V. cholerae non-O1/non-O139 serogroup isolates endemic in Neusiedler See, a large, shallow, moderately saline-alkaline lake in Central Europe. A significant correlation was observed between the seasonal pattern in frequency of occurrence of V. cholerae and increased zooplankton biomass (21).Zooplankton comprise a broad assortment of ecologically important heterotrophic groups, including small crustaceans, i.e., copepods, water fleas of the genera Daphnia, Bosmina, and Diaptomus, fairy...

Seasonal plankton blooms correlate with occurrence of cholera in Bangladesh, although the mechanism of how dormant Vibrio cholerae, enduring interepidemic period in biofilms and plankton, initiates seasonal cholera is not fully understood. In this study, laboratory microcosms prepared with estuarine Mathbaria water (MW) samples supported active growth of toxigenic V. cholerae O1 up to 7 weeks as opposed to 6 months when microcosms were supplemented with dehydrated shrimp chitin chips (CC) as the single source of nutrient. Bacterial counting and detection of wbe and ctxA genes were done employing culture, direct fluorescent antibody (DFA) assay, and multiplex-polymerase chain reaction methods. In MW microcosm, the aqueous phase became clear as the non-culturable cells settled, whereas the aqueous phase of the MW–CC microcosm became turbid from bacterial growth stimulated by chitin. Bacterial chitin degradation and biofilm formation proceeded from an initial steady state to a gradually declining bacterial culturable count. V. cholerae within the microenvironments of chitin and chitin-associated biofilms remained metabolically active even in a high acidic environment without losing either viability or virulence. It is concluded that the abundance of chitin that occurs during blooms plays an important role in the aquatic life cycle of V. cholerae and, ultimately, in the seasonal transmission of cholera.

This proximate study was carried out to determine the nutrient content of six commercially important molluscs. The selected molluscan species were Pila globosa, Bellamya bengalensis, Melania tuberculata, Lamellidens marginalis, Anisus convexiusculus and Helix sp. These species were assessed for their proximate and mineral compositions designed to establish their nutritive values on the wet weight basis. The analysis of muscles revealed that the composition of crude protein varied from 8.272%±0.05% in Pila globosa to 12.927%±0.57% in Anisus convexiusculus, moisture content varied from 74.6%±0.04% in Melania tuberculata to 85.9%±0.68% in Lamellidens marginalis and in case of ash content it varied from 1.036%±0.02% in Pila globosa to 4.607%±0.01% in Anisus convexiusculus. Carbohydrate content varied from 2.902±0.03% in Pila globosa and 7.566%±0.37% in Melania tuberculata. The fat and crude fiber content was marginally small in all of the species. The concentrations of calcium, phosphorus, iron, sodium and potassium in the flesh and shells of the molluscs were determined. It becomes pretty clear that molluscs are excellent sources of some required trace and minor elements needed for the proper growth and development of human being and can also be used as high-nutrient supplementary feed for domestic animals, birds and even for fish culture.

An investigation was carried out on the proximate and mineral contents of widely consumed freshwater small indigenous species (SIS), culture and marine fish species of Bangladesh. Proximate composition (crude protein, fat, ash, moisture, carbohydrate and energy) and selected mineral (Ca, K, Na, Mg, Fe, Zn and Mn) contents were determined eighteen locally available fish species of Bangladesh. Considering proximate composition high protein fishes are Thai Sarpunti 17.5 ± 0.15%, Rui 16.82% ± 0.02; high fat fishes are Thai Pangus 10.03±0.1%, Thai Sarpunti 9.38±0.37%; high Ash contents in Poa 4.78 ± 0.92 %, Ganges Chapila 3.96 ± 0.51%, Thai Sarpunti 3.31 ± 0.14%; high energy found in Thai Sarpunti 157.02 ± 2.61 Kcal/g and Thai Pangus 151.59 ± 2.71 Kcal/g. Considering mineral compositions, Ca rich fishes are Punti 1984.32 ± 1.1 mg, Mola 1267 ± 2.2 mg, Dhela 1717.8 ± 3.1 mg, Chapila 1100.6 ± 1.21 mg, Thai Sarpunti 1373.9 ± 5.32 mg. K rich fishes are Taki 501.47 ± 2.9 mg, Coral 415.24 ± 2.8 mg and Na rich fishes are Thai Sarpunti 780.01 ± 3.8, Ganges Chapila 415.32 ± 2.34 mg, Loitta 497.38 ± 4.21 mg. Trace mineral, Mg is high in Coral 187.98 ± 0.61 mg, Punti 148.16 ± 0.62 mg, Datina 144.05 ± 0.35 mg, Kachki 143.49 ± 0.3 mg fishes, whereas Fe are high in Chapila 15.95 ± 0.03mg, Punti 10.31 ± 0.2, Poa 7.01±0.66 and Zn in Thai Sarpunti 40.20 ± 0.34 mg, Poa 29.32 ± 0.32 mg fishes. Considering Mn, Chapila 6.34 ± 0.04 mg is the highest. This study indicate that small fishes with bones are important source of essential minerals especially Ca. Culture species found to be rich in source of protein, energy and lipids. Marine species exhibit good combination of protein and minerals. This study also encourage to take a culture species like Thai Sarpunti (Barbonymus gonionotus) for its high nutritional meat values and also to consume marine fishes and small fishes with bones for better nourishment. Promotion of the production and consumption of small fishes therefore be encouraged for better nutritional achievement.

We studied the coastal zooplankton community structure of six waterbodies of Mathbaria and Bakerganj from January 2008 to June 2009. In total 35 zooplankton species were identified under 26 genera under 20 families under 8 orders from Mathbaria. Among them 6 were protozoans, 24 were rotifers, 3 were copepods, 1 was cladocerans and 1 was ostracods. From Bakergonj a total of 42 zooplankton species were identified under 23 genera under 17 Families under 7 orders. Among them 3 were protozoans, 25 were rotifers, 7 were copepods, 6 were cladocerans and 1 was ostracods. Results showed that abundance of rotifera group from both area was higher in Mathbaria (64.86%) and Bakerganj (60.98%) than other groups while abundance of ostracoda of Bakerganj area was lowest.