McClelland and Melendy: Heminths as tags in delineating stock o[ Hippoglossoides platessoides 



185 



A=0.09) (Table 1), this acanthocephalan may yet prove 

 to be a useful marker for the detection of southeastern 

 4T migrants among plaice overwintering in Cabot Strait 

 and 4Vn. 



Parasites that contributed to the DFAs above meet 

 MacKenzie's (1987) criteria for biological tags. None 

 of the helminths are known to reproduce directly on 

 or in plaice. Each of the markers is abundant in fish 

 from at least one of the sampling areas, and there are 

 significant geographical variations in the infection pa- 

 rameters of each species within the survey area. The 

 third criterion, that the parasite must be long-lived in 

 the host, is clearly met by five species of larval hel- 

 minth that contribute significantly to classification. 

 Metacercariae of S. baccatum. the larval anisakines A. 

 simplex, C. osculatum. and P. decipiens, and cystacanths 

 of C. strumosum, found variously in the body cavity and 

 musculature, are believed to survive indefinitely in the 

 fish host and have been used as markers in other stud- 

 ies of flatfish stock structure (Arthur and Albert, 1993; 

 Boje et al.,1997; Blaylock et al., 2003). 



Although the life spans of enteric helminths (Fellodis- 

 tomum sp. and E. gadi, herein) in marine fish remain 

 largely unknown, it is possible that species infecting 

 cold-water hosts may persist for several months or even 

 years (Margolis and Boyce, 1969) — sufficient time to 

 meet MacKenzie's (1987) criterion for tag longevity. 

 Echinorhynchus gadi infecting a relict population of 

 Atlantic cod in Lake Mogil'noye, Russia, for example, 

 recruit in the fall and die off in late summer and early 

 fall of the following year (Kulachkova and Timofeyeva. 

 1993). Similarly, E. lageniformis survive for about a 

 year in the intestines of starry flounder (Platichthys 

 stellatus) in the coastal waters of Oregon (Olson and 

 Pratt, 1971). In any event, parasites need not be long 

 lived in order to be suitable as markers, and there are 

 numerous precedents for use of enteric helminths as 

 markers in studies of host stock structure (Williams 

 et al., 1992). Khan and Tuck (1995) identified E. gadi 

 as an important indicator of the discreteness of New- 

 foundland cod stocks, and Power et al. (2005) employed 

 abundances of enteric digeneans in classifying bogue 



(Boops boops) (Sparidae), a demersal species from Span- 

 ish fisheries. 



Abundances of passively transmitted parasites are 

 ultimately a function of host feeding behavior. Hence, 

 geographical differences in intermediate-host abun- 

 dance and frequency in plaice diets would manifest 

 themselves as disparities in infection parameters of 

 passively transmitted helminths in 4T and 4Vn plaice 

 stocks. Digeneans, which mature in the digestive tract 

 of marine fish, are usually acquired through the con- 

 sumption of invertebrates (crustaceans, molluscs, poly- 

 chaetes, and echinoderms, among other taxa) which 

 harbor encysted metacercariae (Rohde, 2005). Brittle 

 stars (Ophiuroidea), which are frequently exploited by 

 both 4Tand 4Vn plaice (Powles, 1965; Minet, 1975), are 

 host to the metacercariae of Fellodistomum sp. (Koie, 

 1980), an important influence in our DFAs involving 

 4Vn plaice. Larval anisakine nematodes (A. simplex, C. 

 osculatum. and P. decipiens), which proved significant in 

 stock delineation herein, are acquired through predation 

 on the parasite's invertebrate hosts, usually crustaceans 

 (Rohde, 2005). Although the life cycle of A. simplex is 

 largely pelagic, the larvae may be transmitted to de- 



