LAUSR

The acquisition of oxygen is fundamental for maintaining metabolic activity in fish, and most species obtain oxygen through aquatic gill respiration. Throughout evolution, different fish lineages have evolved secondary routes to obtain oxygen from atmospheric air, and the spinycheek sleeper, Eleotris pisonis, may be one example of such bimodal respiration. Gill structure and the top epithelium of the head of E. pisonis from the Subae River (Santo Amaro, Bahia, Brazil) were evaluated morphometrically. The gills showed histopathologies, especially proliferation, which was prevalent on 35.6% of the filaments and on 13.7% of the lamellae, probably increasing the water-blood diffusion barrier of the lamellae to 5.48 ± 1.32 μm, similar to the air-blood diffusion distance of the skin (5.77 ± 1.72 μm). Quantitative morphometric analysis of histopathologies and diffusion distances could be considered as biomarkers, and also suggest the presence of cutaneous respiration as a possible strategy for aerial oxygen acquisition.