VISCERAL INFECTION OF PUMPKINSEED SUNFISH (Lepomis gibbosus) WITH Posthodiplostomum minimum centrarchi – ULTRASTRUCTURAL STUDY

Abstract

VISCERAL INFECTION OF PUMPKINSEED SUNFISH (Lepomis gibbosus) WITH Posthodiplostomum minimum centrarchi – ULTRASTRUCTURAL STUDY

P. Ramos1., I. Pereira da Fonseca2, S. Branco3, G. Alexandre-Pires 2

1 Unidade de Aquacultura, INRB, IP/IPIMAR, Av. de Brasília, Lisboa, Portugal 2 Centro de Investigação Interdisciplinar em Sanidade Animal, FMV, UTL, Av. Universidade Técnica, 1300-477 Lisboa, Portugal 3 Instituto de Ciências Agrárias e Ambientais Mediterrânicas (ICAAM). Universidade de Évora

Introduction: Heart, kidneys, liver and spleen of freshwater fish Lepomis gibbosus were found infected by Posthodiplostomum minimum centrarchi metacercariae. Visceral organs contain macroscopically visible white cysts. Ultrastructural studies of the cysts, parasites and infected tissues were performed in order to access tissues damage and a better characterization of the parasite.

Material and Methods: Visceral samples obtained from twenty specimens of fresh pumpkinseed sunfish captured in a dam located at the centre of Portugal were submitted to Scanning Electronic Microscopy (SEM) techniques and histological routine methods.

Results: Histological examination of the samples revealed numerous cysts; empty cysts and cysts with parasites present in the parenchyma of spleen, liver and kidneys; and pericardial region of the ventricle. They were surrounded by a cellular inflammatory response by the accumulation of macrophages, eosinophils and polymorphonuclear neutrophils. Melanomacrophage centres (MMC) were diffusely scattered through spleen and liver. The cyst shows two well discernable walls, the inner wall of the parasite origin and the outer fibroblastic capsule of host origin. A huge amount of calcareous concretions filled and surrounding the metarcercariae.

Conclusion: Although the host reaction to these parasites is a minimal response, the proliferation of MMC was associated with the infection. The metacercariae frequently twisted upon themselves in histological sections, so that discerning the relationship among their internal organs is often difficult. In this work, SEM technique was used to show specific three-dimensional morphological details of the key features used to identify trematodes parasites by optical microscopy, like the oral and ventral suckers attached to the host, their position and relative size, being complementary to the understanding of the histopathological effects inflicted to host tissues.