THE DIFFERENT PATHOLOGY OF GYMNOCYPRIS PRZEWALSKII PRZEWALSKII AND SCHIZOPYGOPSIS PYLZOVI INFECTED WITH ICHTHYOPHTHIRIUS MULTIFILIIS

To investigate pathological features of ichthyophthiriasis in Schizothoracine fishes, we performed a pathological comparison between Gymnocypris przewalskii przewalskii and Schizopygopsis pylzovi infected with Ichthyophthirius multifiliis. The infection of I. multifiliis resulted in high morbidity and mortality rate in G. p. przewalskii and S. pylzovi. The mortality rate of G. p. przewalskii and S. pylzovi increased dramatically at 3 dpi (day post infection) and then decreased gradually. All the infected G. p. przewalskii died after 8 dpi. The mortality rate of S. pylzovi was 97.3% with only two S. pylzovi survived after 14 dpi. There were lots of small white spots on the skin of both infected fish species but with significantly different Symptoms. A large amount of mucus were secreted in G. p. przewalskii to form gelatinous layer on the skin. Tomonts in different developmental stages were embedded in the gelatinous layer. In the infected S. pylzovi, necrosis and exfoliation occurred in the epithelium of the caudal fin and dorsal fin, and ulceration appeared due to the secondary infection by bacteria on the skin. The anatomic examination showed similar pathologi-cal changes in liver of G. p. przewalskii and S. pylzovi with the liver color from light red to faint yellow. Meanwhile, gallbladder was swollen and enlarged in both species. Histological sections and electron microscopy demonstrated the adhesion of gill filaments in infected G. p. przewalskii and S. pylzovi, and the gill lamellas and gill epithelia cells were exfoliated. In G. p. przewalskii, I. multifiliis parasite created huge cavities in the epidermis and altered the structure of the skin epidermis. Skin epidermal cells of infected S. pylzovi showed evident vacuolation, the original tight structure was completely lost, and boundaries between epidermis and tunicae propria was blurred. These results indicated simi-lar targeted organs by I. multifiliis infection but with different symptoms in G. p. przewalskii and S. pylzovi that may explain by the long-term adaptation to salt water and freshwater environments by G. p. przewalskii and S. pylzovi, which laid the foundation to study host-pathogen interaction in Tibetan highland fishes.