Analysis of Tissue Alterations and Quantitative Histopathological Indices in Rhamdia quelen (Quoy & Gaimard, 1824) and Metynnis maculatus (Kner, 1858) During Treatment of Ichthyophthiriasis

Aims: The present study aimed to describe the histological alterations observed in gills of Rhamdia quelen and Metynnis maculatus during treatment of white spot disease and to compare three quantitative indices of gill alterations originally developed by other authors for this type of evaluation.

Study Design: Animals were collected and analysed on days zero, 10, 20, 30, 40 and 100 in relation to the beginning of treatment of ichthyophthiriasis.

Place and Duration of Study: Integrated Group for Aquaculture and Environmental Studies, Department of Animal Sciences, Federal University of Paraná, between January and April 2014.

Methodology: For the analyses, animals presenting clinical signs of a ciliate Ichthyophthirius multifiliis infestation were maintained in a laboratory. Immediately after disease identification, the fish were medicated and monitored for the occurrence and evolution of gill histological alterations. For histopathology, 15 sick fishes (presence of white spot) of each species were collected from each tank on day zero. On days 10, 20, 30 and 40 after diagnosis, 10 individuals of each species were collected. After collection, the fish were subjected to spinal cord section and subsequent biometric analysis. Next a gill arch from the right side of each fish were collected and fixed in Davidson solution for 48 hours (ALFAC) [1]. The biological material was then subjected to a routine histotechnical procedure. Animals were observed daily for behavioural analysis, and the mortality was recorded.

Results: Twelve histological alterations were identified and described throughout the collections. However, it was not possible to establish an unequivocal causal relationship between the observed alterations and the parasitic disease. The application of the different indices suggests that the dynamics of the gill alterations occurred differently for R. quelen and M. maculatus.

Conclusion: The robustness and suitability of the indices as a tool for assessing the severity of the damage caused by the parasitic disease to gill tissue in the two species allow us to better understand of the temporal evolution of the disease are discussed and questioned.