What is the most efficient respiratory organ for the loricariid air-breathing fish Pterygoplichthys anisitsi, gills or stomach? A quantitative morphological study.
The purpose of the present study was to evaluate the morphometric respiratory potential of gills compared to the stomach in obtaining oxygen for aerobic metabolism in Pterygoplichthys anisitsi, a facultative air-breathing fish. The measurements were done using stereological methods. The gills showed greater total volume, volume-to-body mass ratio, potential surface area, and surface-to-volume ratio than the stomach. The water-blood diffusion barrier of the gills is thicker than the air-blood diffusion barrier of the stomach. Taken together, the surface area, the surface-to-volume ratio and the diffusion distance for O2transfer from the respiratory medium to blood yield a greater diffusing capacity for gills than for the stomach, suggesting greater importance of aquatic respiration in this species. On the other hand, water breathing is energetically more expensive than breathing air. Under severe hypoxic conditions, O2uptake by the stomach is more efficient than by the gills, although the stomach has a much lower diffusing capacity. Thus, P. anisitsi uses gills under normoxic conditions but the stomach may also support aerobic metabolism depending on environmental conditions.
Institute of Biology, Department of Zoology, Federal University of Bahia, Rua Barão de Geremoabo 147, 40170-115 Salvador, Bahia, Brazil. Electronic address: cruzfisio@yahoo.com.br.
André Luis
AL
da Cruz
Department of Physiological Sciences, Federal University of São Carlos, Rod. Washington Luis km 235, 13565-905 São Carlos, São Paulo, Brazil.
Marisa Narciso
MN
Fernandes
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D002397:Catfishes / Q000033:anatomy & histology / Q000502:physiology*; D005880:Gills / Q000033:anatomy & histology / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D012143:Respiratory Physiological Phenomena; D013270:Stomach / Q000033:anatomy & histology / Q000502:physiology*; D013499:Surface Properties
D010100:Oxygen
Bimodal respiration; Morphometric partitioning; Oxygen availability; Respiratory surface