水温对多子小瓜虫孵化及幼虫活力的影响

Influence of water temperature on hatchability and activity power of theront of Ichthyophthirius multifiliis

多子小瓜虫引起的白点病是严重危害淡水鱼类的重要疾病之一，该寄生虫的发育繁殖受温度影响极大，因此，温度是影响小瓜虫培养及其疾病发生的重要因素。为了阐明温度在多子小瓜虫生活史中的作用，在实验条件下，研究了水温对该寄生虫包囊形成、孵化和幼虫活力的影响。结果表明：水温在4℃左右或28—32℃，多子小瓜虫都不能孵化，但有少部分虫体以包囊形式存活下来；在9～27℃，随水温升高，包囊形成和孵化时间缩短，孵化率升高至100％，孵出的感染性幼虫活力增强，但活力维持时间缩短至4h。因此，建议在多子小瓜虫培养及人工感染试验中，维持23℃左右的水温较合适，这时感染性幼虫使用的有效时限是孵出后4h内。

Ichthyophthiriasis, commonly known as ＂white spot disease＂, is the most important disease of freshwater fishes. The pathogen, Ichthyophthirius multifiliis, is an obligatory parasitic ciliate that parasitizes the epidermis and gills of freshwater fishes, and is greatly affected by water temperature. In order to illuminate the role of water temperature in parasite life cycle, the authors investigated the influence of water temperature on cyst formation, hatchability, and activity power of theront under experimental condition. The results are as follows. The theronts of I. multifiliis were not able to be produced from parasite cysts when the water temperature was about 4 ℃ or from 28-32 ℃, but a few cysts could survive in such low or high temperatures. While the water temperature was between 9-27℃, the cyst-formation and hatch period gradually became shorter and the hatch rate rose to 100% with the increasing temperature. Meanwhile, the activity power of theronts was enhanced, but kept in a shorter period of about 4 hours with rising of water temperature. Therefore, it is suggested that I. multifiliis should be cultured under water temperature of about 23℃ for various experiments including artificial infection, and the theronts should be used in 4 hours after hatch.