Roy, Alexandra-Sophie (2008) Trans-generational marking of clownfish larvae via maternal transmission of stable isotopes. Masters (Research) thesis, James Cook University.

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Abstract

Recent studies on coral reef fishes have successfully employed chemical tagging techniques to quantify local patterns of larval retention and dispersal. Experiments in which larvae were marked via tetracycline immersion of embryos have shown larval dispersal to be more limited than previously thought. However, this technique is limited to fishes that lay eggs on artificial substrata. More recently, a new chemical marking technique has been developed which can be applied to all reef fishes. Females are injected with enriched stable isotopes, such as 137Ba, and the chemical signature is maternally transmitted to embryos and is deposited at the core of the otoliths of larvae. While this technique has been validated for a few species and applied in the field to estimate local dispersal patterns, further laboratory experiments are necessary to determine appropriate injection concentrations and assess any negative effects on larval and adult condition.

The goal of this study was to conduct a series of laboratory experiments to validate the use of trans-generational marking in clownfishes (genus Amphiprion). In the first experiment, the minimum dose of 137BaCl for successful marking of Amphiprion percula larvae and the period over which females continue to produce marked larvae were evaluated. The effects of barium injections on clutch size, clutch area, size at hatching and subsequent larval growth were also assessed. The fish were subject to three dose levels of 137Ba (0.5, 1.0 and 2.5 Dg 137Ba/g fish weight) and the effectiveness of the mark was quantified by measuring the 138Ba/137Ba ratio at the core of the otoliths of recently metamorphosed larvae. All dose levels were 100% successful in providing unequivocal chemical signatures on offspring otoliths. The two highest dose levels, 1.0 and 2.5 Dg 137Ba/g fish weight, continued to mark larvae over 6 consecutive clutches, extending over a period of 80 days after a single injection. In females injected with the lowest concentration, 0.5 Dg 137Ba/g fish weight, the 138Ba/137Ba ratio returned to the natural barium ratio of 6.385 after 2 clutches (≈40 days). Therefore, while all dose levels could be used to mark larvae, the low dose may require females to be re-injected if longer-term marking is required. Barium injections had no consistent effects on the clutch size (number of eggs) or the clutch area. A significant interaction between treatment and time was detected for both the length and weight of larvae. The females with the highest 137Ba dose, 2.5 Dg 137Ba/g fish weight, produced smaller larvae, but the effect disappeared after the fourth generation. As larval size may be a critical parameter affecting survival, this dosage is not recommended for field studies.

In the second experiment, the effects of 137Ba injections on levels of barium in the tissues of adult females and the period over which barium levels remained elevated were assessed for Amphiprion melanopus. In addition, potential effects on adult condition and stress were also evaluated using plasma cortisol analysis. The barium ratios in four tissues (gonads, liver, muscles and bones) were analysed to determine the retention period of barium following two injection doses (2 Dg and 4 Dg 137Ba/g fish weight). The retained barium level was higher in the bones than in the soft tissues (gonads, liver and muscles) for most sampling times (2, 21 and 56 days). Following the initial elevated barium levels, the ratio of 138Ba/137Ba gradually approached the natural ratio of 6.835, although there was some retention even at 56 days post-injection. The plasma cortisol analysis showed that neither the injection nor the chemical induced any stress to females.

In conclusion, these results suggest barium marking will be 100% effective for marking clownfishes larvae, and provided dose levels are kept to a minimum, there will be no adverse effects on adult females or their offspring.

Item ID:	3257
Item Type:	Thesis (Masters (Research))
Keywords:	Amphiprion percula, clownfish, anemone fish, larvae, tagging, chemical marking, chemical signatures, barium isotopes, maternal transmission, otoliths, dosage, effects, clutch size, clutch area, larval growth, maternal stress, condition
Date Deposited:	14 Jul 2009 04:38
FoR Codes:	06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 100%
SEO Codes:	97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50% 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 50%
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