Melanomacrophage centers in Gymnotus carapo as environmental bioindicators: histological and morphometric analysis in kidney, liver, and spleen

Abstract

AbstractThis study analyzes the morphology of melanomacrophage centers (MMCs) in the kidney, liver, and spleen of Gymnotuscarapo across two different environmental settings with varying degrees of anthropogenic impact, aiming to link habitatconditions to fish health and validate MMCs as bioindicators for environmental monitoring. A total of 28 specimens, capturedand humanely sacrificed under anesthesia, were processed using conventional histological techniques. Morphometricmeasurements were recorded, and tissue samples were examined on an Olympus BX 41 microscope, selecting 10 random10x fields per organ to count MMCs. Macroscopic and histological examination of the liver, kidney, and spleen highlightedMMCs distribution patterns and notable differences across sex and age groups. Adult and juvenile males showedmajor MMCs counts in the kidney and spleen compared to females, while liver samples from both sexes contained onlypigmented cells without significant MMCs formation. Differences in MMCs quantity and structure were also observedbetween environments: natural habitats displayed lower MMCs counts in both sexes compared to samples from locationswith higher anthropogenic impact, where MMCs frequency and pigmentation intensity were notably elevated. Thesefindings suggest that MMCs variations in G. carapo may reflect environmental conditions and stressors, supporting thepotential application of MMCs as health indicators for aquatic organisms and ecosystem monitoring. This work providescomprehensive morphometric and histological data on MMCs distribution in G. carapo, emphasizing its potential as abioindicator species, particularly valuable in regions with varying pollution levels.