Leeches and Their Importance
in the Life Cycle of Fishes
REPRINTED FROM NEW JERSEY FISHERIES SURVEY
Report Number Two, 1951
( PP. / 7"-tS-)
PRINTED OCT. 1953
Leeches and Their Importance
in the Life Cycle of Fishes
CARL
N.
SHUSTER, JR.,* ROLAND
F.
SMITH,t
and
JOHN J. MCDERMOTT*
L
among the most versatile and amazing of all the soft-bodied animals encountered during the fisheries survey of the lakes and
ponds of New Jersey. Their appearance and activity—particularly that of
the blood-sucking species—immediately attracts the attention of anyone
who encounters them. The following brief account on leeches tells something about their structure, habits, and habitats and discusses their role
in the life cycle of fishes.
Leeches belong to the large group of segmented, soft-bodied animals,
the annelids, which also includes the common earthworm and the marine,
sand, or bloodworms. Leeches differ from the other annelids in several
respects. They are more "rugged" animals and have a great tenacity of
life. They have a body with a definite number of divisions or segments—
similar to those of earthworms. An adhesive sucker will be found at one
or both ends. These suckers, which vary in size and development in the
various species, aid the leech in locomotion, attachment and in feeding.
Locomotion of those leeches which habitually "crawl" about is similar to
that of a measuring worm, while the swimming leeches swim by graceful
undulating movements of their entire body. Although leeches are chiefly
predaceous, feeding upon all sorts of aquatic life, some are scavengers,
while others are known for their bloodsucking mode of feeding.t A brief
description of the bloodsuckers may be of particular interest to fishermen
and swimmers.
The bloodsucking leeches secrete an anti-coagulant into the bite which
they "cut" into their victim's skin. It is the anti-coagulant which prevents
the blood from clotting and causes the more or less intense itching at the
site of the leech bite (Moore, 1923). Some people are more sensitive than
others to the irritating qualities of the anti-coagulant—just as some persons are more sensitive to the saliva secreted by the biting flies and mosquitoes. Although the bloodsucking leeches may be so numerous as to be
EECHES ARE
*Department of Zoolo gy, Rutgers University.
t Some leeches have biting mouth parts, others feed by the aid of a powerful muscu-
lar pharynx which "sucks" the food material into the esophagus of the leech.
Fisheries Biologist, N. J. Div. of Fish & Game.
[2]
pests in some bodies of water, they apparently do not transmit any human
diseases. However, since any abrasion of the skin permits the entrance of
bacteria, the wound from the bite may become infected. The danger of
such an infection may 10,Acgased due to the scavenging habits of some
of the bloodsuckers. A wok shaving pencil can be used to allay both the
bleeding and the itching, while witch hazel, ammonia water, calamine lotion, and antiseptics have been used in the treatment of the bites.
Although the practice of blood-letting with leeches is less prevalent today than it has been in previous centuries, there are several wholesale
dealers in New York City alone who specialize in importing and selling
leeches to druggists. In most any city of the United States, where there is
a population of central European stock, the drug stores in the neighborhood regularly sell the specially cultured medicinal leeches. These animals, when properly handled, are entirely harmless and have been successfully used to remove blood from bruises, thus alleviating the swelling.
Leeches are not commonly used as bait in New Jersey; but farther
north they are found to be excellent for smallmouth bass and yellow perch.
The larger species of leeches can generally be found in marshy areas and
in small streams choked with vegetation. They can be kept for several
weeks in a glass jar, with a tightly fitting screen cover, and only an occasional water change. Moore (1923) successfully collected leeches by dragging a muslin bag, baited with freshly killed small animals or staughter
house offal, through the water—catching the leeches with a dip net as they
approached the bag, or removing them by hand from the bait.
There are many kinds of leeches. One of their more striking characteristics includes the amazing shapes and contortions through which they put
their supple bodies. The adults of different species range in size from only
one-half an inch to over twelve inches in length. Many are multicolored,
the color patterns possibly serving as an aid to concealment. Colors vary
from pale grey and cream to black, including greens and browns. In addition, some are brightly marked with yellow and red spots.
Forty or more species of freshwater leeches have already been identified
in North America; one terrestrial species which burrows in the ground
and numerous marine species are also known. The freshwater leeches are
most commonly found in the shallow water of lakes and streams where
there are plants, stones and other material upon which to attach or to
conceal themselves. They also tend to congregate in those places where
favorable food conditions exist—as at the inlets or outlets of bodies of
water and along lee shores where other organisms also collect. From all
reports there are very few waters in which leeches do not exist.
The total leech fauna of a body of water may reach amazing proportions. During a survey of the fauna of Lake Mendota, Wisconsin, Muttkowski (1918) estimated that there were over 100,000,000 leeches between the shoreline and the twenty-five foot depth contour. Richardson
(1928) found as many as 10,000 leeches (mostly snail leeches) per square
[ 31
yard in a section of the Illinois River. A iew leeches have been found by
one of us (Smith) during surveys on acid ponds (pH 5.1) in south Jersey, but the lower limit of their tolerance to acid water is not known. For
recent comprehensive accounts of the ecology of leeches one should consult Herter (1939) and Boisen Bennike (1943). A general account of the
freshwater leeches of the United States may be found in Pennak (1953) .
Leeches and Fishes
Although leeches are usually considered to be of negligible importance
in fisheries problems, it is possible that they will be found to play a greater
role in the life cycle of fishes after more detailed studies of these relationships have been conducted. If one considers the manifold ways in which
the various species of leeches may affect fishes, it seems likely that, at
least under certain environmental conditions, they will be an important
factor in their ecology. In an accompanying diagram (Figure 32) some
of the activities of leeches that may have a direct or indirect bearing upon
the ecology of fishes are depicted. It is well to keep in mind that this diagram represents a "composite picture" of the activity of a leech fauna, as
the majority of the species of leeches do not participate in each of the activities shown. Each of the groups of leeches indicated by the number in
the drawing is the basis for the following discussion:
1. The leech in this bass nest illustrates the fact that certain of the leech
species have been reported feeding upon the eggs of fish and other aquatic
animals (Moore, 1923; Lindeman, 1941; Richardson, 1948). How significant this may be is not known.
2. A considerable number of the species of fish inhabiting or entering
the shallow, or littoral zone of lakes feed upon leeches. Among those
frequenting this region some forty species have been reported : 9 species in
the sunfish family; perch 6; catfish 5; and trout 4 species (Shuster, Mss.).
There are several factors that might affect studies on fish diets. It may be
that the soft bodies of these animals are quickly rendered unrecognizable
by the strong digestive juices of fishes. Furthermore, availability of other
food organisms and the variations in the leech population may determine
the extent to which they will be found in the stomachs of fishes on any
given occasion. Ball (1948) concluded that the size of some leeches is
such that they may volumetrically represent a much higher percentage of
the diet than their numerical presence would indicate.
3. Certain of the leeches feed almost entirely upon the blood of fishes,
hence are called fish-parasites. It has been shown that these leeches may
transmit blood diseases of fishes—just as mosquitoes transmit the malarial
diseases of warm-blooded animals. In some instances, leeches may serve
a intermediate hosts for flatworm larvae which mature in fishes and other
animals. Meyer (1946) gives an excellent critique on the extent of the
damage that leeches may do to fishes:
"It is probable that under normal conditions the 'fish-leeches . . .' infesting freshwater fishes do not become a serious menace to the life of their host. It must be remem-
[ 41
FIG. 32.—In this underwater panorama five groups of leeches are active in phases of their own life history that may, depending upon the incidence of their occurrence, have an effect, favorably or unfavorably, upon the fishes of any body of water.
bered, however that their presence upon the fish is always injurious to the latter and
can never be beneficial nor even indifferent. A single leech withdraws enough blood
and/or mucus from its host for its own sustenance. That amount may be small, but it
nevertheless is a loss, and it weakens the fish's vitality by just that much. The simple
fact that a sufficient number of leeches can weaken or even kill a fish is enough to
prove that each one contributes its share toward that end and is therefore harmful. Not
only may the fish be killed or left in an emaciated condition as a result of heavy infestation, but the value of the commercial and of the game fish may be also materially impaired as a result of the ulcerated spots, which result where the leech has been attached. The blood-shot spots or breaks in the outer mucosal covering, upon which they
may also feed, may serve as a portal of entry for disease producing organisms, resulting
in secondary infection. Fish leeches are commonly found attached to the inside of the
operculum, in the mouth, or if truly external, usually on the body surface protected by
the pectoral and pelvic fins and about the anus of the host."
Two well-known instances can be cited where an epidemic of leeches
greatly affected the fish population. In 1927, Thompson reported a heavy
infestation of leeches upon the redmouth buffalo fish in the Illinois River,
that caused much damage to the fish. Nearly the entire yellow perch population in Shaw Lake, Connecticut, was apparently killed by a heavy infestation of a fish leech, according to Thorpe (1941).
4. Whenever leeches infest or "annoy" fish-eating birds and other animals which prey upon fish, they act in another way to alter factors influencing a fish population. Turtles, particularly snapping turtles, are usually
infested by leeches. Sooter (1937) has found leeches on several fish-eating
birds.
5. There are leeches that feed almost exclusively upon one group of
organisms. Small "snail" leeches feed upon the snails and bivalves (Baker,
1916; Richardson, 1928) , that also make up an important part of the diet
of many young game and pan fish. The larger leeches have been known to
reduce whole populations of snails (Chandler, 1949). Leeches also feed
upon aquatic annelids, earthworms, insect larvae, and crustacea (Miller,
1937). In their feeding habits then, leeches may become important competitors of fish.
The five factors discussed above help to illustrate some of the activities
of a leech population. When analyzing the role leeches may play in the
life history of certain fishes, it is important to consider that both organisms often share the same environment. They are not only "messmates",
so to speak, at the same table, but often feed upon one another.
Fish leeches have been found in many New Jersey lakes and ponds, as
reported in the 1950 Survey Report, although rarely in abundance. The
heaviest infestation thus far was in the two Echo Lakes, Union County
(see 1952 Report). The species of fish most heavily affected were pumpkinseeds. Bluegills were also parasitized, but none of the other species
examined at this time were infested. These included: largemouth bass,
calico bass, golden shiner and brown bullheads. Both the bluegills and
pumpkinseeds were nesting during this period. The species of leech was
Illinobdella moorei.
Forty percent of the pumpkinseeds, from the weedless portion of the
two lakes were infested. In Lower Echo Lake, however, in the region of
[ 6]
the inlet, where water lilies were abundant, the incidence was 80%. Four
bluegills were collected during this study. Two of these were infested.
Since these lakes contain an over-population of stunted pumpkinseeds, it
is difficult to determine what effect, if any, has been produced by this parasite. The problem is presently receiving more study.
The previous discussion has outlined briefly what we believe to be the
significance of leeches in the aquatic environment—particularly as it pertains to fish populations. During the fisheries survey and other field studies, several lots of leeches have been collected. These collections, though
meager, indicate that the leeches of lakes and ponds and other bodies of
water of New Jersey are the same as those in neighboring states. The following list indicates the leeches that have thus far been identified.*
LEECHES
Placobdella parasitica
Placobdella rugosa
Illinobdella moorei
Illinobdella sp.?
Illinobdella sp.?
Cystobranchus sp.?
Macro bdella decora
Haemopis marmoratis
Erpobdella punctata
REGION OF
NEW JERSEY
COMMENTS
Northern and
Central
Northern and
Central
Central
Northern and
Central
Northern
Southern
Delaware Bay
Northern
Northern and
Central
Central
Free and from snapping turtles.
Free and from snapping turtles.
From pickerel.
On yellow perch; bluegill, pumpkinseed,
and redbreasted sunfish.
On fingerling smallmouth bass.
On catfish, Maurice River.
On a seahorse.
In small streams.
In small streams.
In small streams.
LITERATURE CITED
Baker, Frank C. The relation of mollusks to fish in Oneida Lake. N. Y. State College
of Forestry (Tech. Publ. No. 4), 16(21). 1916.
Ball, Robert C. Relationship between available fish food, feeding habits of fish and total
fish production in a Michigan lake. Mich. State College, Agric. Exp. Sta., Tech.
Bull. 206. 1948.
Boisen Bennike, S. A. Contributions to the ecology and biology of the Danish freshwater leeches (Hirudinea). Folia Limnol. Scand., No. 2. 1943.
Chandler, Asa C. Introduction to Parasitology. John Wiley & Sons, Inc. New York.
1949.
Herter, Konrad. Die Okologie der Hirudineen. Bronn's Klassen und Ordnungen des
Tierreichs, Bd. 4, III Abt. Leipzig. 1939.
Lindeman, Raymond L. Seasonal food-cycle dynamics in a senescent lake. Amer. Midl.
Nat., 26(3). 1941.
Meyer, Marvin C. A revision of the leeches (Piscicolidae) living on fresh-water fishes of
North America. Trans. Amer. Micro. Soc., 59(3). 1940.
Further notes on the leeches (Piscicolidae) living on fresh-water fishes of North
America. Trans. Amer. Micro. Soc., 65 (3) . 1946.
* Identifications have been made from the descriptions by Moore (1912, 1918) and
Meyer (1940, 1946).
[7 ]
Miller, John A. A study of the leeches of Michigan, with key to orders, suborders, and
species. Ohio Jour. Sci., 37(2). 1937.
Moore, J. Percy. Classification of the leeches of Minnesota. Geol. & Nat. Hist. Surv.
Minn., Zoo!. Ser., No. 5 (3) . 1912.
The leeches (Hirudinea). In: Ward & Whipple. Fresh-water Biology. John Wiley
& Sons, Inc. New York. 1918.
The control of blood-sucking leeches with an account of the leeches of Palisades
Interstate Park. Roosevelt Wild Life Bull., 2(1). 1923.
Muttkowski, R. A. The fauna of Lake Mendota. A qualitative and quantitative survey
with special reference to the insects. Trans. Wisc. Acad. Sci., Arts and Letters,
19(1). 1918.
Pennak, Robert W. Fresh-water Invertebrates of the United States. Ronald Press Co.,
New York. 1953.
Richardson, L. R. Piscicola punctata (Verrill) feeding on the eggs of Leucosomus corporalis (Mitchill) . Caned. Field-Naturalist, 62(4). 1948.
Richardson, R. E. The bottom fauna of the middle Illinois River, 1913-1925. Bull.
Illinois State Lab. Nat. Hist. Surv., 17 (7). 1928.
Shuster, Carl N. Jr. Leeches (Hirudinea) in the ecology of North American fishes: A
compendium. ( Mss-)
Sooter, Clarence A. Leeches infesting young waterfowl in northwest Iowa. lour. Para.
sit., 23(1). 1937.
Thompson, David H. An epidemic of leeches on fishes in Rock River. Bull. Illinois State
Nat. Hist. Surv., 17(3). 1927.
Thorpe, Lyle M. A fishery survey of important Connecticut Lakes. State of Conn., Pub!.
Doc. No. 47, Bull. No. 63. 1941.