SEASONAL DYNAMICS AND FREQUENCY DISTRIBUTION OF THE ENDOPARASITES PALLISENTIS(NEOSENTIS)CELATUS AND EUSTRONGYLIDES SP. IN THE RICE FIELD EEL MONOPTERUS ALBUS

The acanthocephalan Pallisentis (Neosentis) celatus (van Cleave, 1928) in the intestine and nematode Eustrongylidessp. in the body cavity is harmful to the health of the rice field eel Monopterus albus (Zuiew, 1793). In our study, the population dynamics and frequency distributions of the two helminths were investigated in the period from May 2006 to March 2008. The prevalence and mean abundance of P. (N.) celatus (van Cleave, 1928) of the 1980 individuals of M. albus, was 34.46% and 2.94 8. 37, respectively. The mean abundance was positively related with the body length of the fish (R= 0.16, P0.05). Whereas the highest mean abundance and variance to mean ratio were observed in the fish body length group of 42 cm L48 cm, then declined gradually and showed convex curves. The prevalence of Eustrongylidessp. was 15.14% and the mean abundance was 0.61 2.45.The mean abundance was negatively related with the body length of the fish (R = -0.14, P0.05). The highest mean abundance was observed in the fish body length group of 24 cm L30 cm, and the highest variance to mean ratio was found in the group of 30 cm L36 cm. The prevalence and mean abundance of P. (N.) celatus were higher in spring and summer. There were significant differences in the prevalence and mean abundance of theacanthocephalan among different months (G = 84.44 0.05222= 33.9; F = 10.50, P0.05). The prevalence and mean abundance of Eustrongylidessp. were higher in late spring and early summer, and significant differences were also found in different months (G = 143.88 0.05222= 33.9; F = 6.70, P0.05).