“Population Characteristics, Fishery and Post larval distribution of Macrobrachium rosenbergii (de Man) and M. idella (Hilgendorf) of Vembanad lake”

Macrobrachium rosenbergii (de Man) and M.ide77a (Hilgendorf) form two commercially important Palaemonid prawns of the Vembanad lake (9 28' and 10 10’ N and 76 13' and 76 31' E). Both of them were known to have contributed to a very lucrative fishery during the sixties, however, in recent years these natural resources have badly depleted owing to the impact of many man made alterations brought about in the ecosystem such as habitat reduction, physical obstruction imposed in the migratory pathway of these species, pollution hazards, etc,. Changed environmental conditions and increased fishing pressures caused persistent alterations in the stock size of these prawns during the past so many years, however, no serious attempt was made to monitor the stock size from time to time and also to bring out the resource characteristics. Though, the morphotypic differentiation in grow out male population of M.rosenbergii has been documented, no similar studies were conducted with regard to natural male and female population. Based on the data collected during fishery cruise surveys conducted in Vembanad lake from March '94 to February '96, population characteristics. postlarval distribution, fishery and population dynamics of M.rosenbergii and M.ide77a of the lake were studied in detail.

An assessment of potential public health risk associated with the extended survival of indicator and pathogenic bacteria in freshwater lake sediments

Microcosm studies were performed to evaluate the survival of Escherichia coli, Salmonella paratyphi and Vibrio parahaemolyticus in water and sediment collected from the freshwater region of Vembanad Lake (9 35◦N 76 25◦E) along the south west coast of India. All three test microorganisms showed significantly (p < 0.01) higher survival in sediment compared to overlying water. The survival in different sediment types with different particle size and organic carbon content revealed that sediment with small particle size and high organic carbon content could enhance their extended survival (p < 0.05). The results indicate that sediments of the Lake could act as a reservoir of pathogenic bacteria and exhibit a potential health hazard from possible resuspension and subsequent ingestion during recreational activities. Therefore, the assessment of bacterial concentration in freshwater Lake sediments used for contact and non contact recreation has of considerable significance for the proper assessment of microbial pollution of the overlying water, and for the management and protection of related health risk at specific recreational sites. Besides, assessment of the bacterial concentration in sediments can be used as a relatively stable indicator of long term mean bacterial concentration in the water column above