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The occurrence of aerial respiration in Rhinelepis strigosa during progressive hypoxia
Author(s) -
Takasusuki J.,
Fernandes M. N.,
Severi W.
Publication year - 1998
Publication title -
journal of fish biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.672
H-Index - 115
eISSN - 1095-8649
pISSN - 0022-1112
DOI - 10.1111/j.1095-8649.1998.tb00804.x
Subject(s) - biology , respiration , hypoxia (environmental) , oxygen , oxygen tension , respiratory system , ventilation (architecture) , breathing gas , zoology , botany , breathing , anatomy , chemistry , mechanical engineering , organic chemistry , engineering
Rhinelepis strigosa did not surface for air breathing in normoxic or moderate hypoxic water. This species initiated air breathing when the P i o 2 in the water reached 22 ± 1 mmHg. Once begun, the air‐breathing frequency increased with decreasing P i o 2 . Aquatic oxygen consumption was 21·0 ± 1·9ml O 2 kg −1 h −1 in normoxic water, and was almost constant during progressive hypoxia until the P i o 2 reached 23·9 mmHg, considered the critical oxygen tension (P c o 2 ). Gill ventilation increased until close to the P c o 2 (7·9‐fold) as a consequence of a greater increase in ventilatory volume than in breathing frequency. Gill oxygen extraction was 42 ± 5% and decreased with hypoxia, but under severe hypoxia returned to values characteristic of normoxic. The critical threshold for air breathing was coincident with the P c o 2 during aquatic respiration. This suggests that the air‐breathing response is evoked by the aquatic oxygen tension at which the respiratory mechanisms fail to compensate for environmental hypoxia, and the gill O 2 uptake becomes insufficient to meet O 2 requirements.