Daniel G. Carty

Lake Trout Discovered in Yellowstone Lake Threaten Native Cutthroat Trout

Abstract On 30 July 1994, lake trout (Salvelinus namaycush) were discovered in Yellowstone Lake in Yellowstone National Park, Wyoming, the core of the remaining undisturbed natural habitat for native Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri). Data from this and other lake trout subsequently caught by anglers and the U.S. Fish and Wildlife Service suggest lake trout have reproduced in Yellowstone Lake since at least 1989 and now number in the thousands, perhaps tens of thousands. A highly piscivorous, nonnative species, lake trout will probably thrive in Yellowstone Lake and reduce the lakes cutthroat trout stocks substantially unless preventive management actions are taken. A team of scientists that convened in February 1995 to discuss the lake trout problem concluded that there is little chance lake trout can be eliminated from Yellowstone Lake. The team projected a decline of 90% or more in cutthroat trout numbers in 20 years–100 years if the lake trout population is not controlled. Th...

Efficacy of 35% PEROX-AID (Hydrogen Peroxide) in Reducing an Infestation of Gyrodactylus salmonis in Freshwater-Reared Rainbow Trout

Abstract Gyrodactylus salmonis is a monogenean ectoparasite that can infest a variety of captive-reared salmonid fishes. The physical damage inflicted during severe infestations can cause osmoregulatory disturbances and potentially render individuals more vulnerable to secondary pathogens. If not treated, G. salmonis infestations can reduce growth and survival in affected fish populations. Many chemical compounds have been used to treat Gyrodactylus infestations; however, little information has been published about the use of hydrogen peroxide (H2O2) for Gyrodactylus control. Consequently, we conducted a trial to evaluate the efficacy of H2O2 in reducing a natural infestation of G. salmonis in freshwater-reared, adult rainbow trout Oncorhynchus mykiss. Triplicate tanks of adult rainbow trout (20 fish per tank; length = 45.6 ± 5.8 cm and weight = 1.3 ± 0.4 kg, mean ± SD) were exposed to a static bath of H2O2 at a target dosage of 50 mg/L or hatchery water (sham treatment) for 30 min/d on two alternate days...

Effectiveness of Aquaflor (50% Florfenicol) to Control Mortality Associated with Streptococcus iniae in Freshwater-Reared Subadult Sunshine Bass

We conducted a field trial to evaluate the effectiveness of Aquaflor (50% florfenicol) for controlling mortality associated with Streptococcus iniae in freshwater-reared subadult sunshine bass (female white bass Morone chrysops X male striped bass M. saxatilis). Bacterial samples collected from moribund fish representing a reference population were presumptively identified microbiologically and were later confirmed to be S. iniae by biochemical characterization and polymerase chain reaction. The trial comprised a 1-d acclimation period, 10-d treatment period, and 14-d posttreatment period. During the treatment period, Aquaflor-medicated feed was administered to treated tanks (N = 3) at a target dose of 10 mg of florfenicol x kg of fish(-1) x d(-1), and nonmedicated feed was administered to control tanks (N = 3). At the end of the posttreatment period, mean (+/- SD) cumulative mortality in treated tanks (9 +/- 11%) was significantly (P = 0.040) less than that in control tanks (52 +/- 13%). Analysis of medicated feed samples revealed that treated tanks had received an actual dose of 8.3 mg florfenicol x kg fish(-1) x d(-1) (83% of target). No florfenicol was detected in control feed samples. Although the actual florfenicol dose administered to treated tanks was less than the target dose, the trial was accepted by the U.S. Food and Drug Administration Center for Veterinary Medicine as demonstrating the efficacy of Aquaflor to control mortality associated with S. iniae in cultured sunshine bass populations.

Controlling Mortality Caused by External Columnaris in Largemouth Bass and Bluegill with Chloramine-T or Hydrogen Peroxide

Abstract Columnaris (causative agent, Flavobacterium columnare) is a widespread fish disease of concern among fish culturists in the USA. If left untreated, an entire population of fish may become infected, and morbidity and mortality may reach high levels. In virtually all instances, columnaris outbreaks require intervention to prevent significant losses. A number of sanitizing agents, most notably chloramine-T (CLT) and hydrogen peroxide (HP), have been used to control mortality associated with a variety of bacterial pathogens causing external infections. However, the majority of trials conducted to demonstrate the effectiveness of these chemicals, thereby gaining U.S. Food and Drug Administration approval for their use in treating fish infected with columnaris, have been conducted on salmonids. Accordingly, we conducted seven experiments to evaluate the effectiveness of CLT or HP to control mortality associated with external columnaris in Florida Largemouth Bass Micropterus salmoides floridanus and Blu...

Efficacy of SLICE Premix (0.2% Emamectin Benzoate) for Reducing Infestations of Salmincola spp. on Freshwater-Reared Rainbow Trout

Abstract Salmincola spp. are ectoparasites of major concern in wild and cultured salmonids. These parasites can cause respiratory distress and facilitate the entry of secondary pathogens. Of particular concern in the United States is S. californiensis, which can infest all Oncorhynchus spp. and is restricted largely to freshwater. Bath treatments with formalin and hydrogen peroxide have traditionally been used to control infestations of some parasitic copepods in cultured salmonids; however, these treatments can be difficult to apply, expensive, and stressful to fish and have not been shown to be effective against S. californiensis. A more effective and efficient treatment method needs to be developed. SLICE (0.2% emamectin benzoate [EB]) is a commercial in-feed treatment that has been shown to be effective for the control of sea lice infestations in seawater-reared farmed salmon and trout. We postulated that EB might also be efficacious for the control of parasitic copepods such as S. californiensis on f...

Chloramine-T Margin-of-Safety Estimates for Fry, Fingerling, and Juvenile Rainbow Trout

Abstract Chloramine-T (CLT) is a candidate for approval for use in U.S. aquaculture to control mortality in freshwater-reared salmonids caused by bacterial gill disease (causative agent, Flavobacterium branchiophilum). The proposed treatment regimen is to administer CLT at 12–20 mg/L in a static or flow-through bath for 60 min/d on three alternate or consecutive days. To estimate a CLT margin of safety, defined as the highest dosing regimen above the proposed maximum therapeutic regimen at which no adverse effects are observed, we conducted seven experiments with fry, fingerling, and juvenile rainbow trout Oncorhynchus mykiss that examined mortality and an eighth experiment that examined mortality, gross pathology, and histopathology after CLT exposure. In each experiment, triplicate groups of fish were exposed to a range of CLT concentrations representing 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 5× the highest proposed dose (20 mg/L) for 3× the proposed treatment duration (60 min) on three alternate or consecuti...

Inexpensive Apparatus to Rapidly Collect Water Samples from a Linear-Design, Plug-Flow Hatchery Raceway

Abstract In July 2001, we conducted a study to determine whether a target concentration of chloramine-T (a waterborne chemical) could be achieved and maintained for 60 min in linear-design, plug-flow hatchery raceways (devoid of fish) via a “charged” flow-through treatment methodology. In each of four independent trials, a raceway was charged to achieve the target concentration by turning off the inflow water (creating a static bath) and manually mixing in a premeasured volume of chloramine-T stock solution. Water inflow was then turned on, and the target concentration was maintained by metering additional chloramine-T stock solution into the inflow water via a calibrated chicken-watering system. To help verify chloramine-T concentrations during treatment, we built an apparatus to rapidly collect many water samples from throughout a raceway. The apparatus comprised three fixed sampling stations, each of which was equipped with 9 water collection devices (i.e., nine 60-mL plastic syringes fitted with fixed...