Study On Larva Development, Juvenile Breeding And Growth Characteristics Of Rhopilema Esculenta

Rhopilema esculenta belong to Coelentera, scyphozoa, rhizostomeae and rhizostomatidae, and mainly feed on zooplankton. They go through several metamorphosis during its life span, which consist of an alternation between a sexual stage and an asexual stage. Scyphistoma are the important phase in the asexual life, fertilized eggs produce Planulae larvae and then develop scyphistoma, which also reproduce asexually by podocyst budding. Strobilation is a special asexual reproduction among the most scyphozoa animals, the new released ephyra could grow to juvenile jellyfish with clubbed subsidiary organ after 15 day's culture. The factors which influence ephyra include temperature, salinity, light, nutrition, PH, DO and so on. From cultivating scyphistoma in winter in October 2009 to harvesting Rhopilema esculenta in autumn in September 2010, the two mechanisms of four tentacles scyphistoma, morphological characteristics of Rhopilema esculenta from ephyra to juvenile jellyfish, the effects of temperature, salinity and density on the average daily growth rate of juvenile jellyfish, and the growth characteristics of Rhopilema esculenta breeding in the pond were studied. Also the problems appeared in the process of breeding were discussed in Jinghai bay, Rong cheng, Shandong province.The results were as follows:1 Observation on Two Generation Modes of Four Tentacles Scyphistoma of JellyfishBy continuous observation of embryonic development and podocyst propagation?of? jellyfish,? Rhopilema esculenta,? two generation modes of scyphistoma were discovered. First, fertilized egg turned to scyphostima. This process needed about 6 h from fertilized egg to planulae, and then nearly 25 h from planulae, scyphostoma to stationary scyphistoma with four tentacles at the temperature of 26±1℃; Second, podocyst generated to scyphostima. The ratio of generation was higher with podocyst closed to scyphistoma. In this stage, podocyst first turned into scyphostoma, and then became scyphistoma with four tentacles. In this study, a new structure called scyphostoma was both found in the two scyphistoma generation modes. This discover improved the life cycle of jellyfish.2 Observation on morphological characteristic of Rhopilema esculentaThe morphological characteristics of Rhopilema esculenta from ephyra to juvenile jellyfish were depicted, and the healing process of residual access mouth of gastrovascular cavity was observed for the first time, by which the development phases of jellyfish were redefined. When residual access mouth of gastrovascular cavity was not closed, there is a circular hole in the top, the phase was defined ephyra; when the residual access mouth of gastrovascular cavity was closed, a straticulate membrane was formed, the phase was defined jellyfish larva; when the umbrella edge became hemispheric, the oral healed, and the edge of the oral grew clubbed subsidiary organ, the phase was defined young jellyfish.3 Study on feeding and growth characteristics (diameter and weight)At the temperature of 20±1℃, salinity 28～29 and PH 7.8～8.2, ephyra(2³mm)could grow to juvenile jellyfish (15²0mm) with clubbed subsidiary organ after 20 day's culture. The food consumption and growth characteristics (diameter and weight) from newly liberated ephyra to juvenile jellyfish were analysed. It was found that the daily growth equation of juvenile jellyfish's diameter(2～20mm)is y=2.7488e0.1018x, the relationship between weight and diameter, food consumption and diameter of juvenile jellyfish were y=6×10-5-0.5x^3.5475, y= 43.537x^1.775 respectively.4 Study on optimal temperature,salinity and density in larva breeding of Rhopilema esculentaFrom June5th to July 6th, 2010, the effects of temperature, salinity and density on the average daily growth rate of juvenile jellyfish were studied, and compared with the juveniles cultured in pond. The results showed: (1) the average daily growth rate of juvenile jellyfish varied with water temperature, it increased with the rise of temperature when temperature was below 24℃, and decreased with the rise of temperature when temperature was above 24℃. The optimal temperature for juvenile jellyfish was 24℃, and the average daily growth rate came to 8.41%. (2) The average daily growth rate increased when salinity was below 20, and decreased when salinity was above 20; the average daily growth rate came to maximum when salinity was 20, it came to 9.01%. (3) The average daily growth rate decreased with the rise of density when the temperature was 16～18℃, salinity was 28 .The study showed the optimal environment for juvenile jellyfish was temperature 21～24℃, salinity 16～20, density 4000～8000individuals ?L.5 Study on the growth characteristics of Rhopilema esculenta breeding in the pondFrom early June to August, 2010, the growth characteristics of Rhopilema esculenta breeding in the pond were studied in Rong cheng, Shandong province, and the problems appeared in the process of breeding were discussed. The experiment showed that the juveniles grew fast from June 1st to August 1st and its diameter could grow from 2cm to 30⁴0cm, even up to 50cm. The weight (wet weight) of different Rhopilema esculenta increased exponentially with the diameter, the equation was y=0.176x2.8914(R2=0.9907).Some problems such as shortage of baits, large propagation of Noctiluca scintillans and the breakout of Aurelia aurita emerged in the later period of breeding, which influenced the growth of Rhopilema esculenta.