Studies On The Development Of Morphology Of Ichthyophthirius Multifiliis And Histopathology Of The Trophozoites Experimental Infections In Goldfish

40 goldfish (carassis auratus), initial body weight 25 ± 2g, were randomly divided into 2 groups and experimentally infected with Ichthyophthirius Multifiliis at 800 or 1000 theronts /fish following cyst incubation at 15-20 ℃ .This study included the sequence of morphological events of I. multifiliis, histopathology of experimental I. multifiliis infections in goldfish. The studies showed there were three stages of the life cycle of the parasite, the trophont stage, the cyst stage and the theront stage.Trophont, a size of 350~800×300~500mn in diameter,was ovoid or spheriform. Its cytostome was at the end of the body and the ventral sutural line was obvious. The structure of the trophont was studied by transmission electron microscopy. The cilia was ranged in a regular form and displayed the axoneme tubules to the classic morphology of "9+3 "pattern in cross section.the parasite was possessed of a macronucleus and a micronucleus.The macronucleus generally was reniform in shape,the micronucleus appeard spherical or triangular and lay closely to the concavity of the macronucleus.Both nuclei were bounded by a layer of nuclear membrane. The cytoplast of the parasite contained a large number of mucocysts, contractile vacuoles, food vacuoles, mitochondria et al. organelles. The structure of cyst wall of the free-living encysted stage of I. multifiliis was studied by transmission electron microscopy. The wall consisted of a relatively homogeneous inner layer and a somewhat more electron-dense outer layer.Cyst wall thickness was not uniform in a single cyst and thinner in warmer water.Theront, a size of 30~50×24~43μm in diameter, was ovoid. Its cytostome was at the end of the body and that the ventral sutural line was not obvious. The structure of the theront was studied by transmission electron microscopy, the theront's macronucleus and micronucleus disjoined each other and other organelles were similar to the trophont's.After infecting within 30min, some free-swimming theronts were present in the surface mucus of the fish. The parasite completed its invasion of the epithelial layer within 4h of exposure to the fish.There was a general increase in mucous in the integumentary epithelium.The primary infection did not induce significant histopathological changes in the integument.By 24h,most of the theronts had penetrated the host tissue to the maximum extent and begun to transform into young trophonts,causing epithelium hyperplasy. Thedistinct horseshoe-shaped nucleus of mature trophozoites was recorded at 96 h and the integumentary epithelium were necropsied. At 216h,there were whitish thickenings in the skin and necrosis of peripheral areas. The gill was the most seriously damaged organ. The response of the fish to I. multifiliis infection was limited to the surrounding epithelial cells of the fish. The presence of I. multifiUis cysted in the secondary gill lamellae, encapsulated by respiratory epithelium cells,causing adherence of adjacent lamellae, hyperplasia of epithelial cells,congestion, oedema, epithelial displacement, gill deformation and adhesions.Gill lesions resulting from parasitic infections affected gas and ion interchanging and consequently fish metabolism and living.