DEVELOPMENT AND DEPTH DISTRIBUTION OF THE EGGS OF ORANGE ROUGHY, HOPLOSTETHUS-ATLANTICUS (PISCES, TRACHICHTHYIDAE)

The development of the eggs of deep-sea fish has seldom been described. The eggs of orange roughy (Hoplostethus atlanticus), a mid-slope benthopelagic fish, were fertilized and incubated at three temperatures. Those incubated at 7 degrees C hatched at 13 days; wild eggs were estimated to hatch at 7.3 days. Their development rate was similar to that of eggs of fish from other orders and of shallower-living species. From depth-stratified plankton samples, early-stage eggs were found at 500-700 m. Their buoyancy was estimated to be 6.02 kg m(-3), the upper end of the range of known fish-egg buoyancies. The eggs rose to the upper mixed layer at an estimated 23.8 m h(-1), which is faster than ascent rates reported for other fishes. Their relative buoyancy and large size would be the reason for this faster rate. However, large egg size is apparently not an adaptation to enhance development rate; the more rapid rise into warmer water reduces development time but does not fully compensate for the slower development.