DISTRIBUTION OF EXTERNAL PARASITES INDICATES BOUNDARIES TO DISPERSAL OF SILLAGINID FISHES IN THE INDO-WEST PACIFIC

The distribution of sillaginid-specific ectoparasites permits the dist inction of two provinces with high parasite diversity: one on the cont inental shelf of Australia, and one on the shelf of Asia. The Australi an province has 15 endemics (five monogeneans, one leech and nine cope pods), and the Asian province has 14 endemics (two monogeneans and 12 copepods). These provinces are separated by a region with coastlines t hat descend very steeply to the ocean floor and by deep ocean waters t hat largely inhibit sillaginid movements. Some sillaginids must have d ispersed across eastern Indonesia, however, leading to the occurrence of four parasites in both provinces. Three Australian parasites also a ppear to be presently encroaching onto the southern periphery of the A sian shelf. At least one less-recent invasion of Australian waters by Asian sillaginids would account for the occurrence of six pairs of cop epod congeners that have one member in each province. The most widespr ead sillaginid, Sillago sihama, seems to have dispersed to African sho res from the Arabian Sea as planktonic larvae only (no Asian parasites were present in samples of 29 hosts) and relatively recently (only on e locally endemic parasite appears to have been acquired).