Electroshock Effects on Fish

Session Purposes

• To investigate typical reactions of fish in electric fields generated by various waveforms

• To describe fish trauma issues at the individual, sample, and population levels

• To discuss methods for minimizing the potential of fish trauma

Session Objectives

• List and order typical reactions of fish in AC, DC, and pulsed DC electric fields

• Describe attributes of fish trauma and factors leading to trauma

• Discuss methods for minimizing the potential of fish trauma, including the use of an injury risk model

• Describe injury assessment methods on the sample, reach, and population levels

A. Two Categories of Electroshock Effects

• Behavior (or reactive movements)– Use of certain responses for capture or control

• Trauma (stress or injury)– Stress is usually physiological (no mechanical injury)

• recovery short-term

– Injury is mechanical• recovery long-term (although maybe with reduced growth or fecundity)

B. Fish Behavior in Electric Fields

For Practical Use in Field

• Escape (upright avoidance swimming)

• Inhibited swimming (unbalanced swimming)

• Immobilization (no swimming motions)

Inhibited swimming includes taxis, pseudo-taxis, oscillotaxis

Immobilization includes narcosis & tetany

Common Terms

Inhibited Swimming

•Taxis or electrotaxis: electrically-induced movement, usually toward the anode•False Taxis or pseudo-forced swimming: as electrotaxis except the fish is unconscious and belly-up•Oscillotaxis: electrically-induced movement without orientation

Common Terms (continued)

Immobilization

•Tetany: a state of electrically-induced immobility with rigid muscles

•Narcosis: a state of electrically-induced immobility with slack muscles

Videos of Behaviors

• Inhibited swimming (compromised swimming)

• Inhibited swimming (taxis)

• Immobilization (narcosis)

• Reactions and their neurological causes (Barritz Lab)

Behavior in Electric Fields

From an illustration in Sternin et al. (1972)

Fish Response to AC

Escape (or Fright) response

Inhibited swimming

Transverse oscillotaxis

Tetany

FFish Response to DC

“Immobilization”: tetany or narcosis

Fish Response to DC“Anodic curvature” Taxis

Immobilization

Fish Response to Pulsed DC

• May or may not cause taxis– Taxis response observed (for brown trout, Salmo trutta)– Taxis response not observed (for goldfish, Carassius

auratus)– Lamarque (1990) concluded from lab experiments that

PDC has poorer anodic taxis as compared to DC• Complicated because of the many different types of

PDC waveforms• May be somewhat intermediate between AC & DC

responses (can have taxis, narcosis, and tetany responses)

Quiz Question(Tetany or Narcosis?)

• Narcosis– Gentle curvature of body– Absence of “flared gills” (a characteristic of

tetany)

C. Fish Trauma: Stress• Physiological stress incorporates a wide range of

chemical and physical responses that occur as a direct effect of a stressor causing disruption in the homeostasis of the body.

• Bottom-line: What are the implications for short-term sampling and longer-term fish health and survival?– In other words, does changed physiology translate to

changed behavior, and if so, for how long? Also, under what conditions does stress lead to higher mortality?

TraumaGeneralized Stress Response Model

Fish Physiological Indicators of Stress from Electroshock

• Blood chemistry– Common parameters include: cortisol,

lactate, glucose (others include hematocrit, oxygen saturation, electrolytes [osmolality], enzymes [creatine kinase], minerals [calcium], proteins [albumin]

• Physical– Parameters include: gilling rate (ventilation),

cardiac output

Blood Chemistry Responses• Hormonal

– Immediate adrenergic release of catecholamines (e.g., epinephrine and norepinephrine)

– Followed by corticosteroid release (especially cortisol)

• Metabolic– Increased lactate (from muscle exertion)– Increased glucose– Development of metabolic and respiratory acidosis

which can, in turn, initiate respiratory compensation (increased gilling and oxygen saturation)

Lab Example Using DC (1), PDC (2), AC (3)

O2 %

Time (minutes)

Plasma Cortisol in Fall Chinook Salmon

“a” = shocked mean different from control mean at that time“b” =shocked mean different from mean of all controls“c” =shocked mean different from shocked mean at time 0

*1.5 sec., 500 V DC

Sample at time = 0 taken 4 sec post-shock

Blood Chemistry Recovery Times and Correlations

• Chemical parameters as cortisol, lactate, glucose, and osmolarity typically are resolved within six hours or begin to diminish during that period post-shock

• If the stressor (shock duration) is very short, the cortisol response may be short and have quick recovery

• Glucose and lactate are metabolic responses and may persist for a longer period after shock as compared to cortisol

Blood Chemistry Recovery Times and Correlations

• Multiple shocks have resulted in greater changes in cortisol and lactate

• However, some research has been unable to link blood chemistry changes with intensity of electric shock, duration, presence of hemorrhagic trauma to musculature, or short-term mortality

Physical Responses

• Muscle contraction (tetany) or increased exercise (as beginning of flight response)

• Reduced ventilation

• Lowered followed by amplified cardiac output

Rainbow Trout EKG

Waveform applied: PDC, 100 V, 30 Hz, 2 ms pulse width for 32 sec

Shaded area: electrical power on

Schreer et al. (2004)

Rainbow Trout EKG

Vertical shaded bars: electrical power on

Cardiac output

Heart rate

Stroke volume

Waveform used:100 V, 80 – 8 Hz,2 ms, for 8 sec

Found that longer shock durations increased the duration of cardiac arrest & recovery

Metabolic Implications• Lactic acid may accumulate due to the increased muscular

contraction and reduction of ventilation

• Metabolic acidosis and respiratory acidosis can result

• Recovery from acidosis takes time and energetic resources

• Six hours may see recovery or the start of recovery

• For population assessment, the key is behavior; is the individual fish exhibiting normal behavior

Time Interval between Passes

• Behavioral recovery may lag blood chemistry dynamics; Mesa & Schreck (1989) determined that a waiting period of 6 hours may not be adequate; rather 24 hours were needed for recovery in Westslope cutthroat trout and recommended a day between the first and second sampling events in mark-recapture work

• There may be a balancing act between recovery and movement or predation out of sample sites

• Block nets probably necessary (Peterson et al. 2005)

• Mesa & Schreck (1989) did not see abnormal behavior of un-captured fish remaining in the sampling site during depletion sampling

Predicted Probability of Mortality for Cape Fear Shiners Exposed to 60 Hz PDC

No injures (vertebrae fractures or hemorrhages) were detected

Holliman et al. (2003)

Stress-related Effects of EFWaveform Shape

Recovery time of common carp50 Hz PDC; Vertical line = 1 standard error

D.J. Bird & I.G. Cowx. 1993. Fisheries Research 18:363-376.

Stress-related Effects of EF• Smaller fish usually do not have a high incidence of injuries (<

10%) but are susceptible to stress• Stress-related physiological changes are typically short-term (3 – 6

hours)• Related behavioral effects (e.g., reduced feeding or predator

avoidance, lethargy) may last 24 hours• Holliman et al. (2003) concluded that if small cyprinids appear and

behave normally 1 hr. post-electroshock, then biologists can consider stress minimal and mortality near zero

• Mortality can occur with smaller fish due to stress and is influenced by…– Field intensity ( higher voltage gradient, pulse frequency)– Duration of exposure (longer)– Length of fish (larger)– Waveform shape (1/4 sine-wave PDC highest recovery time)– Waveform type (rule-of-thumb AC>PDC>DC, but 60 Hz PDC

caused less stress-related mortality in Cape Fear shiners than DC [Holliman et al. 2003] and AC and 60 Hz PDC resulted in similar stress-related mortality in spotfin chubs inhabiting low conductivity water [Holliman and Reynolds 2003])

Stress-related Mortality

• In several warmwater game and non-game fishes, lower frequency and duty cycle tended to result in higher mortality

Stress-related Mortality Percentages

• Warmwater fishes: 2-3 day mortality 0.6%, all with fishes ≤ 53 mm (Miranda 2005)

• RBT (> 400 mm ): 4 day mortality 14% (Holmes et al. 1990)

• Bluegill, channel catfish, largemouth bass: 10% mortality (Dolan and Miranda 2004)

• Atlanic salmon (<80mm): no significant effects on mortality when shocked 4 times at 2 month intervals (Sigourney et al. 2005)

• Largemouth bass, smallmouth bass, bluegill, pumkinseed: mortality ≤ 5.3% (Bardygula-Nonn 1995)

• Cape Fear shiner: < 10% mortality with 60 Hz PDC

To reduce stress in the field:

-use the lowest effective level of power-net the fish away from the electrodes-net the fish as quickly as possible-do not re-introduce captured fish back into the field

D. Trauma- Injury (external)

“Brands” (chevron-shaped bruises)

*Can lead to secondary fungal infections

*An indicator of probable internal injuries

Arctic grayling

Trauma- Injury (external)

If brands present, higher likelihood of more severe, internal injuriesInjury severity increases from class 1 to class 3

Branded UnbrandedInjury Status

0

10

20

30

40P

er c

en

t with

Inte

rna

l In

juri

es

321

Injury Class

~50% injuryrate

~98% injuryrate

Trauma- Injury (internal)Internal Hemorrhage Classification System

Class Description

0 No hemorrhage present

1 Mild hemorrhage; one or more wounds in muscle, separate from the spine

2 Moderate hemorrhage; one or more small (≤ width 2 vertebrae) wounds on spine

3 Severe hemorrhage; one or more large (> width 2 vertebrae) wounds on spine

Internal Hemorrhage Classification

Can be frozen before filletingBlood from filleting process easily wipes off; hemorrhages do not

Internal Hemorrhage Classification

E. Trauma- Injury (internal)

Spinal Damage Classification System

Class Description

0 No spinal damage present

1 Compression (distortion) of vertebrae only

2 Misalignment of vertebrae, including compression

3 Fracture of ≥ 1 vertebrae or complete separation of ≥ 2 vertebrae

Spinal Injury Classification

Spinal Injury Classification

Spinal Injury Classification

Spinal Injury Classification

Lateral view

Spinal Injury Classification

Dorsal view

Spinal Injury

Brown trout vertebrae

Normal

Fractured from EF

Spinal InjuryBrown trout vertebrae

Old, calcified injury Recent fracture from EF

Location of Internal Injuries% of Length Posterior from Snout

Dorsal

Anal

Location of Internal Injuries

Most spinal injury in dorsal fin region where dorso-lateral muscle mass is the thickest

Brown trout

Location of Internal InjuriesBrown Trout

Dorsalregion

Electrical Factors Increasing Injury Rates*

• Waveforms leading to injury rule-of-thumb is AC > PDC > DC, although…– AC use in low conductivity waters has been

observed to result in low injury to trout and spotfin chub (Habera et al. 1996; Holliman & Reynolds 2003)

– Three-phase AC did not affect mortality or growth rates in several warmwater and coolwater species.

*These are general patterns; much species-specific variation. Some species may experience extensive harm while others may not.

Electrical Factors Increasing Injury Rates

• The primary PDC attribute leading to injury is: Frequency

• Higher PDC frequency (at least 15 to 120 Hz) = higher injury rates

• Waveform shape (equivocal)**– One-quarter sine wave has caused higher injury rates

than square wave or exponential

• Higher power (voltage) = higher injury rates

Power Density (D) and Voltage Gradient (ε)Goals from Miranda (2005) Refining Boat Electrofishing Equipment to Improve Consistency and Reduce Harm to Fish.

Immobilization Power Density goals (transferred to fish) chosen as 20-400 µW/cm3 and Injury above 2000 µW/cm3. Voltage gradients calculated from power density values. Frequency = 60 pps;

Conductivity D20 D400 D2000 ε20 ε400 ε2000

20 45.7 914 4571 1.51 6.76 15.140 28.9 579 2893 0.85 3.80 8.580 21.6 432 2161 0.52 2.32 5.2140 20.0 400 2000 0.38 1.69 3.8300 23.0 461 2305 0.28 1.24 2.8600 32.6 652 3260 0.23 1.04 2.31200 53.4 1069 5344 0.21 0.94 2.12400 96.0 1920 9601 0.20 0.89 2.0

Power Density vs. Conductivity

Power Density vs Conductivity

0

2000

4000

6000

8000

10000

12000

0 500 1000 1500 2000 2500

Water Conductivity (µS/cm)

Po

wer

Den

sity

(µW

/cm

3)

D20 D400 D2000

Injury threshold

Immobilization

Buffer zone

Voltage Gradient vs. Conductivity

Voltage Gradient vs Conductivity

0

2

4

6

8

10

12

14

16

0 100 200 300 400 500

Water Conductivity (µS/cm)

Vo

ltag

e G

rad

ien

t (V

/cm

)

ε20 ε400 ε2000

Immobilization zone

Injury threshold

Buffer zone

Voltage Gradient vs. ConductivityZoomed In

Voltage Gradient vs Conductivity

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 100 200 300 400 500

Water Conductivity (µS/cm)

Vo

ltag

e G

rad

ien

t (V

/cm

)

ε20 ε400 ε2000

Immobilization

Injury

What about duration of shocking exposure?

% Bluegills (Centrarchidae) with Spinal Injury

Exposure time (sec)

AC 230 V, 1.3 amp

299 Watts

AC 115 V, 2.0 amp

230 Watts

DC 115 V, 1.9 amp

219 Watts

1 14.7 2.7 1.3

5 10.7 5.3 0

10 12.0 2.7 1.3

30 13.3 5.3 2.7

60 10.7 4 1.3

90 16.0 5.3 2.7

120 9.3 6.7 1.3

Mean 12.2 4.6 1.5

Duration of shock does not increase injury rate Spencer 1967

How About Repeated Shocks?

• Repeated shocks, as a fish would receive under a capture-recapture or a removal/depletion sampling protocol, can lead to higher injury rates

• It is probable that the repeated shocks must be significant and with depletion sampling would be individuals that could have been netted but were not (happens)

Operational & Behavioral Factors Increasing Injury and Mortality Rates

• Tetany is the primary fish response leading to higher injury and mortality– Adjust power settings to induce inhibited swimming as

taxis (especially with trout) or narcosis

Biological Factors Increasing Injury Rates

• Greater fish length = higher injury rates

• Higher vertebral # (esp. > 40) = higher injury rates

Fish Injury Risk Model

FISHSIZE

FISHRESPONSE

VERTEBRAL COUNT

RISK OF INJURY

FORCE OF

CONTRACTION

RESISTANCE

TO FORCE

ELECTRICAL INTENSITY

ELECTRICALWAVEFORM

Actions to Lower Probability of Trauma in Fish

• Use boat boom electrodes with the largest effective diameter feasible (≥ 12 – 18 mm or sphere)

• Use continuous DC if possible; otherwise PDC; however, AC can have low injury rates in low or high conductivities; gated burst may present lowest risk with salmonids but catchability may not be optimal– Salmonids: ≥ 50 – 60 Hz likely to cause injury; 30 Hz much

less risky; pulse width 2 to 4 ms (6 – 12 % duty cycle)– Warmwater fishes (as centrarchids): use an intermediate

frequency (as 60 pps) with a catching duty cycle (15 - 50%, 20 – 35% better) under power standardization

Actions to Lower Probability of Trauma in Fish (continued)

• Adjust voltage (power) levels to the minimum needed for effective capture (try to avoid tetany)

• Remove fish quickly from the field as far from the electrodes as possible– Length of exposure does not appear to effect

injury rate– Length of exposure does effect stress levels

Actions to Lower Probability of Trauma in Fish (continued)

• If fishes have a long recovery period, you still may be applying too much power; fine tune by turning down the voltage while maintaining satisfactory capture rates

• Hold captured fish in optimal conditions• Consider using a different sampling

technique for first capture in M-R studies

What does this mean at least for some warmwater fishes?

• There probably needs to be a balance between– duty cycle selected (a function of frequency and pulse

width)• often most efficient at ~ 30% (suggested range 15 – 50%)• as duty cycle decreases, there is a decreasing margin

between narcosis and tetany thresholds

– power levels (levels sufficient to immobilize but not excessive to cause higher rates of tetany and injury/stress)

Evaluate Results of Efforts• Optional: assess injury rates prior to taking injury

reduction measures

• Assess injury after reduction measures are implemented (thus, you can compare injury rates before and after reduction measures taken or just compare injury rates with those extracted from the literature or to some value found inconsequential by modeling)

• Significant changes in the equipment may necessitate re-evaluation

Guidelines for Assessment of EF-induced Injuries…

• See page 6 in Guidelines for Assessment and Reduction of EF Injury.pdf

• Collect 20 similar-sized individuals of larger size category

• Fillet• Calculate proportion of injured fish• If hemorrhage proportion low, then spinal

injury likely unimportant; otherwise, take x-rays of another sample of 20 fish to assess proportion with spinal injuries

Selected Injury Rates(Spinal unless otherwise noted)

• RBT adults: 12% (DC) & 40 – 54% (pulsed DC) (Dalbey et al. 1996)

• RBT juveniles: 15% (DC) & 33% (pulsed DC) (Ainslie et al. 1998)

• RBT adults: 44 – 67% (PDC) (Sharber & Carothers 1988)

• Bonytail chubs & humpback chubs: zero spinal injuries; 13 – 20% spinal hemorrhages (pulsed DC) (Ruppert & Muth 1997)

• Bluegill, channel catfish, largemouth bass: spinal injury averaged 3% and hemorrhage averaged 3% (Dolan & Miranda 2004)

Effects of Injury on Growth, Condition, and Mortality

• RBT: with moderate to severe injury had significantly lower growth and condition after 335 days (Dalbey et al. 1996)

• RBT/BT: growth rates declined with PDC conducted 2 – 7 times over year; recommended shocking > 3 month intervals (Gatz et al. 1986)

• Creek chub, white suckers, and green sunfish- monthly PDC 60 Hz had no to small negative effects on condition, growth; no effect on mortality (Gatz and Linden 2008)

• RBT: No effect on mortality (335 days, Dalbey et al.

1996; 203 days, Taube 1992)

Effects on Eggs

• Egg mortality can occur in vivo (before spawning)

• Fertilized egg mortality can occur and susceptibility is similar to that of mechanical shock (middle to late epiboly)

• Mortality level of fish eggs can depend upon electrical intensity (+), length of electrical exposure (+), stage of development, and whether parents were shocked (+)

• However, increased level of mortality may be negligible, especially given the field map pattern of backpack shockers

Effects on EggsArctic grayling

Except for triangles,

Black symbols are eggsshocked but parents not shocked

Open symbols are bothparents & eggs shocked

Control

Highest mortality occurredat middle – late epiboly whichwas about 7 – 13 days afterspawning with an average watertemperature of 7 ˚C

Mortality usually <5%; highest ~9%

Electroshock Effects on Invertebrates

• Little studied, but...

• An 80% reduction in aquatic invertebrates observed in streams repeatedly electrofished (Elliott et al. 1972; Fowler 1975)

• Drift induced in several aquatic insect species but with no mortality (Mesick and Tesh 1980)

Electroshock Effects on Invertebrates

• Increased stream drift of macroinvertebrates (reaction that may lead to more efficient sampling for biomonitoring; see Taylor et al. 2001)

• No effects on survival, growth rate, development, or longer-term drift behavior of a mayfly (Baetis bicaudatus) (Taylor et al. 2001)

• Mortalities in field noted for Hexagenia mayflies in Michigan

University Wisconsin at Stephens PointAquatic Entomology Lab

Electroshock Effects on Invertebrates

• No effects on Scottish freshwater pearl mussel (Margaritifera margaritifera) (Hastie & Boon 2001);

• Holliman et al. (2007) found that power levels used by typical electrofishing pose little direct risk to freshwater mussels (Unionidae); trama/mortality to mussel host fish, especially during mussel reproductive periods, are a greater concern.

Injury-related Effects of EF

• Injured fish, even if severely injured, can have low mortality (Schille & Elle [2000] found less than 2% mortality with > 80% hemorrhage injury rates in rainbow trout)

• Injured fish often have reduced growth rates

• Injured fish may have reduced reproductive potential

• Population effects (e.g., % of population injured) often considered negligible

Population Effects

• To project sample injury rates to rates on the reach and stream scales (McMichael et al. 1998)

– Reach scale: equals sample site

Rs = n(Es x Cs) where,

Rs = reach injury proportion in a season (for a size class)

n = number of exposures (passes)

Es = sample injury proportion for one exposure

Cs = capture probability of a size class in each pass

Population Effects

• To project sample injury rates to rates on the reach and stream scales (McMichael et al. 1998)

– Stream scale

Ss = (Rs x F) where,

Ss = stream injury proportion in a season (for a size class)

Rs = reach injury proportion in a season (for a size class)

F = fraction of habitat sampled =sampled length/stream

length

Population Effects

• See example in Excel File “Sample injury rate projection”

• Once you get a “population” proportion, does that injury rate matter to population size?

– One way to predict relevance is to model population dynamics as with a population viability analysis (Excel program “PVA for EFishing Mortality.xlsx”)

– Also, fish populations could be directly monitored

Monitored Population Effects

• Carline (2001) found that high sample injury rates for brown trout (~40%) did not lead to lower abundances over a 5-year sampling period with electrofishing

• Kocovsky et al. (1997) found that abundances of three trout species remained stable or increased over an 8-year period of electrofishing sampling; in contrast, longnose sucker populations declined dramatically (longnose sucker had the highest sample injury rate as well).

Next Step

“Safety” (Module 9)