This laboratory experiment asked whether the strontium and barium laid down in fish ear stones (otoliths) comes mainly from the surrounding water or from food. The authors spiked seawater with an enriched stable strontium isotope so that water and food carried different isotopic signatures, then traced which signature ended up in the otoliths. Water supplied most of the otolith strontium.
Key numbers
- Water contributed 83 plus or minus 6 (SD) percent of otolith strontium and 98 plus or minus 3 percent of otolith barium, averaged over the treatment tanks; food contributed roughly 17 percent of strontium (Results, p. 128).
- Strontium-to-calcium molar ratios in the rearing tanks ranged from 8.5 to 9.3 mmol/mol over the experiment (Results, p. 127).
- Fish were reared for 70 days; high mortality left 3 treatment tanks and 1 control tank for analysis (Methods, p. 126).
Methods (brief)
Juvenile mummichogs were held in 10 L tanks; treatment tanks were spiked with strontium-86 and barium-137. Water was analyzed weekly by solution ICP-MS for element-to-calcium ratios and isotope ratios, and otoliths were analyzed by laser ablation ICP-MS. A two-source linear isotope mixing model assumed natural isotope ratios in the commercial flake food, which was not measured directly.
Evidence fitness
Supports the general point that, for a marine fish, dissolved strontium in water dominates over dietary strontium in calcified ear-stone tissue. It does not support statements about human intake, food concentrations or toxicity.
Limitations
Food isotope ratios were assumed rather than measured. Only three treatment tanks survived, so between-tank replication is limited. The result applies to fish otoliths, which are metabolically inert, and cannot be transferred to mammalian bone without further evidence.
Related evidence
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