| Pacific abalone(Haliotis discus hannai Ino) is naturally distributed along the Pacific Northwest and inhabits off the shore of Dalian, Yantai, Weihai, Qingdao, Rizhao City in neritic region of China. From 1980’s China initiated artificial breeding and cultivation of H. discus hannai which was conventionally carried out in Dalian, Yantai, and Weihai City. At the beginning of 1990’s, H. discus hannai was transferred southward to the south sea area of Yangtze River to feed and the East China Sea became a major area for H. discus hannai to overwinter and culture. Rainfall is concentrated and large in South China, so H. discus hannai is more susceptible to low salinity sea water there than in traditional mariculture area. By far, the researches on the response of H. discus hannai are limited to one single environmental factor, and the combined effects of temperature and salinity on H. discus hannai have not been reported. This thesis was aimed to explore the response of H. discus hannai exposed to low salinities at different temperatures and osmoregulatory mechanism of juvenile abalones acclimated to low salinity, including analysis of juvenile abalones’tolerance to low salinity at different temperatures; the influence of temperature and salinity on abalone’s growth; influence of low salinity on biochemical composotions of juvenile abalones.The main results were summarized below:1 salinity-mortality curve of juvenile abalones at different temperaturesJuvenile abalones were studied using a two factorial experiment design with nine levels of temperature (6,10,14,18,22,24,26,28,30℃) and seven levels of salinity(16,18,20,22,24,26,30‰).Three replicate containers were used per treatment, with 30 juvenile abalones in each container. The survivals of 30%o control groups at 10-26℃ after 90 days’cultivation were above 96.7%, so we disscused the the mortality of juvenile abalones at different salinities between 10-26℃:the survival rates of salinity 24-30,10-26℃ groups were above 94%; mortalities at 22%o and 14, 22,26℃ increased significantly at 75th,60th and 60th day and reached 7.8%,8.9% and 26.7% respectively after 90 days’treatment; mortalities at 20%o and 14,18,22,26℃ increased significantly at 45th,60th,60th,60th day and reached 18.9%,21.1%,24.4%, 34.8% respectively after 90 days’treatment; mortalities at 18‰ and 10,14,18,22, 26℃ increased significantly at 75th,45th,45th,30th and 30th day respectively and and reached 18.9%,41.1%,65.6%,65.6%,64.4% after 90 days’ treatment. Mortalities of the groups exposed to 16‰ at 10-24℃ were above 92% after 60 days’ treatment. According to the results above, we can concluded that salinities between 24 to 30‰ were suitable for the survival of juvenile abalones,22‰ and 10 to 22℃ were also suitable for abalones to survive but not at 22‰ and 26℃; salinities between 18 to 20‰ were not suitable for the survival of juvenile abalones; 16‰ was the tolerance limit of juvenile abalones in low salinities, at which almost all the abalones could not survive.2 influence of adaption on juvenile abalones’ tolerance to low salinityAdaptive regimes were composed of five temperature levels (10,14,18,22, 24℃) and three salinity levels (22 and 20‰ as adaptive groups; sea water as unadaptive groups). After 90 days’adaption, all the groups were exposed to 16‰ and the result showed that adaptive groups at 10,14 and 18℃ significantly postponed the death of juvenile abalones exposed 16‰, but the groups at 22,24℃ could not.3 the growth of juvenile abalones in different temperature and salinityExperiment was designed with eight levels of temperature (6,10,14,18,22,24, 26,28℃) and three levels of salinities (30,26,24‰),90 individuals (3x30) were used in each treatment. The length of shells were controlled in the range of 22.1 to 24.9 mm. Shell length, shell width and total wet weight were measured after 63 days’ treatment. Survivals of the groups in 10-26℃ were above 96%.18 to 24℃ were the most suitable temperature range for juvenile abalones’growth, within which appropriately lowering salinity promoted abalone’s growth.4 Influence of low salinity on biochemical compositions of juvenile abalonesThe juvenile abalones pre-cultured at sea water,26℃ and salinity 24,26℃ were stressed with low salinity, and water content of muscle tissue, soluble total protein, hemocyanin, taurine, free amino acid, and inorganic ions in supernatant hemolymph were measured. The result showed that water content in muscle tissue, hemocyanin, free amino acid and taurine increased when salinity decreased. Na+,Cl-、Ca2+ concentration declined significantly with the decreasing of sea water and stabilized within 24h,while K+ concentration did not varied significantly.Preliminary result suggested that hemocyanin, taurine, free amino acid functioned in osmoregulation of juvenile abalones in low salinity; juvenile abalones were actively capable of K+ regulation but not of Na+,Ca2+ or Cl-. |
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