| Nile tilapia is a euryhaline fish, which can survive and grow at high concentrations of salinity-alkalinity water after acclimation, it is an important candidate species for salinity-alkalinity breeding. In order to assess the tolerance and growth performance of the first selection generation and osmotic adjustment mechanism of Nile tilapia in salinity-alkalinity waters, three strains of first selected generation(F1) of Nile tilapia were used in experiments, and the partial c DNA sequence was obtained from gills of O. niloticus, physiological change of serum osmolality, ion concentration(Na+, K+, Cl-, Ca2+), gill carbonic anhydrase(CA) activity, CA and NBCe1 m RNA gene expression under salinity, alkalinity, salinity-alkalinity at different times were compared, the major rsults were as follows:(1) The salinity-alkalinity tolerance of base population(F0) and its first selected generation(F1), which parents were selectd after chronicallyacclimated and cultured in salinity-alkalinity water, of Oreochromis niloticus from Shanghai, Shandong and Hebei strains, were compared under different salinity(10g/L, 15g/L, 20g/L, 25g/L), Na HCO3 alkalinity(2g/L, 4g/L, 6g/L, 8g/L 10g/L, 12g/L) and salinity-alkalinity(Salinity 10 g/L, 15 g/L, 20 g/L; Alkalinity 2 g/L, 4 g/L, 6 g/L. their semi-lethal salinity, Na HCO3 alkalinity and concentration of Na HCO3 under different salinities at 24 h, 48 h, 72 h and 96 h were calculated. The results showed that the 96 h semi-lethal salinity, Na HCO3 alkalinity was 21.625-21.820, 7.903-8.407 for these F1 juveniles, concentration of Na HCO3 under 10 g/L, 15 g/L salinities was 5.577-6.096, 3.940-4.794, respectively, which was significantly higher than that of F0 juveniles(P<0.05). There was some variation on salinity-alkalinity tolerance among three F0 juveniles, among F1 juveniles, Hebei strain showed better tolerance than Shanghai, Shandong strains(P <0.05). The results could provide some basic data for breeding new varieties of salinity-alkalinity tolerance tilapia.(2) In order to assess the tolerance and growth performance of the first selection generation of Nile tilapia in salinity-alkalinity waters, chronic lethal experiment was carried out in juvenile fish and the average growth rates of young fish in different salinity-alkalinity waters(S0A0, S10A0, S10A2, S10A4, S10A6) were compared during 60 days culture experiment.The results showed that the median lethal salinity was 53.95±1.29, 53.36±1.53, 56.25±2.12g/L, the median lethal alkalinity was 19.18±1.24, 18.73±1.20, 20.05±1.37g/L, for Shanghai, Shandong, Hebei strain, respectively. The results of growth performance showed that the average growth rate significantly decreased with the elevation of salinity-alkalinity(P<0.05), there was no significant difference between S10A0 and S10A2 groups(P>0.05), but significantly higher than that in S10A4, S10A6 groups(P<0.05). There was no significant difference among different strains within the same treatment, except that Shandong strain showed a relatively higher growth rate than Shanghai, Hebei strains in S10A6. These results would provide some basic data for salinity-alkalinity selection breeding for Nile tilapia.(3) In order to understand fish osmotic adjustment mechanism under salinity and alkalinity water, the partial c DNA sequence was obtained from gills of O. niloticus, physiological change of serum osmolality, ion concentration(Na+, K+, Cl-, Ca2+), gill carbonic anhydrase(CA) activity, CA and NBCe1 m RNA gene expression under salinity(10, 15), alkalinity(1.5,3g/L Na HCO3), salinity-alkalinity(salinity 10,1.5g/L Na HCO3, salinity 15, 3g/L Na HCO3) at different times(0, 6, 12, 24, 48, 72, 96h) were compared. Results showed that serum osmolality, ion concentration, gill carbonic anhydrase(CA) activity, CA and NBCe1 m RNA gene expressionwere positively correlated with salinity, alkalinity and salinity-alkalinity stress strength. Over time, serum osmolality, ion concentration trends showed increasing and then decreasing, osmotic pressure in salinity, salinity-salinity water was higher than that in alkalinity water. Gill CA activity under alkalinity and salinity-salinity water was higher than that in salinity water. Under low concentrations of streses, CA activity reached the highest at a later time. NBCe1 gene m RNA expression was detected in gill with a slight increase in high concentrations(P>0.05). Gill CA m RNA expression in salinity, alkalinity and salinity-salinity water were raised, but the increase was more evident in alkalinity and salinity-salinity water(P<0.05). The result showed that CA and NBCe1 Nile tilapia were involved in alkali, alkaline mixed regulate the body under osmotic stress. The results provided the basic data for understanding the physiological regulation in salinity-salinity adaptation. |
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