Study of the tail fin rays of rainbow trout (Oncorhynchus mykiss) infected with the parasite Myxobolus cerebralis

: A light, transmission and scanning microscope study of the rays (lepidotrichia) forming the tail fin of rainbow trout (Oncorhynchus mykiss) fingerlings infected with the parasite Myxobolus cerebralis showed that triactinomyxon adherence to the tail fin of host fingerlings occurred 10 min after infection. After 2 h of exposure, it was possible to observe triactinomyxon spores in the epidermis. Although the characteristic symptoms of the disease, such as a black tail and a change in tail morphology, were observed, there was no attack against the tissue forming the tail fin rays and triactinomyxon spores were not observed inside the leptotrichial matrix at any stage, indicating that the spores do not reach the rays or that their observation was not possible under the conditions of the present study.