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Veterinary Medicine International
Volume 2014 (2014), Article ID 210625, 7 pages
Research Article

Morphometric Evaluation of Interrenal Gland and Kidney Macrophages Aggregates in Normal Healthy Rainbow Trout (Oncorhynchus mykiss) and after Bacterial Challenge with Yersinia ruckeri

1Department of Veterinary Sciences, University of Pisa, Viale delle Piagge 2 56124, Pisa, Italy
2Department of Animal Production Sciences, University of Basilicata, 85100 Potenza, Italy
3Experimental Zooprophylactic Institute of Piemonte, Liguria and Valle D’Aosta, 10154 Turin, Italy

Received 8 November 2013; Revised 5 January 2014; Accepted 19 January 2014; Published 24 February 2014

Academic Editor: Lorraine M. Sordillo

Copyright © 2014 Michela Gregori et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Macrophage aggregates (MA) occur in various organs of fish as discrete aggregations of pigmented macrophages. The study presented herein investigates the quantitative modifications from normal anatomical condition, of interrenal gland (IG) and kidney MA in six treatment groups of adult rainbow trout submitted to either specific or aspecific immune stimulation and subsequently challenged with Yersinia ruckeri. Routinely stained tissue sections from both IG and kidney were analysed. The percentage of tissues occupied by MA and the MA density (number/mm2) were calculated on at least 10 randomly selected nonoverlapping fields taken from each tissue section. MA morphometric findings from challenged fish were compared to those from a control group. Results showed that fish from control group displayed a statistically significant () higher percentage of tissue occupied by MA and MA density. Among different treatment groups, anti-Yersinia ruckeri immunized fish, which did not show clinical signs of disease after bacterial challenge, displayed higher values of morphometric parameters compared with symptomatic fish from other groups. Our study demonstrates that the quantification of the area occupied by MA might be an efficient parameter to evaluate the general condition of a salmonid population since it positively correlates with the health status and negatively with stress factor such as the acute bacterial infection.