Effects Of Salinity On The Growth Of Bester And Tongue Sole And Their Eco-physiological Mechanisms

Salinity is one of important environmental factor influenced the growth of aquatic animals. The plasma osmolality of fishes were significantly effected by the change of salinity in their nature habitat, which usually leads to the fluctuation in the growth, survival and reproduction, etc.. When a fish goes into the environment different to its original habitat in salinity, it is necessary to adjust its plasma osmolality to environment. Generally, euryhalous fishes is high capable to adjust themselves to various salinities. However, there are still difference in various fishes.Most of sturgeon are migratory fish, which usually are high capability of various salinity although there are difference between various species. The bester is a hybrid from Huso huso (♀)×Acipenser ruthenus (♂). Due to high capability to salinity of its female parent, it is believed that the bester could be euryhaline. The tongue sole Cynoglossus semilaevis mainly distributed in Yellow Sea and Bohai Sea, which is a typical marine euryhalous fish. In this thesis, effects of salinity on the growth, plasma osmolality, gill Na+/K+-ATPase activity and energy budget were studied in both the bester and the tongue sole, and the capability of two species was compared. Furthermore, based on the data of plasma osmolality, ions, gill Na+/K+-ATPase activity and energy budget at different salinity treatment, effects of salinity on the growth of bester and tongue sole and their eco-physiological mechanisms were analysed. The main results were presented as followings: 1 Effects of different salinity acclimation on the growth and osmophysiology of the bester (Huso huso)(♀)×(Acipenser ruthenus)(♂)The effect of different salinity acclimation on the growth, plasma osmolality, ion concentration and gill Na+/K+-ATPase activity of the Bester was studied an abrupt change in salinity 0(T0), 5ppt(T5), 10ppt(T10) and 15ppt(T15), raised 1ppt once a day then. The results showed that the livability of the Bester was not remarkable, and the specific growth rates of T0 and T5 were higher than T10 and T15 significantly. The plasma osmolality and activity of the gill Na+/K+-ATPase were increased with salinity, but there was no distinct difference among all treatments. The similar trends were observed in the plasma glucoses of the bester. Compared with other treatments, concentrations of Na+, K+, Ca2+, Mg2+ and Cl- in the plasma of T15 were increased remarkably during the acclimation. The results indicated that the optimal range of salinity change was 5ppt for the Bester.2 Effects of salinity on the growth, body composition and energy budget of besterThe effect of salinity on the growth, body composition and energy budget of the bester was studied at 0,8 ppt,16 ppt and 25 ppt. The results showed that the specific growth rate of the Bester decreased with the increase of salinity. The similar trends were observed in food consumption and conversion efficiency. The food conversion efficiency was 6.07%-18.19%. With the increase of salinity, the content of protein in fish body was increased, while the lipid and the energy content were decreased. The energy budget of the bester showed that the energy assimilated from food decreased with increasing salinity, while that spent in metabolism increased with increasing salinity. The results indicated that the Bester was suitable to be cultured in freshwater or low salinity water, and it may be difficult to be stocked in nature seawater with the salinity more than 25 ppt. 3 Effects of salinity on osmophysiology of BesterThe effects of salinity on the osmoregulation of bester were studied at 0, 8, 16 and 25 ppt. Results showed that glucose level in plasma increased significantly with salinity, and there was a trend to decrease with acclimating time. Plasma osmolality, concentrations of Na+, K+, Ca2+, Mg2+ and Cl- in plasma as well as gill Na+/K+-ATPase activity increased with salinity. This study indicated that the bester was more suitable to culture in freshwater or low salinity water than high salinity one.4 Effects of salinity change on plasma osmolality and gill Na+/K+-ATPase of the Sole (Cynoglossus semilaevis)Changes in plasma osmolality and gill Na+/K+-ATPase activity of the Sole (Cynoglossus semilaevis) were studied at an abrupt change in salinity 0, 10ppt, 20ppt, 35ppt and 40ppt. The results showed that the effect of the salinity on plasma osmolality and activity of gill Na+/K+-ATPase of the fish was significant (P<0.05).Upon the salinity changes, both plasma osmolality and gill Na+/K+-ATPase activity showed correlated trends with the increase or reduce of the salinity respectively. On the whole, the bigger the salinity changed, the more remarked trend appeared. Peak values of plasma osmolality appeared on the second day, and 6 days after the experiment start, the plasma osmolality in every group reached their own stable state. The similar trends were observed in the changes of gill Na+/K+-ATPase activity, while peak values of which appeared on the sixth day then resumed slowly to the their previous leve1 from the ninth day. The results indicated that the sole had a great capability of acclimation to different salinity.5 Effects of salinity and temperature on the growth, body composition, osmophysiology and energy budget of the tongue soleEffects of salinity and temperature on the growth, body composition, osmophysiology and energy budget of the Sole were studied. Three salinities (22ppt, 26ppt and 30ppt) and 4 temperatures (18℃, 21℃, 24℃and 27℃) were designed. Growth data was collected during the 8-weeks'experiment. Results showed that the specific growth rate of the sole ranged from 1% to 1.34%. There was no significant difference was found in the growth of the fish at different salinities (P>0.05), while significant difference were found at different temperatures. On the condition of salinity 22 ppt, 26ppt and 30ppt, the greatest growth rate was at 21℃,24℃and 18℃respectively while the lowest growth rate was at 27℃. Similar trends were observed in food consumption and conversion efficiency. With the increase of temperature, the content of protein in fish body increased, while the lipid and the energy content decreased. The effects of salinity and temperature on both plasma osmolality and activity of gill Na+/K+-ATPase were significant (P<0.05). Plasma osmolality and activity of gill Na+/K+-ATPase increased with salinity. Effects of temperature on plasma osmolality of sole were different at different salinity, but Na+/K+-ATPase activity decreased with temperature. Energy alternation of growth and respiratory dominated the mode of energy budget. Percentage of growth energy to feeding energy were the greatest at 18℃and 21℃, and that of respiratory energy to feeding energy increased gradually with the increase of temperature.6 Comparison of salinity capability between the bester and the tongue soleThe capability adapted to salinity was compared between the bester and tongue sole in this study. The result showed that the specific growth rate of the bester decreased with the increase of salinity, which might indicated that the bester was more suitable to culture in freshwater or low salinity water than high salinity one. However, there was no significant difference found in SGR of tongue sole at different salinity in this study, which indicted that the sole was a euryhalinous organism. There were significant differences in both plasma osmolality and gill Na+/K+-ATPase activity of the bester and the sole(P<0.05).When acclimated to 28 ppt, both plasma osmolality and gill Na+/K+-ATPase activity increased with the increase of salinity, and did not show the stability until acclimation finished. Although those in the sole fluctuated with change of salinity, they became stable after 6-9d acclimation, which indicated that the tongue sole was more capable to salinity than the bester.