| The Babylonia areolata larvae were observed in such conditions as 15, 150, 1500, 11700 lx with sunlight as illumination source. As a result, an'S'function existed between percents of larvae sank and light intensity (R2=0.9783). Twice experiments about the effect of light intensity on ingestion rates (IR) of Dicrateria zhanjiangensis by B. areolata larvae with fluorescent lamps as illumination source showed that ingestion rates increased with increasing light intensity from 0 to 10000 lx (P<0.05). But ingestion rates were unstable when light intensity was over 2000 lx. In order to investigate the ingestion diel rhythms, ingestion rates were determined at four phases: around dawn, noon, dusk and midnigh. Ingestion diel rhythms were similar in light conditions such as 186 lx in the first experiment to those in the conditions of weak light, constant dark and 12 hours 1000 lx during the day & 12 hours dark at night (positive photoperiod) in the second experiment. In these conditions, ingestion rates were the highest around dawn and the lowest around dusk in the whole day. However, it was the highest around midnight and the lowest around noon in the light condition of 12 hours 1000 lx at night & 12 hours dark during the day. Differences among ingestion rates at four phases in condition of constant 1000 lx were insignificant. Ingestion rates were influenced markedly by interaction between light intensity and diel rhythm (P <0.05).103,104 and 105 cells/ml three abundance of Dicrateria zhanjiangensis with equivalent volume of fluid mixture containing the same proportion of Dicrateria zhanjiangensis, Platymonas helgolandica var. tsingtaoensi and Gyrodimium instriatum. Respectively three mixed liquid fed to the larvae, of which the shell diameter is 725±61.24 m. We measured the algae concentration before and after the test to calculate the larvae's selective feeding. The results showed that larvae feeding selectivity strengthened with the abundance of food increased. Two mixed algae liquid by cell concentration and the number of such particulate organic carbon content mixed Dicrateria zhanjiangensis, Dunaliella salina, Platymonas helgolandica var. tsingtaoensis and Gyrodimium instriatum four different sizes of single-cell algae. The two kinds of mixed liquid fed to 610.83±50.29μm to 858.33±90.10μm ranging from the size of five species of Babylonia aerolata larvae. By cell volume mixed Dicrateria zhanjiangensis, Dunaliella salina, Platymonas helgolandica var. tsingtaoensis, polystyrene resin particles and Gyrodimium instriatum of the mixture fed to large (1015.29±77.25μm) and small (575.12±45.71μm) larvae. Comparison of selective feeding ratios of various component in the mixture of different particles by different sizes larvae, The results showed that larvae preferd to choose the algae liquid with absolute advantage in volume ratio in the particulate component ; When the mixture composition and volume approaching, the larvae preference suitable particle size; the most suitable size of food particles was different in larvae of different sizes, bigger larvae feed the optimum size bigger and broader.654.58μm larvae were fed nutrient concentrations up to standard f/2 nutrient concentrations of 0, 0.001, 0.01, 0.1, 1 and 10 times the particles of polystyrene (10μm, the same concentration). Ingestion rate by larvae in the experimental group not add f/2 nutrients was the highest in all groups. 0.001, 0.01, 0.1, 1 time f/2 nutrient concentrations of four experimental form no significant difference. But ingestion rates by the four larval were significantly lower than the control group which had no nutrients, significantly higher than the 10 times f/2 nutrient concentrations in the experimental group (α=0.95). The ingestion rate of the 69-day training of Dicrateria zhanjiangensis by larvae was significantly higher than 18 days and 36 days Dicrateria zhanjiangensis (P<0.05). It is confirmed that the Dicrateria zhanjiangensis extracellular metabolites accelerated larvae feeding. Further studies show that centrifugal filtered liquid of the Dicrateria zhanjiangensis and Chlorella sp. would accelerate ingestion rate and that of Platymonas helgolandica var. tsingtaoensis and Gyrodimium instriatum is inhibitor, and Dunaliella salina and Platymonas subcordiformis centrifugal filter were no significant impact on lavae feeding.Specific activities of protease, lipase, amylase and cellulase were measured respectively in 6 different stages from early veliger to juvenile 15 days after metamorphosis of Babylonia areolata Link. Activity of protease measured was found to decrease gradually over time, while activity of lipase was detected to increase step by step with larval development. However, activity of amylase and cellulase measured increased slowly before 12 days after hatching, then increased rapidly at competent larvae and finally decreased sharply after metamorphosis. Comparison was made of two indexes used as indicator of feeding habit: ratio of amylase activity to protease activity (A/P) and ratio of the sum of amylase and cellulase to the sum of protease and lipase ((A+C)/(P+L)). It was concluded that the latter index is more suitable than the former. Digestion pattern was revealed with summations of 4 species of digestive enzymes activities in the same stage. Digestion in juvenile 3 days after metamorphosis is the weakest among 6 stages after comparing summations in different stages. Weak digestion may be one of the most important reasons that influence the survival rate in metamorphosis. The results of specific cellulase activity in the 6 stages indicate that mollusks are able to secrete cellulase themselves. Endogenous cellulase plays a vital role in digestion of cellulose for Babylonia areolata. |
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