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Accumulation and loss of 2' ,5-dichloro-4'-nitrosalicylanilide (Bayer 73) by fish: laboratory studies

Residues of the 2-aminoethanol salt of 2',5-dichloro-4'-nitrosalicylanilide (Bayer 73), as determined by gas-liquid chromatography, were rapidly accumulated by fish exposed to the lampricide -in blood plasma, gallbladder bile, and muscle tissue of coho salmon (Oncorhynchus kisutch) and rainbow trout (Salmo gairdneri), and in bile and muscle of channel catfish (Ictalurus punctatus) and largemouth bass (Micropterus salmoides). Muscle residue levels increased to near the treatment concentration during exposure. After 10 days of withdrawal, residues in plasma, bile, and muscle of rainbow trout and coho salmon decreased to less than 1% of their respective peak concentrations. In all four species, residues in muscle dropped below the limit of detection (0.01 ",gig) within 3 to 14 days. After an initial increase during early withdrawal, bile residues in all species declined steadily but had not dropped below initial levels in channel catfish in 14 days, or below detectable levels (0.01 ",g/mL) in coho salmon after 28 days of withdrawal.

Investigations in Fish Control

Ethyl-p-aminobenzoate (Benzocaine): efficacy as an anesthetic for five species of freshwater fish

Ethyl-p-aminobenzoate (benzocaine) was tested for its efficacy as an anesthetic for rainbow trout (Salmo gairdnerii, brown trout (Salmo truttas, northern pike (Esox lucius). carp (Cyprinus carpio), and largemouth bass (Mieropterus salmoidesi. Since benzocaine is not water soluble, it was applied with acetone as a carrier. Concentrations of 100 to 200 mg!l were required for large adult northern pike, compared with 50 to 100 mg/l for small fish. Rates of sedation and recovery were slower in cold water than in warm water. Water hardness had little influence on the activity of benzocaine. Fish were anesthetized faster and recovered more slowly in acid than in alkaline water. Benzocaine produced deep anesthesia, but concentrations that rendered the fish handleable within 5 min were generally not safe for exposures longer than 15 min. Concentrations of benzocaine efficacious for fish were not acutely toxic to eggs of coho salmon (Oncorhynchus kisutch), chinook salmon (Oncorhynchus tshauiytschas, rainbow trout, brown trout, or lake trout (Salvelinus namaycush). Benzocaine is not registered for fishery use and is neither more effective nor safer than the registered anesthetic, tricaine methanesulfonate (MS-222l.

Investigations in Fish Control