Cell and tissue changes in perch (Perca fluviatilis) and roach (Rutilus rutilus) in relation to water quality

Abstract

Cell and tissue changes were studied in perch, Perea fluviatilis, and roach, Rutilus rutilus, over five seasons from four lakes in central Finland differing both in parasite composition and water quality. Fish gills displayed a variety of abnormalities including cell proliferations, fused lamellae and parasitic nodules. Among the four lakes the occurrence of gill alterations was greatest in the natural Lake Peurunka, the reference area. Prevalence of infection with Henneguya creplini (Protozoa, Myxosporea) on the gills of perch varied among lakes between 26.5 % and 39 .6 % with no apparent relationship with the level of pollution. Infection with Raphidascaris acus (Nematoda, Ascaridoidea) larvae in the intestine, liver and pancreatic tissue of roach showed seasonal and size-related patterns. The most heavily infected fish were recorded from the polluted Lake Vatia whilst abundance was lowest in Lake Peurunka. Histology revealed that most worms in the liver and pancreatic tissue were dead. The typical host response to the parasite was a granulomatous inflammatory reaction. There was no difference in the type of response when fish from the different lakes were compared. Special attention was paid to the occurrence of macrophage centres (MC) in fish. MCs were initially studied in the fish heart in association with tissue inflammation. Subsequently the study focussed on the fish liver, spleen and the hematopoietic part of the kidney. The MC parameters displayed variability among individual fish, species, organs, and lakes. However, none of the observed patterns correlated with water quality and MCs are concluded to have limited value as indicators of pollution. The future role of histopathology in fisheries research is also discussed.