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Target strengths ͑TS͒ of orange roughy ͑Hoplostethus atlanticus͒ 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 ϳ20% wax esters by weight. Estimates of orange roughy near-dorsal aspect tilt-averaged target strength ͑͗TS͒͘ are controversial, varying from ͓Ϫ39, Ϫ35͔ dB to ͓Ϫ52, Ϫ48͔ dB for a 35-cm fish in different studies. ͗TS͘ 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 ϳ12 h as air and oil diffuse out of tissues during rehydration. A ͗TS͘ of Ϫ46.3 dB is predicted for a 35-cm live orange roughy ͑bootstrapped 95% confidence intervalsϭϪ48.0 to Ϫ45.5 dB͒. This value is 3.7 dB higher than Australian estimates of ϷϪ50 dB for ͗TS͘ of a 35-cm live orange roughy. It is shown that the magnitude of the difference between in situ estimates of ͗TS͘ and experimental measurements of ͗TS͘ on live fish can be explained by the effect of strong avoidance reactions to a towed transducer on the tilt angle of the fish. Previously much higher estimates of dead orange roughy ͗TS͘ were an artifact of air pockets caused by freezing. Comparison of orange roughy TS max measured in our experiments with a large dataset for nonswimbladder and swimbladder fish shows that orange roughy have an unusually low target strength at 38 kHz.

Eggs ranged from 1.10 to 1.17 mm in diameter and contained a single oil droplet 0.30-0.35 mm in diameter. Hatching occurred after 146 h at 10-13°C and larvae survived for 4 days.Comparison with other Seriolella species shows features allowing distinction of S. punctata eggs and larvae.