The specific oxygen consumption of the Convict cichlid (Cichlasoma nigrofasciatum) has been determined in two life stages, the young stage (before reaching the reproductive state) and the adult stage (reproductive state). Three clearly distinguishable oxygen consumption rates were observed in the young stage during the first 266 days of life. The oxygen consumption relative to body weight (BW) between these three phases differs significantly (average and standard deviation given) : Phase 1, (0.407 +/- 0.106) mg O-2 h(-1) g(-1) BW (age 40-60 days); Phase 2, (0.343 +/- 0.113) mg O-2 h(-1) g(-1) BW (age 76-236 days); and Phase 3, (0.266 +/- 0.057) mg O-2 h(-1) g(-1) BW (age 256-266 days). The oxygen consumption drops significantly to (0.132 +/- 0.051) mg O-2 h(-1) g(-1) BW in the adult stage. No significant effect of body weight on the specific oxygen consumption was observed when the age was taken into account.