Large Parasites in a Crowded Space: Variation in Prevalence and Volumetric Effects of Sarcotaces arcticus (Collett, 1874) in Two Host Rockfish (Sebastes spp.) Species
2025
Raquel Wilson | Samantha A. Tilden | Catherine C. Snyder | Mark C. Belk
Sarcotaces arcticus (Collett, 1874) is a relatively large, internal parasitic copepod that infects many marine fishes. Although its large size suggests it may have a negative effect on host reproduction by reducing space available in the abdominal cavity (i.e., volumetric effect), such quantitative aspects of host-parasite relationships for S. arcticus have never been documented. We compared the prevalence and the ratio of live to dead parasites among sizes and sexes of two species of rockfish hosts (Sebastes ciliatus, Tilesius, 1813, dark rockfish: and Sebastes variabilis, Pallas, 1814, dusky rockfish) and quantified the reduction of internal space available in infected hosts. Samples were collected in southeast Alaskan waters where the two host rockfish species coexist in sympatry. Both total prevalence and prevalence of live S. arcticus were significantly higher in S. variabilis compared to S. ciliatus, because of higher prevalence in female S. variabilis. The relationship between body cavity volume, volume available for reproduction, and total length was isometric for both host species combined. An average live S. arcticus with a volume of 8.1 milliliters occupied about 45% in smaller hosts and about 5% in larger hosts of the volume available for reproductive organs. The high prevalence and large size of this parasite could significantly reduce fecundity and fitness of rockfish hosts through reductions in internal volume available for reproduction.
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