| Pacific abalone, Haliotis discus hannai, has become the predominantly farmed abalone species in Fujian, southern China since 2006. As an introduced abalone species from northern China, mass mortality of the farmed Pacific abalones often occurred during summer days in Fujian in recent years. In order to better understand the phenomenon of summer mortality in the farmed Pacific abalones in southern China, we would make the thorough investigation about this phenomenon and elucidate preliminarily the molecular mechanism of resistance to heat stress in Pacific abalone.In this study, we aimed to provide data in terms of summer mortality occurrence and management in this abalone species reared in sea-based farming system of southern China. For the first time, we conducted a field investigation to monitor biological condition of the two-year-old animals including the monthly survivals and visual gonad index in Sansha Bay, Fujian, a major Pacific abalone farming site from April to October 2014. We also measured the monthly variation in metabolic parameters and antioxidative capacities in the same experimental animals. A range of environmental parameters were assessed and correlated with biological indicators for abalone condition, metabolic parameters and antioxidative capacities. Results showed that a total of 58.58% mortality rate finally occurred after summer days in the sea-based farmed abalones according to the filed investigation. Visual gonad index assessment showed that the sampled animals had similar gonad ripeness levels during each sampling date. Environmental parameters and the abalone mortalities monitored in the study showed significant positive correlation between seawater temperature and the mortality of abalones. The metabolic parameters include protein, glycogen, nonesterified fatty acid(NEFA) content, and the enzyme activities of lactate dehydrogenase(LDH) and glutamic pyruvic transaminase(GPT) were analyzed. Analysis showed all the metabolic parameters, except enzyme activity of GPT, had significant variations during the sampling times. Despite the different levels of variation in each parameter in varying tissues, all energy resources showed a decrease tendency after summer. The analysis of antioxidative capacities included superoxide dismutase(SOD) and total antioxidative capacity(T-AOC). Results showed that both of these two parameters increased in the first few months and then decreased in September and October subsequently. The variations of the metabolic parameters and antioxidative capacities detected indicated that the insufficient energy supply and the peroxidative damage happened in the farmed animals during summer days. These findings might guide further molecular genetics-based studies that focus on the above-mentioned two aspects to elucidate the physiological processes underlying summer mortality in Pacific abalone and are applicable to the management and development of Pacific abalone aquaculture in sea-based farms of southern China.Determination of the survival ability in abalones under heat stress is an important part in this study. We can get the survival indicator of Pacific abalones by measuring the heart rate of abalones. Heart rate were measured using the non-invasive method then get the Arrhenius break temperatures as the biomarker that determine the heat resistance of abalones with higher accuracy and faster way. Heart rate of abalones would rise as temperature increases then drop abruptly. The temperature that induce the cardiac failure in abalone is the Arrhenius break temperature(ABT). In this study, we measured the heart rate in 17 resistant abalones and 17 contrast abalones that from two different groups. The result illustrated that the ABT of resistant abalones seemed higher(P<0.05) than that of contrast abalones. Significant(P<0.05) positive correlation was found between shell height of abalone and ABT. In the first time, we determine the heat resistance of Pacific abalones by measuring the heart rate and its feasibility was verified.Based on resistant and susceptive families as experimental materials, we applied transcriptome profiling analysis to investigate the molecular mechanism of resistance to heat shock stress in Pacific abalone respectively. There were 96,803 unigenes produced in total with high integrity. And the result of annotation showed that 26,006 unigenes were annotated in Nr, Swiss-Prot, KEGG, COG, GO, Pfam database. We screened differentially expressed genes(DEGs) between different treatment groups. We founded 7,912 DEGs between before and after heat stress groups; 4,933 DEGs between susceptibility group and resistance group; 6,463 DEGs between one-year-old and twoyear-old abalones groups. Different treatment include different resistances to heat stress, before and after heat stress and different ages would result in genes expressed differentially. These finding could be helpful in future selection of Pacific abalone with enhanced resistance to heat stress. |
