Seasonal changes in the biochemical composition of wedge clam, Donax scortum from the Padukere beach, Karnataka

Seasonal variations in protein, lipid and carbohydrate along with dry tissue weight and water in Donax scortum were studied for a period of 12 months (from February 2009 to January 2010). Water content remained at high level during monsoon and post monsoon periods. Dry tissue weight parentage exhibited an inverse relationship with water content in all months in the present study. Protein content was high relatively in all months except low during the breeding months. Glycogen content during the maturation period declined showing the utilization active gamete production. Fat content increased during the period of active formation of gametes. Afterwards, it decreased during the spawning period. Ash content in our present study shows similar seasonal pattern in percentages of lipids and proteins. However, changes in carbohydrate percentage show a completely different resulting in an inverse relationship between carbohydrate and protein. Calorific values of D. scortum are well within the known limits reported in the literatures for other bivalves.&nbsp

Status of heavy metals in tissues of wedge clam, Donax faba (Bivalvia: Donacidae) collected from the Panambur beach near industrial areas

The wedge clam, Donax faba are edible bivalves and consumed as seafood. We found out the concentrations of Cu, Pb, Fe, Cr and Ni in the tissues of the wedge clams in coastal site, Panambur located along the south west coast of Karnataka. The concentrations of heavy metals in the samples were determined by atomic absorption spectrophotometer (AAS, GBC 932plus) working with an air acetylene flame. D. faba showed seasonal variations of metals accumulation with maximum concentrations during all seasons occurred in our study. The analysis of Fe content showed higher average concentrations for wedge clam collected from the study site. The concentration was in the order of Fe>Cu>Cr>Ni>Pb in our present study. The levels of heavy metals like Cu, Pb and Cr in the whole tissue of D. faba were below permissible limits except Ni. High concentrations of metals in the whole tissue of wedge clams collected may be derived from the industrial areas and a variety of anthropogenic activities

Factors influencing shell size and shape in Donax incarnatus (Gmelin) inhabiting Panambur sandy beach, Mangalore, India

475-483The samples of wedge clam Donax incarnatus (Gmelin), sediment and seawater were collected for a period of 12 months from Panambur sandy beach, near Mangalore. A total of 2258 individuals of D. incarnatus were subjected to analysis. The air (27.5-31.2 oC), sand (28.5-36 oC) and seawater (25-32.2 oC) temperatures showed seasonal fluctuations. The dissolved oxygen (3.29-4.55 ml L-1) and salinity (30.24-34.84 x 10-3) of seawaters showed variations. Fine sand dominated (75.09 to 94.2%) throughout the period of study, followed by medium sand (1.51 to 20.65%). The density (89 to 39446 no. m-2) and biomass (124 to 1892 g. m-2) of wedge clams showed marked variations during breeding season. Principal component analysis of biological variables and environmental parameters showed six components which together accounted for 90.39% of total variance. The component 1 (dissolved oxygen, density, biomass, wet weight, dry) accounted for 24.02% of total variance followed by component 2 (air, water and sediment temperatures, salinity and b values of length-breadth and length-dry weight relationships) for 20.64% of total variance and component 3 (mean shell length, mean shell breadth, mean shell width) for 17.27% of total variance. The rest of the variance of 28.46% was accounted for component 4 (medium sand, fine sand, very fine sand), component 5 (coarse sand, b value of length-wet weight relationship, b value of length-width relationship) and component 6 (silt & clay). The hierarchical cluster analysis produced a dendrogram with six sub-groups of clusters. The temporal variability of six factor scores was delineated using factor analysis