When Panfish Look Sick

							                                                 Calls like these come daily to De-
                                              partment of Natural Resources Fish-
                                              eries offices. The answer to the ques-
                                              tion above is: In most cases, the fish
                                              are edible, but one must use com-
                                              mon sense.
                                                 If you catch a fish on hook and line,
                                              the fish is feeling good enough to feed.
                                              In this respect, fish are like people.
                                              When we get sick, the first thing we
                                              usually do is stop eating. The same
                                              with fish. You're not going to catch a

         When                                 really sick fish by hook and line. It
                                              may have sores on its body or fins,
                                              but these irritations may be no more

        Panfish                               important to the animal than a boil or
                                              pimple to us.
                                                  Should a fish that you've caught
         Look                                 have a suspicious sore or lesion — a
                                              wound or injury — then discard that
                                              portion of meat before you cook it.
         Sick                                     A mistake some people make is
                                              picking u p dying fish from the shal-
     Or bass, pike, or perch.                 lows, taking them home, then clean-
   Fish are subject to many                   ing and eating them. That's the worst
      ailments — including                    thing to do. That fish could have a va-
                                              riety of illnesses and gives you no idea
   blindness and tapeworms                    of what it is dying from. Caution dic-
        — in their watery                      tates that you leave that animal alone
    environment. The ques-                    and catch your fish on hook and line.
    tion anglers ask: Which                       Even handling a lethargic fish is
       fish are safe to eat?                   unwise, since some bacteria that in-
        Guidelines follow                     fected the fish could infect humans.
                                                  Aeromonas hydrophilia, for exam-
            John B. Daily                      ple, is a serious fish pathogen. In hu-

A     PHONE CALL c o m e s to m y d e s k .
      The caller has been fishing. Some
fish in his cooler show black spots on
                                               mans, it creates a persistent skin in-
                                              fection that requires treatment with
                                              antibiotics. It can also cause inner ear
their flanks. His question: Are the fish      and bladder infections, and other
safe to eat? Can his family have them          problems. Staph and strep also are
for dinner tonight?                           well known bacterial agents that can

JULY-AUGUST 1 9 8 7                                                               43
Fish Ailments
infect both fish and humans.

   Bacteria and Parasites. Be cau-
tious if you suspect a fish of having a
bacterial infection. L e t h a r g i c fish
found in the shallows may well have
a generalized blood poisoning, which
means the infection is in the system
of a fish rather than being localized as
a lesion might be. Bacterial toxins in
the meat can cause illness even though
the fish is well cooked. Don't pick up
that fish, and don't take it home or
eat it.
   Parasites, however, are a different
matter. Generally, p a r a s i t e s are a
problem to the fish, not to the angler.
Very few fish parasites can infect
humans.
   One parasite, though, that can in-
fect humans is the broad tapeworm.
This tapeworm can also be found in                  Top: Examining internal organs of rainbow
                                                    trout for discoloration or bleeding. Bottom:
cats, dogs, and bears. It is always un-
                                                    Probing kidney (black area along
wise to eat undercooked or raw fish.                  backbone) for spots, w o u n d s , Injuries.
Who knows? You could be the one to
d e m o n s t r a t e that t h e b r o a d tape-       H e r e is a summary of disease con-
w o r m is s t i l l a r o u n d in t h e           ditions M i n n e s o t a a n g l e r s may
environment.                                        encounter:
   Tapeworms, however, used to be a                                  Black Spot
much greater problem. Modern san-                   Common among many species of fish
itation and sewage treatment plants                 in our state, this parasite is usually
have minimized the amount of raw                    found on rock bass, northern pike,
sewage being d u m p e d into our rivers            perch, and sunfish. The infection is
and streams. These measures alone                   caused by a tiny grub that burrows
have reduced the incidence of the                   into the skin or flesh of the host fish
broad tapeworm in the wild.                         and appears as tiny black spots on the
                                                    body and fins.
                                                       The grubs themselves are white,
John Daily is fish production supervisor, DNR
Fisheries, St. Paul. An occasional contributor      but the fish form a black pigmenta-
to the Volunteer, he wrote "Why Do Fish Travel      tion around the cyst which results in
in Schools?" in the July-August 1986 issue.         a black spot. Grubs seldom burrow

44                       Right: DNR Fisheries pathologist Joe Marcino examines scrapings of
                        rainbow trout's skin and gill tissue and slices of internal organs under
                              m i c r o s c o p e for evidence of bacterial, viral, or parasitic diseases.
Fish Ailments
d e e p e r than the skin and can be re-
moved when the angler skins the fish.
Anglers usually get very upset when
they find spots in the flesh. Although
this grub is harmless to people, most
anglers usually discard the fish.
   The life cycle of this parasite in-
volves the fish, a bird — the king-
fisher — and a snail. The adult worm
lives in the intestinal tract of the
kingfisher, a fish-eating bird. Eggs       Leeches attached to yellow perch's caudal
from the worm in the bird's feces are      fin a n d a l o n g b o d y o p e n s k i n , i n v i t e
dropped into the water where they          bacteria to enter, and cause stress in fish.
hatch.
    Larval grubs then take up resi-                        White Grub
dence in the snail. Later, when the        This parasite is mainly found in sun-
mature grub leaves the snail, it comes     fish and minnows and is not harmful
into contact with a fish and burrows       to people. It does not attract as much
into its skin. There it stays — for up     attention as other parasites because
to m years — waiting for a king-           it is so small and takes up residence
fisher to eat the fish so the cycle can    in the spleen, heart, and other inter-
begin again.                               nal organs of a fish and, therefore, is
                Yellow Grub                unseen.
Its life cycle is similar to the black-       Anyone who has ever eaten a blue-
spot grub, but the bird host is usually    gill has probably eaten a fish severely
a wading shorebird, such as the egret      infected with this grub and never
or great blue heron.                       knew it. Bluegills have a very high
   G r u b eggs pass into the water from   tolerance to large numbers of this
the bird's saliva when it feeds. The       parasite without being stressed.
yellow grub then seeks a new host, a                       Eye Fluke
specific snail of the genus Helisoma.      On occasion anglers may catch a fish
Because of small numbers of this par-      that is blind in one or both eyes —
ticular snail, the yellow grub is less     the eye lens looks milky and opaque.
common than black spot.                       Cause of the blindness is a micro-
   This is another parasite that upsets    scopic, larval fluke — a flatworm —
anglers; the grubs reside in the mus-      hundreds of which invade the eye. Its
cle of the fish — usually whitefish,       life cycle is similar to other flukes. The
tullibee, yellow perch, walleye, and       adult worm lives in a gull. Infected
sauger. They are edible and don't in-      fish eaten by this bird starts a new life
fect humans. Normal cooking kills          cycle. Another harmless-to-humans
them.                                      parasite.

46                                                               THE MINNESOTA VOLUNTEER
               Tapeworms                            nodules usually disappear by fall. They
This w o r m is usually found in large-             don't affect the meat. T h e s e fish can
m o u t h and smallmouth hass which                 b e eaten.
may have both adult and larval forms                              Protozoans
present in the intestine. Later the eggs            A microscopic, one-celled organism
pass into t h e water in the fish's feces.          called a protozoan can cause several
T h e life cycle continues w h e n small            fish maladies. T h e one that sports-
aquatic animals called copepods eat                 m e n m a y n o t i c e is c a l l e d Ichly-
the eggs. T h e n small fish like sunfish           ophthirius mutlifillis, popularly known
eat the copepods.                                   as "Ich.
    T h e larvae live in the sunfish until             People who maintain an aquarium
a bass eats t h e sunny. T h e worm t h e n         for tropical fish recognize these or-
develops into an adult. This parasite               ganisms as a c o m m o n problem. Be-
can cause the bass great p r o b l e m s            cause protozoans are so lethal in the
should it ingest the infected copepod               wild, fish die quickly, sometimes lit-
r a t h e r than eating the sunny. T h e n          tering a beach with their bodies —
the prolarvae — i m m a t u r e larvae —            anglers may not b e aware of what
may w a n d e r t h r o u g h o u t the bass tis-   caused t h e massive die-off. T h e in-
sues causing adhesions in the inter-                fection is most observable on catfish;
nal organs. If a female bass is in-                 it looks as if s o m e o n e sprinkled the
fected, its ovaries could be destroyed,             fish with salt.
causing sterility.                                      " I c h ' is lethal to fish b u t causes no
  A t a p e w o r m — or prolarvae — in-            p r o b l e m f o r h u m a n s . L i g h t l y in-
fected bass is scrawny and emaciated;               fected fish are edible w h e n cleaned
very little meat hangs from its bones.              and properly cooked. Nodules that
But the fish can b e safely cleaned and             form on fish may b e white, cream, or
eaten. This w o r m can infect people               tan in color and range in size from a
only if t h e fish isn't properly cooked.           p i n h e a d to the size of a pea.
               Lymphocystis
This viral disease forms light or cream-            T h e r e you have it, just some of the
colored, wart-like growths on the body              maladies that affect fish and cause
and fins, usually on walleyes and oc-               concern to anglers around the state.
casionally on largemouth bass.                         Minnesota is p r o u d of its reputa-
  T h e nodules are of little impor-                tion as a great place to fish. In gen-
tance. T h e y are unsightly, but are               eral, fish can,glit in our waters are very
harmless both to humans and fish. The               safe fish indeed to eat. •

                          Where      Ducks     are Born     and      Raised
   ABOUT HALF of all wild ducks in North America are produced in the prairie pot-
   holes of south-central Canada and north-central U.S.
                                                             — National Geographic Society
JULY-AUGUST 1 9 8 7                                                                                 47