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At least 883 records · Page 49Linked to original sources
USGS2002

Isolation of thiaminase-positive bacteria from alewife

Evidence pointing to thiamine deficiency as a primary factor in early mortality syndrome in feral salmonids from the Great Lakes and New York's Finger Lakes continues to mount. Such deficiency is believed to be the result of the consumption of nontraditional forage fish, such as alewife Alosa pseudoharengus , that contain thiaminase activity. The source of thiaminase within these forage fish has not been reported. In this study, we report finding thiaminase-positive Paenibacillus thiaminolyticus and other Paenibacillaceae that are closely related to P. thiaminolyticus in the viscera of frozen alewives. Thiaminase-positive bacteria associated with alewife viscera have not previously been reported. Because viable thiaminase-positive cultures were found in only 25% of the fish, bacteria should be considered as only one potential source of thiaminase in alewives.

Transactions of the American Fisheries Society↗
USGS1999

Influence of infection with Renibacterium salmoninarum on susceptibility of juvenile spring chinook salmon to gas bubble trauma

During experiments in our laboratory to assess the progression and severity of gas bubble trauma (GBT) in juvenile spring chinook salmon Oncorhynchus tshawytscha , we had the opportunity to assess the influence of Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease, on the susceptibility of salmon to GBT. We exposed fish with an established infection of Rs to 120% total dissolved gas (TDG) for 96 h and monitored severity of GBT signs in the fins and gills, Rs infection level in kidneys by using an enzyme-linked immunosorbent assay (ELISA), and mortality. Mortality occurred rapidly after exposure to 120% TDG, with a LT20 (time necessary to kill 20% of the population) of about 37 h, which is at a minimum about 16% earlier than other bioassays we have conducted using fish that had no apparent signs of disease. Fish that died early (from 31 to 36 h and from 49 to 52 h) had significantly higher infection levels (mean ?? SE ELISA absorbance = 1.532 ?? 0.108) than fish that survived for 96h (mean ?? SE ELISA absorbance = 0.828 ?? 0.137). Fish that died early also had a significantly greater number of gill filaments occluded with bubbles than those that survived 96 h. Conversely, fish that survived for 96 h had a significantly higher median fin severity ranking than those that died early. Our results indicate that fish with moderate to high levels of Rs infection are more vulnerable to the effects of dissolved gas supersaturation (DGS) and die sooner than fish with lower levels of Rs infection. However, there is a substantial amount of individual variation in susceptibility to the apparent cumulative effects of DGS and Rs infection. Collectively, our findings have important implications to programs designed to monitor the prevalence and severity of GBT in juvenile salmonids in areas like the Columbia River basin and perhaps elsewhere.

Journal of Aquatic Animal Health↗
USGS2000

Molecular epidemiology reveals emergence of a virulent infectious hematopoietic necrosis (IHN) virus strain in wild salmon and its transmission to hatchery fish

Infectious hematopoietic necrosis virus (IHNV) has been known to be a significant salmonid pathogen in the Pacific Northwest of North America for decades. The goal of this study was to characterize the IHNV genetic heterogeneity and viral traffic over time at a study site in the Deschutes River watershed in Oregon, with an emphasis on the epidemiology of IHNV types causing epidemics in wild kokanee Oncorhynchus nerka between 1991 and 1995. The study site included kokanee spawning grounds in the Metolius River and Lake Billy Chinook downstream, in which the IHNV epidemics occurred in 2- and 3-year-old kokanee, and the Round Butte Fish Hatchery at the outflow of the lake. Forty-two IHNV isolates collected from this area between 1975 and 1995 were characterized on a genetic basis by ribonuclease (RNase) protection fingerprint analyses of the virus nucleocapsid, glycoprotein, and nonvirion genes. Analysis of the 16 identified composite haplotypes suggested that both virus evolution and introduction of new IHNV strains contributed to the genetic diversity observed. The results indicated that the 1991–1995 epidemics in kokanee from Lake Billy Chinook were due to a newly introduced IHNV type that was first detected in spawning adult kokanee in 1988 and that this virus type was transmitted from the wild kokanee to hatchery fish downstream in 1991. Twelve IHNV haplotypes were found at Round Butte Fish Hatchery, indicating a series of virus displacement events during the 20-year period examined. This work shows that IHNV traffic can be much more complex than was previously recognized, and the results have implications for fisheries management at the hatchery and throughout the watershed.

Oregon↗
USGS2001

Comparison of blood chemistry values for samples collected from juvenile chinook salmon by three methods

Thirteen blood chemistry indices were compared for samples collected by three commonly used methods: caudal transection, heart puncture, and caudal vessel puncture. Apparent biases in blood chemistry values for samples obtained by caudal transection were consistent with dilution with tissue fluids: alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), creatine kinase (CK), triglyceride, and K+ were increased and Na+ and Cl- were decreased relative to values for samples obtained by caudal vessel puncture. Some enzyme activities (ALT, AST, LDH) and K+ concentrations were also greater in samples taken by heart puncture than in samples taken by caudal vessel puncture. Of the methods tested, caudal vessel puncture had the least effect on blood chemistry values and should be preferred for blood chemistry studies on juvenile salmonids.

Journal of Aquatic Animal Health↗
USGS2001

Evidence that coded-wire-tagging procedures can enhance transmission of Renibacterium salmoninarum in chinook salmon

Binary coded wire tags (CWTs) are used extensively for identification and management of anadromous salmonid populations. A study of bacterial kidney disease (BKD) in two brood year groups of hatchery-reared spring chinook salmon Oncorhynchus tshawytscha provided strong evidence that horizontal transmission of Renibacterium salmoninarum, the causative agent of BKD, might be enhanced by CWT-marking procedures. About 4 months after CWTs were implanted in the snouts of juvenile fish, 14-16 different tissues were sampled from each of 60 fish per brood year group for histological analysis. Of the fish that were positive for R. salmoninarum by histological examination, 41% (7 of 17) of the 1988 brood year fish and 24% (10 of 42) of the 1989 brood year fish had BKD lesions confined to the head near the site of tag implantation. These lesions often resulted in the destruction of tissues of one or both olfactory organs. No focal snout infections were observed in fish that had not been marked with CWTs. Further data obtained from tissue analyses by use of an enzyme-linked immunosorbent assay and a fluorescent antibody test for detection of R. salmoninarum supported the hypothesis that infections of R. salmoninarum can be initiated in the snout tissues of CWT-marked fish and then spread to other organs. The tagging procedures might promote transmission of the pathogen among fish via contaminated tagging needles, by facilitating the entry of pathogens through the injection wound, or both. Limited evidence from this study suggested that implantation of passive integrated transponder tags in the peritoneal cavities of fish might also promote the transmission of R. salmoninarum or exacerbate existing infections. The results indicated a need for strict sanitary procedures during the tagging of fish in populations positive for R. salmoninarum to reduce the probability of enhanced horizontal transmission of the pathogen.

Journal of Aquatic Animal Health↗
USGS1992

Effect of stocking season and technique on survival of lake trout in Lake Ontario

To identify the stocking season and technique that resulted in maximum contribution of hatchery‐reared lake trout Salvelinus namaycush to the population in Lake Ontario, paired lots of yearlings were stocked near shore in March, near shore in May, and offshore by helicopter in May. All mortality associated with stocking season and technique apparently had occurred by age 2. Therefore, survival comparisons were based on combined recoveries of age‐2 and older fish. We found statistically significant differences in survival ratios for 19 of 30 comparisons among individual paired lots, but results were not consistent. For example, among 17 comparisons of lake trout stocked near shore in May and offshore in May, survival was significantly better for fish stocked near shore in four cases and for fish stocked offshore in six cases. With fish stocked near shore in May used as the control group, mean survival ratios (near shore March : near shore May : offshore May) were 0.86:1.00:1.12. However, the 95% confidence interval indicated that the survival ratios were not significantly different from 1:1:1. Variables other than stocking date and technique apparently had a major influence on survival of lake trout following stocking in Lake Ontario. Predation by large salmonids may have been the dominant mechanism affecting survival.

Lake Ontario↗
USGS1998

Evaluation of a new miniature pressure-sensitive radio transmitter

A miniature pressure-sensitive radio transmitter (tag) was evaluated and field tested as a tool for determining the depths of juvenile salmonids. The tag had an effective radiated power of −19.7 decibels (1 mW reference), dimensions of 23 mm × 7 mm, and a weight of 2.2 g in air. The pulse rate of the tag increased with pressure, resulting in an expected tag life of approximately 11 d at the water surface and 7.5 d at 10.5 m. The tags were accurate to within 16 mm with 95% of observations within ±0.32 m of the true depth. The resolution of the tags was 0.2 m. Errors in indicated depth resulting from differences between the calibration and operating temperatures were minimized by means of a correction factor. Tags surgically implanted in juvenile steelhead Oncorhynchus mykiss indicated a depth 0.2 m less than the same tags in water. This difference was not affected by pressure or temperature and was rectified by adjusting data from tags in fish. A test tag in a Columbia River reservoir was detected from distances of 1,133 m at a depth of 2 m and 148 m at a depth of 14 m. Results ind

North American Journal of Fisheries Management↗
USGS2000

Preliminary study of gill NA+,K+-ATPase activity in juvenile spring chinook salmon following electroshock or handling stress

We compared gill Na+,K+-ATPase in subyearling and yearling spring chinook salmon Oncorhynchus tshawytscha 3 h, 24 h, and 7 d after exposure to either a short pulsed DC electroshock (300 V, 50 Hz, 8-ms pulse duration) or an acute handling stress. Mean gill Na+,K+-ATPase values ranged from 7.5 to 11.8 ??mol inorganic phosphate (Pi) ?? (mg protein)-1 ?? h-1. No significant differences were detected, with the exception of electroshocked subyearlings 7 d after treatment. Increased activity was attributed to the presence of two influential values. No significant differences were detected after removal of these observations, so the increase was not considered biologically significant. Inclusion of the outliers did not alter our interpretation of the results given that the observed increase was slight compared with the magnitude of changes reported under experimental conditions and in migrating juvenile salmonids. The treatment groups underwent a typical stress response and had significantly elevated cortisol and glucose levels 3 h after treatment. Recovery to control levels occurred within 24 h for cortisol and from 24 h to 7 d for glucose. Our results lead to the conclusion that neither acute electroshock nor acute handling stress alters Na+,K+-ATPase activity in juvenile spring chinook salmon.

North American Journal of Fisheries Management↗
USGS2001

Residence times and diel passage distributions of radio-tagged juvenile spring chinook salmon and steelhead in a gatewell and fish collection channel of a Columbia River Dam

The amount of time radio-tagged juvenile spring chinook salmon Oncorhynchus tshawytscha and juvenile steelhead O. mykiss spent within a gatewell and the juvenile collection channel at McNary Dam, Columbia River, USA, was measured to determine the diel passage behavior and residence times within these portions of the juvenile bypass system. The median gatewell residence times were 8.9 h for juvenile chinook salmon and 3.2 h for steelhead. Juvenile spring chinook salmon spent 83% of their time in the 18-m-deep gatewell at depths of 9 m or less, and juvenile steelhead spent 96% of their time in the upper 11 m. Fish released during midday and those released in the evening generally exited the gatewell in the evening, indicating that fish entering the gatewell during daylight will have prolonged residence times. Median collection-channel residence times of juvenile chinook salmon were much shorter (2.3 min) than those of steelhead (28.0 min), most likely because of the greater size of the steelhead and the high water velocities within the channel (2.1 m/s). This and other studies indicate most juvenile salmonids enter gatewells of several Columbia and Snake river dams in the evening and pass into the collection channels quickly. However, this is not consistent with the natural in-river migration patterns of these species and represents a delay in dam passage.

Washington; Oregon↗
USGS2002

Tag retention and survival of Age-0 Atlantic salmon following surgical implantation with passive integrated transponder tags

We evaluated an alternative to using hypodermic needles to implant passive integrated transponder (PIT) tags in the body cavities of juvenile salmonids. We used surgical techniques to place PIT tags into the body cavities of 3,037 age-0 Atlantic salmon Salmo salar and then held fish under hatchery conditions for 9 months. Tag retention was 99.8% (six fish lost tags), and survival was 94.3% (174 fish died) after controlling for initial mortality (0.7%). A single tagger was able to tag 80–100 fish per hour. Surgically implanting PIT tags into the body cavities of age-0 Atlantic salmon proved to be a viable alternative to using hypodermic needles.

North American Journal of Fisheries Management↗
USGS2002

Quantifying flow-dependent changes in subyearling fall chinook salmon rearing habitat using two-dimensional spatially explicit modeling

We used an analysis based on a geographic information system (GIS) to determine the amount of rearing habitat and stranding area for subyearling fall chinook salmon Oncorhynchus tshawytscha in the Hanford Reach of the Columbia River at steady-state flows ranging from 1,416 to 11,328 m3/s. High-resolution river channel bathymetry was used in conjunction with a two-dimensional hydrodynamic model to estimate water velocities, depths, and lateral slopes throughout our 33-km study area. To relate the probability of fish presence in nearshore habitats to measures of physical habitat, we developed a logistic regression model from point electrofishing data. We only considered variables that were compatible with a GIS and therefore excluded other variables known to be important to juvenile salmonids. Water velocity and lateral slope were the only two variables included in our final model. The amount of available rearing habitat generally decreased as flow increased, with the greatest decreases occurring between 1,416 and 4,814 m3/s. When river discharges were between 3,682 and 7,080 m3/s, flow fluctuations of 566 m3/s produced the smallest change in available rearing area (from -6.3% to +6.8% of the total). Stranding pool area was greatly reduced at steady-state flows exceeding 4,531 m3/s, but the highest net gain in stranding area was produced by 850 m3/s decreases in flow when river discharges were between 5,381 and 5,664 m3/s. Current measures to protect rearing fall chinook salmon include limiting flow fluctuations at Priest Rapids Dam to 850 m3/s when the dam is spilling water and when the weekly flows average less than 4,814 m3/s. We believe that limiting flow fluctuations at all discharges would further protect subyearling fall chinook salmon.

Washington↗
USGS2003

Evidence of sexually dimorphic introgression in Pinaleno Mountain Apache trout

The high-elevation headwater streams of the Pinaleno Mountains support small populations of threatened Apache trout Oncorhynchus apache that were stocked following the chemical removal of nonnative salmonids in the 1960s. A fisheries survey to assess population composition, growth, and size structure confirmed angler reports of infrequent occurrences of Oncorhynchus spp. exhibiting the external morphological characteristics of both Apache trout and rainbow trout O. mykiss. Nonlethal tissue samples were collected from 50 individuals in the headwaters of each stream. Mitochondrial DNA (mtDNA) sequencing and amplification of nuclear microsatellite loci were used to determine the levels of genetic introgression by rainbow trout in Apache trout populations at these locations. Sexually dimorphic introgression from the spawning of male rainbow trout with female Apache trout was detected using mtDNA and microsatellites. Estimates of the degree of hybridization based on three microsatellite loci were 10-88%. The use of nonlethal DNA genetic analyses can supplement information obtained from standard survey methods and be useful in assessing the relative importance of small and sensitive populations with a history of nonnative introductions.

North American Journal of Fisheries Management↗
USGS2003

Factors associated with stocked cutthroat trout populations in high-mountain lakes

High-mountain lakes provide important fisheries in the Rocky Mountains; therefore we sought to gain an understanding of the relationships among environmental factors, accessibility to anglers, stocking rates, and features of stocks of cutthroat trout Oncorhynchus clarki in high-mountain lakes of the Bighorn Mountains, Wyoming. We sampled fish with experimental gill nets, measured lake habitat features, and calculated factors affecting angler access among 19 lakes that lacked sufficient natural reproduction to support salmonid fisheries and that were stocked at 1-, 2-, or 4-year intervals with fingerling cutthroat trout. We found that angler accessibility was probably the primary factor affecting stock structure, whereas stocking rates affected the densities of cutthroat trout among lakes. The maximum number of years survived after stocking appeared to have the greatest affect on biomass and population structure. Our findings suggest that control of harvest and manipulation of stocking densities can affect the density, biomass, and structure of cutthroat trout stocks in high-elevation lakes.

North American Journal of Fisheries Management↗
USGS2005

Can diet-dependent factors help explain fish-to-fish variation in thiamine-dependent early mortality syndrome?

To provide insight into the reasons why offspring of certain salmonine females exhibit early mortality syndrome (EMS) in the Great Lakes whereas others do not, we measured the egg concentrations of potential biochemical markers (stable isotopes of nitrogen and carbon, fatty acid signatures, and lipid-soluble carotenoids and vitamins) that are indicative of differing food web and trophic structure. To corroborate the presence of EMS, we also measured the egg content of thiamine vitamers. For all the stocks of coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha we studied, there was a very high correspondence between EMS and low concentrations of unphosphorylated thiamine in unfertilized eggs. For salmonine stocks in the Platte River, Thompson Creek, and the Swan River, Michigan, small but significant shifts occurred in measures of egg carotenoids, retinoids, ??15N depletion, and fatty acid profiles of fish producing normal offspring relative to those exhibiting EMS. Egg thiamine concentrations in Chinook salmon from the Little Manistee River, Michigan, in the low-EMS group were only marginally above the threshold for EMS induction. Along with this small thiamine differential, there was no evidence of differing food web or dietary factors between EMS-positive and normal Chinook salmon from the Little Manistee River. Further investigations are required to determine the potential dietary sources for the observed differences in biochemical markers between EMS-positive and normal fish. These findings are generally consistent with the hypothesis that a more diverse forage base may help to limit overall dietary content of species that contain thiaminase, such as alewives Alosa pseudoharengus, and may lead to improved embryonic survival for feral salmonids. ?? Copyright by the American Fisheries Society 2005.

Journal of Aquatic Animal Health↗
USGS2005

The effect of thiamine injection on upstream migration, survival, and thiamine status of putative thiamine-deficient coho salmon

A diet containing a high proportion of alewives Alosa pseudoharengus results in a thiamine deficiency that has been associated with high larval salmonid mortality, known as early mortality syndrome (EMS), but relatively little is known about the effects of the deficiency on adults. Using thiamine injection (50 mg thiamine/kg body weight) of ascending adult female coho salmon Oncorhynchus kisutch on the Platte River, Michigan, we investigated the effects of thiamine supplementation on migration, adult survival, and thiamine status. The thiamine concentrations of eggs, muscle (red and white), spleen, kidney (head and trunk), and liver and the transketolase activity of the liver, head kidney, and trunk kidney of fish injected with thiamine dissolved in physiological saline (PST) or physiological saline only (PS) were compared with those of uninjected fish. The injection did not affect the number of fish making the 15-km upstream migration to a collection weir but did affect survival once fish reached the upstream weir, where survival of PST-injected fish was almost twice that of controls. The egg and liver thiamine concentrations in PS fish sampled after their upstream migration were significantly lower than those of uninjected fish collected at the downstream weir, but the white muscle thiamine concentration did not differ between the two groups. At the upper weir, thiamine levels in the liver, spleen, head kidney, and trunk kidney of PS fish were indistinguishable from those of uninjected fish (called "wigglers") suffering from a severe deficiency and exhibiting reduced equilibrium, a stage that precedes total loss of equilibrium and death. For PST fish collected at the upstream weir, total thiamine levels in all tissues were significantly elevated over those of PS fish. Based on the limited number of tissues examined, thiamine status was indicated better by tissue thiamine concentration than by transketolase activity. The adult injection method we used appears to be a more effective means of increasing egg thiamine levels than immersion of eggs in a thiamine solution. ?? Copyright by the American Fisheries Society 2005.

Journal of Aquatic Animal Health↗
USGS2007

Genetic diversity of infectious hematopoietic necrosis virus from Feather River and Lake Oroville, California, and virulence of selected isolates for Chinook salmon and rainbow trout

Infectious hematopoietic necrosis virus (IHNV) is a significant pathogen of young salmonid fishes worldwide but particularly within the historical range of the Pacific Northwest and California. In the Sacramento and San Joaquin River drainages of California, IHNV outbreaks in juvenile Chinook salmon Oncorhynchus tshawytscha have been observed regularly at large production hatcheries, including Coleman National Fish Hatchery (established in 1941) and Feather River State Fish Hatchery (FRH; established in 1967), since facility operations began. Recent severe epidemics at the FRH in 1998 and 2000-2002 prompted investigations into the characteristics and potential sources of virus at this facility. Both phylogenetic analyses of a variable portion of the glycoprotein gene and serologic comparisons based on neutralization with three polyclonal rabbit sera were used to characterize 82 IHNV isolates from the Feather River watershed between 1969 and 2004. All isolates examined were in the L genogroup and belonged to one of three serologic groups typical of IHNV from California. The IHNV isolates from the Feather River area demonstrated a maximum nucleotide sequence divergence of 4.0%, and new isolates appeared to emerge from previous isolates rather than by the introduction of more diverse subgroups from exogenous sources. The earliest isolates examined from the watershed formed the subgroup LI, which disappeared coincidently with a temporal shift to new genetic and serologic types of the larger subgroup LII. Experimental challenges demonstrated no significant differences in the virulence for juvenile Chinook salmon and rainbow trout O. mykiss from selected isolates representing the principal types of IHNV found historically and from recent epidemics at FRH. While most isolates were equally virulent for both host species, one isolate was found to be more virulent for Chinook salmon than for rainbow trout. ?? Copyright by the American Fisheries Society 2007.

Journal of Aquatic Animal Health↗
USGS2008

Effectiveness and retention of thiamine and its analogs administered to steelhead and landlocked Atlantic salmon

We investigated the feasibility of enhancing the reproduction of steelhead Oncorhynchus mykiss and landlocked Atlantic salmon Salmo salar in lakes where the consumption of alewives Alosa pseudoharengus and other forage fishes containing thiaminase can cause them to become thiamine deficient and thereby reduce the survival of their fry. We evaluated feeding fingerling steelhead excess thiamine hydrochloride (THCl) for 1 or 2 weeks or equimolar amounts of thiamine mononitrate, thiamine-tetrahydrofurfuryl-disulfide, benfotiamine, or dibenzoyl thiamine (DBT). We found minimal internal reserves of thiamine after 6 months. We also compared the ability of injections of thiamine and its analogs to prevent mortality in thiamine-deficient steelhead and Atlantic salmon sac fry and found all forms to be effective, although benfotiamine was the least effective on an equimolar basis. Further, we injected yearling steelhead and found that DBT was tolerated at approximately 11,200 nmol/g of body weight, about 10 times more than thiamine in any other form. When yearling steelhead were injected with near-maximal doses of thiamine hydrochloride and several analogs and then fed a thiamine-deficient diet, DBT was retained for approximately 2 years - in contrast to other forms, which were retained for less than about 6 months. Therefore, these results suggest that neither feeding nor injecting young hatchery salmonids with DBT is likely to enhance their reproduction for more than 2 years after stocking. However, injecting DBT in nearly mature fish (either cultured fish from hatcheries or wild fish captured in lakes) may provide them with enough thiamine to successfully spawn within 2 years even though they consume mainly thiaminase-containing forage fishes. ?? Copyright by the American Fisheries Society 2008.

Journal of Aquatic Animal Health↗
USGS2004

Injury and mortality of warmwater fishes immobilized by electrofishing

Most studies of injury associated with electrofishing have focused on salmonids: few have given attention to warmwater fishes. Under controlled laboratory conditions, we treated bluegill Lepomis macrochirus, channel catfish Ictalurus punctatus, and largemouth bass Micropterus salmoides of various sizes to duty cycles ranging from 1.5% to 100%. This range of duty cycles represented continuous DC and pulsed-DC frequencies ranging from 15 to 110 Hz and pulse durations of 1 to 6 ms. At each duty cycle, fish were exposed to power densities in excess of those required to immobilize them within 3 s, and we subsequently determined the incidence of hemorrhage, spinal injury, and mortality. Incidence of hemorrhage averaged 3% (range, 0-25%), differed among species, and was not related to duty cycle or fish size. Incidence of spinal injury averaged 3% (range, 0-22%) and mortality averaged 10% (range, 0-75%); both differed among species and were related to duty cycle, fish size, and interactions among these variables. Largemouth bass was the species most vulnerable to hemorrhage, spinal injury, and mortality, channel catfish the least vulnerable; bluegills exhibited effects that were intermediate. Small centrarchids were especially susceptible to mortality. Fish tetanized by the electrical treatment were more likely to experience injury and mortality than fish that were only narcotized. However, mortality was not related to the injuries studied because hemorrhage and spinal injuries were similar in fish that survived electroshock and in those that died. We suggest that electrofishing with intermediate to high duty cycles could reduce electrofishing-induced injury and mortality to warmwater fish. Additionally, the power output and electrode system should be managed to induce narcosis and prevent tetany and to avoid the large peak powers required to immobilize small individuals.

North American Journal of Fisheries Management↗