Respiratory responses and tolerance to hypoxia in two marine teleosts, Epinephelus akaara (Temminck & Schlegel) and Mylio macrocephalus (Basilewsky)

Abstract

The respiratory responses and tolerance of hypoxia were studied in two marine teleosts, the red grouper (Epinephelus akaara, a sluggish species) and the black sea bream (Mylio macrocephalus, an active species). Neither species showed abnormal behaviour or mortality when exposed to 2 mg O2 l-1 for 7 h. The black sea bream was, however, comparatively more tolerant when exposed to 1 mg O2 l-1, but tolerance of both species became similar under extremely hypoxic conditions (i.e. 0.5 mg O2 l-1). In contrast to most other teleosts, both species showed a reduction in opercular beating rate during hypoxia, and oxygen conformity was found in the range of 0.5 to 7.0 mg O2l -1. O2 dissociation curves were constructed, and the P50 value of the black sea breams (27 ± 5.6 mm Hg) was found to be much lower than that of the red groupers (50 ± 2.5 mm Hg). For both species, the general levels of venous PO2 showed a direct relationship to ambient PO2, and were markedly reduced after 1 h exposure to various levels of hypoxia. Compared with the red groupers, the black sea breams appeared to be more able to maintain its venous PO2 levels during prolonged hypoxic exposure. © 1984 Dr W. Junk Publishers.