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INFESTATIONS OF THE COPEPOD PARASITE, LERNAEA CYPRINACEAE, IN NATIVE FISHES OF GRAND CANYON

Steven W. Carothers, James W. Jordan, Charles 0. Hinckley, and Howell D. Usher Museum of Northern Arizona, Flagstaff, Arizona 86001

ABSTUACT

An examination of the native fish species, Gila cypha, Rhinichthys osculus, Catostomus latipinnis and Pantosteus discobolus collected from the Little Colorado River and Kanab Creek in Grand Canyon National Park, Arizona, revealed infestations of the copepod, Lernaea cyprinaceae. In the same streams, no copepods were found on the exotic fish species, Cyprinus carpio, Ictalurus punctatus, Pinephales promelas, Fundulus zebrinus, and Salmo gairderni. Although L. cyprinaceae has been identified previously in Grand Canyon, the present investigation reports the first case in which the incidence of infection has been high, and the only documentation of copepod parasitism on the endangered G. cypha population in Grand Canyon.

INTRODUCTION _ The copepod (Crustacea), Lernaea cyprinaceae Linnaeus, is an introduced fish parasite known to cause considerable mortality in pond and hatchery habitats, especially where conditions of high temperatures and high population densities exist simultara ly it,zman and Rayner 1958). Although first described as parasitic on European fishes (Wilson 1918), L. cyprinaceae is thought to have been introduced to North America from )Asia in shipments of ornamental and tropical fish (Tidd 1934). Although L. cyprinaceae parasiti= is less common in natural streams than in lakes and ponds (Bulow et al. 1979), James (1968) found near epizootic infestations in some Arizona desert streams where summer and fall discharges were typically low, resulting in high water temperatures, ponding, and relatively crowded fish population densities.

1 The present investigation was performed under research contracts from the National Park Service (CX821070012) and Bureau of Reclamation (7-07- 30-40026).

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- During i recent survey of the fishes of the Colorado River and :ributaries in Grand Canyon, we encountered heavy infestations of L. :yprinaceae in fishes taken from two low gradient tributaries, Kanab :reek and the Little Colorado River. Only juveniles of the native species, Zatostomus latipinnis, Pantosteus discobolus, Rhinichthys osculus and ila cypha were infested, while sympatric exotic species were found to be free of parasites.

Previous reports on the ichthyofauna of Grand Canyon have failed to reveal the occurrence of any significant ectoparasite infestations from either the mainstem Colorado River or its tributaries (Miller 1944, 1975; Minckley and Blinn 1976; Suttkus et al. 1976). However, Suttkus (Johnson 1976) has inlicated finding one L. cyprinaceae on each of two specimens, "Gila sp. nd Cyprinus carpio" from the Little Colorado River. This report represents ..: he first account of heavy L. cyprinaceae parasitism on native fishes in the Grand Canyon, and the only documentation of heavy infestations in the 1 1st remaining breeding population of the endangered Gila cypha. This .-port also offers an explanation as to why the infestation is almost exclusively limited to juvenile native pecies

BACKGROUND

In an unaltered state, the Colorado River and its tributaries in Greed Canyon were known to support ei;Iht species of native fish. Today, with Hoover Dam (Lake Mead, Arizona/Nevada) backing impounded waters some 50 km into the western end of the Canyon and Glen Canyon Dam (Lake Powell, Arizona/Utah) controlling daily and seasonal discharge, sediment transport and water temperature of the River as it..enters the Grand Canyon from the east, the system has undergone significant ecological changes (Carothers et al. 1976, Dolan et al. 1974, Johnson 1976). The habitat alterations, and to some extent, the subsequent invasion of exotic fish species have led to the decline, and in some cases, total extirpation of certain elements of the native ichthyofauna (Minckley and Blinn 1976, Minckley and Carothers in press, Suttkus et al. 1976).

Ptychocheilus lucius, Gila robusta and G. elegans, once common in the Grand Canyon, are now apparently extinct there, as well as in other portions of their former range. Another previously common species, Xyrauchen texanus, on-. recently proposed for "threatened" status (USF&WS 1978) due to a general decline throughout its former range in the South- west, has only recently been "rediscovered" (one specimen) near the eastern end of the Grand Canyon (Minckley and Carothers in press). Three of the remaining four species of native fish, C. latipinnis, P. discobolus and R. osculus, are found in relatively high densities. The endangered G. cypha, though found in limited numbers throughout most of the upper portions of the mainstream river in the Canyon, is apparently restricted to breeding only near the confluence of the mouth of the Little Colorado River, the largest of the tributaries in the Grand Canyon (Minckley et al. in press).

453 Due to the major habitat alterations, accidental "bait bucket" releases and sport fishery stocking programs, the four native fish species still represented by viable populations now share the Colorado River and its tributaries in Grand Canyon with twenty-one exotic fish species (Minckley and Blinn 1976, Suttkus et al. 1976).

METHODS AND STUDY SITES

Collections were made during November, January, May, August and October 1977-1978. Standard tied seines 2to 6.5 m long with 3.2 mm mesh were used for capturing the fish. With the exception of G. cypha, fish were preserved in 10% formalin immediately upon collection and were stored therein until analyzed with a light stereoscopic microscope. Individuals of the endangered G. cypha, were examined in the field and released.

For each fish, total lengths were measured to the nearest mm. Measurements of preserved spscimens were taken from three weeks to several months after preservation and no correction factor was utilized to account for possible shrinkage. Adult parasites on each fish were counted and the location of each on the fish body was recorded. All preserved specimens are now located in the vertebrate collections of the Museum of Northern Arizona.

Although the mainstem Colorado River was seined and electro- , fished approximately every 30 km, and most perennial tributaries were seined and/or trapped during each of the aforementioned sampling periods, only the Little Colorado River and Kanab Creek produced fish with parasite infestations. In each of these two tributaries, the sampled portion of the stream included the confluence zone of the Colorado River and 200 m up the tributary.

Little Colorado River

The Little Colorado has a drainage area of approximately 141,120 km2. It flows northwest from its source in the White Mountains of east-central Arizona, 412 km to its confluence with the Colorado River at River Mile 61.2 (Belknap 1969). Numerous springs enter the Little Colorado River between 5 and 21 km upstream from its confluence. The combined discharges of these springs range between 6.1 and 6.6 m3/sec (Johnson and Sanderson 1968) and at certain times of the year, provide the only runoff when the river above the springs ceases to flow. Measurements taken 51.2 km upstream from the springs indicate that discharge from this stream range from no flow to 703 m2/sec. The average stream bed gradient is 12.3 m/km. Along the margins and in the stream 4 channel, deposits of travertine (CaC04) impede stream flow causing dams and pools. Stands of Tamarix chinensi4 Salix exigua and Phragmites -. australis form a sparse vegetative cover on the470 streambank. During the study, water temperatures ranged from 8,5 to. C at the confluence and from 15 to 23° 200 m upstream.

454 'Kanab Creek

Kanab Creek originates on the Paunsagunt Plateau of southern Utah and flows in a southerly direction approximately 105 km into Arizona where it enters the Colorado River at River Mile 143.5 (Belknap 1969). Kanab Creek drains approximately 5698 km2 in southern Utah (LaRue 1916). The mean discharge of the stream is 0.14 m3/sec with extremes ranging from 131.1 m3/sec to no flow. The streambed gradient is approximately 16 m/km. Riparian vegetation consists of Tamarix chinensis, 4uncus spp., Vitis arizonica and Typha latifolia. Water temperature from the confluence and 200 in upstream ranged from 9° to 24° C during the study.

RESULTS AND DISCUSSION

The incidence of L. cyprinaceae infestation was first observed during the August 1978 sampling period (Table 1). At that time, juvenile R. osculus (6.5%) and P. discobolus (20.7%) of Kanab Creek were found to be infested. By the next sampling period, October 1978, parasitism had become more pronounced, both in terms of the number of species parasitized and the relative frequency with which infested fish were -encountered. During October, juvenile R. osculus (10.0%), P. discobolus (55.1%) and C. latipinnis (33.3%) in Kanab Creek carried one or more copepods, and for the first time, the parasite was found on G. cypha, (53.8%) and C. latipinnis (50.0%) in the Little Colorado River. Although adults of all four native species mentioned above were taken during both sampling periods, none showed any evidence of copepod parasitism. The largest number of parasites on any one juvenile fish was ten on a P. discobolus from Kanab Creek,taken in October. Most of the parasitized fish contained from one to two parasites per individual.

None of the collected individuals of exotic species (C. carpio, Ictaturus punctatus, Pimephales promeles, Fundulus zebrinus and Salmo gairdneri) taken from either tributary carried parasites. These species have no apparent resistance to L. cyprinaceae parasitism since each has been previously reported as hosting this copepod in other aquatic sys- tems (Hoffman 1967, James 1968, Wilson et al. 1966).

Data relative to the attachment sites of the parasite are included in Table 1. As has been found in previous studies (Bulow et al. 1979, Haley and Winn 1959, James 1968), the attachment site was most frequently near the base of the pectoral, pelvic or dorsal fin.

The occurrence of L. cyprinaceae on juvenile fish of the native species inhabiting the Little Colorado River and Kanab Creek is apparently a recent outbreak. Suttkus et al. (1976) reported collecting in the Little Colorado River near the confluence on nine separate occasions from 1972 to , 1976; they also reported collecting in Kanab Creek four times between 1978--and 197§.'4Although .many of their sample periods were during late - summer and fall, Suttkus (jOhnson'1976) reported observing L. 'cyprinaceae) only once on G. cypha and C. carpio in the Little Colorado River. Our

455 Table 1. Incidence of Lernaea cyprinaceae on native fishes of the Little Colorado River (LCR) and Kanab Creek (KC) in Grand Canyon, Arizona, 1978.

Gila cypha Rhinichthys osculus Catostomus latipinnis Pantosteus discobolus LCR KC LCR KC KC October August October October October August October

Number of fish examined 65 46 30 8 3 29 49 Length of fish (mm): Mean 73 33 35 98 87 39 68 Range 58-189 17-87 21-44 64-130 56-126 31-45 44-87 41 Number of fish with crt Lernaea 35 3 3 4 1 6 27 Or Percentage of fish parasitized 53.8 6.5 10.0 50.0 33.3 20.7 55.1 Number of Lernaea 1-5 1-4 1-2 1-2 1 1-2 1-10 per fish Location of Lernaea attachment pectoral fins 31.4 33.3 25.0 20.0 - 13.0 pelvic fins 31.4 16.7 - - 22.2 20.8 dorsal fins 23.5 33.3 25.0 80.0 100.0 22.2 37.5 anal fin 3.9 25.0 - 6.9 caudal fin - 25.0 - - 22.2 2.8 body wall 7.8 16.7 - - - 22.2 11.2 mouthparts - - - - - (external) opercle 2.0 - - 11.2 2.8

100.0 100.0 100.0 100.0 100.0 100.0 100.0

COFTLATI; .4.FEAIRISOO .ZIOMAIESPAS.OSKATY. collecting records (Minckley and Blinn 1976, and unpubl. data) from the spring of 1975 to the present indicate that L. cyprinaceae was virtually absent from the system until August of 1978.

The origin of L. cyprinaceae in these two Grand Canyon tributaries is unknown. It is most probable that parasitized exotic species from the Lake Mead area, or hatchery Salmonids originating below Lake Powell, are the original source.

The presence of copepod parasitism on the native species in Kanab Creek and the Little Colorado River, its absence in the mainstem Colorado River, and the relative absence of L. cyprinaceae on the exotic species throughout the system can be readily explained on the basis of the thermophilic nature of the parasite and habitat selection by both native and exotic fish species. The optimum temperature0 range for the development of L, cyprinaceae is from 23° to 30 C; below 14° C the parasite fails to complete its life cycle (Bauer 195S, Putz and Bowen 1964). Since the discharge of the Colorado River in Grand Canyon now comes through penstock gates in Glen Canyon Dam approximately 60 in below- the surface 'of Lake Powell, the temperature of the hypolimnetic river water ranges from 70 to 100 C throughout the year (Cole and Kubly 1976). The exotic species presently inhabiting the Colorado River in Grand Canyon (see Minckley and Blinn 1976, Suttkus et al. 1976 for a complete list) show a wide range of temperature tolerance. Although the exotics utilize the warmer tributaries and move freely between the warm and cold habitats of the tributaries and mainstem, for the most part they demonstrate a preference for the mainstem habitat. The adults of the native species tolerate and are frequently captured in the mainstem river, however, they seem to require the warmer tributary areas for spawning and rearing (Minckley and Blinn 1976, Suttkus et al. 1976). During August and October of 1978, the temperatures of Kanab Creek and the Little Colorado River were both well within the optimum range for L. cyprinaceae maturation. Also, during low discharges of late summer and fall, both tributaries tend to have sluggish currents and standing pools, further characteristics of optimum copepod habitat (Bulow et al. 1979). The only fish restricted to the optimum copepod habitat for any period of time are the immature native species. We therefore suggest that once the juvenile native fish reach some unknown critical size:, they can then take advantage of the colder Colorado : River habitats where any; L. cyprinaceae they host will most likely perish. As yet, however, the :survival: rates of. parasitized imma-stures of native species in this system are unknown. ' ..., GaTe.: ^ • , .. ' .• _ , ' L...G. cypha, though once common throughout the Colorado River Basin .(Minckley 197.3),is noW,...... extremely rarevit .is presently included on the Federal list of Endangered Species OU.S:F.MS..1973). Although it is known to persist in isolated Portions Of the Green and Yampa Rivers in Utah and Colorado (Holden and Stalnaker 1970), the, only-Iii&ony locality where reproductive efforts are obviously successful ,J. 'near the mouth - . - 7 .!"."..e.c.0,".•••••■37-"T-7mor.--...... 457 of the Little Colorado River in Grand Canyon. It is very likely that since this remaining breeding refugium has been invaded by L. cyprinaceae, an already endangered species may be further threatened. James (1968) found that another member of the genus, G. robusta, was parti- cularly susceptible to parasitism by L. cyprinaceae, and it is well 1 known that this particular copepod can cause substantial injury to its host (James 1968, McNeil 1961, Tidd 1934).

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Belknap, B. 1969. Powell Centennial Grand Canyon River Guide. Canyon- lands Press, New York, N. Y.

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Carothers, S. W. et al. 1976. An ecological survey of the riparian zone of the Colorado River between Lee Ferry and Grand Wash Cliffs. Colorado River Research Program Technical Report No. 10, Grand Canyon National Park.

Cole, G., and D. Kubly. 1976. Limnologic studies on the Colorado River from Lee Ferry to Diamond Creed. Colorado River Research Program Technical Report No. 8, Grand Canyon National Park.

Dolan, R., A. Howard, and A. Gallenson. 1974. Man's impact on the Colorado River in Grand Canyon. Amer. Sci. 62(4):392-401.

Haley, A. J., and H. E. Winn. 1959. Observations on a lernaean parasite of freshwater fishes. Trans. Amer. Fish. Soc. 88:128-129.

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Holden, P. B., and C. B. Stalnaker. '1970. Systematic studies of the . cyprinid in.the upper Colorado River Basin., Copeia 3409-429.: "

„ijames, A. E. 1968. Lernaea (Copepod) infection of three native fishes from the Salt River Basin, Arizona. Unpubl. M.S. ”Thesis, Arizona State University.

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McNeil, P. L., Jr, 1961. The use of benzene hexachloride as a copepo- dicide and some observations on lernaean parasites in trout rearing units. Progr, Eish-Cult. 23:127-133.

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Minckley, C. O., and S. W. Carothers. 1980. Recent collections of the Colorado River squawfish and razorback sucker from the San Juan and Colorado Rivers in New Mexico and Arizona. Southwes- tern Nat., in press.

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Suttkus, R. D., G. H. Clemmer, C. Jones, and C. R. Shoop. 1976. Survey of fishes, mammals and herpetological fauna of the Colorado River in Grand Canyon. Colorado River Research Program Technical Repert No. 5, Grand Canyon National Park.

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Uzmann, J. R., and H. J. Rayner. 1958. Record of the parasitic copepod,Lernaea cyprinaceae,in Oregon and Washington fishes. The Journal of Parasitology, 44(4):452-453.

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