| The veined rapa whelk Rapana venosa (Valenciennes,1846) is an important andvaluable fishery resource in China. This species has however been overexploited andits habitat degraded, which has resulted in a major population decline. In the presentstudy, these three color morphs of Rapana venosa was compared based onmorphological traits and partial sequences of the mitochondrial DNA16S rRNA andcytochrome oxidase I (COI) genes. We analyzed predation preference and feedingdisciplinarian under different temperature and specification. We conducted laboratorystudies on growth and survival rates of larvae and also assessed the effects oftemperature and salinity on hatching times. We studied the effects of environmentfactors, temperature, salinity, dietary microalgae and rearing density, on growth andsurvival of larvae to investigate the optimal artificial culture conditions. This study onRapana venosa will reveal the optimal conditions giving the highest growth andsurvival rates in artificial rearing system of Rapana venosa, contribute to furtherunderstanding of conservation in natural populations, provide further insights into thepotential range of invasions, as well as the potential ecological impacts of the invasionof Rapana venosa to recipient ecosystems. The mean results are as follows:In Rapana venosa, there are three color morphs of aperture: black and whitestiped, orange, and intermediate type. The results of morphological analysis showedthat morphological traits were all significantly different in three color morphs.Correlation coefficient between each phenotypic traits and whole mass were allsignificantly different. Aperture length and aperture width had effects on whole massfor “black and white stiped”, while for “intermediate type” and “orange” there wereno key factor that affecting whole mass. Using Stepwise method establish Multiple linear regression equation. Tree diagram constructed with morphological traits of thethree color morphs demonstrated that “intermediate type” and “orange” were moreclosely related to each other than they are to “black and white striped”. Results ofphylogenetic analysis based on partial mtDNA16S rRNA and COI gene fragmentsindicated that there was no genetic divergence among the three color morphs.Predation of Rapana venosa was species selective, and a clear preference forSinonovacula constricta. There were no Stichopus japonicus and Haliotis discushannai Ino be preyed. The average wet weight consumption rate didn’t depend on thekind of diets. The feeding amount was changed with the temperature and shell length.Predation of Rapana venosa started when temperature reached8°C, massive increasedwhen temperature higher than16°C, and reached peak when temperature around22°C.Rapana venosa whose shell length range from50to70mm had the most feedingamount and lowest predation temperature than others, whereas Rapana venosa whoseshell length longer than90mm had the lest feeding amount and highest predationtemperature. Moreover, wet weight growth rate of Rapana venosa was increased withthe decrease of shell length.We studied the effects of hatching temperature (16-34°C with the salinity of30g L-1) and salinity (5-45g L-1at25°C) respectively on hatching time and larvaldevelopment. After hatched all the larvae were acclimated at25°C at30g L-1. Eachtreatment contained three replicates in which stocking density of larvae was200veligers L-1. In the temperature experiment, the shortest hatching time was12days at34°C, the lower temperature limit was16°C, the longest mean shell length(1193.08±17.46μm) occurred at25°C and the highest survival rate (72.28±5.62%)was observed at28°C. In the salinity experiment, the shortest hatching time was15days at25g L-1. The salinities tolerance range was15–40g L-1, the longest mean shelllength (854.81±9.46μm) and the highest survival rate (72.93±4.85%) was bothobserved at35gL-1. This study showed that during the egg–mass stage temperatureand salinity regimes influenced the later growth and survival of larvae. The development of larval was effected by environmental conditions. Theoptimal temperature was25-31°C at30ppt. The optimal salinity was20-25ppt at25°C. The optimal food was mixed diet, Pseudoisochrysis paradoxa+Tetraselmischui+Chlorella vulgaris (1:1:1). Tetraselmis chui and Chlorella vulgaris couldimprove shell length and survival rate respectively. Whereas larval will had goodperformance only when fed the mixed diets of Chlorella vulgaris or Tetraselmis chuiwith Pseudoisochrysis paradoxa. Shell length of larval decreased as increase ofstocking density, and interaction between survival rate and stocking density wasintricate and unknown. The optimal stocking density was300veligers per liter at thefirst5days and was100veligers per liter afterward at25°C at30ppt. |
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