COMMON PARASITES OF FISHES

U.S. Department of the Interior

Fish and Wildlife Service

kVUOUi' HULE, ^Jii^^,

COMMON PARASITES OF FISHES

UNITED STATES DEPARTMENT OF THE INTERIOR Stewart L. Udall, Secretary- Fish and Wildlife Service Clarence F. Pautzke, Commissioner

CIRCULAR 144 1962 CONTENTS

Page

Int reduction 1

FRESH-WATER PARASITES 3

of the body surfaces and gills 3

of the body muscles 6

of the viscera 8

SALT-WATER PARASITES 10

of the body surfaces and gills 10

of the body mu scles 13

of the viscera 14

Suggested references 15 COMMON PARASITES OF FISHES

Glenn L. Hoffnnan, Bureau of Sport Fisheries and Wildlife, Leetown, W. Va. and Carl J. Sindermann, Bureau of Comnnercial Fisheries, Boothbay Harbor, Maine

Fish taken conamercially, for sport, or Much of the damage to fish appears to be raised by fish fanciers are sometimes found mechanical. Parasites may injure tissues to be abnormal due to injury, deformity, and blood vessels by their burrowing, or disease, or the presence of parasites. This block blood vessels entirely with their paper is concerned with connnnon parasites bodies or their eggs. Some actually eat of fishes and their recognition. Life cycles skin, other tissues, mucus, or body fluids. and biology are mentioned briefly, and Some parasites are known to release toxic references to more detailed literature are materials in other hosts, but this has never included. been demonstrated in fish. Probably fish weakened by parasites are easily captured Parasites nnay be defined as "animals by predators. that live on or in another animal, the host, at the expense of that animal." There are Fishermen who find parasites when they many kinds of parasites which may be clean their catch frequently discard the found on the surfaces of fish, including the fish. This is an unnecessary waste. Although gills, as well as in the flesh and internal worms and other parasitic fornns are un- organs (fig. Those on the surface are 1). sightly, none of them can possibly harm known as external parasites, and those that live humans if the fish is thoroughly cooked. inside are called internal parasites. Several Freezing and hot smoking of the fish will types may occur together in a single fish. also kill nnost parasites, but sonne may Some parasites are fairly large (up to remain alive in brine for a month. A few several inches) and can be seen easily, parasites may develop in man if the fish but many are microscopic. Scientists who containing them is eaten raw. Best known work on parasites describe the organisms, in this category is the broad fish tapeworm study the life cycles (some have several (Diphyllobothrium latum), whose larvae may be intermediate hosts), survey the kinds and found in the muscles and among the viscera numbers found in fish, study damage done of pike and perch, particularly in our north- to fish, and attempt to control them. Re- ern lakes. Most fish parasites will not live search is carried on by the U. S. Fish in man. and Wildlife Service and some colleges and universities. The commercial fishing industry suffers Under natural conditions in both fresh great losses each year because of parasit- and salt water, nnost of the parasites pro- ized fish which are condemned for human duced are lost to enemies or to the expanse consumption and can be sold only for of water before they can infect fish. Ap- animal feed at reduced price. In Minnesota, parently a light parasitic infection does for example, tullibees (ciscos) are infected little harm to the host. Under crowded with tapeworm cysts (Triaenophoras) \vhichdo conditions or inadequate water and oxygen not infect humans but are unsightly. The supply, however, fish may become heavily annual catchof 2-l/2 to 3 million pounds, if parasitized; in such cases, more uninfected, would find ready markets for damage is done and the fish may even human use, but as much as 1,500,000 pounds die. Such conditions sometimes occur have been condemned by governmental in hatcheries, causing heavy loss of agencies. Sinnilar losses occur in marine fish. fisheries. At present there is no known control for Nematodes - Unsegmented roundworms (ac- nnost parasites except in relatively small tually cylindrical) which occur as lar- bodies of water such as fish hatcheries, vae in tissues, and as adults in the small ponds, and aquaria. References to alimentary tract, occasionally else- the methods of treatment of fish parasites where. Adult female contains eggs, nnay be found in Hoffman (1959). larva does not.

Acanthocephala - "thorny-headed" worms, The major parasite groups discussed in which occur as larvae or adults in this report are listed and explained fishes. below:

Parasitic copepods - Small highly special- Protozoa - single-celled animals, usually ized crustaceans related to crayfish microscopic. Parasitic groups of pro- and crabs, often called "fish lice," tozoa important to fishes include usually found on external surfaces; Ciliata, Flagellata, Myxosporidia, and sonnetimes embedded, sometimes Microsporidia; may be either external loosely attached; shape may be louse- or internal parasites. While the in- like to wormlike. dividual protozoan is usually micro- scopic, aggregations nnay cause effects recognizable by the naked eye. Leeches - External worms recognizable by their external segmented appear- ance, frequently bright coloration, and Monogenetic trematodes - External flatworms, a large sucker at the posterior end. usually small, commonly calledflukes, often found on the gills; are called monogenetic because they complete Glochidia - Fresh-water clam larvae in their life-cycle on one host (mono = cysts on gills or fins of fish. single, genetic - origin). Posterior or- gan of attachment (haptor) well de- Lampreys - Primitive fishlike vertebrates veloped with chitinous clamps and and the largest of the fish parasites, hooks. ranging up to 3 feet in length. They may be recognized by the large cir- Digenetic trematodes - Internal flatworms, cular mouth containing many ro%vs of often very small, but occasionally large thornlike teeth. enough to be seen easily; are called digenetic because at least two hosts are In most instances marine and freshwater needed for their life-cycle (di = two, fish have different parasites, therefore, genetic = origin). Larva (metacercaria) they are discussed separately under FRESH- or adult may be found in fish, first WATER PARASITES and SALT-WATER internnediate host is snail or clann; PARASITES. possess oral and ventral suckers; eggs present in adults which may be found in alimentary tract, occasionally else- The following plan of organization is where; metacercariae in various or- followed \inder each category: gans (skin, muscle, mesenteries, etc.). (1) Parasites of the body surfaces and gills

Cestodes - Tapeworms, are also flatwornns, (2) Parasites of the body muscles but are distinct from "flukes" in that the adult worm is usually composed of (3) Parasites of the viscera a head (scolex) and many egg-producing segments. Found as adults or larvae in fish; intermediate stages in "water A sinnplified drawing (fig. 1) of an opened fleas". fish is included to show the various organs. LIVER SWIM BLADDER STOMACH KIDNEV DORSAL FIN

ANAL FIN

INTESTINE 'ENTRAL FIN HEART PVLORC CAECA

Figure 1.- -Drawing of Lepomis cyaneltus, (from Hile, 1960, U. S. Fish and Wildlife Service. Fishery Leaflet 132).

FRESH-WATER PARASITES to be found on fish. Under the microscope the most striking characteristics that can Parasites of the Body Surfaces and Gills be seen are the constantly beating hair- like cilia, which completely cover the para- 1. Fun^. White cottony growths on wounds site (fig. 2.). or ulcerations are usually fungi of the genera Saprolegnia and Achlya. The filaments All other protozoa that live on the skin can be seen easily under the microscope. of fish are very small in comparison to The fungus often develops as a secondary Ichthyophthirius. Although some of them are infection following wounding or ulceration serious fish disease agents, none is harm- due to other agents. ful to man.

2. Protozoa. These are the smallest ani- Myxosporidian cysts containing many mals. They consist of a single cell, and spores (fig. 3) are whitish and usually nearly all are too small to be seen with- large enough to be seen easily. They are out a microscope. Some protozoa fornn found in many organs including the skin \vhitish cysts containing many spores. Such and gills. cysts are large enough to resemble worm larvae superficially. They may be found 3. Internal flukes (digenetic trematodes). in many organs including the skin and gills. These small worms are flat, leaflike forms from 1/250- to l/S-inch long with two Often in aquaria and fish hatcheries, a suckers. The trematodes most frequently condition develops which is known as "Ich" seen are larvae ("grubs") encysted in the or "white spot." The fish are seriously skin or flesh. The largest of these larvae ctffected, and many little white spots can is the yello^v grub, Clinostomum marginatum (fig. be seen - some of them moving slowly over 4). The cyst is yellowish, about 1/8 inch the fish. These are individual protozoa, in diameter, and is usually seen in the Ichthyophthirius muUifilis, the largest protozoan gills and at the bases of the fins but nnay *- *

KiKure JT, — Vrllow grubs in lltwh of yt-Uow pcTch. (Courlray of

llif Nf>v York loiuuTvutiiiii I >Fpartiiirut '

Figure 4.-- Clinostomum marginatum "yellow grubs" in the flesh of yellow perch. (Courtesy of the New York Conservation De- partment).

produces eggs which pass out in the feces into the water. After a suitable period, these hatch into a microscopic free-swim- ming larva (miracidium) which has about 8 hours to find the right kind of snail. If it succeeds, it burrows in and continues to develop. It produces many of the next stage larvae (cercariae) which burrow out of the snail. To survive, cercariae have about a day in which to contact a fish and burrow into the tissue. In the fish, the worms may Figure 2.-- Ichthyophthirius multifilis, ciliated protozoan, the migrate a short distance before "Ich" of aquarium and fish hatchery fish. reaching their final site where they secrete a cyst wall about themselves and become the "yellow grubs", completing the cycle.

Another type of fluke that is often noticed is the "black grub" (fig. 6), a very small larva enclosed in a black cyst about l/l6 inch in diameter. These may be the larvae of any one of many trematodes but the most common is known as Neascus. The life cycles are similar to that of the "yellow grub." Different fish, birds, and snails may be Figure Z,- - Myxobolus spore from white cysts. involved. occur almost anywhere, including intern- 4. Gill flukes (monogenetic trematodes). ally. If the cyst is removed and opened, the Most of these are microscopic, but one of larva can -be seen. The life history (fig. 5) the larger ones, Discocotyle salmonis (fig. 7) is typical for the group. When the fish is often occurs on the gills of trout and salmon. eaten by a heron the larva is digested free It is about 1/4 inch long and attaches by from the cyst and continues development its large rear suckerlike attachment organ in the intestine of the bird. Most trematodes to the gill of the fish. Sometimes these develop to maturity in the intestine of the flukes become so numerous that the fish host, but the "yellow grub" migrates to the are seriously affected. Another very com- esophagus where it matures. The adult mon monogenetic trematode, Gyrodactylus, HERON BECOMES INFECTED BY EATING FISH WORM BECOMES ADULT IN MOTTTH CAVITT

EGG PASSES OUT IN FECES OR SALIVA

BODY OF CERCARIA PENETRATES FISH, BECOMES YELLOW GRtJB

MIRACIDIDM PENETRATES HELISOMA SNAIL

MOTHER SPOROCTST CERCARIA EMERCES FROM SNAIL - - LARVAL STAGES IH SNAIL

Figure 5.--Life cycle of the "yellow grub," Clinostomum marginatum. Outer circle (solid line) includes the worm stages. Inner circle (broken line) includes the hosts. is usually found in greater numbers on the become modified into a very efficient "an- body than on the gills; most of the others chor." This parasite goes through several occur on the gills only. microscopic developmental stages usually on the gills of fish other than the one on 5. Parasitic copepods. In some ponds and which it finally matures. Because it can do hatcheries, the "anchor worm" copepod considerable damage to fish if present in CLemoeoj flourishes. It protrudes wormlike large numbers, it should be eradicated from from the fish, usually at the base of a fin, fish rearing ponds and hatcheries, and with its head buried in the fish. The visible parasitized fish should not be used for portion is cylindrical, whitish, and about stocking. 1/2 inch long (fig. 8). There are often two egg sacs extending from the end of the Sometimes "fish lice" (Argulus) may be creature. With care, the head can be dis- seen crawling over a fish. They are among sected out of the fish, and one can then see the largest of external parasites and can be that some of the forward appendages have seen easily. They are round to oval when Figure 7.-- DiscocotyU salmonis, an ectoparasitic trematode from the gills of trout (after Price).

Figures,— Crossiphiala bulboglossa,i Neascus metacercaria cause considerable damage to the of one of the several "black spot grubs" of fish in the fathead fish. minnow, Pimephales promelas.

7. Bloodsuckers (leeches). Except for seen from above and are flattened from top lampreys, these are the largest external to bottom. Four pairs of swimming legs parasites, sometimes reaching an inch in extend from their sides (fig. 9). The eggs length. There are suckers at each end of are borne in sacs at the end of the female. the flattened, segmented body. The front The eggs drop off when developed, hatch, sucker contains the mouth with which the and the larvae must eventually find a fish parasite rasps a small hole in the fish skin or perish. There are several larval stages to obtain its meal of blood (fig. 10). Leeches which precede final development of the adult. often attach near the bases of or on the fins.

Other fornns , Ergaailus , Achtheres, and Salmincola, They transmit certain protozoan parasites are usually found attached to the gills. from fish to fish through their feeding. The kinds of leeches that parasitize fish do 6. Glochidia. These small larvae of some not attack humans. of the large fresh-water clams clamp onto the gills or fins of fish where they remain for 10 to 20 days. Some of the fish tissue Parasites of the Body Muscles grows up and over the glochidiunn (larva) forming a small translucent cyst about 1. Protozoa. Myxosporidian cysts contain- 1/8 inch in diameter. If nunnerous, they ing many spores (fig. 3) are whitish and Figure d.--Argutus irilineaius, the "fish louse" (after Guberlet).

3. Tapeworms. A tapew^orm that is con- sidered important because it may infect man through eating improperly cooked infected fresh-water fish is the broad fish tape- worm, /;i;)Ay/io6o«^rium Zoium. The white larva (plerocercoid) may be found among the viscera as well as in the flesh, and may be up to an inch in length, but has no other outstanding characteristics. Normally the parasite will attain maturity in the intestine of bears, man, dogs, and perhaps other animals if they eat infected fish (fig. 11). It grows into a large worm - up to 30 feet in length - and produces millions of eggs which pass out with the feces of the animal. If the eggs fall or are washed into the lake, a small swimming larva (coracidium) hatches out. This very active creature develops into the next larval stage (pro- cercoid) when eaten by certain species of "water fleas" (copepods). Small fish feed on the infected copepods, and if a pike or perch eats such fish, the larva will continue Figure 8.-- Lemaea tortua, the "anchor worm" of fish (after Wilson). to develop. Humans beconne infected by eating raw fish containing the larval stages. large enough to be seen easily. They are 4. Roundworms (nematodes). The largest found in many organs but some species one seen in muscle is Kustrongylides (fig. 12). found in the muscle produce a large ugly- It is a red worm coiled up in a cyst about looking "boil." These are not infective for inch in diameter and is sometimes man. 1/4 seen while dressing a fish. It may also be 2. Flukes. Some of the "grubs" discussed found in the body cavity. The life cycle is in the previous section may be found in the not entirely known, but it is probable that nnuscle. a bird is the final host. somewhat similar to the "yellow grubs" discussed previously, and are not harmful to man. Adult flukes of fish occur in the intestine and stomach, but are usually small and not seen.

3. Tapeworms (cestodes). Two forms of these are seen in fish. One, the adult, lives in the intestine of fish. It is flat like a tape, and often several inches long. It is this stage that is seen when the intestine is accidentally cut or torn during cleaning of the fish. The other form is the larva (plerocercoid), which may or may not be the same species as the adult seen in the fish. Larvae are smaller, nonsegmented, and may occur among the internal organs as well as in the flesh of the fish. Cal- careous corpuscles (round concretions of lime) can be seen microscopically in all tapeworm larvae; this is sometimes a very helpful characteristic for identifying a lar- val tapeworm parasite. The adult from fish is never harmful to man, but some of the larvae, if eaten raw, can develop in man. We have previously discussed the best known one in this group, the broad fish tapeworm (p. 7).

One of the most noteworthy fish tape- worms is the bass tapeworm, Proteocephalus ambloplitis (fig. 13). The larvae (plerocer- coids) often cause sterility in black bass. The adult lives in the intestine of black bass and produces large numbers of eggs which pass out with the feces of the fish into the water. The small larva in the egg will develop to the next stage larva (pro- cercoid) if eaten by the proper kind of copepod. After development in the copepod, this larva invades small fish which eat the infected copepods. The larva is freed in the intestine of the small fish, burrows through the intestinal wall, and wanders among the Figure 10.-- cicola salmositica, a leech or "blood-sucker" Pis internal organs. When large numbers of (after Meyer). these larvae (plerocercoids) are present they cause considerable damage to the fish. Parasites of the Viscera Small bass, once infected, will retain the larvae for a long period of time. Larger 1. Protozoa. Internal fish protozoa are usually not seen by the casual observer bass accumulate larvae by eating small except for the myxosporidian cysts dis- fish that have recently fed on infected cope- cussed in previous sections. pods. Larvae, if still in the stomach or intestine of the small fish when eaten by the 2. Flukes. "White grubs" are sometimes larger fish, will migrate through the intes- found in the visceral organs. These are tinal wall and into the visceral cavity of II III I IJIIIIIIIII mrn 'Mmnim m TrnrtncnnnixcarnT J//i'UJJ/Trrrn77TTrPTrm-rn-rr [jmrrnTrmTiiiiiiiiiJiijiiiDnnin^^ ADULT WORM IN SWAIX lUTESTINE /" CF BEAR, MAN, DOG

MAN IS INFECTED BT EATING EGGS ARE PASSED IN FECES MPROPERXT COOKED INFECTED FISH AND REACH WATER

EGGS HATCH IN WATER AND REIEASE CORACIDIDM NORTHERN PIKE, WALLEYE PIKE, PERCH, TROTTT EATS INFECTED COPEPOD OR SMALL FISH

.^ :^\ < PLEROCERCOID LARVA DEVELOPS IN MUSCLE SMALL OR VISCERA OF FISH FISH EATS IHFECTH) COPEPOD

CORACTrrtIM IS INGESTED BY WATER FIEA (COPEPOD)

PROCERCOID LARVA DEVELOPS IN COPEPCJ)

Figure ll.--Life cycle of the broad fish tapeworm, Diphyllobothrium latum. Outer circle (soLd line) includes the worm stages. Inner circle (broken line) includes the hosts.

the larger fish. The damage done by the fish that it causes the body wall to burst, larvae moving among the reproductive or- releasing the worm. This worm develops gans may render the fish sterile. The life into an adult in the intestine of fish-eating cycle is completed when a larger bass eats birds. an infected smaller fish in which the larvae 4. Roundworms (nematodes). The red worm, have had time to become established in the Eustrongylides (fig. 12 and p. 7) may occur visceral cavity. The larva is then freed among the viscera. Some smaller larval in the intestine of the larger bass and nematodes may also be present. A very long, grows into the adult tapeworm. thin nematode, Philonema, causes serious damage to the reproductive organs of sal- The large larva of another tapeworm, monid fish. Usually the adult nematodes in Ligula intestinalis, is often seen in the body the intestine are not noticed because of their cavity of minnows and suckers (fig. 14). small size. None of these is harmful to Sometimes it becomes so large in small man. or disc-shaped and characteristically pos- sess a conspicuous attachment organ of hooks and/or suckers. Trematodes are also common on the gill bars and filaments of marine fishes, but are usually quite small and not easily observed, unless the fish is heavily parasitized.

3. Grubs of marine fishes --larval trema- todes that localize beneath the skin or in the fins--are common in inshore waters. So-called "pigment spot" of cunner, herring, mackerel, butterfish, and other fish is caused by encystment of such larvae be- neath the skin. The life cycle of the worm (Cryptocotyle) that is responsible involves suc-

Figure 12. -The "red worm," larval nematode, Eustrongylides, cessively a snail, a fish, and a sea gull from the flesh of fish. (fig. 16a, 16b). The adult fluke inhabits the bird's digestive tract and sheds its 5. Thomy-headed worms (Acanthocephala). eggs with the droppings of the host. Snails These cylindrical worms have rows of hooks become infected by eating the worm eggs. on their heads which become embedded in After a period of larval development in the the intestinal wall of the fish. Unless large tissues of the snail, an infective stage, numbers are present no harm is apparent. known as the cercaria, emerges from infected snails and is free -swimming vintil it contacts the fish host, where it penetrates the skin and encysts. The cycle is com- SALT-WATER PARASITES pleted when fish carrying encysted larval worms are eaten by the bird. Other larval trematodes may also cause "pigment spot" Parasites of the Body Surfaces and Gills of marine fish, but they are not as well understood, except that a fish-eating bird When a fish is first taken from the water and a snail are usually necessary for com- it may be carrying a variety of external pletion of the life cycle. Flounders are parasites or external evidences of disease. often invaded by larval flukes which do not The mouth and gill chambers are favored cause pigment accumulation. Encysted lar- sites for certain parasites because these val worms appear as tiny opaque white areas afford protection and are in close patches in the fins and on the light under- proximity to the host's blood supply. surface of the fish.

1. Fungi and protozoa ulcerations of the skin 4. Parasitic copepods --fish lice--may be may be due to underlying protozoan or found on external surfaces of many species fungus infection of the flesh (as in young of marine fishes. These may be of various sea herring). Such infections kill tissues forms. Some are temporary and retain their and cause the skin to slough, creating the mobility, moving freely from fish to fish, external ulcers. Two groups of the protozoa while others, such as Sphyrion on the ocean (Myxosporidia and Microsporidia) may in- perch (redfish), are permanent tissue in- vade the muscles, producing ulcers of the vaders (fig. 17). Anchorlike projections of skin (fig. 15). Fungus organisms, such as the head of this particular copepod grow Ichthyosporidium hoferi, rnay also cause ulcers. into the flesh, often causing an \insightly ulcer. This projection persists as a brown- 2. Trematodes or flukes may be found on ish mass in the flesh eifter the parasite dies. the body surfaces of the larger marine fishes such as halibut, sharks, skates, and Copepods may also be found attached to the ocean sunfish. These worms may be leauf- gills and gill regions of marine fishes. An

10 C3I^

ADULT T/LPEWORll Bi INTESTINE CF BUCK BASS '^^

"RIPE" SEGMENTS CF WORM PASS OUT WITH FECES

BECOIIBS ADULT WORM IF BATKN BY BLACK BASS /

/ \ REMAIKS AS LAFVA IK ADULT BASS "HIGH MAY ALSO RAT PROCERCOIDS THAT ARE IN THE STOMACH OF FOOD FISH \ V

BGGS ARE FREED AND KATEN BY COPEPOD

COPEPOD

BECOMES PROCERCOID LARVA IN COPEPd) BECOMES PliROCERCOH) LARVA lU VISCERA CF FISH

Figure 13,--Life cycle of the bass tapeworm, Proteocephalus ambloplitis. Outer circle (solid line) includes the worm staRcs. Inner circle (brol

Figure 14.--LigiJa intestinalis (tapeworm larva) in the chub, Couesius plumbeus. (C>ourtesy of the New York Conservation D^>artment).

11 Figure 15,--Skin ulcers in young herring caused by underlying muscle infection with the myxosporidian. Kudoa dupeidae.

METACERCAfllA ENCYST BENEATH SKIN CAUSING PIGMENT SPOT

CERCARIAE DEVELOP IN REDIA REDIAE DEVELOP

AND EMERGE FROM SNAIL I SNAIL DIGESTIVE GLAND

Figure 16a.--Life cycle of CryptocotyU lingua, the worm whose larvae cause '•pigment spot" of herring and other fish,

Figure 16b.--Pigment spot of herring caused by CryptocotyU lingua.

12 extreme example is Lemaeocera branchialis 1 /Z inch in length or so-called "pus pockets" found on cod and some other species (fig. in the flesh of small herring, alewives, 18). The copepod is located in the gill and menhaden from the east coast. chamber, but roots formed by extensions Myxosporidia are also responsible for the of the body extend into the host, eventually conditions known as "jellied swordfish" on penetrating to the heart region. The life the Atlantic coast and "wormy halibut" on cycle includes lumpfish, flatfish, and pos- the Pacific coast. Both are characterized sibly others as intermediate hosts. by progressive destruction and liquefaction of the muscles, producing unsightly areas in the flesh that must be cut Parasites of the Body Muscles out and dis- carded, or else the entire fish may be Because the flesh of fish is the part that discarded. is usually consumed by man, parasites and diseases Eiffecting the body muscles of fish Z. Fungus infections may produce muscle are of primary concern. Though parasites abnormalities. A fungus infection of herring are killed by proper cooking, the presence on the east coast of North America produces of worms or other abnormal conditions in the small yellow- white nodules. Advanced in- flesh of food fish is esthetically and phy- fections result in extensive degeneration of chologically disturbing, and many fish thus muscles, and diseased fish are difficult to affected are discarded unnecessarily. salt or smoke (fig. 19). Another symptom of this fungus infection is the accumulation 1. Protozoa are significant and sometimes of black pigment around spores in the flesh, conspicuous parasites. Myxosporidia form making the fish less desirable for filleting either spindle-shaped white nodules up to and pickling.

3. Larval trematodes occur commonly in the

flesh of many coastal marine fishes . Con- spicuous in this respect are young Atlantic herring, in which larvae of the fluke Cryptocotyle frequently localize in the mus- cles as well as underneath the skin, causing black pigment accumulation and the forma- tion of a conspicuous "pigment spot." Floun- ders are frequently invaded by another larval trematode which appears as a small opaque white cyst in the flesh although there is no pigment response.

Figure 17.- -Parasitic copepods (Sphyrion lumpi) embedded in redfish. Dissected copepod is shown at right. 4. Larval nematodes in the flesh of marine fishes best fulfill the popular conception of "worms." They may occur free or encysted in the muscles, and may become very active when released. The so-called "codworm" PoTocaecum has received particular attention, especially on the Canadian east coast. This larval roundworm encysts, sometimes in great numbers, in the flesh of cod, smelt, and other fishes (fig. ZO). Its life cycle is not completely understood, but it involves a succession of fish hosts, with the seal as the final host for the adult worm. Other kinds of larval roundworms may be found in haddock and other Figure \6.-- Lemaeocera branchialis from cod. Note the commercial marine antlers"--anterior projections of the copepod tliat anchor it fish, occasionally in great numbers, but in the flesh of the host. usually only a few in any single fish.

13 Usually they are cooked, eaten and never Parasites of the Viscera noticed, but occasionally they may be seen and may result in unnecessary waste of the Inhabitants of the visceral mass of fishes fillet or the fish. None has been demon- are many, and are often apparent when fish strated to be harmful to humans. Usually a are dressed. Adult worms--cestodes, tre- fish-eating bird or mammal serves as host matodes, nematodes, and acanthocephala-- for the adult worms. usually occupy the digestive tract, while larval stages of members of these groups may be foiind, usually encysted, in the gut 5. Larval cestodes may localize in the flesh wall, the liver, or the supporting mem- of marine fishes, although this condition branes. In addition to worm parasites, seems less frequent than in fresh water. there may be protozoan and fungus infec- Butterfish of the U. S. east coast fre- tions. quently have tapeworm larvae in small 1. Protozoa may occur in nodules or cysts (less than l/Z5-inch) white to yellow cysts on and in the viscera of fish. These are in the body muscles. Occasionally enormous actually masses of thousands of spores, numbers of such cysts may be found in much like the nodules or cysts in the flesh. individual fish (fig. 21). Other tapeworms Conspicuous in this respect are such forms may occur as contorted opaque white as Glugea hertwigi, a nnicrosporidian that pro- ribbons in the flesh of fish, often in suf- duces white cysts in the viscera of eastern ficient numbers to require discarding the smelt (fig. 22). This parasite nnay occa- fish. sionally be sufficiently abundant to interfere with reproduction. It varies in abundance geographically, and may occur in over one- quarter of all fish sampled in particular areas.

2. Fungus infections and resulting involve- ment of the viscera are found in such marine fishes as the Atlantic herring, mackerel, and flounder. A fungus disease

Figure 19.--Adult herring infected with fungus. Top--skin has been sliced away to show normal muscle. Lower --shows ad- vanced decay of muscles. Figure 21.--Larval tapeworms in the flesh of bunerfish.

Figure 22.--Visceral cysts of the microsporidianC/ugea hertwigi Figure 20,- -Smelt with codworms encysted in flesh. in a smelt.

14 of marine fishes, caused hy Ichthyosporidium extended white ribbonlike appearance--the hoferi, has received some attention in recent ribbon being composed of many egg-pro- years, especially in North America, where ducing segments. Such worms may occa- it has periodically assunned epidemic pro- sionally be found extruded from the vent portions in the Atlantic herring. Visceral of the fish after death (this often happens symptoms often include extensive white with smelt, for example). Worms are usually nodules on and in the heart, liver, gonads, few in number in any single host, but may and mesenteries (fig. 23). occupy the entire length of the intestine.

3. Adult trematodes are connmon, but their small size and location within the gut make them inconspicuous. Occasionally hundreds SUGGESTED REFERENCES or even thousands of these small adult worms may be found in the digestive tract General of a single fish. They are usually less than 1/4 inch long, opaque white, with a Allison, Leonard N. brownish patch of eggs near the center or 1950. Common diseases of fish in posterior part of the body. Michigan. Michigan Department of Conservation, Miscellaneous Pub- 4. Larval nematodes may localize in the vis- lication No. 5, 27 p. cera, particularly in the mesenteries ad- Bang'nam, Ralph V. jacent to the digestive tract. They are 1941. Parasites of game fish. often found encysted in tightly coiled spirals The Aquarium Journal, vol. 14, No. in the Atlantic and Pacific herrings, red- 3, p. 29-31. fish, and many other species, and may 1948. Parasites of freshwater become very active when released--moving fishes. State of Ohio Department of Agricul- in a typical whiplike manner. Numbers per ture, Bulletin No. 229, 12 fish range from a few to many hundreds. p. Cameron, T. W. M. 5. AduU nematodes may also be found in the 1945. Fish-carried parasites in Can- digestive tract, but as a rule are not con- ada. Canadian Journal of Compara- spicuous . tive Medicine, vol. 9, p. 245-254.

6. Larval cestodes maybe regionally abun- Davis, Herbert S. dant in the viscera of many fish species. 1953. Culture and diseases of game Frequently these are larvae of tapeworms fishes. University of California which mature in sharks and skates or in Press, Berkeley and Los Angeles, fish-eating birds. The larvae encyst in the 332 p. mesenteries or wall of the digestive tract Haderlie, Eugene Clinton as white ovoid or club-shaped nodules, fre- 1953. Parasites of the fresh-water quently 1/8 to 1/2 inch in length. fishes of northern California. Uni- versity of California Publications in 7. Adult cestodes inhabit the digestive tract Zoology, vol. 57, 303-440. of fish, and may be recognized by their p. Hargis, William J. 1958. Parasites and fisheries prob- lems. Proceedings of the Gulf and Caribbean Fisheries Institute. Elev- enth Annual Session, p. 70-75. Heller, Anita F. 1949. Parasites of cod and other ma- rine fish from the Bay of Chaleur

Figure 23.--Visceral nodules in herring caused by the fungus region. Canada Journal of Research, Ichthyosporidium hoferi. vol. 27, p. 243-264.

15 -

Hoffman, Glenn L. Van Cleave, Harley J., and Justus F. 1959. Recomnfiended treatnnent for fish Mueller

parasite diseases. U. S. Fish and 1934. Parasites of Oneida Lake fishes . Wildlife Service, Fishery Leziflet Part III. A biological and ecological 486, 4 p. survey of the worm parasites. Roose- velt Wildlife Annals, vol. 3,Nos.3& Hugghins, Ernest J. 4, p. 161-334. (Bulletin New York 1959. Parasites of fishes in South State College of Forestry, vol. 7, No. Dakota. South Dakota Departnnent Game, Fish and Parks Bulletin No. 1.) 484, 73 p. Van Duijn, C., Jr. Hunter, George W., Ill 1956. Diseases of fishes. Water Life, 1942. Studies on the parasites of fresh- Dorset House, London, 174 p. water fishes of Connecticut. Con- necticut Geological and Natural His- Viruses, bacteria, fungi tory Survey Bulletin No. 63, p. 228- U. S. Fish and Wildlife Service, Fish- 288. ery Leaflets 453 - 467, 494, and 497. Meyer, Marvin C. larger animal parasites of 1954. The Protozoa the fresh-water fishes of Maine. Maine Department of Inland Fisher- Davis, Herbert S. ies and Game, Fishery Research and 1947. Studies on the protozoan para- Management Division Bulletin No. 1, sites of fresh-water fishes. U. S. 92 p. Fish and Wildlife Service, Fishery Northcote, T. G. Bulletin 41, vol. 51, p. 1-29. 1957. Common diseases and parasites of fresh-water fishes in British Co- lumbia. British Columbia Game 1953. Culture and diseases of game Commission, Management Publica- fishes. University of California tion No. 6, 25 p. Press, Berkeley and Los Angeles, 332 p. Pratt, Henry S. 1929. Parasites of fresh-waterfishes, Kudo, Richard R. comprising some general considera- 1954. Protozoology. Charles C. tions. U. S. Department of Commerce, Thonnas Publisher, Springfield, Illi- Bureau of Fisheries Econonnic Cir- nois, 966 p. cular No. 42, 10 p. Schaperclaus, W. 1954. Fischkrankheiten. 3rd ed. Aka- Trematodes demie- Verlag, Berlin, 708 p. Bychowsky, B. E. Sindermann, Carl J. 1957. Monogenetic trematodes; Their 1953. Parasites of fishes of North systematics and phylogeny. Moscow Central Massachusetts. Massachu- Leningrad (in Russian), 509 p. (Eng- setts Division Fisheries and Game, lish translation by Pierre C. Ous- Fisheries Report for lakes of North tinoff, edited by William J. Hargis, Central Massachusetts (1950), 4- p. American Institute of Biological 28. Sciences, Washington, 627 p.) Sindermann, Carl J., and Aaron Rosenfield 1954. Diseases of fishes of the western Sproston, Nora G. North Atlantic. I. Diseases of the sea 1946. A synopsis of the monogenetic herring. Maine Department of Sea and trematodes. Transactions Zoological Shore Fisheries Research Bulletin Society of London, vol. 25, No. 4, No. 18, 23 p. p. 185-600.

16 Wolfgang, Robert W. Meehean, O. Lloyd 1954. Studies of the trematode 1940. A review of the parasitic Crus- Stephana stomum baccatum (Nicoll, 1907). tacea of the genus Arffulus in the col- II. Biology, with special reference lections of the United States National to the stages affecting the winter Museum. Proceedings U. S. National flounder. Journal of the Fisheries Museum, vol. 88, No. 3087, p. 459-522. Research Board of Canada, vol. 11, No. 963-987. 6, p. Pennak, Robert W. Yamaguti, Satyu 1953. Fresh-water invertebrates of 1953. Systema Helminthum. Part I. the United States, Ronald Press Co,, Digenetic trematodes of fishes. In- New York, 769 p. terscience Publishers, Inc., New York, 405 p. Wilson, Mildred S. Cestodes 1959. Branchiura and parasitic Cope- poda (In Ward, Henry B., and G. C. Miller, Richard B. Whipple. Fresh-water biology, 2d 1952. A review of the Triaenophorus ed., John Wiley & Sons, New York, problem in Canadian lakes. Fisher- p. 862-868), ies Research Board of Canada, Bul- letin No. 1-42, 95. p. Wilson, Charles B. Wardle, Robert A. 1901 - 1942. A series of monographs 1932a. The Cestoda of Canadianfishes. on the parasitic copepods. Most of I. The Pacific Coast region. Contri- these were published in the Pro- butions to Canadian Biology and Fish- ceedings of the U. S, National Mu- eries, vol. 7, p. 220-243. seum (complete bibliography may be 1932b. The Cestoda of Canadianfishes. found in "Index-catalogue of Medical II. The Hudson Bay drainage system. and Veterinary Zoology," Part 17, Contributions to Canadian Biology p. 5542-5544). and Fisheries, vol. 7, p. 377-403.

Wardle, Robert A., and J. A. McLeod Leeches 1952. The zoology of tapeworms. Uni- versity of Minnesota Press, Min- Meyer, Marvin C. neapolis, 780 p. 1940. A revision of the leeches (Pis- Yamaguti, Satyu cicolidae) living on fresh-water 1959. Systema Helminthum, Vol. 2. fishes of North Annerica. Transac- The cestodes of vertebrates. Inter- tions American Microscopical Soci- science Publishers, Inc., New York, ety, vol, 59, No. 3, p. 354-376. 860 p. 1946. Further notes on the leeches (Piscicolidae) living on fresh-water Nematodes fishes of North America, Transac- tions of the American Microscopical Yorke, Warrington, and P. A. Maplestone Society, vol. 65, No. 3, p. 237-249. 1926. The nematode parasites of ver- tebrates. J. & A. Churchill, London, Moore, J. Percy 536 p. 1959. Hirudinea, (In Ward, Henry B., and GeorgeC, Parasitic Copepods Whipple, Fresh-water biology. 2d ed,, John Wiley and Harding, J. P. Sons, New York, p. 542-557). 1950. On some species of Lemaea (Crustacea, Copepods: parasites of Pennak, Robert W. fresh-water fish). Bulletin British 1953. Fresh-water invertebrates of Museum. (Natural History). Zoology, the United States, Ronald Press Co., vol. 1, p. 1-27. New York, 769 p.

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GPO 9 2a 6a I

MBL WHOI Ctbrnry Serial

SE 00229 The Department of the" Interior, created in 1849, is our Nation's De- partment of Natural Resources, concerned with management, conservation, and development of water, wildlife, fish, mineral, forest, and park and recreational resources. It also has major responsibilities for Indian and Territorial affairs.

As America's principal conservation agency, the Department works to assure that nonrenewable resources are developed and used wisely, that park and recreational resources are conserved for the future, and that re- newable resources make their full contribution to the progress, prosperity, and security of the United States, now and in the future.

UNITED STATES DEPARTMENT OF THE INTERIOR Stewart L. Udall, Secretary- Frank P. Briggs, Assistant Secretary for Fish and Wildlife FISH AND WILDLIFE SERVICE Clarence F. Pautzke, Commissioner BUREAU OF SPORT FISHERIES AND WILDLIFE Daniel H. Janzen, Director BUREAU OF COMMERCIAL FISHERIES Donald L. McKernan, Director