This study examined the effects of an encysted trematode parasite, Stomachicola magnus, found in the stomach linings of weakfish (Cynoscion regalis) in North Carolina. Weakfish were collected from gill net and trawl surveys. The parasite was identified as S. magnus, which was found in 64% of weakfish examined. Parasite occurrence was significantly higher in gill net (85.5%) versus trawl (40.3%) samples. Statistical analyses found the presence of the parasite did not significantly impact weakfish condition based on length-weight comparisons. While the parasite is common in weakfish, its cysts have not been observed in other local fish

1. Conclusion
ResultsMethods
Results
Table 1: Results from the ANCOVA model examining if Stomachicola
magnus has an effect on weakfish condition from (a) trawl and (b) gill
net samples.
Model: Weight ~Length + Parasite + Length * Parasitized.
(a) Trawl Net Samples
df Sum Sq F p
Length 1 196.8 18490.6 < 0.001
Parasite 1 0.013 1.209 0.272
Length * Parasite 1 0.019 1.771 0.184
Residuals 398 4.236 - -
(b) Gill Net Samples
df Sum Sq F p
Length 1 148.7 28820.5 < 0.001
Parasite 1 0.007 1.370 0.243
Length * Parasite 1 0.004 0.767 0.382
Residuals 437 2.254 - -
Acknowledgements
Methods
Introduction
 Weakfish (Cynoscion regalis) primarily inhabit coastal waters from Massachusetts
to the eastern coast of Florida.
Encysted Trematode Stomachicola magnus in the Stomach Linings of Weakfish (Cynoscion regalis):
Frequency of Occurrence and Effects on Condition
Samantha M. Binion1,Cameron A. Luck2, and Jeffrey A. Buckel1
1Department of Applied Ecology, North Carolina State University, Center for Marine Sciences and Technology, 303 College Circle, Morehead City, NC 28557
2Environmental Sciences Program, North Carolina State University, Jordan Hall, 2800 Faucette Drive, Raleigh, NC 27606
 Population has been in decline for the last 20 years
and high natural mortality is suspected (Fig.1).
 There is a demographic bottleneck between age-0
and older fish.
 During a food habits study, encysted parasites were
often observed in the stomach linings of weakfish
(Fig. 2).
 Objectives of this study:
 Identify the parasite causing the
cysts.
 Describe the prevalence of cysts in
sampled weakfish.
 Determine if the presence of cysts
has an effect on weakfish
condition.
Figure 1: Weakfish maximum
spawning potential. From asmfc.org
Figure 2: (a) Melanistic or dark-colored
cysts in the stomach lining of weakfish
and (b) magnified image of the cyst.
We would like to thank J. Daniel, B. Kornegay, J. Merrell, and
T. Westbrook for help with sample processing. Funding is
provided by a NC Coastal Recreational Fishing License Grant.
Sample Collection
 Weakfish were collected from two fisheries-independent monitoring programs
conducted by North Carolina Division of Marine Fisheries in Pamlico Sound, North
Carolina (Fig. 3).
 Program 1: Gill Net Survey
 Stratified random design
 February 15th – December 15th
 2012-2013
 n = 441
 Program 2: Trawl Survey
 Stratified random design
 54 stations
 June and September
 2012
 n = 402
Sample Processing
 Total length (TL; mm) and weight (kg) were recorded for each weakfish.
 Stomach contents were weighed (g).
 Number of cysts in stomach lining counted for each weakfish.
Figure 3: Sampling locations where weakfish were
collected in NCDMF gill net and trawl surveys.
Parasite Identification
 Excised cysts and whole parasites removed from the cysts were sent to Drs. Craig Harms and James
Flowers at NCSU College of Veterinary Medicine for identification using histology and
morphometric techniques.
Statistical Analyses
 Gill and trawl net fish were analyzed separately.
 Rate of parasite occurrence between fish sampled in the gill net and trawls were compared using a
chi-squared test.
 Differences in fish condition between parasitized and non-parasitized fish were evaluated.
 Prey weight was subtracted from total weakfish weight to get true fish weight.
 Length and weight were natural log transformed prior to analysis.
 Used presence/absence data, not cyst count in the model.
 ANCOVA Model: Weight ~ Length + Parasite + Length*Parasitew
Parasite Identification and Frequency of Occurrence
 The parasite was identified as immature Stomachicola magnus (Fig. 4).
 Trematode in the Order Digenea
 Poorly studied
 Initially described in 1934 by Manter in spotted
seatrout (Cynoscion nebulosus) collected in Beaufort,
NC.
a.
b.
Figure 4: Immature Stomachicola
magnus removed from a weakfish
stomach lining cyst.
 64% of the examined weakfish had encysted parasites in the stomach lining.
 Weakfish sampled from the gill net (85.5%) survey were parasitized at a significantly higher rate (χ2
= 179.92, df = 1, p < 0.001) than fish from the trawl (40.3%) survey.
Figure 5:
Length-
weight
comparison
of
parasitized
and non-
parasitized
weakfish
from trawl
and gill net
surveys
using the ln-
transformed
data.
Weakfish Condition
 Weakfish with the parasite
did not have a lower
condition (Table 1).
Discussion
 Cysts are common in age-1+ weakfish, but have not been observed in other
fish in Pamlico Sound, NC.
 Digenean trematodes need multiple hosts to complete their
life cycle and weakfish are serving as an intermediate host.
 Mature S. magnus have been only observed in the stomachs
(n = 284) of inshore lizardfish (Synodus foetens) in a multi-
predator (n = 25) diet study in Pamlico Sound, NC..
 Stomach contents of inshore lizardfish contain juvenile
weakfish.
 The presence of S. magnus cysts did not have a significant effect on
condition.
 Trematode parasites can remain dormant in intermediate
hosts.
 Length-weight can be a poor indicator of condition and other
metrics (e.g. total energy) might have more power.
 The number of macroparasites can influence an individual’s
health; however, counts of cysts were unreliable.
Future Work
 Examine whether the observed increase in inshore lizardfish could be
responsible for the high natural mortality in juvenile weakfish.
 Determining parasite prevalence in other major weakfish nursery areas (e.g.
Delaware Bay) and its influence on fish growth and natural mortality.