1890

Tms report describes an open-jaw condition (Fig. 1)observed in fingerling spring chinook salmon (Oz-corhynchus tshawytscha),8-10 cm in length, at theEagle Creek National Fish Hatchery, Estacada,Oregon. Attention was given to anatomy of thecondition, possible causes, and whether it might betransmissible.

Mortalities exhibiting this condition were foundmainly in two of 16 ponds containing approxi-mately 1.2 million fish. The approximate lossesfor each of the two ponds in July, August, andSeptember 1972 were 2000, 1500, and 1000, re-spectively. The average losses in the remainingponds for the same 3 months were 600, 600, and500 fish, respectively. The mortalities from thetwo ponds were mainly of fish affiicted with theopen-jaw syndrome (OJS), while relatively few ofthe losses from the other 14 ponds were associatedwith the abnormality. Steelhead (Salmo gairdneri)held in adjacent ponds were not affected by theopen jaw condition.

Printed in Canada (J3091)

JOURNAL FISHERTES RESEARCH BOARD OF CANADA, VOL. 30, NO. 12, PT. 1) 1973

Open-Jaw Syndrome in Chinook Salmon (Oncorhynchustshautytscha) at a Hatchery

DBNNIs E. Cnoucn. Wrlrrllr T. Ynsurarc. lNp Rossnr R. Rucrrn

Western Fish Disease LaboratorySand Point NSA, Seattle, ltash. 98115, USA

Cnoucu, D. E., W, T. Yasuuxe, aNo R. R. Rucrsn. 1973. Open-jaw syndrome in chinooksalrnon (Oncorhynchus tshawytscha) at a hatchery. J. Fish. Res. Board Can. 30:r890-1892.

Nearly 0.5/6 of the yearling spring chinook salmon (Oncorhynchus tshawytscha) at anational fish hatchery were observed with mouth agape, the condition occurring in two of 16ponds. X-radiographs and histological preparations indicated that the articular bone of thelower jaw was malformed and dislocated dorsal and posterior to its normal point of attach-ment. The bone appeared to be embedded in the mandibular muscle and surrounded by anextensive fibrous tissue network. Genetic aberration, environmental interaction, and teratogenicsubstances are discussed as possible causes of the anomaly.

Cnoucn, D. E., W. T. Ylsurlru, lND R. R. Rucrrn. 1973. Open-jaw syndrome in chinooksalmon (Oncorhynchus tshawytscha) at a hatchery. J. Fish. Res. Board Can. 30:1890-1892.

Nous avons remarqu6 que prds de O ,5/s des saumons chinook (Oncorhynchus tshawtyscha)de printemps Ag6s d'un an, dans un 6tablissement national de pisciculture, avaient la bouchegrande ouverte, cette condition se rencontrant dans deux de 16 6tangs. Des radiographies etdes pr6parations histologiques d€montrent que I'os articulaire de la mdchoire inf6rieure 6taitdifforme et decroch6 vers le haut et I'arriire de son point d'attache normal. L'os semblaitenrob6 dans le muscle mandibulaire et entour6 d'un rdseau volumineux de tissu fibreux. Nousexaminons une aberration g6n6tique, une interaction environnementale et diverses substancest6ratogEnes comme causes possibles de cette anomalie.

Received July 4,1973

The eggs of the spring chinook salmon werecollected in September and October l97l at theEagle Creek hatchery. Aller hatching, 480,000 fryfrom the eggs collected in October were transferredto the Little White Salmon National Fish Hatchery,Cook, Washington; none of these fish exhibitedthe open-jaw syndrome.

There have been undocumented accounts of"gapers" occurring at other locations. Dr K.Bonham (personal communication) mentionedseeing fish with this condition for several yearsamong chinook fry at the University of Washing-ton, College of Fisheries. Two-year-old rainbowtrout were similarly affected in an Oregon Statefish hatchery (B. Earp personal communication).This condition was also observed in l8-month-oldbrown trout (5. traua) at a California fish hatchery(R. J. Toth personal communication). There havebeen several other unpublished reports.

Materials and methods-Samples of OJS fish weretested for the presence of virus using standard tissueculture techniques. Bacterial examination was ac-

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Flcunrs I 3.

Frc. i . (1 ,5 x ) Spr ing chinook salnon : normal and af fecte d wi th open- jaw; Ftc. 2. (7 x ) X-radiograph of spr ing

chinook salmon jawbones: A, open jaw, showing dis locat ion of lower jaw and mal format ion of ar t icular bone; B,

normal ; F lc.3. Open- ju* an, l normal jawbones: NPA, normal point of at tachment of ar t icular bone wi th

quadraie bone; PA, abnormal point of at tachment of ar t icular bone, which over laps quadrate bone. l , dentaly; 2,

a l t icular ; 3, qua<lrate; 4, metaptcrygoid; 5, hyomandibular ' ; 6, preopercular ; 7, symplect ic '

Crouch ct a l . - J . F ish. Res. Borrd Can'

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Frc. 4. (126x) Articular-quadrate joint in normal spring chinook salmon: A, articular bone; Q, quadrate bone.Arrow shows area of articulation. Frc. 5. (1 17 x ) Open-jaw in spring chinook salmon showing malformation anddisplacement of articular bone. Note the articular bone (A) embedded in the surrounding muscle. Q is a portion ofthe quadrate bone.

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complished by gram stain and plate culture methods, andparasites were identifled using wet mount preparations.Histological material was prepared for microscopicevaluation of the tissues.

Material from afected fish was ground with saline ina tissue grinder and inoculated into normal fingerlingspring chinook salmon (0.1 ml/fish, intraperitoneally)to see if the condition could be reproduced. Groupscontaining 20 fish each were inoculated with one ofthe following preparations: 1) visceral homogenate,2) ground material from the jaw area at the point wherethe lower jaw articulates with the skull, and 3) the abovehomogenates mixed and heated in boiling water 5 min.The fish were held for 2 months in partitioned troughs.A group of 20 normal fish and 20 uninoculated OJSfish were included to see if the condition could be passedfrom affected to nonaffected fish.

In another experiment, brain material from OJS fishwas homogenized with saline and injected (0.1 ml/fish)into the neural canal of five anesthetized normal chinookyearlings. Five control fish were similarly treated withphysiological saline.

Chemicals which relax and contract muscle were usedto determine whether the condition was due to a nervousdysfunction. Five OJS fish were injected with 0.2 ml/fishof Prostigmin (0.5 mg/cme neostigmin methylsulfate)intramuscularly. Five additional OJS flsh were similarlyinjected with Flaxedil, (20 mg/cms gallamine triethidide).Prostigmin increases muscle tension and therefore themuscle contraction caused by the drug should close thejaw. Flaxedil blocks nervous activity to the muscles andthe use of this substance should let the jaw relax andclose by removing nervous stimulation to the muscles.

Affected and normal chinook salmon were dissectedto delineate the anatomical differences in the jaws. Theskull was defleshed as outlined by Maclean (1971).The bones were studied while wet and movable and thendried for later examination. Measurements of the lowerjaw were made from the anterior portion of the dentaryto the posterior portion of the articular bone. X-radio-graphs of whole fish and skeletons were made to definethe structure and placement of the jaw bones.

Results and dlscussion - When the jaws of theOJS fish were closed manually the lower jaw ap-peared shorter than the maxilla. Measurements ofthe maxilla and the lower jaw of normal and OJSfish (10 fish each group) indicated that the lowerjaw of the OJS fish was significantly shorter thanthe normal (P <0.05). The means (:t standard de-viation) were:

Lower jaw (mm) Maxilla (mm)

1891

tion of the lower jaw and a malformation of theafiicular bone in the OJS fish (Fig. 2). The boneappeared to be shortened, increased in height at itsdorsal curvature, and lacking the posterior portion'which includes the articulating surfaces. The lowerjaw overlapped the quadrate, to which it is normallyattached, and is located posterior and dorsal to thispoint (Fig. 3).

Histologically, the dislocation of the articular-quadrate joint was also apparent (Fig. 4 and 5).In the OJS fish the proximal end of the articularbone was embedded in the cephalic portion of theadductor mandibulae muscle. Others of this groupshowed that the muscle may have been simplypushed aside by the articular bone. Extensive fibrousconnective tissue formation in the involved areamay explain the chronic nature and the rigidityof the open mouth. The inflammatory responsewas minimal.

No bacterial or viral pathogens were isolated fromthe fish examined. Gill amoebae, Costia ar'd Hex-amita spp., were found on some of the fish; butthere was no indication of a relationship betweenthese parasites and the open-jaw condition. Noevidence was obtained to suggest that the conditionwas laterally transmitted from fish to fish. Thejaws of the OJS fish could be closed using manualpressure, but when the pressure was released thejaws flexed open to the original position. Thedrugs Prostigmin and Flaxedil had no effect onjaw closure and the jaws would not close when thefish were pithed or anesthetized.

Mortality in the OJS fish was most likely due toprogressive starvation rather than infectious pro-iesr"s ot toxicity. Although some fish having thiscondition were able to feed, as evidenced by foodin the digestive tract, they were not able to taketbod as effectively as the normal fish and thereforeprobably succumbed to the pressures of competition.

No definite conclusion was drawn as to the speci-fic cause of the OJS, howeYer, there are some pos-sibilities to be considered. Certain substancesproduce teratogenic anomalies in man and animals(Ferm 1972; Filippi 1967; and Smithells 1966).Some of these substances include heavy metals,endocrine preparations, cytotoxic agents' anti-biotics, and sulfonamides. DeCew (1972) describeda mandible teratogenicity in the progeny of broodspring chinook salmon treated prior to spawningwith a mixture of procaine penicillin G, dihydro-streptomycin sulfate, and oxytetracycline HCl.None of the OJS brood fish were treated withchemicals except some malachite green prior tospawning.

Another possible explanation of the deformitymight be the interaction of environmental and

NormalOJS

14 .6+0 .712.5) :O.64

1 ,2 .4x0 .6I t . 9+0 .82

The dissections of the jaw showed a congestionof tissue in the area of the jaw articulation. Photo-enlargements of the radiographs revealed a disloca-

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genetic factors on the developing eggs. Waterquality and temperature would be the major envi-ronmental f-actors. The OJS eggs were incubated atl0 C to start and 7 C at hatching. Detailed waterquality data are not available for the incubationperiod in 1971, however, the eggs were treated twiceweekly with a malachite green flush at a concentra-t ion of 1.67 ppm.

The open-jaw syndrome might have been due toa chromosomal aberration transmitted to the off-spring by genetic carriers of the trait.

Acknowledgments -We gratefully acknowledge thehelpful suggestions and cooperation of R. Bigej, EagleCreek National Fish Hatchery, Dr A. Wellander, Uni-versity of Washington, and the staff of the Bacteriologyand Virology sections of the Western Fish Disease Labo-ratory. We are especially grateful to Dr K. Bonham,University of Washington for the X-radiographs.

JOURNAL FISHERIES RESEARCI{ BOARD OF CANADA, VOL. 30, NO. 12, PT. I, 1973

DeCrw, M. G. 1972. Antibiotic toxicity, efficacy andteratogenicity in adult spring chinook salmon (On-corhynchus tshawytscha). J. Fish. Res. Board Can.29 :1513-1517.

FERM, V. H. 1972. The teratogenic effects of metals onmammalian embryos, p. 51-70. InD"H" M. Woollam[ed.] Advances in teratology. Vol. 5. AcademicPress, New York, N.Y.

Fnrerr, B. 1.967. Antibiotics and congenital mal-formations: evolution of the teratogenicity of anti-biotics, p. 239-255. In D. H. M. Woollam [ed.]Advances in teratology. YoL 2. Academic Press,New York, N.Y.

Maclrlu, D. G. 1971, A simplified procedure fordetecting Myxosoma cerebralis (whirling disease)spores in large lots of fish. Progr. Fish-Cult. 33:z v J .

SMTTHELLs, R. W. 1966. Drugs and human malforma-tions, p. 251J74. In D. H. M. Woollam [ed.] Ad-vances in teratology. Vol. 1. Academic Press,New York. N.Y.

Taxonomic Status of Homoiotes palliala Wilson, 1905(Copepoila: Caligidae)

Z. Kaslrl

Fisheries Research Board of CanadaPacific Biological Station, Nanaima, B.C.

Kas^'tA,, Z. 1973, Taxonomic status of Homoiotes palliata Wilson, 1905 (Copepoda:Caligidae). J. Fish. Res. Board Can. 30: 1892-1893.

Type material of Homoiotes palliata was examined and found to consist of a mixture ofthree species of Lepeophtheirus (L. pravipes, L. breviventris, and L. bifidus), all well establishedin the literature. It is suggestedthat H. palliala should be rejected as a taxon in the interest ofnomenclatural stability. An approach to the International Commission on Zoological Nomen-clature is being made, with this action in view.

Kl.r1.rn, Z, 1973. Taxonomic status of Homoiotes palliata Wilson, 1905 (Copepoda:Caligidae). J. Fish. Res, Board Can. 30: 1892-1893.

Nous examinons le matdriel type d'Homoiotes palliata.Il est constitu6 d'un m6lange detrois expdces de Lepeophtheirus (L. pravipes, L. breviventris et L. bifidus), toutes bien dtabliesdans la litt6rature. Nous sugg6rons l'6limination de H. palliata comme taxon, dans l'int6r€tde la stabilit6 de la nomenclature. Nous nous adresserons i cette fin d I'Intemational Com-mission on Zoological Nomenclature.

Received May 31, 1973

IN one of his earliest publications on parasitic locality on an unknown date. The chief interestcopepods of North American fishes, Wilson (1905) concerning the genus was in the fact that it provideddescribed a new caligid genus, Homoiotes, with a link between the two subfamilies of Caligidae,the only species II. palliata. The description was Caliginae, and Euryphorinae (the latter is now re-based on one lot of specimens collected from the cognized as an independent family Euryphoridae)."blue cod," Ophiodon elongatus, at an unknown Conforming in all details to the diagnosis of Cali-

ginae, it was shown by Wilson (1905, Pl. >O(IXprr'nted in canada (J3054) fig.379,379)tohavedorsalplates,developingfrom

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