Abstract: The assay was aimed to understand the effect of Ichthyophthirius multifiliis on mitochondria of livers,kidneys and muscle tissues of grass carp.Health grass carps were infected by Ichthyophthirius multifiliis with artificial method,after successful infection,the mitochondria ultrastructure changes of livers,kidneys and muscle tissues of grass carp in the control and infection groups under the transmission electron microscope (TEM) were observed,contents of SOD and MDA were tested.The results showed that the quantities of the mitochondria decreased in the livers,kidneys and muscle tissues in infection group;The mitochondria of infection group swelled,ruptured or disappeared under the TEM compared with the control group;The contents of SOD in livers and kidneys in infection group were significantly higher than that of control group (P <0.05),the muscles' were not significantly different (P >0.05);Then the contents of MDA in livers and kidneys in infection group were significantly lower than that of control group (P <0.05),the muscles' were not significantly different (P >0.05).It could be seen that Ichthyophthirius multifiliis had effects on the mitochondria and contents of SOD and MDA in livers,kidneys and muscle tissues of grass carp after infection.

Key words: Ichthyophthirius multifiliis; grass carp; tissue and organ; mitochondria