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2012 SOUTHEASTERN NATURALIST 11(1):35–42
Impact of a Gill Parasite Upon the Minnow
Andrew B. Adrian1,2, Brittany Holmes1, and Bruce W. Stallsmith1,*
Abstract - Dactylogyrus is a holarctic genus of monogene flatworms that infects the
gills of cyprinid fishes. Dactylogyrus species are usually highly host specific, and little is
known about their life history in North America. The purpose of this study was twofold:
to determine 1) whether Dactylogyrus exhibits seasonality in its life cycle, and 2) if there
is any potential effect upon reproductive effort of the host as a result of Dactylogyrus
infection. Over a 12-month period, 967 Dactylogyrus were found on the gills of 383
Notropis telescopus (Telescope Shiner), a cyprinid fish collected in the upper Paint Rock
River system in northeastern Alabama. A significant positive relationship was found between
prevalence of infection and host somatic weight and gonadosomatic index (GSI).
The assumptions that parasite presence is evenly distributed among individual host fish
and within each month were rejected by chi square tests, with the months of March
through July as a peak for the extent of Dactylogyrus infection. These months are the time
of gonadal development and reproduction in Telescope Shiners.
Dactylogyrus Diesing (Phylum Platyhelminthes: Class Monogenoidea) is a
holarctic genus of flatworm gill flukes that infect freshwater fishes, primarily
Cypriniformes. These highly host-specific gill flukes attach to host gills with the
use of their unique haptor, armed with a series of 14 hooks and 2 large anchors
(Mueller 1936). They irritate gill tissues, causing significant mortalities in aquaculture
and the ornamental fish industry. Dactylogyrus have a direct life cycle,
with no intermediate host. New hosts are infected by free-swimming larvae, and
at 20 °C, European Dactylogyus species hatch in five days and mature in six to
ten days, with the life cycle completing in 18 to 20 days (Olsen 1986). There are
no data describing reproductive impacts of Dactylogyrus species upon any North
American fish, and, with the exception of Knipes and Janovy (2009), no studies
Dactylogyrus spatulus Cloutman, has been found upon the gills of Notropis
telescopus Cope (Telescope Shiner) (Cloutman 1988). The Telescope Shiner occurs
throughout the river drainages of the Tennessee River on the Cumberland
Plateau of eastern North America, and within the White and Black river systems
in Arkansas and Missouri (Mettee et al. 1996). Where found, it is a common
species that prefers small to medium-sized upland streams in flowing water near
riffles over gravel or rock substrates. Its reproductive biology in Alabama was
1Department of Biological Sciences, University of Alabama in Huntsville, Huntsville, AL
35899. 2Department of Biological Sciences, University of Iowa, Iowa City, IA 52242-
1324. *Corresponding author - email@example.com.
36 Southeastern Naturalist Vol. 11, No. 1
recently described (Holmes et al. 2010), and its diet consists of small terrestrial
insects and aquatic insect larvae (Mettee et al. 1996).
Parasites play an important role in the biology of animals. They often are
responsible for host mortality and may attenuate success or alter timing of reproduction
(review in Michalakis and Hochberg 1994). Interactions between hosts
and parasites have been cited as major evolutionary forces, providing for the maintenance
of sex and greatly influencing rates of speciation (review in Hudson and
Greenman 1998). Although ecologists acknowledge the importance of parasites
in communities, their effects remain under-investigated (Thomas et al. 2000). The
purpose of this study is to elucidate the host-parasite interaction between the Telescope
Shiner and Dactylogyrus parasites, specifically, the seasonal prevalence and
abundance of gill flukes upon the host, and whether increased prevalence of infection
may coincide with peak reproductive potential.
Fish used in this study were collected from two sites: Estill Fork of the
Paint Rock River, Jackson County, AL (34°57'54"N, 86°09'14"W), and Hurricane
Creek, also a tributary to the Paint Rock River, Jackson County, AL
(34º59'12"N, 86º05'41"W). The latter is within the Walls of Jericho tract of Alabama’s
Forever Wild land holdings. These streams are clear, shallow riffle and
run systems over gravel, sand, and cobble. They range from 10–15 m wide and
rarely more than 1 m deep. Both run through narrow incised valleys between
ridges about 350 m high.
Materials and Methods
Collection of fish
Fish collections were performed using seine nets (3 m long x 1.3 m deep;
3-mm mesh). Monthly collections were made in late morning. Fish were not selected
by size or sex. Water temperature (°C) was recorded during each collection.
Monthly collections made at Hurricane Creek (Feb 2007–Sep 2007) consisted of
≈30 Telescope Shiners (as per our permit), which were euthanized using MS-222
(tricaine methanesulfonate) and immediately transferred to Sörensen’s solution
for fixation (Weydert and Cullen 2010). Fish collected from Estill Fork (Oct
2008–Jan 2009) were euthanized with MS-222 and then placed on ice for an hour
until being fixed in Sörensen’s solution.
Visual inspections were performed on removed gill arches from the collected
fish. To remove gill arches, the operculum was forced anteriorly, and each gill
arch was removed with forceps. All gill arches from the right and left sides of
each fish were removed and examined. Intact gill arches were stained in a 1% acetocarmine
solution for 24 to 48 hours before being inspected under a dissecting
microscope at 30X magnification. Parasites were counted by feathering through
the gill filaments with a dissecting needle on both sides of each gill arch to ensure
all of the parasites on a given arch were counted. Approximately 15 parasites
2012 A.B. Adrian, B. Holmes, and B.W. Stallsmith 37
were examined for species determination, and all showed the characteristics
of D. spatulus as described by Cloutman (1988). Because such a small number
of the total parasites counted were identified to species, this study refers to all
observed parasites simply as Dactylogyrus, although no other species of Dactylogyrus
are known to occur on Telescope Shiners.
Length and mass data collection and determination of sex and gonadal condition
Standard length (nearest 0.01 mm) was recorded for each fish with digital
calipers. Individuals were weighed after blotting to remove excess fluid. Gonads
were removed, and gonad mass was recorded to 0.01 g. Sex was determined
through visual gonadal examination. The gonadosomatic index (GSI) was calculated
as: (gonad mass/somatic mass) x 100. An Ohaus Explorer balance (Pine
Brook, NJ) was used for the collection of all mass data. These methods follow
those described in Holmes et al. (2010).
The terminology of Bush et al. (1997) is used to describe the percentage of
hosts infected with one or more parasites (prevalence) and the number of individual
parasites in an infected host (intensity of infection). The abundance of
infection per fish was organized into a frequency distribution for each month, and
the monthly counts were totaled over the entire year to give a frequency distribution
for the entire year.
To determine if parasites infect Telescope Shiner individuals at random, the
yearly distribution of parasites per fish was compared with that of the expected
Poisson distribution. The expected values were calculated by the equation
Expected = nke-n/k!*N,
where n equals the average number of parasites per fish, N equals the total
number of fish examined, and k equals the number of parasites found for the
frequency being examined. These calculated expected values were compared to
the observed yearly distribution through a chi square analysis. In order to keep
expected values greater than 1 for this calculation, the fish with more than 8
parasites were combined into one category of 8 or more parasites. Because the
prevalence appeared to increase during the Telescope Shiner breeding season
(Holmes et al. 2010), the percentage of infected and non-infected individuals
in both breeding and non-breeding seasons were compared using a chi square
In order to determine what is related to whether an individual is infected by
parasites, a binary logistic regression was performed in the software program
SPSS. The initial independent variables used to create the logistic model were
standard length, GSI, and somatic weight, a calculated weight adjusted by removing
the weight of the gonad for each individual fish. The dependent variable
was infection, where 0 was used to represent a fish that was non-infected, and 1
38 Southeastern Naturalist Vol. 11, No. 1
Table 1. Summary of intensity, mean abundance, and prevalence and calculated expected values for the Poisson distribution based on the observed total
distribution for Dactylogyrus infecting Telescope Shiners. Data are separated into breeding and non-breeding seasons to show the differences in parasite
Hurricane Creek, breeding season Estill Fork, non-breeding season
infection per fish Feb March April May June July Aug Sept Oct Nov Dec Jan Total Exp
0 13 10 9 3 3 10 18 17 9 12 25 11 140 30.67
1 7 1 1 1 2 4 15 10 3 6 8 3 61 77.43
2 7 3 4 4 9 3 5 8 5 1 4 1 54 97.75
3 2 5 1 4 5 3 1 2 1 1 2 0 27 82.27
4 0 4 2 1 5 2 0 0 1 0 2 3 20 51.93
5 1 2 7 2 6 2 0 0 1 1 0 0 22 26.22
6 1 4 3 1 3 2 0 0 0 0 0 0 14 11.03
7 1 0 1 3 0 0 0 1 0 0 2 0 8 3.98
≥8 0 4 5 0 3 1 0 0 0 0 0 0 37 1.26
Total fish 32 37 39 25 42 29 39 38 20 20 42 18 383
Total parasite 45 149 194 147 183 80 28 39 25 11 35 31 967
Average parasite 1.41 4.03 4.97 5.88 4.36 2.76 0.72 1.03 1.25 0.55 0.83 1.55 2.52
%infected 59 73 77 88 93 66 54 55 55 40 40 39 63
2012 A.B. Adrian, B. Holmes, and B.W. Stallsmith 39
A total of 967 Dactylogyrus were counted on the gills of 383 individual Telescope
Shiners, for an overall mean abundance of 2.52 ± 0.54 SE parasites per fish.
Mean abundance was higher than the annual average from March through July
(highest in May) and lower during August through February (lowest in November)
If it can be assumed that parasites would be equally likely to develop an association
with any Telescope Shiner individual, there should be a random assortment of
parasites per fish, which can be tested against the Poisson distribution of the yearly
parasite intensity counts (Table 1). The chi square test (χ2
5 = 1493, P < 0.001) was
found to be statistically significant, showing that the abundance of parasites does
not appear to be random. Fewer fish than expected had 2 parasites, three times fewer
fish than expected had 3 parasites, and about 2.5 times fewer fish than expected
had 4 parasites. Greater than four times more fish than expected had no parasites,
two times more fish than expected had 7 parasites, and significantly more fish than
expected had 8 or more parasites. The observed number of fish having 1, 5, or 6
parasites were close to the expected intensity of infection.
The chi square analysis of the contingency table (Table 2) comparing the number
of infected and non-infected fish during the breeding and non-breeding seasons
was statistically significant (χ2
1 = 22.40, P < 0.01), showing that the prevalence of
infection differs strongly between breeding season and non-breeding seasons. The
chi square analysis also showed that there were almost 2 times more non-infected
fish during the non-breeding season than expected, while there were about twothirds
as many infected fish during the non-breeding season as expected. This finding
supports the idea that parasite infection of Telescope Shiners is more likely to
occur during the breeding season than the non-breeding season.
An initial binary logistic regression using length, somatic weight, and GSI
as independent variables indicated that length was not significantly related to
presence or absence of Dactylogyrus. The regression was run without length as
a variable (Table 3) and determined that presence or absence of infection was
Table 2. Comparison of Dactylogyrus parasitizing Telescope Shiners during the breeding versus
non-breeding season (χ2
1 = 22.40). Bold values are statistically significant (P < 0.05).
Hurricane Creek, breeding season Estill Fork, non-breeding season
Observed Expected Chi square Observed Expected Chi square
Non-infected 83 102.72 3.78 57 37.28 10.43
Infected 198 178.28 2.18 45 64.72 6.01
Table 3. Results of binary logistic regression showing the relationships of somatic weight and GSI
of Telescope Shiners with presence or absence of infection of Dactylogyrus.
B S.E. df P Exp(B)
Somatic weight 1.369 0.405 1 0.001 3.930
GSI 0.074 0.033 1 0.027 1.077
Constant -1.213 0.525 1 0.021 0.297
40 Southeastern Naturalist Vol. 11, No. 1
statistically significant when incorporating the variables of somatic weight and
GSI of examined fish. The overall equation
Log (Presence of Infection) = 1.369(Somatic Weight) + 0.074(GSI) – 1.213
showed that the largest contribution to infection was somatic weight. This variable
might be attributed to the age or overall health of individual fish, since sex
and time of year were removed from this variable.
Parasite abundance in the host Telescope Shiners showed a strong seasonal
pattern, with low abundance from August to February followed by higher
abundance from March to July. Stream water temperatures varied from a low
of 9 ºC in February to a high of 24 ºC in July. While the Dactylogyrus life
cycle is known to be somewhat temperature dependent (Olsen 1986), the temperature
maximum in July does not correspond with peak parasite abundance.
The months of peak abundance coincided with reproductive effort of the host
Telescope Shiners as observed through GSI and gonadal condition (Holmes
et al. 2010). This general seasonal Dactylogyrus abundance pattern was
found by Knipes and Janovy (2009) in the cyprinid host Pimephales promelas
Rafinesque, although the seasonal fluctuations in abundance were not as pronounced
as those in this study.
Such close association with reproductive timing has been attributed to coevolutionary
processes whereby the parasites have matched their reproduction
with the time when the host is least capable of fighting off the infection due to
the dramatic energy costs of reproduction (Lamková et al. 2007). A significant
correlation between fish weight and the prevalence of infection (Table 3) can be
attributed to higher gill surface area of older, larger fish.
Elevated prevalence of infection by Dactylogryus is positively correlated with
the GSI of Telescope Shiners (Table 3), indicating that when fish are reproductive,
the parasite prevalence increases. This result raises the question of the effects of
parasite infection on the host’s reproductive effort, since an individual’s GSI is a
good measure of reproductive effort. It is unclear whether Dactylogyrus preferentially
infects certain individuals, or if the infection of an individual is due to a
series of purely random factors. Laboratory studies with the Trinidadian Guppy,
Poecilia reticulata Peters, have shown that different Guppy populations vary in
their resistance to monogene trematodes (van Oosterhout et al. 2003), and individual
Guppy’s resistance to infection is replicable (Cable and van Oosterhout
2007a). This finding strongly suggests that the action of parasite-mediated selection
on host immunity can be a major influence on the ecology and evolution of
freshwater fishes including the Telescope Shiner and its congeners (Cable and
van Oosterhout 2007b).
Although not determined in the present study, the presence of Dactylogyrus
during May at the peak of Telescope Shiner gonadal development may impact
gonad development as the intensity and prevalence of infection also peak
2012 A.B. Adrian, B. Holmes, and B.W. Stallsmith 41
(Table 1; Holmes et al. 2010). Diminished GSI and heightened Dactylogyrus
intensity of infection during the spawning season was found in the European
cyprinid Leuciscus cephalus L. by Lamková et al. (2007). It is likely that such
a relationship exists between other North American cyprinids and their specific
Part of this work was performed in the Walls of Jericho state lands tract with a permit
from the State Lands Division of the Alabama Department of Conservation and Natural
Resources. We wish to thank Nick Sharp of the State Lands Division for his assistance
acquiring and using that permit. Taito Eguchi and James Swarthout assisted with much
of the field and laboratory work.
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