The marine diatom Chaetoceros calcitrans f. pumilus has been examined for its potential source as live feed in aquaculture. The present study investigated e¡ects of temperature (20, 25 and 30 1C), salinity (25 and 35) and carbon dioxide addition (air1CO 2 ) on the growth and proximate composition of C. calcitrans under laboratory conditions. The growth and biomass of C. calcitrans were primarily a¡ected by carbon dioxide addition, and to a lesser extent by temperature and salinity. In general, lipid and carbohydrate contents were higher at lower temperatures (20 and 25 1C), while the protein content was unaffected. Carbon dioxide addition increased protein, while lowering carbohydrates, but had no e¡ect on lipid content. Carbohydrates were increased while lipids and protein decreased at the highest salinity (35 AE 0.9). These results should be taken into consideration when evaluating the dietary value of this micro alga for aquaculture.

R e t r a c t e dEffects of diet, stocking density and environmental factors on growth, survival and metamorphosis of clam, Abstract A series of experiments were conducted to evaluate the e¡ects of diet, stocking density and environmental factors on the growth, survival and metamorphosis of short neck clam Paphia malabarica larvae. These experiments examined the following factors: diet [Isochrysis galbana, Nannochloropsis salina and a mixture of I. galbana and N. salina (1:1 w/w)], stocking density (1, 3, 5 and 7 larvae mL À1 ), light intensity (unshaded, partially shaded and fully shaded) and water ¢ltration (un¢ltered and sand ¢ltered). Results indicated that N. salina could replace 50% of I. galbana as a food source for the clam larvae with an increase in growth, survival (47.2%), metamorphosis (33.5%) and early settlement. Larval growth decreased signi¢cantly with increasing stocking density. A density of 1^3 larvae mL À1 appeared to be optimal for normal growth of clam larvae. Neither diet nor stocking density used in the study had a signi¢cant e¡ect on larval survival. Under partially shaded (light intensity 51000^5000 lx) and fully shaded (light intensity o1000 lx) conditions, larval growth was signi¢cantly faster than under direct sunlight (unshaded). Larvae grew signi¢cantly faster in the un¢ltered water than in the ¢ltered water.

The e¡ects of food availability on the larval growth and survival of Paphia malabarica were studied in two experiments by feeding the larvae with six algal diets. Newly hatched larvae of P. malabarica were fed with six di¡erent marine microalgae species, singly and in a combination of two species. The best growth was with Isochrysis galbana and Nannochloropsis salina as a single species of diet. The nutritional value of single-species diets was in the order of N. salina, I. galbana, Dicrateria inornata, Chaetoceros calcitrans,Tetraselmis gracilis and Dunaliella salina. Of the mixtures tested, 50% I. galbana/50% N. salina supported growth and metamorphosis equivalent to those of the I. galbana control.

Venerid clam, Paphia malabaricaChemnitz, is the commercially exploited species distributed exclusively in Vembanad Lake and Ashtamudi estuary, along the south west coast of India. In this study, the survival rate and development of P. malabarica larvae were studied for 3 days in ambient salinity (33), copper (2.5 μg Cu 2+ l −1 ), reduced salinities (25 and 20) and a combination of copper in low salinities. No significant differences were found in larval development between treatments. The survival rates decreased considerably with low salinities although the combination of copper and low salinity gave synergistic effects. The reduced survival in low salinities would limit population growth of this species in estuarine areas experiencing low salinities and also explains the absence of larval settlement on habitats close to harbors or river mouths.