Organic carbon in the sediments of the lower reaches of Periar River

Sediments are indicators of the quality of water overlying them and hence, useful in the assessment of environmental pollution. Temporal and spatial variations in sediment characteristics and organic carbon content from 9 stations in the lower reaches of Periyar River an area in Cochin Backwater, India which is polluted from different sources were studied for one year during 1981. Variations in colour and texture of sediments were brought about by changes in the grain size and state of oxidation of organic matter. The colour of the sediment varied from greyish black at stations 1 and 2, brownish at station 3, black at stations 4 to 8 and reddish at station 9. Organic carbon and sediment texture showed a direct relationship at all stations except at station 9 where organic carbon content showed an irregular pattern. Overall range of organic carbon content was between 1.19 and 29.6 mg.g super(-1). The mean organic carbon of the stations ranged between 6.8 mg.g super(-1) (station 5) and 20.8 mg.g super(-1) (station 9). On the whole temporal variations were considerable with high values at station 9 and low values at station 5. Fluctuations were more at stations 6, 7 and 8.

Respiratory metabolism in Oreochromis mossambicus, Peters under different environmental conditions

Oxygen consumption in Oreochromis mossambicus, Peters (3-60g in weight) was measured under different stress conditions at a constant temperature of 20±1°C. The rate of oxygen consumption was significantly higher (0.170 ml gˉ¹hˉ¹)at a salinity of 30x10ˉ³ compared with that (0.132ml gˉ¹hˉ¹) in freshwater. The oxygen consumption was also found to be affected by changes in pH. Weight specific rate decreased significantly from 0.113 to 0.045 ml gˉ¹hˉ¹ with increasing body weight. A positive correlation was recorded between availability of dissolved oxygen and the rate of oxygen consumption by the fish. While copper sulphate and malachite green inhibited the respiratory metabolism, formaldehyde treatment raised it from 0.088 to 0.118ml gˉ¹hˉ¹.

Factors influencing colour production from the sugar medium used for the rapid approximation of bacterial counts in fishery products

Results of the studies carried out to elucidate the factors influencing colour production from the sugar medium used for the rapid approximation of bacterial counts in fishery products are reported. The effect of particle size, trace elements, salt soluble protein and non-protein fractions, rate of multiplication of bacteria, in the medium, surface bacteria and the rate of colour production by individual strains of bacteria were studied. It is observed that the best results are obtained when a sea-water homogenate is used.

Occurrence of a deeper red colour in prawn pulp prepared from iced-prawns

In commerce, great importance is given to the color of the dry prawn pulp in its quality evaluation. The possible correlation between this color factor to the iced or not iced condition of the raw prawn used, is investigated. The study reveals that as the icing period of the raw material increases the color of the finished product proportionately intensifies to a bright red compared to light brownish yellow or orange color of the product from the not iced prawn, and at the same time the other characteristics like flavor and taste deteriorates as the time of icing advances. This finding tends to show that the color factor does not reflect the true quality of prawn pulp. Based on chemical data it is suggested that "browning" due to Maillard reaction may have an important role in this color phenomena.

Environmental parameters and incidence of white spot disease in Penaeus monodon (Fab.) farming

An investigation was carried out to monitor management practices and to find out whether there is any relationship with occurrence of deadly white spot disease and environmental parameters. Three semi-intensive and a improved traditional shrimp farms were selected in which mass mortality of shrimp (Penaeus monodon) by white spot disease occurred previously. The farms were situated at two different geographical locations. Two ponds from each farm at random were selected for the study. Out of eight investigated ponds, 6 ponds in three farms were affected by the disease during investigation period. The non-affected ponds had relatively lower stocking density, lightly different management practice and were located at different geographical area. There was no significant variation in water quality parameters among the affected and non-affected ponds. No significant variations were recorded in pond preparation, source of Post Larvae (PL), water and feed management among the affected and non-affected ponds. The observation indicated that pond micro-organisms in a farm may not the only cause of the disease but some external factors also might be responsible for the outbreak of this disease.

Optimization of stocking density for environmental-friendly improved extensive shrimp farming system in south-west part of Bangladesh

An experimental culture practice of P. monodon on extension approach was conducted in two brackish water earthen ponds of Demonstration Farm and Training Center (DFTC), Kaliganj, Satkhira. The experiment was aimed to provide farmers with appropriate technology that can immediately improve pond yield with keeping the environment in friendly condition. For optimization of stocking density of a cost effective environmental friendly improved extensive shrimp farming, the ponds were stocked with coastal river post larvae of P. monodon at the stocking rates of 2 pls/m² and 2.5 pls/m² without supplementary feeding. To control experimental error another five farmer's gher were used as replicates of each demo-pond. Considering the farmers buying ability, cost of inputs and other facilities kept minimal. The impact of stocking density was evaluated on the basis of growth, survival rate, production and economic return. Better production (average 299.01 kg/ha) with same survival rate (39.33%) were found with a stocking density of 2.5 pls/m² without causing any deterioration in the culture environment.

Effect of some environmental factors on the acute toxicity of deltamethrin to common carp: a laboratory study under aerobic condition

The toxicity of xenobiotic in aquatic ecosystems is influenced by many factors such as ambient temperature, water hardness, pond soil type, etc. In the present study, it was observed that air temperature, water hardness and soil sediment have profound influence on the toxicity of deltamethrin to common carp fry (ay. length 3.5 ± 0.5 cm, ay. weight 0.58 ± 0.25 g); 96h LC(sub)50 values for common carp at 38.07 ± 2.20°C maximum and 27.86 ± 1.22°C minimum air temperature in soft and very hard water were 0.102 and 0.495 µg lˉ¹, respectively. This value had increased significantly to 2.37 and 3.02 µg at 30.55 ± 1.21°C maximum and 26.04 ± 0.61°C minimum air temperature, respectively. When sediment was included, 96h LC(sub)50 at 38.07°C maximum temperature in very hard water was 1.808 µg 1ˉ¹ and this had increased to 8.073 µg 1ˉ¹ when tested at 30.55°C maximum temperature. Due to the 7.5°C increase in maximum and 1.7°C in minimum temperature, toxicity increased significantly. Lower toxicity in very hard water in comparison to soft water may be due to the lower solubility of deltarnethrin and high level of calcium. Adsorption reaction of deltamethrin with clay, humus, FeOOH, MnOOH and particulate organic carbon, and complexation reaction with dissolved organic carbon were responsible for the lowered toxicity in the experiment with sediment. Exposure time had no significant effect on acute toxicity of deltamethrin.