Evaluation of potential anesthetics for the freshwater mussel Elliptio complanata

A series of experiments was conducted to develop a safe. rapid, and reliabl e method to relax and anesthetize freshwater mussels for collection of biol ogical samples and assessment of reproductive status. Various concentration s and combinations of eight potential anesthetic agents were administered b y bath, slow drip, or injection into the foot or incurrent aperture of 10-4 0 Elliptio complanata per treatment group. Mussels were considered relaxed when the foot extended 2 cm beyond the shell and anesthetized when the valv es gaped, and the animal became impervious to touch. Buffered MS-222 (pH 7) produced relaxation within 60 min at concentrations greater than 50 ppm an d anesthesia within 3 h at 500-1,000 ppm. Mussels exposed to unbuffered MS- 222 at concentrations greater than 250 ppm (pH 3-4) ceased siphoning and cl osed tightly. Phenoxyethanol at 1.5-3.0% produced anesthesia within 20-50 m in bat had associated mortality. The effective dose of phenoxyethanol could be reduced to 0.25% with no mortality if mussels were first relaxed with M S-222. Injection of 0.5-5.0 mg succinylcholine chloride into the foot produ ced rapid immobilization that lasted 20-30 min. Dichlorvos at concentration s of 25-50 ppm induced anesthesia in 3-5 h, bur mussels were extremely slow to recover. Clove oil at 0.25-1.00 mL/L anesthetized 65-95% of the mussels tested but proved difficult to work with in confined spaces. Magnesium chl oride, potassium chloride, and menthol crystals had no apparent affect on E lliptio complanata. This study identified several anesthetic agents for fre shwater mussels, each differing in induction time, duration of effect, and degree of foot relaxation. We recommend 500 ppm buffered MS-222 for general laboratory use on Elliptio complanata because of ease of handling and safe ty for both humans and animals.