Research On The Growth Models Of Aeromonas Salmonicha In Atlantic Salmon Recirculating Aquaculture Systems

With the expansion of the Atlantic salmon recirculating aquaculture scale, the disease problem caused by Aeromonas salmonicha is becoming serious. Which is a key obstacle for the development of the Atlantic salmon aquaculture. In this study, we investigated the effects of different environmental factors on the growth of Aeromonas salmonicha which was isolated from the Atlantic salmon recirculating aquaculture systems (RAS). In addition, this paper established temperature predicting modles of the growth of Aeromonas salmonicha.This study selected the key environment factors, which have great effect on microbial growth, including temperature, pH, C/N and salinity. The results showed that the change of temperature can impact on the growth rate of Aeromonas salmonicha significantly. In the four temperature gradients (28℃,15℃,10℃,5℃), as the temperature increased, the growth rate of Aeromonas salmonicida increased significantly. When the temperature reached 28℃, the growth rate of Aeromonas salmonicida quickly rose in 2 hours and the number of the bacteria reached the maximum value 6.6×108CFU/mL at 8h. However, the number of Aeromonas salmonicida showed no significant change within 36h when culture temperature reduced to 5℃. Aeromonas salmonicida grew under the pH 6.0,6.5,7.0,7.5,8.0 and its growth rate changed within different pH. Compared with acid conditions(pH6.0-6.5), Aeromonas salmonicida had faster growth rate in neutral or weak alkaline conditions(pH7.0～8.0). When the pH of culture in the scope of 7.0～8.0, Aeromonas salmonicida growth reached the logarithmic phase at about 6h and reached plateau after 20h. Acid medium inhibited the growth of Aeromonas salmonicida abviously. Within this condition, as well as pH6.0 or 6.5, the growth rate of Aeromonas salmonicid significantly decreased and the bacteria reached the logarithmic phase at about 14h. C/N ratio is another factor affecting the growth of Aeromonas salmonicida. When the C/N ratio in the range of 1-10, Aeromonas salmonicida grew relatively stable and there’s no significant differences among different groups. When 15 ≤ C/N ratio≤ 25, the number of Aeromonas salmonicida gradually reduced with time prolonged. There’s a significant difference(P<0.01) compared with other groups. Low C/N ratio was suitable for Aeromonas salmonicida growing. In the range of 0-40, salinity has little effect on the change of Aeromonas quantity. For salinity≤30, the number of the bacteria had almost the same change trend and remained stable. When the medium salinity increased to 40. its number presented a downward trend. High salinity condition may inhibited the growth of Aeromonas salmonicida.The interaction experiment result showed that the temperature was the main factor which can affect the growth of Aeromonas salmonicida significantly, the pH followed. C/N ratio had minimal impact on the growth of Aeromonas salmonicida. The optimal conditions for Aeromonas salmonicida growing was T=15 ℃, pH=6.0, C:N=25.Furthermore, the primary and secondary’growth prediction models were established based on the observed growth data of Aeromonas salmonicida under different temperature(8℃,10℃,13℃,15℃, 18℃,28 ℃). The result showed that the Logistic model was applied to fit the data best, whose correlation was above 0.98. The growth rates calculated by the primary models were 0.0337,0.0465,0.0533,0.0735, 0.0696,0.0122, respectively. In addition, this paper used Square root model to fit the temperature influence of the growth rate of Aeromonas salmonicida. The result showed that the model equation was (?)= 0.0076×[T-(-18.178)]. Square root of μm had linear correlation with temperature. Within the above temperature range, Aeromonas salmonicida would grow faster under higher temperature. The above model accuracy was tested by residual value, accurate factor and deviation factor. The residual value of this model fell in the range of ±0.01 and the accurate factor and deviation factor values were close to 1.0. Therefor, the models which have been established in this paper can be used well to predict the growth regularity of Aeromonas salmonicida.