One of the indications of decreasing
water quality is an increase in the number of pathological conditions in aquatic
animals and an increase in the number of individuals effected by them.
One
of these pathological conditions of considerable interest to muskellunge fishermen
in North America and to pike anglers in Britain and Ireland, is the cancerous
Lymphosarcoma, which causes very ugly lesions in that species. The obvious
concerns of the angler are: 1) danger to anglers handling effected fish; 2) edibility
of effected fish; 3) survival of the effected individual; 4) likelihood that the
release of an effected fish will transmit the problem to other individuals. The
published works of Dr. R. A. Sonstegard, of McMaster University, Hamilton, Ontario,
including a paper in the proceedings of the 1984 Muskie Symposium, address all
these points. Publications by Maire F. Mulcahy, University College, Cork, describe
Lymphosarcoma in the pike in Ireland as well as survey reports of other
tumors in that species.
In regard to anglers catching pike in North America, these same concerns have
usually been directed toward problems known as: 1) Blackspot Parasite, and 2)
Red Sore or Red Disease.
1) Blackspot or Black Grub Parasite in Pike
Fish with this condition are covered externally to an extremely variable extent
with small, circular black spots. The spots are about the size of the head of
a pin and are slightly raised. They are found on, or just under, the surface of
the scales and fins.
The raised area contains an immature stage (metacercaria)
of a fluke or trematode. Its existence in the fish is a developmental stage only.
The final host of the parasite, in which it becomes a reproductive adult, is one
of several fish eating birds, depending on the fluke involved. To complete the
life history, the fluke must "pass through" two intermediate hosts — a snail
and a fish. It is rare that the parasite, unsightly as in heavy infestations,
does any damage to the intermediate fish host, the pike. Also, since the final
host is a fish eating bird, the parasite is not viable humans. As a result, there
is no danger in handling the pike or in eating the pike. If the fish are skinned
rather scaled, virtually all of the parasites are removed. In addition, the stage
of the fluke in the black spot cannot survive the temperature usual in cooking
There is an Information Leaflet available from the Department of Ichthyology and
Herpetology, Royal Ontario Museum, which provides more details on this problem.
2)
Red Sore and Red Disease in Pike
The increasing interest in toxic substances
in water seems to have re-kindled interest of North American anglers in an even
older problem in the pike — Red Disease or Red Sore. This name is
applied to pike which have either a general condition on parts of the body and
fins resembling a haemorrhage, or isolated, red, slimy areas of dying tissue.
It has long been considered that the problem is related to a superficially similar
problem in frogs called "Redleg". Redleg in frogs in crowded conditions in captivity
can kill large numbers of individuals in a very short period of time.
As with muskellunge with Lymphosarcoma, anglers are often apprehensive
about handling pike with this unsightly problem, and often ask what they should
do with individuals effected in this way.
It appears that "red diseases"
are a group of diseases which may be associated with certain groups of bacteria.
There may be viruses associated with these bacteria but this is not definitely
known. A virus has been found associated red sore in European E. lucius
and some consider this reason to eliminate bacteria as the cause of red sore,
at least in that species. Other people feel red sore on E. lucius may be
caused by a bacterium different from the causative organism of red sore in other
animals. They also state that some of the confusion may be the result of contamination
of samples when they cultured for identification.
Poissibly the first
discussion of the “disease" called Red Sore appeared in print in a 1941
article in the Canadian Journal of Research (Vol. 19, Sec, D, No. 5). The authors
were a bacteriologist, Dr. G. B. Reed of Queen's University.
Kingston,
and Mr. George Toner, an active naturalist in that part of Ontario. They
stated (p. 139) that "the disease in pike is extremely varied. In its mildest
form, it varies from reddened points in the skin suggesting slight petechial haemorrhage,
to deep red areas several square centimetres in extent, the scales frequently
being displaced. In the more severe form, it appears as red, slimy, necrotic areas
extending through the skin and in some instances, deep into the muscle. The visceral
organs, in gross appearance, are unchanged or in some instances the kidney appears
darker in colour and softer in texture than the normal." Reed and Toner cultured
material from several pike, from differ ent lakes, which had severe lesions. A
number of bacteria were identified but they concentrated on Proteus hydropholis
because that bacterium was considered the causative organism of the superficially
similar "red leg disease" in frogs.
The story after that point is never
as clear again. Later accounts considered that the problem was not caused by Proteus
hydropholis. In 1970, Snieszko, in publication derived from a Symposium on Diseases
of Fishes and Shellfishes, suggested it was a form of haemorrhagic septicaemia
caused by one or more of the bacteria Areobacter liquefaciens, Pseudomonas
flourescens and Vibrio anguillarum, which were said to be similar taxonomically.
Poor environ mental conditions and stress appeared to trigger and spread the problem.
The last named bacterium was said to produce a similar problem in marine and brackish
conditions.
In a 1971 book entitled "Diseases of Fishes", edited by Sniezko
and Axelrod, it was suggested that red sore of pike was probably caused by Aerobacter
cloacae. In the same year, Bootsma, in a paper in the Journal of Fish Biology,
said that red disease killed large numbers of pike fry in European hatchery situations,
that it might be related to red sore disease but that the fry died before visual
sores developed. He stated also that on culturing material from the fry, no pathogens
were found and that "considerable confusion exists concern ing the etiology of
red sore disease in pike".
In 1973 Bootsma and co-authors writing in
Nature claimed to have isolated and identified the causative agent of European
Red Disease of pike. They stated that it was a haemorrhagic disease which causes
epidemics but could find no evidence of a bacterial cause. They did find evidence
of an unknown rhabdovirus in the infected fish. When they inoculated this virus
into healthy fish, those fish became diseased. These authors said it was a disease
which attacks young fry, that the mode of transmission was unknown, and that it
might be transmitted by adults at spawning time.
In 1973 van Duijn wrote,
in the book Diseases of Fishes, about a disease caused by the bacterium Vibrio
anguillarum which causes reddening of fins, etc., of the perch and the pike
in the brackish waters of the Baltic Sea.
In 1975 Ribelin and Migaki,
in an article in the book Pathology of Fishes, stated that some authors thought
Aerobacter cloacae might be the cause of red sore in pike, but suggested
that A. cloacae may, in fact, have replaced the original pathogen after
the samples were taken. Ribelin and Migaki stated also that Aeromonas liquefaciens
leads to haemorrhagic septicemia and several diseases including red sore in pike,
that there were several synonyms for the bacterium, and that the etiology of the
disease and the involvement of a virus are uncertain.
I could find no
more recent literature on the subject so it seems that Red Sore or Red Disease
in pike is one of the continuing enigmas of the fish world.
A check with
a microbiologist revealed that there was little probability of problems to humans
from handling an infected pike since the intact skin forms an adequate barrier
to bacteria. Since the causative organism has apparently never been satisfactorily
identified, it is impossible to forecast consequences of direct human contact
via a cut or other break in the skin.
The general rule with bacteria
suggests that returning a severely infected individual to the water could transmit
the infection to other pike and possibly to other species of fishes. Effective
control of the causal organism in the wild is virtually impossible. The condition
on individual fish probably could be treated but even this would be difficult
without identification of the causal organism. It appeared that the European hatchery
fry died too quickly of red disease to be saved by prophylac tic treatment.
I would like to acknowledge the work of searching the literature which was
carried out by Steve Campbell.
NEWS