Comparative analysis of anesthetic agents used in pre-operative therapy for pearl culture in the red abalone Haliotis rufescens (Swainson, 1822)

Abstract

In pearl culture, the proper selection of anesthetic agents may be a key step to reduce stress and facilitate handling of the organisms, either bivalves (pearl oysters) or gastropods (abalone). This study evaluated the visual (rate of relaxation and recovery, selection of organisms suitable for bead-nucleation) and physiological (glycogen and mucopolysaccharide indices) responses in the red abalone Haliotis rufescens exposed to different types and concentrations of anesthetics. The treatments were: Eugenol at 0.15 mL L−1 (EUA) and 0.25 mL L−1(EUB); Phenoxyethanol at 1.5 mL L−1 (PEA) and 3.0 mL L−1(PEB); Benzocaine at 0.15 g L−1 (BZA) and 0.30 g L−1(BZB); and CO2 to saturation. A different treatment with abalone maintained in fresh seawater without anesthetics was included as the control group. EUB, PEB and CO2 promoted higher proportions of anesthetized abalone (>80%) and abalone suitable for seeding surgery. Mortalities only occurred with the use of Eugenol at both concentrations. With CO2 in particular, 90% of the abalone were suitable for seeding, fully recovered in 168 min, and showed no side effects. The greatest significant decrease in the glycogen index occurred in the abalone treated with EUB, compared to the control group and the rest of treatments. The same trend occurred with the mucopolysaccharide index, where a maximum increase occurred in those abalone anesthetized with EUB, whereas PEB and CO2 showed similar values to the control. Based on these results, the therapy with CO2 is recommended to anesthetize H. rufescens prior to pearl culture; conversely, we suggest avoiding Eugenol as anesthetic due to its various side effects.