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Target strengths (TS) of orange roughy (Hoplostethus atlanticus) are difficult to measure in situ because this species lives at 800–1200 m, has low TS at 38 kHz, shows strong avoidance behavior, and sometimes co-occurs with species having much higher TS. Orange roughy have wax-invested swimbladders and fish are ∼20% wax esters by weight. Estimates of orange roughy near-dorsal aspect tilt-averaged target strength () are controversial, varying from [−39, −35] dB to [−52, −48] dB for a 35-cm fish in different studies. is estimated using experiments on both live and dead fish, and new swimming orientation data. Target strength of previously frozen and thawed fish decline rapidly, stabilizing after ∼12 h as air and oil diffuse out of tissues during rehydration. A of −46.3 dB is predicted for a 35-cm live orange roughy (bootstrapped 95% confidence intervals=−48.0 to −45.5 dB). This value is 3.7 dB higher than …