Rates of Swim Bladder Parasite Infection and PIT Tag Retention in Upstream Migrant American Eels of

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Rates of Swim Bladder Parasite Infection and PIT
Tag Retention in Upstream Migrant American Eels
of the Upper Potomac River Drainage
Jennifer Zimmerman Thesis Defense November 7, 2008
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Life History of A. rostrata
Range from South America to Greenland
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Life History of A. rostrata

• Facultative catadromy
• Spend up to 30 years in rivers before migrating
  downstream

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Life Cycle of American Eels

• Five Life History Stages
• 1. Larval
• 2. Glass eel
• 3. Elver
• 4. Yellow eel
• 5. Silver eel

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Why are Eels Important?

• Commercial and recreational fishery
• Food Source
• Humans
• Animals

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Eel Populations are in Decline
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Threats to Eel Populations

• Fishing Pressure
• Habitat Modification
• Swim bladder parasite

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Topic 1Anguillicola crassus in Upstream Migrant
American Eels
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Anguillicola crassus

• Native to East Asia and common in Japanese eels.
• Introduced to European eels in 1980s and has
  spread rapidly.
• First documented in American eels in Winyah Bay,
  South Carolina and in Texas aquaculture
  facilities (Fries 1996).
• Has been documented in a number of other states.

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Rates of Infection in the United States
ME 0-65 MA 7-76 RI 28-69 NY
0-100 MD 10-29VA 27-61NC 35-52
Infected State
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Life Cycle of A. crassus
Adults enter the swim bladder and lay eggs
Paratenic Host
L2 Released
L2 molts to L3
Intermediate Host
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Successful Invader

• Invaded an empty niche
• Has a short life cycle
• High reproductive potential
• Can survive a wide range of conditions
• Occupies a vast array of host species
• Infects eels of all sizes

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• Impacts of A. Crassus
• Swim bladder rupture
• Enlarged abdomens
• Thickened swim bladder wall
• Dilation of blood vessel in swim bladder
• Skin ulcers in abdomen
• Red and swollen anus
• Secondary bacteria infections
• Decreased swimming ability
• Mortality
• May ultimately impact reproduction and eel
  populations

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Dam Locations on the Shenandoah River, Virginia
and West Virginia
Shenandoah River Valley
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Eel Collection Methods
242 eels were taken from Millville Dam eel ladder
in the summer and fall of 2006-2008
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Eel Collection Methods
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Methods Continued

• Eels were euthanized with an overdose of clove
  oil
• Measured to the nearest mm TL

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• Methods Continued
• The swim bladder was removed and examined for
  the presence of adult nematodes
• Classic parasite identifiers were quantified
  including prevalence, intensity, and mean
  intensity

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Definitions
Prevalence - of infected eels Intensity -
Total of nematodes per infected host Mean
Intensity - Average of nematodes per infected
hosts in a sample of hosts
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However, classic parasite identification methods
may underestimate the impact of A. crassus
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Swim Bladder Degenerative Index (SDI)

• Used on a subsample of 50 eels. Three criteria
  considered
• Transparency and opacity of the swim bladder
  wall
• Presence of pigmentation and exudates
• Thickness of the swim bladder wall
• Scores of 0 to 2 were assigned to each category
  with increasing swim bladder degradation

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SDI Scoring Continued
Transparency 0 Normal 1 Intermediate
opacity 2 completely opaque Presence of
exudate/pigment 0 None 1 Either 2
Both Swim bladder thickness 0 lt1 mm 1 1 to 3
mm 2 gt3 mm
Photo Credit Palstra et al. 2007
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SDI Scoring Continued

• The final cumulative index ranged from 0 to 6

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Ageing

• Paired sagittal otoliths were removed embedded
  in epoxy resin
• A transverse cut was made using a diamond
  wafering saw
• Sections were placed on a slide with
  crystalbond, ground, polished.
• The slides were etched and stained using 2 EDTA
  5 tolueidine blue

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Ageing Continued

• Ages were estimated by counting the number of
  annual rings along multiple axes
• Ages were tripled checked
• An additional year was added to the age estimate
  to account for the larval salt water phase

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Results
Lengths All Eels (n 242) Range 200-527 mm
TL µ 351.5 58.8 Eels w/ previous or current
infection (n24) Range 255-473 mm TL µ 341
53.3 Ages Ranged from 4 11 years old, µ 5.7
1.8 (n42) Infected eels (n15) 4-11 years old,
µ 5.6 1.86
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Results of Classic Parasite Identifiers
Prevalence 2 Intensity 1 Mean Intensity 1
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SDI Results
n 31
n 10
n 9
38 of the eels showed signs of previous infection
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Conclusions
Results for Shenandoah River very low compared to
other Chesapeake Bay tributaries. Why?
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Conclusions Continued

• Potential Reasons
• Parasite has not spread upstream yet
• Presence of dams
• Previous infections have rendered swim bladder
  unsuitable for further reinfection

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Conclusions Continued

• Reasons eels with damaged swim bladders may not
  contain worms
• Insufficient food supply
• Contain an unsuitable habitat for larval
  development
• Development of an immune response against the
  parasite
• No room remaining in the lumen for the parasite

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Conclusions Continued

• 38 of the eels showed signs of previous
  infection, but only had moderate damage to the
  swim bladder
• This indicates that
• Shenandoah eels are not severely infected
• Those that were severely infected may have
  incurred mortality downstream
• - mass mortality
• - less tolerance to high temps and hypoxia
• - more susceptible to predation and capture

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Additional Research

• Continued monitoring of eels in the Shenandoah
• Identification of eel parasite hosts
• Role of other factors like presence of ports and
  urbanization on the spread of the parasite

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Topic 2PIT Tag Retention in Small (205 370
mm) American Eels, Anguilla rostrata
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What are passive integrated transponders (PIT
tags)?

• Tiny microchips inserted into an animal. Once
  activated by a reader, a unique ID code is
  retrieved.

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Uses of PIT Tags

• Assess use of fish ladders
• Measure movements
• Analyze growth rates
• Estimate survival
• Identify individual
• animals

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Advantages of PIT Tags

• Tags are internal and permanent
• Handling time of animal reduced
• Little influence of animal behavior
• High detection rates and reader accuracy
• Animals need not be
• sacrificed

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Tag Loss

• Results from
• Improper tagging technique
• Rejection by animals body
• Migration of tag within the body

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Tag retention is influenced by placement of the
tag The success of tagging technique is
determined almost solely by placement of the
tag - Gibbons and Andrews (2004)
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American eel tag retention
However, no studies exist that directly compare
the different tagging locations..
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Objective

• Quantify retention rates of three PIT tag
  locations in American eels

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2
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Drawing by S. Welsh
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Methods

• 18 eels collected at Millville Dam

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Methods Continued

• Held in 380 L tank in lab
• Anesthetized with clove oil solution
• PIT tagged in 3 locations
• Tag retention checked for 9 weeks
• Handheld reader used
• to check for tags

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Results
Tag Retention 100 - dorsal fin 100 -
abdominal 88 - head
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Discussion

• Results support
• tagging in 2 locations
• dorsal musculature near dorsal fin origin
• abdominal cavity
• Recommend tagging in dorsal fin origin

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Discussion Continued

• Findings comparative to literature
• Lab studies may overestimate retention
  rates in natural environments
• Tags likely exited through tag wound
• Loss of tags probably from improper implantation
  or tag rejection
• Need for longer-term studies

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Acknowledgements The WVU Cooperative Research
Unit Advisor - Dr. Stuart Welsh Committee Members
Dr. Todd Petty and Dr. Ken Oliveira Funding
Source Alleghany Energy Lab Field Assistance
Evelyn Michael, Alison Mynsberge, Ken Sheehan,
and Dustin Smith
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Questions