PRELIMINARY-OBSERVATIONS ON THE SPAWNING BEHAVIOR OF CORAL TROUT, PLECTROPOMUS-LEOPARDUS (PISCES, SERRANIDAE), ON THE GREAT-BARRIER-REEF

The spawning behavior of the coral trout, Plectropomus leopardus, was studied from August to December 1990 at Scott Reef on the northern Gre at Barrier Reef A spawning aggregation was located in an area of appro ximately 1,700 m2, in which coral trout density was monitored using vi sual census surveys. Trout aggregated in large numbers in October, wit h 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 o ver the new moon (44 fish.1,000 m-2), and dropped rapidly after the fi rst quarter. A smaller spawning aggregation (13 fish.1,000 m-2) was de tected during the following new moon. Distinct courtship coloration an d displays were observed in males. Courtship displays occurred at all times of the day. Towards dusk small numbers of males established terr itories in which they courted and spawned with females. Trout spawned in pairs, exhibiting a rapid rush towards the surface, presumably to r elease gametes. Spawning was only observed in a 22-min period on sunse t. We discuss the contribution of location, timing, and behavioral cha racteristics of spawning aggregations to spawning success.