Temperature effect on behaviour, oxygen consumption, ammonia excretion and tolerance limit of the post larvae of shrimp Penaeus indicus.

The present study has been carried out to know the effect of temperature on behaviour, equilibrium loss and tolerance limit of the post larvae of shrimp Penaeus indicus. The experimental temperatures were selected based on the thermal tolerance limit. The experiments were conducted at a specific temperature for duration of 48 hr. The thermal tolerance experiments were conducted in two ways: in direct exposure and in gradually increasing temperature. The upper and lower lethal temperatures for the post larvae of shrimp P. indicus were 43.5 degrees C and 8 degrees C respectively. During tolerance experiment, no mortality was observed at 33 degrees C and 35 degrees C. But at 38 degrees C with gradual increase in temperature, 30% loss of equilibrium and mortality were recorded in 24.31 hrs and 25.07 hrs, and the remaining 70% were alive. On the contrary, when the post larvae of shrimps were directly exposed to 38 degrees C, almost 80% loss of equilibrium and mortality were recorded in 30.22 hrs and 30.40 hrs, remaining 20% were alive. At 40 degrees C with gradual increase in temperature, 100% loss of equilibrium and mortality were recorded in 25.32 hrs and 25.56 hrs. On the other hand, when the post larvae of shrimps were directly exposed to 40 degrees C, 100% loss of equilibrium was observed in 0.37 hrs and mortality in 1.40 hrs. These behavioral responses include an elevated temperature of 12 degrees C, surfacing, dashing against glass wall, jumping out of the water, etc. In general, the rate of oxygen consumption and ammonia excretion was found to enhance with increasing temperature. In the present study, it was found that gradual increase in temperature favours the shellfish population to escape from the thermal exposure as compared to direct exposure.

A study on distribution of natural radionuclide polonium-210 in a pond ecosystem.

This paper presents the results of an investigation on the distribution of 210Po in Mutharasanallur pond ecosystem. It has been demonstrated that 210Po is non-uniformly distributed within the ecosystem. The results of the study show a dissolved 210Po concentration in pond water of 1 4mBq l–1 . The sediment samplso recorded a 210Po activity of 59 9 Bq kg–1. The aquatic organisms showed differential accumulation of the radionuclide with enhanced bioaccumulation in soft tissues and muscle. The 210Po activity in the biota fell within the range of 1·2 —53 3 Bq kg-1 (wet wt). The bivalve mussel, Lamellidens marginalis was identified to accumulate higher concentration of 210Po in soft tissues, suggesting that these organisms could serve as a bio-monitor of 210Po radionuclide in a freshwater system. The concentration factors of 210Po for the biotic components ranged from ~ 102— ~104 . Analyses of the results indicate that prawn and fish represent an important source of supply of 210Po to humans via dietary intake. Results of210Po activity in the abiotic and biotic components of the pond ecosystem were higher when compared with those of Cauvery river system, the primary water source of the pond.

Radium-226 levels in the Cauvery river ecosystem, India.

We studied the natural radioactivity distribution of an α-emitting radionuclide, 226Ra in water, sediment and biota (plankton, weed, snail, bivalve, prawn and fish) of Cauvery river ecosystem extending a stretch of 95 km. The dissolved 226Ra concentration in river water ranged from 0·82mBq.I-1 to l 06mBq.l-1 (mean: 0·93mBq.l-1) and the activity in river sediments from 4·7Bq.kg-1 to 6·9Bq.Kg-1 (mean: 5·6Bq.kgg-1 dry wt.). The 226Ra activity levels in the biota were within a narrow range from below detection limit to 3·80 Bq.kg-1 (wet wt). Generally higher 226Ra concentrations are observed in the shells and bones of aquatic organisms than in their tissues and muscles. The concentration factors (CFs) of 226Ra for the biotic components ranged from ~ 101 to ~ 103. The significance of 226Ra activity in the abiotic and biotic components of Cauvery river are discussed.

Distribution of natural radionuclide 40K in biotic and abiotic components of the Cauvery river system, Tiruchirapalli, India.

Abiotic components like water and sediment, and biotic components such as mussels, fish and grass collected from Cauvery river at Tiruchirapalli were analysed for 40K activity. The highest level of 40K activity was found in the sediment (342 mBq g–1 dry weight) and the lowest activity was found in water (2·209 mBq ml–1). In the freshwater mussel Parreysia favidens (Benson) 40K activity was estimated in the total soft tissues and shells of mussels belonging to three different size groups· In all the size groups 40K activity was two times higher in shells (68–39 mBq g–1 fresh weight) than in the total soft tissues (25–17 mBq g–1 fresh weight)· The results indicate that the younger mussels accumulated more 40K than the older ones. The ability of internal organs of mussels belonging to group III to accumulate 40K was in the following order: gills > digestive gland > foot > mantle. The values ranged from 47 to 18 mBq g–1 fresh weight in the various organs. Concentration of 40K in the mussel was distinctly higher than in the grass Echinochloa colonum (J Koenig) (95 mBq g–1 fresh weight), and the concentration of 40K in the bone of the fish Cirrhina cirrhosa (Bloch) (126 mBq g–1 fresh weight) was higher than to that of muscle (113 mBq g–1 fresh weight)·