183 



Use of parasites in stock identification of the 

 deepwater redfish (Sebastes mentella) 

 in the Northwest Atlantic 



David J. Marcogliese 



St Lawrence Centre 



Environment Canada 



105 McGill, 7"^ Floor 



Montreal, Quebec H2Y 2E7, Canada 



E-mail address- david-marcogliese(giec,gc.ca 



Elaine Albert 



Department of Fisheries and Oceans 

 Maunce Lamontagne Institute 

 PO Box 1000 

 Mont-Joli, Quebec G5H 3Z4, Canada 



Pierre Gagnon 



St Lawrence Centre 



Environment Canada 



105 McGill, 7"' Floor 



Montreal, Quebec H2Y 2E7, Canada 



Jean-Marie Sevigny 



Department ol Fishenes and Oceans 

 Maunce Lamontagne Institute 

 PO Box 1000 

 Mont-Joli, Quebec G5H 3Z4, Canada 



An important aspect of fisheries man- 

 agement is the correct dehneation of 

 boundaries between fish stocks. With 

 the recent collapse of the groundfish 

 fishery in eastern Canada, redfish 

 (Sebastes spp.) has become an increas- 

 ingly important resource. Currently, 

 the two most economically important 

 redfish species (S. fasciatus and S. 

 mentella) are partitioned into eight 

 management areas in the Northwest 

 Atlantic (Fig. 1). In this study, we 

 examined the parasite fauna of the 

 deepwater redfish S. mentella, col- 

 lected from different areas in the 

 Northwest Atlantic, to determine if 

 the distribution and abundance of the 

 parasite fauna can aid in stock dis- 

 crimination of this species and focused 

 on differentiating fish from the Gulf 

 of St. Lawrence (unit 1) from those 

 from the Cabot Strait and Lauren- 

 tian Channel (unit 2). The deepwater 



redfish is the most common redfish 

 species in the Gulf of St. Lawrence and 

 is considered to have a more northerly 

 range and deeper distribution than its 

 congeners (Atkinson, 1987; Scott and 

 Scott, 1988). 



In eastern Canada, parasites have 

 been successfully employed to discrim- 

 inate among stocks of another deep- 

 water fish, the Greenland halibut iRe- 

 inhardtius hippoglossoides) (Arthur 

 and Albert. 1993), as well as Atlantic 

 cod {Gadus morhiia) (McClelland and 

 Marcogliese, 1994). Moles et al. (1998) 

 suggested that parasites could be used 

 to discriminate among stocks of rock- 

 fishes (Sebastes spp.) in the Gulf of 

 Alaska, and Stanley et al. (1992) used 

 the monogenean Microcotyle sebastis 

 to confirm that the yellowtail rockfish 

 Sebastes flavidus was distributed in 

 discrete groups along the Pacific coast 

 of North America. However, there is 



not much information on Sebastes spp. 

 from the Northwest Atlantic because 

 studies of redfish parasites prior to 

 that of Bourgeois and Ni (1984) must 

 be treated with caution because of the 

 possible confusion in identification of 

 redfish species (Moran et al., 1996). 



Materials and methods 



Host and parasite collections 



A total of 170 deepwater redfish of size 

 >22 cm were sampled by bottom trawl 

 from five areas representing four man- 

 agement units off the Atlantic coast 

 of Canada between August 1996 and 

 January 1997. Summer and winter 

 samples were available only in unit 2 

 (Fig. 1, Table 1). Fish were measured 

 on board, individually bagged, and 

 deep frozen immediately after capture 

 for later examination. Because fish 

 from southwestern Labrador Sea and 

 Flemish Cap were not measured on 

 board, estimates of fresh length were 

 made for these fish by using a regres- 

 sion of fresh length on frozen length 

 obtained from the other fishes. 



Fish were thawed in the laboratory, 

 measured (total length), and weighed. 

 Prior to parasitological examination, 

 species of redfish were identified by 

 the number of soft anal-fin rays. Only 

 those that had 8 or more soft rays 

 at the anal fin were retained for the 

 analyses (Ni, 1981). Examinations for 

 metazoan parasites were performed 

 with a stereomicroscope using stan- 

 dard parasitological methods. The ex- 

 ternal surface was examined and scars 

 from previous infestations of S. lumpi 

 were noted. The gills were removed, 

 rinsed, and their arches were detached 

 and examined separately. Because of 

 the pressure changes when redfish 

 were hauled out from the deep water 

 most of the stomachs were everted. The 

 internal organs (heart, liver, spleen, 

 gall bladder, swim bladder, digestive 

 tract, gonads, kidney, urinary bladder) 

 were inspected for parasites (lying 

 free or encapsulated on the exterior). 



Manuscript accepted 21 August 2002. 

 Fish. Bull. 101:183-188 (2003). 



