This study assessed the potential of five fluorochromes in marking shells of the abalone Haliotis rubra, using an immersion technique. Such marks are required to 'time stamp' the shells and thus determine whether shell layers are deposited regularly enough to be used to age abalone. The stains used were: oxytetracycline and tetracycline at 300-1000 mg L-1; calcein at 10-120 mg L-1; alizarin red S at 10-60 mg L-1; and xylenol orange at 20-100 mg L-1. Immersion times were 12, 24 and 48 h. Mortality rates were low in all treatments, and clearly discernible marks were produced when abalone were immersed for 24 and 48 h at high concentrations in all the stains. Three problems were encountered when tetracyclines were employed: (i) the solutions were acidic, so the pH had to be adjusted with NaOH to prevent mortality; (ii) there was excessive foaming of the solutions; and (iii) a natural fluorescence in the shells closely resembled that of the tetracyclines. Problems also arose in assessing alizarin red and xylenol orange because they have long emission wavelengths, so that simultaneously viewing natural layers on the sections is difficult. Calcein, although expensive, was the most effective, as at high concentrations it consistently produced bright, extensive marks. The success of marking appeared to depend on the growth rate of the abalone, as feeding before staining increased the intensity of marks, and marking varied between batches of abalone collected at different times.

No abstract

8Jacklip abalone, Haliotis rubra (L.), were immersed for 48 to 144 hours in buckets containing sea water to which MnCl z .4H 2 0 was added at concentrations ranging from 9.5 to 1890 mg L-t, in order to determine the optimum concentrations for marking. Manganese concentrations above 945 mg L-t over the immersion period were lethal to abalone. Cathodoluminescence microscopy was used to detect manganese mineralised within shell layers in situ. Although the average length and width of manganese carbonate marks at the outer growing margin of the abalone shell increased with higher concentrations, marks in the shell area under the spire appeared to be maximal at intennediate concentrations. Better marks were found at the growing edge than under the spire, although this appeared ·to depend on the seasonal timing of marking. Manganese concentrations of 378 mg L-t or less in sea water for 48 h were not lethal to abalone after 10 days, but the scores of marks indicated a possible sub-lethal toxic effect of 144 h immersion at 272 mg L-t. In a field trial we obtained 93% survival after 14 days of abalone exposed to 200 mg L-t of manganese for 48 h and of these 60% showed marks in the spire region, where age is estimated, so this technique can be used in age validation studies. However, the effectiveness of manganese as a time-marker for increment analysis appears to depend on the growth of abalone when exposed to the marker and the ambient levels of manganese in the natural habitat.