Retention of a transgenerational marker (137Barium) in tissues of adult female anemonefish and assessment of physiological stress

Recently it was shown that female fish injected with enriched stable isotopes maternally transmit a chemical signature to larval otoliths. Validation of this larval marking technique requires laboratory experiments to determine appropriate injection concentrations and to assess any negative effects on larval and adult condition. This study investigated the temporal profile of ¹³⁷barium assimilation and retention in tissues of adult female anemonefish Amphiprion melanopus (Pomacentridae) following intraperitoneal injection with either 2 or 4 μg ¹³⁷Ba g^?1 body mass. Mean barium isotope ratios (¹³⁸Ba:¹³⁷Ba) in the two groups of treated fish were not significantly different from each other, but were significantly different from those in the control group up to 56 days post-injection. This pattern of ¹³⁷Ba retention was consistent across gonad, muscle, liver and bone tissues. Mean plasma cortisol concentration (an indicator of non-specific physiological stress) was not significantly different among groups and was considered to be representative of unstressed fish. Together, these results indicate that (1) A. melanopus suffer minimal physiological stress and cope well after treatment with ¹³⁷Ba, (2) ¹³⁷Ba is retained in female A. melanopus for a prolonged period (at least 56 days), such that multiple clutches of offspring are likely to be marked with an isotopic signature, and (3) a lower dosage of 2 μg ¹³⁷Ba g^?1 appears sufficient for transgenerational marking. It is concluded that ¹³⁷Ba is suitable for use as a transgenerational marker and is a powerful tool to resolve long-standing enigmas such as larval dispersal distances and the fishery benefits of marine reserves.