The spawning behavior of the coral trout, Plectropomus leopardus, was studied from August to December 1990 at Scott Reef on the northern Great Barrier Reef. A spawning aggregation was located in an area of approximately 1,700 m2, in which coral trout density was monitored
using visual census surveys. Trout aggregated in large numbers in October, with a density increase of up to 12.5-fold above the “normal” density (4 fish⋅1,000 m–2): the density recorded outside the aggregation period. Trout numbers began increasing on the
full moon in October, peaked over the new moon (44 fish⋅1,000 m–2), and dropped rapidly after the first quarter. A smaller spawning aggregation (13 fish⋅1,000 m–2) was detected during the following new moon. Distinct courtship coloration and displays
were observed in males. Courtship displays occurred at all times of the day. Towards dusk small numbers of males established territories in which they courted and spawned with females. Trout spawned in pairs, exhibiting a rapid rush towards the surface, presumably to release gametes. Spawning
was only observed in a 22-min period on sunset. We discuss the contribution of location, timing, and behavioral characteristics of spawning aggregations to spawning success.
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