Politis, G.P.: Internal Parasites of a Sanddab Page 2
INTRODUCTION
Parasitologists have been aware for many decades that fishes
serve as hosts for a variety of helminth and protozoan parasites. In
1965, Mackenzie and Gibson reported a diverse parasite community ex¬
isting in the flat fishes flounder and plaice from the coast of England.
Their study is probably the only detailed study ever published on para¬
site distribution and incidence in flat fish, and it is safe to say
that there have been no published studies on parasites of the flat fish
Citharichthys sordidus, the Pacific Sanddab. This paper describes five
prevalent internal parasites of Citharichthys sordidus, and reports on
the incidences of infection, average parasite loads per sanddab, and
distributions of parasites within the host and host population.
MATERIALS AND METHODS
Sanddabs were collected by bottom fishing in Monterey Bay, nearly
one mile northwest of Lovers Point, during the month of May. The study
began with complete examinations of five sanddabs. The fishes were
killed just prior to examination, by slicing the spinal cord immediately
posterior to the operculum, and all the internal organs were inspected
according to methods described by Amlacher (1970). Four parasites were
found during this initial survey, and the study was narrowed to these
more prevalent parasites.
The weight, length, and sex were recorded prior to the inspection
of each fish. The visceral cavity (Figure 1) was inspected with a di¬
Politis, G.P.: Internal Parasites of a Sanddab Page 3
secting microscope before any organs were removed. Physiological
saline (0.9% Nacl) was periodically applied to the surface of organs
during the examination. Gall bladder fluid was extracted with a sy¬
ringe and examined microscopically. The stomach and esophagus were re¬
moved, cut open, and viewed with a disecting microscope. The light
source was put below the tissue, and forceps were used to spread the
folds of the wall to locate hidden helminths. The intestine and py¬
loric caeca were examined in the same manner as the stomach and esoph¬
agus. The intestinal wall was inspected by cutting a small piece,
rinsing it in distilled water, and flattening it for microscopic exam¬
ination.
The ability of Trypanorhynchid larvae to survive an anaerobic en¬
vironment was evaluated by placing them in a stoppered test tube of
deoxygenated (nitrogenated) physiological saline. The experiment was
run at a temperature of 220 and a pH of 6.
An attempt to induce Trypanorhynchid larvae to develop to their
adult stage was done by putting the larvae in physiological saline
solutions of pHs equal to 2, 3, and 4. Solutions were prepared by mix¬
ing dilute HCI with physiological saline, and using a pH meter to ob¬
tain the desired pHs.
Viability of trypanorhynchid larvae was determined by preparing a
slide and examining the scolex region for motion. When no motion was
observed, gradually increasing pressure was applied to the coverslip
until either motion was observed or the larva exploded.
Politis, G.P.: Internal Parasites of a Sanddab Page 4
RESULTS
The following data has been tabulated by assuming that parasite
loads are independent of sanddab size and sex. The basis for this
assumption was that Mann Whitney U-tests indicated no coorelation ex¬
ists between host sex and parasite loads, and scatter plots showed no
coorelation between host size and parasite load.
Fifteen out of fifteen gallbladders examined were infected by
Ceratomyxa hopkinsi, a myxosporidean of the family Ceratomyxidae.
Identification was made according to Kudo (1966). Ceratomyxa spores
ranged in length from approximately 25um to 50gm, averaging about 40m.
Mature digenetic trematodes of the family Hemiuridae (identifica¬
tion was according to Schell (1970)) were present in either the stomach
or esophagus in 49% of the sanddabs. Figure 2 shows the hermaphroditic
sac which is chacteristic of the family Hemiuridae. Hemiurids ranged
from 1.5mm to 2.8mm, averaging 2.4mm (n=5), and had a mean load of 2.0
per sanddab. The concentration of hemiurids was greatest in the anter¬
ior end of the stomach; 21% were found on the esophagus, and 54% were
found on the anterior half of the stomach (Table 1). Assuming that
sampling of sanddabs was random, a Xø test determined that there was a
significant difference between the number of trematodes found on the
anterior half of the stomach and the number found on the posterior
half (p-.05).
Nematodes of the family Anisakidae were abundent in the pyloric
caeca and intestine. The muscular pharynx and intestinal caecum were
identifying characteristics, according to Hyman (1951). Six of 7
Politis, G.P.: Internal Parasites of a Sanddab Page 5
sanddabs were infected inside the intestine, with a mean of 3.6 Anis¬
akidae. Four of 7 were infected in the pyloric caeca, with a mean load
of 1.6. The length of Anisakidae from inside the digestive tract
ranged from 2mm to 8mm, with a mean of 5.4mm.
Larval nematodes were found encysted in the walls of both the py¬
loric caecae and intestines in 6 out of 6 sanddabs. They were not
encapsulated and were approximately .5mm in length.
Anisakidae were also found in the body cavity, and occured with an
incidence of 90%. They ranged from 5mm to 30mm in length, with a mean
of 12.9nm. Of 57 anisakids from the visceral cavity, 30% were found
attached to either the pyloric caeca, or it's adjacent mesentaries,
and 30% were found on the mesentary in the cavity below the liver.
On one occasion 7 metacercaria of the digenetic trematode Acantho¬
colpidae Stephanostomum sp. were found, and were attached to mesentary
between the intestine and spleen.
Plerocercoid larva of a cestode from the order Trypanorhyncha
were abundant in the visceral cavity. These encapsulated larvae had
a fully developed scolex, equipped with four spiny proboscides. The
scolex region was invaginated in the receptaculum of the blastocyst
(Figure 3) but could be extruded. Trypanorhynchids ranged from Imm
to Amm in length, with a mean of 1.9mm (n-10), and had a mean load of
10 per sanddab. A concentration of trypanorhynchids were located in
the area of the spleen and pyloric caeca; 28% were on the mesentaries
adjacent to the spleen, and 28% were on the pyloric caeca or it's
Politis, G.P.: Internal Parasites of a Sanddab Page 6
adjacent mesentaries. Trypanorhynchids were typically found in clumps,
and often were in close proximity with nematodes; 11% had nematodes
coiled around them.
A Poisson distribution was calculated to determine what would be
the expected number of sanddabs with various trypanorhynchid loads, pro¬
vided each infection was independent of all others (Figure 4). A X
test value showed that the observed values were significantly different
from the expected values (p is less than .01), indicating some type of
dependence of infections upon one another.
Five trypanorhynchid larvae were put into solutions of pH
equal to 2, 3, and 4, to try to induce development. All five larvae
in a pH of 2 had died by eight hours, while the larvae in pHs of 3 and
4 were still alive after 10 days. None of the larvae showed any sign
of a morphological or behavioral change. Also, no change was observed
in larvae that had been living for six weeks in a solution with a pH
of 6.
DISCUSSION
The myxosporidean Ceratomyxa hopkinsi was consistently present
in the gall bladder of Citharichthys sordidus. Jameson (1929) reported
that Ceratomyxa hopkinsi was present in the gall bladder of Citharich¬
thys xanthostigma, but this is the first report of its occurence in
Citharichthys sordidus.
The significantly greater (p-.05) concentration of trematodes in
the anterior region of the stomach is hard to explain. Mackenzie and
Politis, G.P.: Internal Parasites of a Sanddab Page 7
Gibson (1970) reported that osmotic pressure of the gut fluid decreases
down the length of the gut. If there is a difference in osmotic pressure
within the stomach, the trematodes positioned anteriorly would be under
greater osmotic stress and less likely to survive there. Perhaps the
most interesting thing about the Hemiuridae data is the strange occur¬
ence of twenty-four hemiurids on a single sanddab. The life cycle of a
digenetic trematode involves intermediate hosts and so we know the
large number of hemiurids was not a result of reproduction on behalf
of hemiurids already in the stomach. Possibly, metacercaria of this
hemiurid are clumped within the population of the intermediate host on
which sanddabs prey, or intermediate hosts are clumped in areas along
the bottom.
Taxonomy was a problem with the Anisakidae nematodes; the number of
species of Anisakidae present in the sanddab was not determined. How¬
ever, all the Anisakidae found should be of the genera Contracaecum or
Porocaecum, since Hyman (1951) reports that species of those two genera
are the only anisakids found in marine fish. The occurence of larger
nematodes in the visceral cavity andishorter ones in the digestive tract,
indicates that the genus Contracaecum is probably present. According to
Hyman, the typical life cycle of Contracaecum begins with eggs being
passed into the water along with feces of the definative host. These
eggs develop into an infective juvenile which is eaten by an intermedi¬
ate host (usually a fish). The juvenile develops in the host's intest¬
ine, and as it gets larger it bores through the intestine and inhabits
body spaces. The intermediate host is eaten by the definative host
Politis, G.P.: Internal Parasites of a Sanddab Page 8
and the life cycle is complete. Perhaps the sanddab's anasakids are
immature Contracaecum with the sanddab serving as their intermediate
host. Mackenzie and Gibson (1970) reported that Contracaecum aduncum
was present in the flounder Platichthys flesus and in the plaice Pleuro¬
nectes platessa, taken from the coast of England. Contrary to Hyman,
they state that mature Contracaecum were in the digestive tract and lar-
vae were in the visceral cavity.
The infections of trypanorhynchid larvae appear to be dependent on
one another. Figure 4 shows that there is a disproportionately high
number of fish with both few and many trypanorhynchids, implying that the
distribution of larvae within the sanddab population is clumped. As with
the trematodes, clumping is probably due either to clumping of larvae
within the population of the previous intermediate host or to clumping
of the previous host.
The complete life cycle is not known for any marine trypanorhynchid,
according to Hyman (1951). Rays and sharks are known to be definitive
hosts, but it is not known how the larvae get to an intermediate host.
Furthermore, how larvae get into the visceral cavity from inside the di¬
gestive tract is unknown. All trypanorhynchids found, including those
encysted in the stomach wall and those inside the intestine, were encap¬
sulated and could not be using proboscides to bore. Interestingly, the
trypanorhynchids found loose inside the intestine did seem more active
than those in the visceral cavity; movement of the whole body was ob¬
served in the former while the latter were always motionless. Trypano¬
rhynchids in the visceral cavity may have entered a state of torpor.
Politis, G.P.: Internal Parasites of a Sanddab Page 9
The fact that trypanorhynchids survive for over a week without
oxygen indicates that they use a very small amount of oxygen or have
an extraordinary capability to go into oxygen debt. Their ability to
live for over six weeks in an anaérobic environment implies that their
respiration rate is extremely low. Probably they enter a state of tor¬
por, and wait for an external cue to resume development. What the cue
might be is unclear, but it does not seem to be a low pH.
Coexistence of anisakids and trypanorhynchids suggests that there
may be a symbiotic relationship between them. On the other hand, these
helminths could be found together soley because of a shared interest
in some resource or enviromental condition.
Three points about this study are worth mentioning. Firstly, time
was limited, making sample sizes smaller than desirable. Consequently,
the assumption that there is not a coorelation between parasite loads and
host size or sex could be incorrect. Secondly, an analysis of statisti¬
cal significance of trypanorhynchid and anisakid distributions could
not be done since surface areas of organs and mesentaries were not com¬
puted. Thirdly, the information in this paper is probably specific
for the community of Citharichthys sordidus studied, and for the time
of year the study was done.
The parasites of Citharichthys sordidus offer several opportunities
for future work. Some possibilities include: illucidating the life cycle
of Ceratomyxa hopkinsi, determining reasons for the observed helminth
distributions, investigating the life cycle of the trypanorhynchid ces¬
tode, and determining the damaging effects of the various helminths on
Politis, G.P.: Internal Parasites in a Sanddab Page 10
the host.
SUMMARY
1. Five prevalent parasites were found during an investigation of
26 sanddabs.
2. Ceratomyxa hopkinsi, a myxosporidean, was present in 100% of the
gall bladders examined.
Trematodes of the family Hemiuridae were in the stomach and
esophagus. A greater number were in the anterior stomach than the
posterior.
Nematodes of the family Anisakidae were in the intestine, pyloric
caeca, and visceral cavity. Those in the visceral cavity were
larger than those in the digestive tract.
5. Larval nematodes were in the wall of the intestine and pyloric caeca
in 6 out of 6 examinations.
6. Cestode larvae of the order Trypanorhyncha were present in the
visceral cavity. A concentration was noted in the area of the
spleen and pyloric caeca.
7. Trypanorhynchid larvae do not randomly infect sanddabs; individual
infections depend on one another.
8. Trypanorhynchid larvae can live in an anaerobic environment for at
least 10 days.
Politis, G.P.: Internal Parasites of a Sanddab
Page 11
ACKNOWLEDGMENTS
Thanks is due to several people who aided me during this study. I
am grateful to: Dr. Robin Burnett for his statistical assistance and
his comments on my sleeping habits; Dr. Norm Levine for his outgoing
and modest nature; Dr Don Abbott for his enthusiastic attitude and his
good ideas; Dr. Gary Wagenbach for his help editing this paper; Bill
Magruder for his fishing talent; and Dragon Popoy for eating the sanddabs.
Politis, G.P.: Internal Parasites of a Sanddab Page 12
LITERATURE CITED
Amlacher, E.A., 1970. Textbook of Fish Diseases. T.F.H. Publications,
Neptune City, New Jersey, pp. 25-26.
Hyman, L.H., 1951. The Invertebrates, Vol. 3. McGraw-Hill, New York,
New Vork. pp. 321-328.
Jameson, A.P., 1929. Myxosporidia from California fishes. J. Para¬
sitology, 16:59.
Kudo, R.R., 1966. Protozoology. Charles C. Thomas, Springfield,
Illinois. pp. 774-806.
Mackenzie, K. and Gibson D., 1970. Ecological Studies of Some Parasites
of Plaice, Pleuronectes Platessa (L.) and Flounder, Platichthys
Flesus (L.). In Taylor A.E. and R. Muller (Eds.), Aspects of
Fish Parasitology. Sympos. British Soc. Parasitology, 8:1-42.
Schell, S.C., 1970. How To Know The Trematodes. Wm. C. Brown Company,
Dubuque, Iowa.
Politis, G.P.; Internal Parasites of a Sanddab Page 13
Table Legends:
Individual parasite distributions in Citharichthys sordidus.
Table 1
Each value represents the percentage of the population of the
parasite in the left hand column found on the organ listed
above. Abbreviations are as follows: SP, splenic mesentary;
P, pyloric caeca or adjacent mesentary; CL, mesentary in cavity
under the liver; IM, intestinal mesentary; OS, on stomach wall;
IS, inside stomach wall (encysted); E, in esophagus; AS, in
anterior half of stomach; PS, in posterior half of stomach;
IP, in pyloric caeca; I, in intestine; 0, other.
1 - 0 —.
30



8




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Politis, G.P.: Internal Parasites of a Sanddab Page 14
Figure Legends:
Figure 1
Dorsal view of anatomical feature that are discussed in this
paper.
Figure 2
Ventral view of a flattened hemiurid tremitode, taken from the
stomach. The distance from the center of the anterior sucker
to the center of the ventral sucker represents approx. Imm.
Figure 3
Flattened trypanorhynchid larvae from the visceral cavity.
Figure 4
Representation of the expected number of sanddabs with a given
trypanorhynchid load (according to a Poisson distribution)
versus the observed number. The bars represent the observed
number and the lines represent the expected. Groupings of
trypanorhynchid loads were divided unequally to obtain expect-
ed values of at least five so that a X test could be run.
ESOPHAGUS
LIVER
BLADDER
CAVITY
UNDER
LIVER
RECTUM
—
PYLORIC
STOMACH
CARDIAC
STOMACH
SPLEEN
PYLORIC
CAECA
Figure 1: Sanddab
Anatomy
Figure 2 Digenetic trematode from the stomach
Figure 3 Trypanorhynchid larva from the visceral cavity
Figure 4
Observed
Expected
9—10 11—12
TRYPANORHYNCHID
LOAD
13 Up
0
Appendix:
Legend
Parasites in individual Sanddabs. Also, Sanddab weight, length
and sex. Abbreviations are as follows: Lg, length; Wt, weight;
VA, visceral cavity anisakidae; DA, anisakidae from the digestive
tract; LA, larval anisakidae; LT, larval trypanorhynchids; H,
hemiuridae; CH, ceratomyxa hopkinsi. A "+" symbol means the para¬
site was present but too prevalent too count. A blank indicates
that data was not collected.
Appendix:
(cm)
Sanddab
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Parasites in individual Sanddabs.
12
40
18
40
33
4
6
f
LA
+
+
20
+
O +
1 +
1 +
0
1 +
O +
4 +
O +
2 +
24 +
27
100
150
200
15