Pollard et al : Chemical marking of Pagrus auratus 



123 



had similar concentrations 

 to the wild-caught control 

 fish. 



Discussion 



Persistence of strontium 



CO 



+1 



1,000 



800 - 



Q. 



CO 



600 



400 



o 

 O 



Fish that were chemically 

 tagged with strontium 

 could be distinguished 

 from control fish, and the 

 chemical marks were per- 

 sistent for at least 36 days, 

 showing no decrease and no 

 regular pattern of change. 

 Although in practice the 

 length of a tagging experi- 

 ment would be likely to ex- 

 ceed this time frame, per- 

 sistence over 36 days may 

 indicate that the stron- 

 tium signal is also likely to 

 persist over longer peri- 

 ods. This conjecture, however, remains to be validated 

 and may be dependent on factors such as bone me- 

 tabolism and growth. Artificially induced strontium 

 signals in fish scales (Ophel and Judd, 1968) and 

 otoliths (Brown and Harris, 1995; Schroder et al., 

 1995, 1996) have been shown to be detectable for 

 periods of greater than a year, and other studies in- 

 vestigating these components have also shown suc- 

 cessful strontium incorporation (Table 3). 



Scales (Lapi and Mulligan, 1981) and otoliths 

 (Edmonds et al., 1989) are relatively metabolically 

 inert tissues, and there is little biological reworking 

 of trace elements deposited within them. On the other 

 hand, the living cells of bone tissue may be meta- 

 bolically active during growth and there may be some 

 turnover of material over the long term. This bone 

 remodeling is related to morphogenesis and physi- 

 ological factors and involves a balance between bone 

 resorption and bone redeposition (Francillon-Veillot 

 et al., 1990). Nevertheless, it is likely that spines are 

 fairly inert components of the skeleton and that ac- 

 tive resorption is unlikely to be high, indicated by 

 the ability to age some fish by the growth rings in 

 spines (e.g. McFarlane and Beamish, 1987; Brennan 

 and Cailliet, 1989; Welch et al., 1993). In addition, 

 similar chemical processes of strontium incorpora- 

 tion during calcification exist between scales, otoliths, 

 and bone, and it was expected that the incorpora- 

 tion of strontium into the spines would result in a 

 relatively constant mark. 



■nil 



fi 



 Sr5x 

 H SrlOx 



 Sr40x 



6 12 24 36 48 6 12 24 36 48 6 12 24 36 48 



Exposure time (hours) 



Figure 2 



Differences in *''Sr incorporation into the spines of juvenile snapper treated with different 

 immersion concentrations and exposure periods. 



Figure 3 



Naturally occurring levels of "''Sr in the spines of wild 

 Pagrus auratus from four estuaries in New South Wales, 

 Australia, compared wirh those of hatchery-reared fish 

 (controls from Port Stephens, N.S.W.) and fish treated 

 with strontium. 



Behrens-Yamada et al. ( 1979) found that strontium 

 appears to become metabolically inert in the verte- 

 brae of coho salmon, Oncorhynchus kisutch, after 



