The effects of
sulfide on the energy metabolism of Boleophthalmus boddaerti in normoxia and
hypoxia were examined. The 24-, 48-, and 96-h LC50 values of
sulfide for B. boddaerti with
body weight ranging from 11.6 to 14.2 g were 0.786, 0.567, and 0.467 mM, respectively. The tolerance of B. boddaerti to
sulfide was not due to the presence of a
sulfide-insensitive
cytochrome c oxidase. There was no accumulation of
lactate in the muscle and liver of specimens exposed to
sulfide in normoxia. In addition, the levels of
ATP,
AMP, and energy charge in both the muscle and the liver were unaffected. These results indicate that B. boddaerti was able to sustain the energy supply required for its metabolic needs via mainly aerobic respiration when exposed to
sulfide (up to 0.4 mM) in normoxia. Exposure of B. boddaerti simultaneously to
hypoxia and 0.2 mM
sulfide for 48 h resulted in decreases in the
ATP levels in the muscle and liver. However, the energy charge in both tissues remained unchanged, and the level of
lactate accumulated in the muscle was too low to have any major contribution to the energy budget of the fish. Our results reveal that B. boddaerti possesses inducible mechanisms to detoxify
sulfide in an ample supply or a lack of O2. In normoxia, it detoxified
sulfide to
sulfate,
sulfite, and
thiosulfate. There were significant increases in the activities of
sulfide oxidase in the muscle and liver of specimens exposed to
sulfide, with that in the liver being >13-fold higher than that in the muscle. However, in
hypoxia,
sulfide oxidase activity in the liver was suppressed in response to environmental
sulfide. In such conditions, there were significant increases in the activities of
sulfane sulfur-forming
enzyme(s) in the muscle and liver that were not observed in specimens exposed to
sulfide in normoxia. Correspondingly, there were no changes in the levels of
sulfate or
sulfite in the muscle or liver. Instead, B. boddaerti detoxified
sulfide mainly to
sulfane sulfur in
hypoxia. In conclusion, B. boddaerti was able to activate different mechanisms to detoxify
sulfide, producing different types of detoxification products in normoxia and
hypoxia.