Bulletin STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY STEPHEN A. FORBES. Chief Vol. XVII. BULLETIN Article III. An Epidemic of Leeches on Fishes in Rock River BY DAVID H. THOMPSON PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS November, 1927 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION A. M. Shelton, Director BOARD OF NATURAL RESOURCES AND CONSERVATION A. M. Shelton, Chairman William Trelease. Biology Henrt C. Cowles, Forestry Edson S. Bastin, Geology William A. Noyes, Chemistry John W. Alvord, Engineering Charles M. Thompson, Representing the President of the University of Illinois THE NATURAL HISTORY SURVEY DIVISION Stephen A. Forues, Chief ScHNEPP & Barnes. Printers Springfield, 111. 1927 701)51—1200 Vnl. X\n. Art. III. AN EPIDEMIC OF LEECHES ON FISHES IN ROCK RIVER DAVID H. THOMPSON IX the cuurse of field work in aqtiatic biology on Rock River it was noticed in the winter of 1925-1920 that almost every red-mouth but^'alo {Ictiobus cypriiiclla Cuv. & Val.) was heavily infested with the leech, Piscicola punctata V'errill.* This leech had not been taken dur- ing the two [^receding years of almost continuous work on this river, which included the collecting of hundreds of samples of the bottom fauna and the handling of many thousands of red-mouth butTalo at all seasons of the year. Moreover, fishermen at many points on the river reported that no such infestation had occurred in the last half-century and that the only time they had ever seen any such leeches on the bufialo w-as about ten years ago when a few were noticed during some early spring fishing. The first appearance of Piscicola punctata in epidemic propor- tions was on February 25, 1926. about four miles above Rockford. The river's winter covering of ice having "gone out" of most of the channel the previous day. the remaining ice was moved off an eddy, and a seine haul was made which included, among a number of other fishes, 45 red- mouth bniTalo weighing one to two pounds each, 38 of which were infested with this leech. The number of leeches on each of the infested fishes ranged from 1 or 2 up to 50 or more with an average of about 20. The point of attack was most often in the axils of the fins and about the anus, where the cuticle is relatively thin ; however, clusters of leeches were often found attached to other parts of the body, especially in places where the cuticle had been broken by injuries. .\ missing scale or a cut usually ofl^ered a place of attachment for several leeches. Those which had penetrated the cuticle or had found an opening in it were usually well filled with blood and mucus: others contained mucus only or were quite empty. E.XTEXT OK THE EPIDEMIC During the remainder of February and throughout March, leeches were found on the red-mouth buffalo in ninch the same numbers and pro- portions as just described for the first haul. Seine hauls made in this period over a 20-mile stretch of Rock River in the vicinity of Rockford netted 2831 red-mouth bufTalo, averaging about 2 pounds in weight. The leeches were so numerous that the bottom of a boat in which fishermen had handled a few hundred pounds of fishes was almost completelv cov- ered with them. Pre.served speuhnens of this leech were identified by Professor J. Percy lloore. 196 Illinois Natural History Survey Bulletin "Thin" fishes usually bore more leeches than "fat" ones. Whether the leeches made the fishes thin, or whether thin fishes were predisposed to leeches, is uncertain. The fishermen picked oflf the leeches before the fishes were sold on the retail market. When the leeches were removed, the place of attachment was raw and bleeding and was surrounded by a halo of inflamed flesh. Fishes infested with leeches were less desirable for market, partly because the wounds and blood-shot flesh injured their appearance and partly because the mere thought of leeches was repulsive to buyers. Many thin, infested buiifalo were thrown back by the fisher- men while sorting the marketable fishes out of the seine. At this same time fishermen seining farther down the river near Oregon also found the red-mouth buffalo very heavily infested with leeches. Those taken in the channel of the river were reported to have about the same number of leeches as described for the Rockford region, but those taken in sloughs and backwaters were much more heavily in- fested, individual fishes often bearing more than a hundred leeches. Fishermen at other points on Rock River found leeches on the buffalo during the same winter, but there is no evidence that the epidemic ex- tended into other streams of the State. One commercial fisherman, of many years experience in catching buft'alo at all seasons of the year on the lower Illinois River near Meredosia and on the Mississippi River near Savanna, reported that he had never seen leeches in any consider- able numbers on the fishes. The most that he had ever seen were on some red-mouthed bufifalo taken on the Mississippi during some early spring fishing five years ago, but they numbered only two or three to a fish. Fishermen on the Wabash River at Lafayette, Indiana, saw no such epidemic. During the epidemic on the red-mouth bufifalo, other fishes were occasionally found infested with small numbers of the same leech. The small-mouth buiTalo (Ictiobiis bitbaliis) was thus attacked, most often in the axils of the fins and about the anus. The common red-horse (Moxos- toma aurcolum) , which is somewhat more abundant in Rock River than the small-mouth bufifalo, was afifected even less ; on it, no leeches were seen which were filled with blood, although many were well filled with mucus. The mongrel buiifalo, the European carp, the common river carp (or quillback), and the common (or black) sucker were found with small numbers of leeches on them. It is possible that the leeches attached them- selves to these other fishes after having been dislodged from red-mouth bufifalo in the seine. Seasonal Habits of the Leeches The epidemic began while the river was covered with ice and ended soon after the ice had gone and the water temperature had risen a few degrees above freezing. There were no leeches on any of the 1481 red- mouth buffalo taken by the writer during November, 1925, in the same locality. Fishing was continued by the commercial fishermen in the same locality until late in December, when the river froze over for the winter, but no leeches were noticed. It seems probable, therefore, that the red- 1.3 198 Illinois Natural History Si-rvky Bullktix IT only 2 leeches were seen on 51 red-niijuth buft'al(3, and the last leech was seen on a buffalo on April 30, althf)Ugh several hundred red-mouth buft"alo were examined for them during the summer. An eft'ort was made to find out what became of these leeches after they left the fishes. The bottom of the river was sampled in many places where the leech-infested buffalo had been abundant. A number of them were found on April 29 among the fauna living on the vegetation in Long Slough above Rockford. There, on clumps of Elodea, they appeared empty and quite active, in contrast to their well-filled and sluggish con- dition when found on fishes. Earlier in the spring the fishermen had taken many leech-infested buffalo from this slough. Late in April in the same place, red-mouth buffalo were seen with fungous infections in wounds evidently made by the leeches. Since the leeches had not been found until late in l'\'bruary, it is not known exactly when they first attacked the buft'alo, there having been no fishing since December, when the river had frozen over. It was with considerable interest, therefore, that the buff'alo were examined in the fall and early winter of 1926. Leeches first reappeared on them at Rock- ford and Sterling on November 30, which was after the temperature of the water had dropped to less than 1° C. and the more quiet parts of the river had frozen over. They were also taken by the writer on December 5 and on following days, near Sterling and Oregon, from buffalo in seine hauls made where the ice had been moved away. The leeches at this time were very small and active, translucent and apparently empty. They measured S-10 mm. in length, as contrasted with those measuring 20-30 mm. which were taken the preceding spring. They grew rapidly and reached adult size during Januai-y. While young, they apparently fed on mucus alone, but as they became larger they were seen to be filled with blood as well as mucus. The number found during this winter was only a small fraction of the number found the preceding winter. Counts made at Sterling in December showed that about one- fourth of the buft'alo were infested, and that the average number of leeches per fish was 2. Just as in the preceding spring, they left their hosts as soon as the water temperature had risen a few degrees above freezing. The river remained at or near the freezing point and the leeches remained on the fishes up to March 19, when a three-day rain melted the ice and raised the temperature of the water. On March 22, when the temperature was 40° F. (-±.4° C), very few leeches were left on the fishes, and a few days later there were none. Since that time, a very thorough search has been made for Piscicola punctata, including more than 100 collections taken in all sorts of situa- tions in the river and adjacent waters, but not a single individual has been found. Moore' sums up what is known of the habits of this leech, as follows : "This is our commonest fresh water fish leech. It is common in the ponds ^ Moore, J. Percy. Classification of the Leeclies of Minnesota. Geological and Natural History Survey of Minnesota, Zoological Series, No. V, Part III, p. 105 (1912.) Lekchcs o.\ Fisiiks in Ro( k Rivkh 199 and lakes of the northern states and the Mississippi X'alley and is espec- iall\- abundant along the Ohio shore of Lake Erie. It lives upon the ex- terior of the body of various species of small fishes, feeding upon the mucus which covers the surface as well as upon their blood. It appears to be in no way injurious to its hosts. Many examples may also be found living among water plants, to the stems of which there is good reason to lielieve its stalked cocoons are attached." DESCRirTIOX The following description, which is based in all particulars on exam- ination of specimens taken on the red mouth buft'alo in Rock River, in- cludes the external characteristics only, and in a few items, where there is no disagreement, uses language earlier employed by ^loore. Usual size 15 to 25 mm., but extensible to a greater length; greatest diameter 2 or 3 mm. A narrow neck-like constriction embracing the first few somites behind the anterior sucker; the posterior two-thirds much flattened when the animal is contracted. The posterior sucker when expanded is wider than the widest portion of the bod.v, and normall.v three or tour times the diameter of the anterior sucker. One pair of e.ves, with conspicuous bar-like pigment cups, which are place obliquely, convei'ging anteriorly, and which in length are each equal to more than a fourth of the breadth of the anterior sucker. Behind these are two smaller pigment spots, also somewhat bar-like, and easily mistaken for a second pair of eyes. Living specimens had a translucent greenish ground-color, as described by Verrill, when containing little or no blood; both the upper and lower sur- faces of both body and suckers were densel.v covered nearly everywhere witli minute black specks, irregularly arranged. Along each side are eight or more sub-equally spaced pale spots which are partly visible from above, and which are connected with each other lengthwise by narrower pale areas, forming a continuous pale lateral stripe for most of the animal's length. The pale dorsal stripe found by Verrill is only faintly developed or wholly absent in a majority of the specimens which were closely examined. When filled with blood the greenish groundcolor is largely submerged, except on the two suck- ers, and the general appearance is speckled brownish. Color \".\ri.\.\t During this epidemic on the red-mouth buffalo, a dift'erent-appearing leech, provisionally identified as a color variant of P. punctata, was found on the small-mouth black bass and the wall-eyed pike. It is smaller than the buffalo leech and is dark brown instead of an iridescent pale green. It occurred almost exclusively on the head of its host; fifty were once found about the mouth and branchial region of a small-mouth black bass weighing 1^ pounds. These leeches moved about rather actively and were closely ajiplied to the host throughout their length, while the buffalo leech was usually seen hanging by its caudal sucker, the remainder of the body dangling in the water. These smaller brown leeches apparently fed upon nnicus alone, since none were seen filled with blood and no injuries 200 Illinois Natural History Sirvey Bi i.lktin were found on the host which could be attributed to them. They curl up tightly when killed in formalin while the buffalo leech dies straight or but slightly bent. These leeches disappeared from the small-mouth black bass at the same time as did those on the buffalo, and they reappeared in reduced numbers in the following winter. Other Species of Piscicola Another leech of this genus, P. inihicri Verrill, is reported by Milner" to have been taken in large numbers on fishes in Lake Michigan : "The Ichthyobdellan, a leech of three-fourths of an inch long, grayish white in color, with brown tesselated markings, was seen in great numbers in the month of April, while the fishermen were lifting their nets from about fifty fathoms some fifteen miles out from Kenosha, Wis. They cov- ered the nets and fishes of all species, and fell in such numbers on the deck that it became slippery, and an old coat was thrown down for the man who was lifting the gang to sand upon. They were very tenacious of life, living for a long time on the deck, and for several days in the bilge-water of the fish-boats. They were in such numbers that it was diffi- cult to decide whether they had a preference for any species, and were found filled with blood both in the gills and while attached to the body, though it was difficult to imagine that they could fill themselves with blood fi'om the epidermal sheath of the scales. They were thought to be most numerous on the white-fishes, as they were in greater numbers on them than on the trout, the lawyer, or the cisco, the only other fishes taken. A prevailing but mistaken opinion in the vicinity was that the white-fish fed upon the leech. Dr. Hoy's investigations disproved the notion, and all examinations of stomach-contents confirmed this fact." Dr. F. B. Adamstone is quoted by Moore^ in regard to P. iniliwri in Lake Nipigon as follows : "this leech (piscicola) is found by hundreds on whitefish, and the decks of the tugs are strewn with them when the nets are lifted." This species is parasitic on whitefish throughout the year, although it is also found free-living (presumably in summer) on floating vegetation and in the more shallow waters. In view of the fact that P. punctata infests the red-mouth buffalo only when the water is cold, it may be of some significance that the whitefish spends the warmer months in the deep waters of the lakes where the temperature is close to 4° C. The European species, P. gcomctra L., is a common pest and well known to fish culturists. According to Plehn,* it not only seriously dam- ^ Milner, James W. Report on the Fisheries of the Great Lakes; the Re.suUs of Inquiries Prosecuted in 1871 and 1872. Rept. U. S. Comm. Pish & Fisheries, Part II, for 1872 and 187.3, p. 64. ' Moore, .1. Percy. The Leeches (Hirudinea) of Lake Nipigon. University of Toronto Studies, Biological Series, No. 25: Publications of the Ontario Fisheries Research Laboratory, XXII-XXVI, page IS. (1D24.) Plehn, Marianne. Praktikum der Fischkrankheiten. Handbuch der Binnen- flscherei Mitteleuropas. Band I. Page 339. (1924.) Leeches on Fishes in Rock River 201 ages its hosts but also transmits the blood parasite Trypanoplas)iia cyprini. This leech apparently attacks the fishes at all seasons and does not have its parasitic habit restricted to a narrow temperature range. No evidence of any special seasonal relationship to the host has been found in the literature on other species of this genus occurring in various parts of the world. Effect on Fish Yield The epidemic of Piscicola punctata appreciably affected the fish yield of Rock River for the spring of 192(3, and the possibility of its continuing to do so should be considered, since the red-mouth buffalo is second only to the carp in commercial importance. \\'hile other species of this genus regularly appear in large numbers on fishes in other waters, this is the only known instance where this species assumed the proportions of a pest with which it would be necessary to reckon. Within the memory of the oldest fishermen of Rock River, it has never been seen except in small numbers and at long intervals. During the winter of 192G-192T, it was present in only about one-tenth of the numbers found the previous winter. There were no unusual conditions known to be prevalent in Rock River during these years which could obviously ])redispose to such an epidemic. Considering these things, it seems likely that Piscicola punctata will not continue to occur in sufficient numbers to afl:"ect the fish yield and that it may again be relegated to the rarer species of the river fauna. Acknowledgments I am indebted to Mr. R. E. Richardson, biologist, and to i\Ir. H. C. Oesterling, editor, both of the Survey staff, for aid in the preparation of this paper, and to Mr. F. 13. Hunt, zoological assistant, and others for aid in the collection of material and information.