Tetracycline as a fluorescent shell-marker in the abalone Haliotis iris

Abstract

Ageing of abalone by counting rings laid down internally in the shell has presented problems of validation. Three methods of tetracycline marking were tested in Haliotis iris. Juvenile (<70 mm shell length) and adult (>115 mm) abalone were injected intramuscularly with tetracycline hydrochloride, injected with oxytetracycline, or immersed in tetracycline hydrochloride. After treatment, shells were cut sagitally and examined under ultraviolet light using a stereomicroscope. In treatments where juveniles were injected with tetracycline hydrochloride or oxytetracycline hydrochloride at dosages ranging from 20 to 600 mg per kg body weight, no fluorescent marks were visible from treatments≤80 mg/kg, but 83% of juveniles treated with greater dosages retained a visible mark. In treatments where juveniles were immersed in seawater solutions of tetracycline hydrochloride at five concentrations ranging from 200 to 1000 mg per litre of seawater and sampled at 5 h intervals for periods ranging from 5 to 40 h, all showed clear fluorescent markings. Shells of adult abalone injected with tetracycline hydrochloride at four dosages ranging from 200 to 800 mg/kg all showed clearly visible marks 18 d post-treatment. Abalone injected at dosages of 600 and 800 mg/kg exhibited tissue fluorescence around the injection site 2 wk after treatment. Adults immersed for 48 h at four concentrations ranging from 200 to 800 mg/l produced marks comparable to those of injected adults. Abalone were clearly stressed by some treatments. Only 50% of adults injected at 200 mg/kg were able to right themselves within 10 min, while all those injected at higher concentrations either were incapable of righting themselves after treatment or were extremely sluggish. All immersed adults quickly righted themselves. These results show that both injection and immersion are effective in marking abalone, but that immersion is less stressful to them.