Journal of Fish Biology (2002) 61, 448–455 doi:10.1006/jfbi.2002.2051, available online at http://www.idealibrary.com on

Ligulosis associated with mortality in largescale suckers

B. A. S*‡, K. L. G†, C. R*  R. B* *Department of Fisheries and Wildlife, Oregon State University, 104 Nash Hall, Corvallis, OR 97331, U.S.A. and †USDA Forest Service, NFJD Ranger District, Highway 244, Ukiah, OR 97880, U.S.A.

(Received 4 December 2001, Accepted 27 June 2002)

Investigations of a fish kill at an irrigation reservoir in the Deschutes River basin, Oregon, documented at least 153 dead largescale suckers Catostomus macrocheilus, all heavily infected with large Ligula intestinalis (Cestoda). Moribund fish nearshore were similarly infected, with no evidence of secondary disease or infection. Morbidity and mortality in all cases was probably due to severe mechanical damage to internal host organs resulting from infection with multiple, large L. intestinalis. The pathology of L. intestinalis documented in largescale sucker in this study contrasts sharply with previous accounts and may represent a new and emerging disease for largescale suckers.  2002 The Fisheries Society of the British Isles Published by Elsevier Science Ltd. All rights reserved.

Key words: Ligula intestinalis; largescale sucker; Catostomus macrocheilus; plerocercoid; wildlife infection.

INTRODUCTION Several species of cestode have been implicated in mass fish kills, including Ligula intestinalis (Bloch). The pathogenic nature of L. intestinalis in cyprinids in Europe has been discussed in detail (Arme & Owen, 1968; Bauer et al., 1973; VanDuijn, 1973; Sweeting, 1977; Dubinina, 1980; Scha¨perclaus, 1991; Arme 1997b), but infections reported in North American populations of catostomids have not been extensive (Lawler, 1964; Dauble, 1985). Pathogenesis was noted recently in bridgelip sucker Catostomus columbianus (Eigenmann & Eigenmann) in the Crooked River of central Oregon after infection with unusually large L. intestinalis (Groves & Shields, 2001), but prevalence was low and mortality was not documented. In the present study an apparent L. intestinalis-induced mortality of largescale suckers Catostomus macrocheilus Girard in Haystack Reservoir was investigated.

MATERIALS AND METHODS STUDY AREA Filled in 1957, Haystack Reservoir is part of the North Unit Irrigation District of Central Oregon, and is supplied with water diverted from the Deschutes River just north of the city of Bend. It is located in Jefferson County, Oregon at 443001 N; 121912 W. The reservoir is managed for recreational fisheries for rainbow trout Oncorhynchus mykiss (Walbaum), brown trout Salmo trutta L., kokanee Oncorhynchus nerka ‡Author to whom correspondence should be addressed. Tel.: +1 541 737 1939; fax: +1 541 737 3590; email: [email protected] 448 0022–1112/02/080448+08 $35.00/0  2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.      449

(Walbaum), brown bullhead Ameiurus nebulosus (Lesueur) and centrarchids, including largemouth bass Micropterus salmoides (Lecepe´de), bluegill Lepomis macrochirus Rafinesque and black crappie Pomoxis nigromaculatus (Lesueur). Surface area and depth of the reservoir varies with seasonal and daily water use, with a useable storage of 2280 ha, maximum capacity of 3116 ha, a maximum depth of 24 m and an average depth of 8·1 m. Water clarity in the reservoir at the time of the study was very good, with snorkelling visibility of up to 3 m. No algal blooms were noted, and no other affected or dead fish species were observed. Input of water from the supply canal increased water level by nearly 1·5 m during the 5 h collection and observation period on 7 April 2001. Water temperature was c. 5 C and air temperature fluctuated between 0–8 C.

DATA COLLECTION AND ANALYSIS Observations of fish were made from shore as well as underwater with SCUBA gear, but dead suckers observed by SCUBA were not included in total mortality counts. Fish and bird mortalities were counted through a survey on foot around the perimeter of the reservoir, during which all wildlife species observed (and their feeding activity) were noted. Plerocercoid ingestion by wildlife was confirmed from direct observation of feeding and inferred from the presence of plerocercoids in faeces. Body cavities of dead fish were opened to determine presence or absence of L. intestinalis and associated tissue damage, but were not studied further due to the advanced state of specimen decay. Live fish were captured by angling with bait, hand nets, jigging, spear and snagging. All fish were euthanized with clove oil (Cho & Heath, 2000) immediately after capture. Total length (LT) and mass (M) were measured for each fish before the body cavity was opened. All plerocercoids were removed, measured, and weighed. Host gonad development, as well as tissue and organ damage, was documented. Plerocercoids were identified according to Hoffman (1998). A modified Fulton’s condition factor KF (Simpkins & Hubert, 1996) was calculated for 5 3 each fish from KF=10 MLT , where M is in g and LT is in mm. The parasite index (IP) 1 was calculated from IP=100 (total mass of parasites) (total mass of host plus parasites) (Arme & Owen, 1968), where IP=50 would indicate a mass of L. intestinalis equal to M, the mass of the host’s body. Regression analysis of data was performed with StatGraphics Plus (StatGraphics, 1998).

RESULTS A total of 153 dead largescale suckers (all heavily infected with L. intestinalis) as well as abundant L. intestinalis-infected wildlife faeces were documented during the shoreline survey. Heavily infected fish were slow swimming and ‘ docile ’ to the approach of observers, yet two live fish with plerocercoids protruding from abscesses in the host body wall, as observed elsewhere in the basin (Groves & Shields, 2001), evaded capture. ‘ Free-living ’ L. intestinalis plerocercoids (Barus et al., 1997) were observed moving actively on the sub- stratum in shallow waters after emerging from the body walls of fish hosts. Animals ingesting plerocercoids included ducks Anas sp. L. and Mergus sp. L., geese Branta canadensis L., gulls Larus sp. L., great blue heron Ardea herodias L., Brewer’s blackbird Euphagus cyanocephalus Wagler, osprey Pandion haliaetus L., river otter Lutra canadensis Schreber and mink Mustella vison Schreber. Other wildlife observed in the area, but for which there was no direct or indirect evidence of L. intestinalis ingestion included scrub jay Aphelocoma coerulescens Bosc, raven Corvus corax L., belted kingfisher Megaceryle alcyon L., raccoon Procyon lotor L. and coyote Canis latrans Say. A great blue heron and Brewer’s blackbird, both recently dead and in emaciated condition, were found near the 450 . .   . reservoir, but necropsies could not be performed to confirm L. intestinalis infection due to a lack of scientific permits. Only one of 18 live largescale suckers collected was uninfected, indicating a prevalence of 94%. Infected fish were characterized by a firm, distended abdomen, with discrete ‘ lumps ’ externally visible and palpable. Most of the fish examined contained multiple plerocercoids with up to 12 in the body cavity of a single host (Table I). The sex of heavily infected fish with vestigial gonads could be readily determined from external secondary sexual characteristics, with intense spawn- ing colours, pearl organs and elongated anal fins in males compared to uninfected fish observed elsewhere. This is an indication that L. intestinalis- induced castration may not inhibit spawning activity completely in largescale suckers, consistent with reports from European populations of large cyprinids (Sweeting, 1977; Scha¨perclaus, 1991). Pathology observed in largescale suckers from the current study was comparable with reports from other species. This included liver degeneration and necrosis (Arme & Owen, 1968), internal haem- orrhages and adhesions (Sweeting, 1977), organ compression and displacement (Bauer & Stolyarov, 1961), parasitic castration (Orr, 1966; Arme, 1997a) and emaciation (Bauer & Stolyarov, 1961). Fish with severely reduced livers also had greatly enlarged gall bladders, symptomatic of anorexia. Plerocercoids were interwoven among the mesenteries and organs of the fish, and were constricted at several points along their bodies by adhesions, consistent with larval migrans exhibited by L. intestinalis plerocercoids infecting an ‘ unpreferred ’ fish host (Orr, 1968). Variation in the size, colour and dimensions of the plerocercoids was consider- able. Plerocercoid length-mass-width relationships were all positive but not well correlated with prevalence or host size or condition. Plerocercoids stored in plastic bags on ice for up to 1 week after removal from fish hosts subsequently matured and produced fertile eggs when cultured in vitro, evidence of the duration of viability of ‘ free-living ’ plerocercoids in the cold water of the reservoir. Host condition declined with level of infection (Fig. 1). Although intensity of infection increased with host LT (indicating cumulative lifetime burdens of L. intestinalis), IP values were negatively correlated with host size (Fig. 2). Higher IP values in smaller hosts suggest a lack of compensatory inhibition of parasite growth within the physical constraints imposed by a smaller host body. Such proportionally large masses of parasites may be incompatible with host survival, especially of smaller hosts.

DISCUSSION Despite anecdotal accounts, there is no mention of L. intestinalis infection in the Crooked River Basin Plan (Oregon Department of Fish and Wildlife) or any reports prior to 1996, when the first specimens of L. intestinalis in largescale sucker in Haystack Reservoir were noted during a routine lake survey (B. Hogdson, pers. comm.). Since then, anecdotal reports of L. intestinalis in largescale suckers in Haystack Reservoir have increased in numbers, and the first major fish kill was documented in spring 2001. T I. Data collected from 17 Catostomus macrocheilus infected with the plerocercoid stage of Ligula intestinalis at Haystack Reservoir, Jefferson County, Oregon, 7 April 2001. The table does not include data from a single uninfected female, LT 399 mm, mass, 639·7 g; KF , 1·007

Host measurements (n=17) Plerocercoid measurements (n=88) PI L Total Average Length Width Maximum Minimum Total mass T (total mass worms) K Intensity (mm) mass (g)  F mass (g) (mm) (mm) mass (g) mass (g) per host (g) (total host mass) 1

Maximum 411 633 35·1 1·34 12 56·0 941·0 27·0 56 16 91 Minimum 236 139 5·8 0·45 1 7·5 174·7 3·4 7 1 16 Average..31251 307145 169 0·80·2 5·1+3·2 9·01·0 338·67·0 10·93·0 1811 554525 452 . .   .

IP (%) 03010 20 40 1.4

1.2

1 F K

0.8

0.6

0.4 084 12 Intensity F. 1. Changes in the Fulton condition factor of Catostomus macrocheilus with parasite index ( ; r2=0·392) and intensity (; r2=0·166). The findings of the current study contrast with the largest single study on infection of largescale suckers with L. intestinalis in the nearby Columbia River (Dauble, 1985, pers. comm.). In the latter study, thousands of fish were examined over a decade, yet the prevalence was low (<1% at all times) and the plerocercoids were <200 mm length, present as single specimens in a given host, and not associated with host morbidity or mortality. Review of the literature suggests differences in the biology of L. intestinalis in Europe and North America despite their morphological similarities; the characteristics of the population associated with this fish kill more closely resemble reports from European populations than North American ones (Table II). Parasite distribution documented in the current study were not the negative binomial distribution characteristic of parasite-host populations in equilibrium, as the majority of examined hosts were heavily infected. Such non-equilibrium dynamics are characteristic when an infection is new to a host species or the host and parasite populations are expanding, both typical of ‘ emerging diseases ’ within a local host population (Kennedy & Burrough, 1981), and cannot be sustained. Heavy or lethal infection is also typical in a host that has inadequate resistance to infection, as is seen with exotic parasites in a ‘ new ’ host (emerging diseases) or during geographic range expansion into unexposed populations of host species (Sakanari & Moser, 1990; Stewart, 1991). The entanglement of plerocercoids throughout the body cavity of the largescale suckers may be evidence of ‘ larval migrans ’, behaviour typical of parasites in a non-preferred fish host. Since ligulosis castrates hosts (Arme, 1997a) and is fatal to largescale suckers in this system, the natural outcome would be abatement of infection without input of new hosts to sustain infections of this intensity (Sweeting, 1977; Wyatt & Kennedy, 1989).      453

40 14

35 12

30 10

25 8 P

I 20

6 Intensity 15

4 10

5 2

0 0 200 250 300 350 400 450

Host LT (mm) F. 2. Changes in the parasite index ( ; r2=0·196) and intensity (; r2=0·042) of Catostomus macrocheilus with host total length. The slight increase in infection intensity with increasing host

size (– – –) indicated an accumulating life time burden. In contrast, IP values had a negative correlation with host size (——), consistent with lack of inhibition of parasite growth within the physical constraints of smaller fish hosts.

T II. Comparison of the current Ligula intestinalis infection with previous reports in largescale sucker in the Pacific north-west and with reports from Eurasian cyprinid hosts

Dauble VanDuijn (1973), Current (1985, Dubinina (1980) and study pers. comm.) Scha¨perclaus (1991)

Host species Largescale sucker Largescale sucker Cyprinidae Geographic location Pacific north-west Pacific north-west Europe (Deschutes River— (Columbia Basin) Columbia Basin) Plerocercoid size Large Small Large (nearly 1 m) (<20 cm) (some over >1 m) Host pathology Severe Negligible Severe (ligulosis) Mass mortality (fish kill) Yes None Yes Prevalence High (>90%) Low (<1%) High (>90%) Plerocercoids per host Multiple Exclusively single Multiple (Intensity)

In the more benign co-evolved host-parasite association between threespine stickleback Gasterosteus aculeatus L. and the cestode Schistocephalus solidus, plerocercoid growth may have been constrained within the carrying capacity of the host at sub-lethal levels (Arnott et al., 2000). Thus, average worm mass was negatively correlated with intensity of infection and positively correlated with 454 . .   . host size, in part due to the positive effect on host growth induced by a growth hormone-like factor secreted by the S. solidus plerocercoid. No such correlation, however, was observed in L. intestinalis infections in the current study (Fig. 2), indicating the growth trajectory of these parasites may be inconsistent with host survival. Since intact ingestion by a bird is required for L. intestinalis to mature (Bauer & Stolyarov, 1961) and only a limited number of bird species in the study region would be capable of ingesting a large fish intact, it may be advantageous for a plerocercoid to emerge from a host that has grown large if this increases the parasite’s chances for successful completion of the life cycle. Changes in host behaviour induced by plerocercoids (Holmes & Bethel, 1972) resulted in fish host congregation in shallow waters, so the emergence of ‘ free-living ’ plerocercoids from fish hosts in these nearshore areas may facilitate transmission of plerocercoids to foraging avian hosts. Ducks and geese were observed feeding actively on these plerocercoids. Abundant cestode-infected faeces around the study area indicated successful transmission of large numbers of intact plerocercoids to a variety of wildlife hosts, though active infections in wildlife were not confirmed by necropsy. The impact this could have on survival and fitness of wildlife remains unknown but warrants additional study. The L. intestinalis observed in the current and prior report (Groves & Shields, 2001) are unusually large and pathogenic to catostomid hosts, exhibiting similarities to well-documented outbreaks of ligulosis reported in Europe. Haystack Reservoir, however is also characterized by many of the environmental criteria typical of sites susceptible to outbreaks of ligulosis (Bauer & Stolyarov, 1961; Lawler, 1964). There are insufficient data to determine if this represents a newly-introduced strain of L. intestinalis to the system, or if current pathology is due to a native strain emerging in some fish hosts due to either host switching (from cyprinids to catostomids) or to ecological conditions favouring extremely heavy levels of infection. Genetic tests and ecological assessment may support one of these explanations.

Our thanks to B. Hogdson and crews of the Oregon Department of Fish and Wildlife (ODFW) and to personnel of the North Unit Irrigation District for providing informa- tion about the history of the reservoir and its fishes. Thanks to P. Rossignol for critical review of this manuscript. Thanks to C. Banner, M. Engelking, T. Armandi and others in the ODFW Fish Pathology group for positive identification of parasite specimens, culture of Ligula, and technical review of the manuscript. This is Technical Paper 11845 of the Oregon Agricultural Experiment Station, who supported this research.

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