Philip A. Gilderhus

Comparative Efficacy of 16 Anesthetic Chemicals on Rainbow Trout

Abstract Presently there are no legally registered fish anesthetics that allow for the release of fish or use of the fish for food soon after they have been anesthetized. MS-222 (tricaine), the only anesthetic registered for use on fish in the United States, cannot be used within 21 d of harvesting the fish for food. As the start in a search for an anesthetic that can be used with little or no withdrawal period, we tested the efficacy of 16 chemicals as anesthetics on rainbow trout Salmo gairdneri. Efficacy was defined by the fish (1) becoming handleable (quiet enough to be manipulated and handled readily) in 3 min or less, (2) recovering in 10 min or less, and (3) showing no mortality after 15 min in the anesthetic solution. Four chemicals—MS-222, quinaldine sulfate, benzocaine, and 2-phenoxyethanol—met these criteria for efficacy. Chemicals that yielded excessive induction or recovery times or caused excessive mortality were methylpentynol, chlorobutanol, etomidate, metomidate, Piscaine, propanidid, car...

Benzocaine as an Anesthetic for Striped Bass

Abstract Benzocaine was tested as an anesthetic on juvenile and mature adult striped bass (Morone saxatilis). Concentrations of 55 mg/L at 22°C to 80 mg/L at 11°C effectively anesthetized fish in about 3 min. Recovery was more rapid as temperature increased. Fish survived concentrations of twice the effective concentration and exposure times up to 60 min at the effective concentration. Striped bass required higher concentrations for anesthetization than had been previously demonstrated for salmonid fishes, but safety margins for both concentration and exposure time were wider than for the salmonids.

Persistence of Rotenone in Ponds at Different Temperatures

Abstract Two ponds were treated with liquid rotenone (5% rotenone), one with 3 mg/L at 24°C and the other with 2 mg/L at 0°C (concentrations of active rotenone were 0.15 and 0.10 mg/L, respectively). Water samples were collected and analyzed by high-performance liquid chromatography. The concentration of rotenone declined to 0.02 mg/L in 48 h in warm water and in 11 d in cold water. The half-life of rotenone was calculated at 13.9 h in warm water and 83.9 h in cold water.

Rotenone Persistence in Freshwater Ponds: Effects of Temperature and Sediment Adsorption

Abstract The persistence of rotenone was compared between a cement-lined pond (0.04 hectare) and an earthen-bottom pond (0.02 hectare) treated with 5 μL Noxfish/L (250 μg rotenone/L) during spring, summer, and fall. Water temperatures on the days of treatment in each season were 8, 22, and 15°C, respectively. Both ponds were filled with pond water from a common source 1 week before each of the three treatments. Water samples (filtered and unfiltered) and sediment samples were analyzed by high-performance liquid chromatography to monitor the decrease of rotenone until residues were at or below the detection limit (<2.0 μg/L for water and < 25 ng/g for sediments). The loss of rotenone from water generally followed a first-order rate ofdecay. Rotenone disappeared two to three times faster in the earthen pond than in the concrete pond. The rotenone half-life times in the spring, summer, and fall treatments were 3.7, 1.3, and 5.2 d, respectively, in the concrete pond, and 1.8, 0.7, and 1.8 d in the earthen pon...

Efficacy of Benzocaine as an Anesthetic for Sahnonid Fishes

Abstract Benzocaine was tested in the laboratory to determine the effective concentrations for anesthetizing juvenile chinook salmon Oncorhynchus tshawytscha and rainbow trout O. mykiss (formerly Salmo gairdneri). Tests were conducted at three water temperatures, in waters ranging from very soft to very hard, and with groups of rainbow trout from 5 to 47 cm long and chinook salmon 20 cm long. Effective concentrations were defined as those that rendered the fish fully handleable in 3 min or less, allowed recovery of most fish within 10 min, and caused no mortality after 15-min exposures. Concentrations of 25–45 mg/L anesthetized both species over the entire range of conditions tested. Although efficacy was essentially unrelated to species or water quality, it was related to water temperature and size offish; the concentrations of benzocaine required were highest at the lowest water temperatures and for the largest fish.

Benzocaine as a Fish Anesthetic: Efficacy and Safety for Spawning-Phase Salmon

Abstract The anesthetic benzocaine was tested for efficacy and safety for spawning-phase chinook salmon (Oncorhynchus tshawytscha) and Atlantic salmon (Salmo salar) at federal fish hatcheries. Tests were conducted in the existing hatchery water supplies (soft water; temperatures, 10–13 °C. Crystalline benzocaine was dissolved in ethanol (1 g/30 mL), and aliquots of that stock solution were added to the water in test tanks. Benzocaine concentrations of 25–30 mg/L anesthetized most fish in less than 3.5 min, and most fish recovered in less than 10 min after 15 min of exposure. Safety margins were narrow; both species tolerated 30 mg/L for about 20 min, but 25 min of exposure caused deaths. For 15 min exposures, concentrations of 35 mg/L for chinook salmon and 40 mg/L for Atlantic salmon were lethal.

Effects of an aquatic plant and suspended clay on the activity of fish toxicants

Abstract Rotenone, antimycin, permethrin, pydrin, and Salicylanilide I were tested for their toxicities against fathead minnows (Pimephales promelas) in the presence of Canadian waterweed (Elodea canadensis) or suspended clay. The plants had little effect on the activity of rotenone and antimycin but substantially reduced the activity of permethrin and pydrin (synthetic pyrethroids). Bentonite severely inhibited the activity of all chemicals tested. Salicylanilide I was affected least and pydrin most (27 times as much pydrin was required when I g/liter of bentonite was present in 96-hour tests). The efficacy of the registered fish toxicants rotenone and antimycin is probably not significantly affected by vegetation under field conditions, but is greatly reduced by suspended bentonite clay.

Selective Control of Common Carp: Ineffectiveness of 2-(Digeranylamino)-ethanol (GD-174) in Pond Trials

Abstract The candidate piscicide, 2-(digeranylamino)-ethanol, (commonly known as GD-174) was subjected to efficacy trials in ponds under a wide variety of conditions. Results of the trials were disappointing considering that laboratory tests had shown the compound to be selectively toxic to common carp (Cyprinus carpio). Results of pretreatment, on-site toxicity tests were misleading and indicated concentrations that failed to kill all of the carp in 19 of 23 ponds. In a few instances, the chemical killed the carp with little or no effect on nontarget fishes. No fish were killed in some trials and large numbers of nontarget fishes were killed in others. Twenty of 25 pond trials were judged to be unsuccessful. Success or failure of pond treatments could not be correlated with any particular combination of physical, chemical, and biological factors. Because the activity of GD-174 against mixed populations of fish cannot be predicted, further development of this compound as a selective toxicant for carp has ...