118 



Abstract.— The aim of this project was 

 to investigate the use of strontium as a 

 chemical tag in the dorsal spines of the 

 marine teleost Pagrus aiiratus that 

 would allow the mass tagging of juve- 

 nile fish. Previous studies in which the 

 incorporation of strontium has been ex- 

 perimentally manipulated for the pur- 

 poses of marking have generally con- 

 centrated on freshwater and anadro- 

 mous species. This is the first study to 

 investigate the tagging of spines with 

 strontium, the removal of which is non- 

 destructive. Inductively coupled plasma- 

 mass spectrometry (ICP-MS) was used 

 to measure isotopic concentrations. The 

 dorsal spines of juvenile P. auratus 

 that had been immersed in salt water 

 containing 0.125 g/L SrCU-6H.,0 (5x 

 ambient strontium) and 0.250 g/L (lOx 

 ambient) for five days incorporated *^Sr 

 at levels greater than those in control 

 fish. The strontium signal was persis- 

 tent in spines for at least 36 days and 

 showed no sign of decay during the ex- 

 periment. No effects of the treatments 

 on fish health or growth were detected. 

 Short-term immersion experiments (6 

 hours to 5 days) indicated that treat- 

 ments of lOx ambient or greater for 4- 

 5 days were required to tag fish reli- 

 ably with strontium. Natural levels of 

 strontium in the spines of juveniles 

 varied among locations separated by 

 tens of kilometres along the coast of 

 New South Wales. Natural variations 

 in strontium concentrations were not 

 great enough, however, to obscure the 

 differences between tagged and wild 

 fish. It was concluded that strontium 

 immersion is a useful and relatively 

 environmentally safe method of tagging 

 large numbers of small fish. 



Chemical marking of juvenile snapper, 

 Pagrus auratus (Sparidae), by incorporation 

 of strontium into dorsal spines 



Morgan J. Pollard 

 Michael J. Kingsford 



School of Biological Sciences A08 



University of Sydney 



New South Wales 2006, Australia 



E-mail address (for M J, Kingsford, contact author) MikekiSbio usyd edu au 



Stephen C. Battaglene 



ICLARM, Coastal Aquaculture Centre 



PO Box 438 



Honiara, Solomon Islands 



Manuscript accepted 22 April 1998. 

 Fish. Bull. 97:118-131 (1999). 



Calcium is incorporated into the 

 calcium carbonate matrix of otoliths 

 and into the calcium phosphate 

 matrix of the skeleton, spines, and 

 scales as fish grow (Francillon- 

 Vieillot et al., 1990). In addition to 

 calcium, trace elements, such as 

 strontium, are also incorporated 

 into the calcified components offish. 

 The chemical similarities of Ca"* 

 and St'^* ions (i,e. similar ionic ra- 

 dius and identical valence) allow 

 strontium ions to act as replace- 

 ments for calcium during the pro- 

 cess of calcification, Ca and Sr con- 

 centrations in calcified components 

 have been explored for their rela- 

 tionships with variations in envi- 

 ronmental conditions (Edmonds et 

 al„ 1989; Gallahar and Kingsford, 

 1992), such as temperature (Kalish, 

 1989;Radtkeetal., 1990;Townsend 

 et al,, 1992, 1995) and salinity 

 (Kalish, 1990; Coutant and Chen, 

 1993; Secor et al., 1995), 



The manipulation of ambient lev- 

 els of chemicals such as strontium 

 can allow fish to be marked or 

 tagged invisibly. The marking of 

 skeletal structures with isotopes 

 offers a potential method for rapid 

 tagging of large numbers of small 

 juvenile fish. Nonradioactive stron- 



tium has been investigated, and 

 artificially induced strontium marks 

 have been detected in otoliths 

 (Brown and Harris, 1995; Mugiya 

 and Satoh, 1995; Mugiya and Tan- 

 aka, 1995; Schroder et al,, 1995, 

 1996; Gallahar and Kingsford, 

 1996), scales (Ophel and Judd, 

 1968; Behrens-Yamada and Mul- 

 ligan, 1982; Snyder et al„ 1992), 

 vertebrae (Behrens-Yamada et al,, 

 1979; Behrens-Yamada and Mul- 

 ligan, 1982, 1987; Schroder et al„ 

 1995), and opercular bones (Guillou 

 and de la Noue, 1987; Schroder et 

 al,, 1995), The majority of this work, 

 however, has been done on freshwa- 

 ter or anadromous species. 



The species investigated in this 

 study was the snapper or red sea 

 bream, Pagrus auratus (Pisces; 

 Sparidae), The northern hemi- 

 sphere and southern hemisphere 

 forms (previously Pagrus major and 

 Chrysophrys auratus, respectively) 

 are now considered to be morpho- 

 metrically identical (Paulin, 1990), 

 This highly valued commercial spe- 

 cies supports a very well established 

 intensive aquaculture industry in 

 Japan (Foscarini, 1988; Davy, 1990, 

 1991; Fukusho, 1991) and shows 

 good potential for aquaculture in 



