Effects Of Carbonate Alkalinity Stresses On The Growth And Reproduction Of Exopalaemon Carinicauda

Saline-alkaline water is relatively prevalent throughout China, there are about 99.07 million hm2 saline-alkaline land and more than 30.67 million hm2 saline-alkaline waters. And because of the complex ion composition and the high alkalinity and pH value, only a few saline-alkaline water areas have carried out the cultivation of freshwater fish. Most of them are still fallen into a state of neglect. So it is of great significance to strengthen the development and utilization of saline alkali soil and water resources. Retinoid X receptor is a member of the nuclear receptor superfamily. It is an important regulatory factor, which plays an important role in the growth, development and reproduction. The experiments were carried out to explore the effects of water carbonate alkalinity on the growth, reproduction, EcRXR gene expressions and immune enzyme activities of E. carinicauda.This study provided a scientific basis for the cultivation and development of E. carinicauda in saline and alkaline waters.The study consists of three parts:In recent years, Exopalaemon carinicauda has been rapidly expanded, and has become one of the most extensive and important farming shrimps. And because of its strong adaptive ability to the environment, especially the ammonia nitrogen and pH stresses, E. carinicauda can be the ideal targeted shrimp in the saline-alkaline water aquaculture. Thus, the experiments were carried out to explore the effects of water carbonate alkalinity on the survival, growth, reproduction of E. carinicauda. The LC50 of the E. carinicauda was determined by the experiment of acute stress. According to LC50, carbonate alkalinity gradient was set to 3.5, 5, 6.5 and 8 mmol/L, effects of carbonate alkalinity on the growth and reproduction of the E. carinicauda was measured. The results showed that the LC50 was 8.73 mmol/L at 96 h. With the increase of carbonate alkalinity, the mortality rate, specific growth rate, spawning rate, eggs incubation rate, ovarian maturation and metamorphosis larvae survival rate of E. carinicauda decreased.The experiments were carried out to explore the effects of water carbonate alkalinity on immune enzyme activities of E. carinicauda. The carbonate alkalinity gradient was set to 5, 6.5, 8 mmol/L, effects of carbonate alkalinity on the ACP, AKP, SOD enzyme activity(at 0, 3, 6, 12, 24, 48 and 72 h) was measured. The activities of ACP, AKP and SOD in gill and hepatopancreas of E. carinicauda showed the first increase after decline over the time of carbonate-alkalinity stress. Our results indicated that E. carinicauda can be better adapted to the high alkali environment by regulating the activity of the immune enzyme. And E. carinicauda was suitable to be cultured at 3.5mmol/L of carbonate alkalinity, and cannot normal growth and reproduction at more 5mmol/L of carbonate alkalinity. So in the high carbonate alkalinity environment, the artificial treatment of saline alkali water must be carried out in order to reach the best effect and improve the efficiency of culture. This study provided a scientific basis for the cultivation and development of E. carinicauda in saline and alkaline waters.Retinoid X receptor is an important endogenous regulatory factor for the growth and reproduction of crustacean. We cloned full-length c DNA of a retinoid X receptor in Exopalaemon carinicauda by RACE(rapid amplification of cDNA ends). The full-length cDNA of EcRXR was 1323 bp, containing an open reading frame(ORF) in 855 bp, encoding a 284 amino-acid polypeptide; molecular weight was predicted for 30.918 kDa and isoelectric point estimated for 6.788. The predicted amino acid sequence of EcRXR shared 71%-90 % identity with those of other crustaceans as showed in homologous analysis, and EcRXR is clustered with crustaceans RXRs in phylogenetic tree. Homologous analysis showed that EcRXR has the highest homology to RXR of Macrobrachium nipponensis. The quantitative real-time RT-PCR showed that EcRXR gene could be detected in all tested tissues of E. carinicauda. And the eyestalk is in highest expression level, hemolymph in lowest, and the other six tissues in intermediate. During the moulting cycle, the expression of EcRXR gene in eyestalk, hepatopancreas, stomach and intestine, kept rising. However, in gill, fell first, then rose. Andin cuticle kept falling. After challenged by temperature and salinity, the expressions of EcRXR gene in gill and hepatopancreas of E. carinicauda showed different trends. The expressions of EcRXR gene in gill rose first, then fell under temperature stress; the expressions of EcRXR gene in hepatopancreas increased after the first drop rise again under salinity stress. After challenged by carbonate alkalinity, the expressions of EcRXR gene in gill showed inhibiting action. The expressions of EcRXR gene in hepatopancreas increased under lower salinity stress.Analysis of the moulting cycle, temperature and salinity stimulation provided further evidence that EcRXR played pivotal roles during moulting in osmotic regulation. Future investigations should focus on the functions of RXR in E. carinicauda and other crustaceans.