1-3 mmol / L is better for alkalinity of aquaculture water. The total alkalinity of the pool water is too low, and the daily variation range of the acidity and alkalinity of the water is large, which may be too high or too low. At the same time, too high alkalinity will be harmful to fish. According to the average alkalinity of natural seawater is 116 mg / L CaCO3, and that of fresh water is 47.5 mg / L. According to the water quality evaluation standard issued by the U.S. Environmental Protection Agency, except for those with lower natural concentration, in order to protect freshwater organisms, the alkalinity expressed by CaCO should not be less than 20mg / L. The risk index value of alkalinity of water for aquaculture is 10mmol / L. The so-called danger index refers to the alkalinity reaches this value, and special care should be taken when it is used for fish farming. The increase of pH will cause a large number of dead fish. The optimum alkalinity of Silurus asotus is 80 mg / L CaCO3. Davidson et al. Showed that the alkalinity of juvenile rainbow trout was maintained at 195 mg / L CaCO3. Summerfelt et al. Showed that there was no significant difference between 70 mg / L CaCO3 and 200 mg / L CaCO3 in the recirculating aquaculture system of Atlantic salmon. For the sake of cost, 70 mg / L CaCO3 was recommended. The alkalinity of 160 mg / L CaCO3 is the best in the mariculture of Litopenaeus vannamei. The results showed that the growth rate and survival rate of Macrobrachium rosenbergii decreased with the increase of alkalinity, and there would be obvious death under the condition of 250 mg / L CaCO3 alkalinity. Different species of fish have different tolerance to high alkalinity water. For example, Qinghai Lake naked carp > wallaby > crucian carp > carp > tilapia > grass carp > bighead carp > mud carp > silver carp.<br>
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