Effects Of Environmental Factors And Food On The Energy Budget And Larval Development Of Meretrix Meretrix

1. Effects of temperatures and salinities on the energy budget of clam Meretrix meretrix were studied in laboratory from Oct. 2003 to Jan. 2004. From 10 to 25℃, filtration, respiration and excretion rate all increased with increasing temperature. Accordingly, the ingested energy, respiration energy and excretion energy increased with the increasing temperature. One-way ANOVA analysis indicated the physiological parameters yielded highly significant difference at this temperature range (P<0.01), but no difference was found between 15 and 20℃. The highest Q₁₀ value was acquired between 10 and 15℃ (12.27), and Q₁₀ value was about 1.0 between 15 and 20℃, indicating M. meretrix could well acclimate to temperature changes at this range. Salinities also had significant effects on filtration, respiration and excretion rate (P<0.05). The highest values were acquired at the condition of 16.0 salinity (20℃), after that the physiological parameters decreased with increasing salinity until reached the minimum value at 31.5 (20℃), then they increased with increasing salinity from 31.5 to 41.0. M. meretrix might catabolize body protein to cope with osmotic pressure stress when environmental salinity is away from its optimal range. There was no significant difference observed over 26.0-36.0 range (P>0.05), suggested that an adequate metabolic salinity range for this species might lie between 26.0 and 36.0. The ingested energy acquired maximum value at salinity 26.0, while respiration energy and excretion energy had minimum value at salinity 26.0, indicating that M. meretrix can make fast growth under this salinity.　　2. The effects of body size, different kinds and concentration of algal diets on the energy budget of M. meretrix were studied from April 2004 to May 2004. Three kinds of diets (Isochrysis galbana, Phaeodactylum tricornutum and Platymonas subcordiformis) were used. The results showed that the filtration rate decreased with the increasing food concentration, while the respiration and excretion rate do the reverse. The ingestion rate was not affected by the change of food concentration, indicating that M. meretrix could modulate the energy ingested by controlling the filtration. The respiration and excretion rate of M. meretrix fed P. subcordiformis were higher than those of fed I. galbana　and　P. tricornutum, indicating that M. meretrix had to consume more energy to ingest and digest P. subcordiformis. The body size had significant effects on the filtration, respiration and excretion rate. With the increasing body size, the filtration, respiration and excretion rate per dry tissue weight decreased, suggesting that small clams could ingest more energy to support growth. The assimilation efficiency decreased with the increased food concentration and was independent of the body size. M. meretrix fed I. galbana　andP　. tricornutum had higher assimilation efficiency than fed P. subcordiformis, showing that food quality had effects on the assimilation efficiency. The maximum values of SFG were acquired at 2.75-3.75 mg POM/L fed P. tricornutum, at 3.05 mg POM/L fed I. galbana and at 4.55 mg POM/L fed P .subcordiformis. The SFG value decreased with the increasing body size. So in aquaculture industry the clam with larger body size must be taken out in time to enhance the resource utilizing efficiency. 3. Effects of food availability on the larval survival and development of M. meretrix were studied by feeding the larvae with different algae diets at Jun. 2004. The larvae of M. meretrix just hatched from zygotes were fed five different marine microalgae species singly and in various mixtures. Greatest growth was with Isochrysis galbana as a single species diet. Nutritional value of the other single species diets was in the order Dunaliella sp.> Phaeodactylum tricornutum > Platymonas subcordiformis > Pavlova viridis. Of the mixtures tested , 50% I. galbana /50% Dunaliella sp. (v/v), 50% I. galbana /50% P. tricornutum, 50% I. galbana /50% P. subcordiformis, supported growth and metamorphosis rate equivalent to the...