Iron status of adult dogfish (Scyliorhinus canicula) tissues and sources of iron during embryonic development

Concentrations of iron in embryos and yolk sacs of dogfish Scyliorhinus canicula (Elasmobranchii: Squaliformes) reared in natural and artificial (iron-free and iron-augmented) seawater were measured and compared with the iron content of adult dogfish tissues in order to investigate the iron budget of dogfish embryos. No difference in iron concentration between sexes was observed in adult dogfish. Liver iron concentration (89.6 ±5.8 μg g^-1) showed the highest value among the three tissues investigated and was significantly higher than that measured in muscle (22.6±2.1μg g^-1), or developing eggs from females (40.5 ±2.5 μg g^-1). The iron concentration in the entire contents of early eggcases (27.1 ±4.8 μg g^-1) was lower, but not significantly different from that of eggs taken from the females. Dogfish yolk sacs from eggcases maintained in (a) natural seawater, (b) artificial seawater, and (c) artificial seawater with supplementary iron, for periods of up to six months, did not show any differences in iron content. Developing embryos from the artificial seawater with supplementary iron treatment demonstrated elevated iron concentrations (62.4 ±12.0 μg g^-1) when compared with those from the remaining two treatments (35.8 ±5.8 and 35.1 ±2.7 μg g^-1 respectively). The results identify maternal investment as the primary contributor to the iron burden of juvenile dogfish, and demonstrate the ability of the embryos to supplement this supply from their environment.