SEASONAL DYNAMICS OF MYXOSPORIDIANS IN LEIOCASSIS LONGIROSTRIS AND SAUROGOBIO DABRYI IN MIDDLE REACHES OF THE CHANGJIANG RIVER

Fish for the examination of Myxosporidian were collected from June 1984 to April 1985 in Tuanfeng (30°20′N, 111°5′E), Hubei province. About 20 fish of each species were collected bimonthly, thus, a total of 107 Leiocassis longirostris and 230 Saurogobio dabryi were examined. The results are summarized as follows:1. Generally, there are three species of myxosporidian in Leiocassis longirostris. Myxidium macrocapsulare and Chloromyxum sp. were found in gallbladder, having the infection rates of 55% and 17% respectively. Myxobolus sp. was found in kidney, with 22% infection. In Saurogobio dabryi, two species of myxosporidian are present. Myxobolus hupeiensis may infect brain, gill, kidney, body cavity and intestine, but occurs mainly in brain, where it forms white cysts and has 53% infection. Zschokkella sp. was found in gallbladder only, with 4% infection. 2. Infection rate of myxosporidian in Leiocassis longirostris and Saurogobio dabryi shows an obvious seasonal variation. In Leiocassis longirostris, the infection curve has only a single peak, with the maximum value (95%) in 3une and the minimum (43%) in February. The annual mean value is 65%. In Saurogobio dabryi, peaks of the infection curve are double, with the higher one (63--67%) appearing from December to February and the lower (58%) in August. Infection rate in spring and autumn are rather low (36--44%) and the annual mean value is 51%.3. The relationships between infection rate (IR) and total length of fish(TL) are expressed as follows:For L. longirostris:IR=0.956—0.009TL For S. dabryi:IR=-2.0678+0.3838(TL)-0.0136(TL)2 S. dabryi less than 8 cm are free from being infection4. The relation between infection rate of myxosporidian and different sex of both fishes was found to be inconspicuous, as indicated by x2-test.5. The reduction of weight and plumpness of L. longirostris after being infected by myxosporidian is not conspicuous, with plumpness reduced only 0.04 in average. However S. dabryi infected myxosporidian reduces 0.12 in plumpness and 12.4% in weight.6. Positive relationship between infection rate (IR) of myxosporidian in L. longirostris and water temperature (T) of the Changjiang River was observed and may be described as IR=0.3129-0.019T°(C). In S. dabryi relationship between these two factors may be described as IR=1.1228-0.073777 T+0.001795 T2.