Morphological changes in the lymphoid organs of Saprolegnia -infected brown trout, Salmo Trutta Fario

Vol. II, No. 2

ISDCI ECTOTHERM SYMPOSIUM

439

ABSTRACTS OF POSTERS DEALING WITH FISH IMMUNOLOGY

M O R P H O L O G I C A L CHANGES IN THE LYMPHOID INFECTED BROWN TROUT, SALMO TRUTTA FARIO

ORGANS

OF

SAPROLEGNIA-

F. Alvarez, B.E. Razquin, A. Villena and A. Zapata I

D e p a r t a m e n t o de Morfologia Microscopica, F a c u l t a d de Biologia, Universidad de Leon, and 1 D e p a r t a m e n t o de Morfologia Microscopica, F a c u l t a d de Biologia, Universidad Complutense, Madrid, Spain.

I n f e c t i o n s by Saprolegnia diclina have r e c e n t l y caused a high m o r t a l i t y in wild populations of brown trout, Salmo t r u t t a fario, in Leon (Spain). Due to the seasonal incidence of the disease and the d e m o n s t r a t e d e f f e c t s of some environmental p a r a m e t e r s on the immune system of the e c t o t h e r m s , we have c o m p a r a t i v e l y studied the status of the lymphoid organs of h e a l t h y (without external signs of disease) and infected trouts at d i f f e r e n t months of the year. Healthy and i n f e c t e d brown trouts were caught weekly from F e b r u a r y 1984 to April 1985 in several rivers of Leon. The trout, whose age was d e t e r m i n e d by s c a l i m e t r y , were brought to the laboratory, a n e s t h e t i z e d and weighed, and their thymuses, spleens, pronephroi and mesonephroi were r e m o v e d and processed for light and e l e c t r o n microscopy. The g r e a t e s t number of i n f e c t e d trout were caught from J a n u a r y to April (the spawning period) and in September. No i m p o r t a n t d i f f e r e n c e s o c c u r r e d b e t w e e n the lymphoid organs of males and females in both h e a l t h y and ill trout. D e c r e a s e d numbers of circulating l y m p h o c y t e s o c c u r r e d in the ill trout in all considered months. By contrast, the amount of lymphoid tissue in h e a l t h y t r o u t showed a gradual increase from winter to spring. I n f e c t e d t r o u t did not show.this increase, however, containing in any month, lesser amounts of lymphoid tissue than found in h e a l t h y fishes of winter. Thymi of infected trouts displayed a few t h y m o c y t e s , increased c o n n e c t i v e tissue, enlarged epithelial cells and a r e d u c e d outer region. F u r t h e r m o r e , splenic and renal lymphoid tissues appeared devoid of l y m p h o c y t e s and had r e m a r k a b l e vascular modifications. A p h a g o c y t i c r e t i c u l a r sheath was lacking in the splenic ellipsoids of ill t r o u t while large a r e a s were filled with p y c n o t i c cells. In any case, the most striking f e a t u r e in the spleen and kidney of i n f e c t e d trouts was the existence of h y p e r t r o p h i c lining sinusoidal cells containing p h a g o c y t o s e d material, possibly of a fungal nature. The significance of our results will be discussed from the p e r s p e c t i v e of the relationships b e t w e e n the status of the immune system and the evolution of the disease.