Seasonal Population Dynamics Of The Parasitic Ciliates In Hybrid Tilapia Oreochromis Aureus×Oreochromis Niloticus

From May 2006 to April 2007 the present author investigated the species and population dynamics of the parasitic ciliates in the Oreochromis aureus×Oreochromis niloticus from East Minghu Lake which located in Jinan University,Guangzhou.260 specimen were examined.In twelve months we found six species of parasitic ciliates in the hybrid tilapia in the lake.They are Ichthoyophthirius multifiliis Fouquent,1876,Trichodina domerguei f.latispina Dogiel,1940, Trichodina parasiluri Chen et Hsieh,1964.Trichodina centrostrigata Basson et al.1983, Tripartiella clavodonta Basson and Van As,1987 and Apiosoma minuta Chen et Hsieh,1964. The infection prevalence of T.clavodonta kept the same form October 2006 to April 2007.The annual graph of infection prevalence of three species of Trichodina was the general "V" or "U", it decreased first and then increased gradually,they were the lowest in July 2006,it showed that three species of Trichodina increased in spring and winter,it might be a reason that the Trichodina infected the hybrid tilapia in winter.The graph of the infection prevalence of Apiosoma minuta was undulatory.They were the lowest in July 2006 and February next year. Some different physical and chemical parameters in the lake had different effect upon the five parasitic ciliates.When the water temperature was from 15.6℃to 31.4℃,the relationship between the infection prevalence of three trichodinid,Tripartiella clavodonta and water temperature was a negative correlation with the water temperature,they decreased along with the increase of water temperature.The relationship between the relationship between Apiosoma minuta and the water temperature were not significant.The infection prevalence of the five parasitic ciliates and pH(7.22-7.85),transparence(28.3-42.8cm),dissolved oxygen (1.7978-3.4203 mg/L),nitrite nitrogen(0.1528-3.0442 mg/L) were not significant expect I. multifiliis.According to the correlation between T.domerguei f.latispina,T.parasiluri and the content of ammonia nitrogen(1.0282-5.2573 mg/L),they were positive correlation.There were not significant relationship between the infection prevalence of T.centrostrigata,Tripartiella clavodonta and Apiosoma minutav and the content of ammonia nitrogen(1.0282-5.2573 mg/L).The host had significant effect on the infection prevalence besides water quality parameters.The results showed that the percentage of the lymphocyte and granulocyte in the infection blood were much remarkably higher than those in the non-infection blood.The relationships between the parasitic ciliates and the total length of host were different.There was negative relationship between the infection prevalence of T.domerguei f.latispina and the total length of host.The infection prevalence of Tripartiella clavodonta decreased and then increased along with the increase of the total length of host,on the contrary,the infection prevalence of Apiosoma minuta increased and then decreased along with the increase of the total length of host. There were not significant relationship between T.centrostrigat and T.parasiluri and total length of host.