may be divided into two periods (Bakun 1973), 

 "upwelling" (March-August) and "oceanic" 

 (September-February). Upwelling periods are 

 characterized by an increase in the flow of 

 nutrient-rich bottom water to the surface and in- 

 creased plankton abundance. Olive rockfish food 

 habits change with these seasons (Love and 

 Westphal 1981). Zooplankton (particularly pelagic 

 tunicates and euphausids), squids, and juvenile 

 rockfish are eaten in greater quantity during the 

 upwelling season, due to increased availability. 



The secondary intermediate hosts for hemiurids 

 and Opechona sebastodis are planktonic (Shotter 

 1973; Yamaguti 1971), and the prevalence increase 

 may be due to greater seasonal predation on the 

 planktonic intermediate host. Similarly, as fish 

 are possible intermediate hosts of Hystero- 

 thylacium aduncum, its infection pattern may re- 

 flect the rockfish's heavy predation on juvenile 

 rockfish during the upwelling period. 



All of the parasite species infecting olive rock- 

 fish infect at least some other rockfish species. The 

 genus Sebastes has exhibited an explosive radia- 

 tion in the northeast Pacific (Kabata 1970). This 

 rapid speciation has occurred relatively recently, 

 probably during and after the Miocene 1 . Despite 

 extreme morphological and behavioral differences 

 between species, there is little species specificity 

 among rockfish parasites, perhaps because of the 

 rapidity of the host speciation events. Eighty-nine 

 adult metazoan parasites have been reported from 

 rockfishes between Alaska and California (Love 

 and Moser 1983). Of these, 30 species have been 

 found to infect only Sebastes spp. and 10 of the 89 

 species were unique to one host species. 



Some of this specificity may be a function of host 

 behavior or habitat preference rather than 

 physiological differences (Kennedy 1975) between 

 rockfish hosts. Holmes (1971) found that a rock- 

 fish's proximity to rocky reefs influenced the prev- 

 alence of the digenetic trematodes Psettarium 

 sebastodorum and Aporocotyle macfarlani. 

 Aporocotyle macfarlani was found in species as- 

 sociated with inshore reefs, P. sebastodorum in 

 those hosts living away from rocks or in deeper 

 waters. Olive rockfish, limited to relatively shal- 

 low reefs, occasionally harbored A. macfarlani but 

 was not infected with P. sebastodorum . 



Some parasites, particularly ectoparasites, are 

 widespread among rockfishes. For example, Mi- 

 crocotyle sebastis has been reported from 22 



1 W. Eschmeyer, California Academy of Science, Golden State 

 Park, San Francisco, CA, pers. commun. 1982. 



species, Naobranchia occidentalis from 13, Neo- 

 branchiella robusta from 21, and Chondr acanthus 

 pinguis from 19. These and other parasites exhibit 

 an extensive latitudinal range, considerably 

 longer than some of their hosts. Further surveys of 

 those species only lightly studied (such as Sebastes 

 eos, S. melanostomus, S. mystinus, S. rastrelliger, 

 and S. semicinctus) will show that some of those 

 parasites infect nearly all rockfish species. 



Acknowledgments 



We thank Mike Moser and Larry Jensen for 

 their assistance in parasite identification. Dave 

 Behrens, Richard Bray, Craig Fusaro, Robert 

 Henderson, Lew Halderson, Ralph Larson, Dave 

 Laur, Gerry Robinson, and Jerry Wellington as- 

 sisted in collecting specimens. We are also indebt- 

 ed to Waheedah Muhammad for typing the final 

 manuscript. 



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