• kelp forest fishes;
  • mating systems;
  • Paralabrax clathratus;
  • Serranidae;
  • spawning aggregations

The reproductive behaviour of the kelp bass Paralabrax clathratus was studied on Santa Catalina Island, California, U.S.A. from April 2000 to September 2002. Adults formed aggregations of three to > 200 individuals, and spawning occurred within subgroups of three to 23 individuals that contained a single female. The gonado-somatic index (IG) of collected ripe males (mean = 5·8%, range = 0·5–13·1%) indicated a large investment in sperm production that is common in group-spawning fishes characterized by intense sperm competition. Spawning occurred 32 min before sunset to 120 min after sunset, and both males and females were capable of spawning multiple times during a single evening. Behavioural observations of adults and estimates of spawning periodicity from the collection of females with hydrated oocytes suggested that spawning occurred continuously throughout the summer months and showed no significant relationship with the lunar cycle. In general, the spawning behaviour of kelp bass was similar to other functionally gonochoric, group-spawning serranids. The dynamics of P. clathratus spawning aggregations, however, were inconsistent with that of tropical reef fish spawning aggregations, including the transient spawning aggregations of some tropical serranids. Aggregation spawning appeared to be an important component of the annual reproduction of this species.