5 p. : ill. ; 24 cm.Includes bibliographical references

Gudger, E. W. (Eugene Willis), 1866-1956.

Nichols, John T. (John Treadwell), 1883-1958.

American Museum of Natural History Scientific Publications

AMERICAN MUSEUM NOVITATESPublished byNumber 613 THE AMERIcANMusEum oF NATURAL HISTORY May 8, 1933New York City59.7, 58 B:12.93A ROUND-HEADED SILVER PERCH, BAIRDIELLACHRYSURA; WITH NOTES ON THE EARLIESTFIGURED ROUND-HEADED FISHBY E. W. GUDGERThere is in the collections of the American Museum a young round-headed specimen of Bairdiella chrysura without any data as to its source.My attention was called to it by my colleague, Mr. J. T. Nichols, whoidentified and catalogued it. Since I have in recent years described anumber of pug-headed fishes, and since this is a very closely allieddeformity, I will now briefly describe this specimen also. To this accountwill be added the figure of and a brief note on the earliest recorded caseof this deformity in fishes.A.M.N.H. NoW51fFig. 1. Lateral view of the little round-headed Bairdiella chrysura in the collec-tions of the American Museum. The figure shows the fish in natural size 67 mm.over all.Our specimen of Bairdiella chrysura has been in strong alcohol foryears, is somewhat contracted and distorted in the abdominal parts, andis as hard as leather. However, the head has been little affected by this.Figure 1, drawn life size, shows the shrunken abdomen and the frayedfins. The head-parts have been drawn with great care and the figureshows them exactly as I see them in the specimen before me. Forcomparison's sake a normal young specimen of the silver perch of aboutthe same stage of development as the deformed fish has also been drawn(Fig. 2 herein).Now the body of the fish in Fig. 1 is little changed in length be-tween any fixed points, excluding the snout. So taking as a standardAMERICAN MUSEUM NOVITATESlength the distance between the hinder point of the operculum and theend of the tail (the beginning of the caudal fin), the drawing reproducedin Fig. 2 has been reduced to the same length (38 mm.), between thesame points, the head and tail being reduced in the same degree. Sincethe little fish in Fig. 2 is normal in every way, we can use its head as astandard of comparison for that of the teratological fish and can readilysee how much deformation this has undergone.This abnormal fish, measured from the anterior point of the roundedhead to the dorsal tip of the frayed caudal fin, is 67 mm. long. The un-broken tail as shown in the dotted line would have added about 3 mm.more, making the "over-all" length as it is drawn about 70 mm. How-ever, had the snout been normal it would have added probably not morethan 5 mm. to the total length. The over-all length of this specimen, ifnormal, would probably be about 75 mm. The depth in the shoulderFig. 2. Lateral aspect of a normal silver perch of about the same stage of de-velopment as the fish shown in Fig. 1. For comparison of head-parts, this drawing isreduced to the same length (operculum to base of caudal-38 mm.) as Fig. 1 betweenthe same points. The head and the caudal fin are of course reduced proportionally;After Hildebrand and Schroeder, 1928.region is 18 mm., and this is probably fairly close to the normal depthin this deforrned fish.In pug-headed fishes the whole anterior part of the head includingthe upper jaw is shortened and the forehead of the fish falls abruptly offinto the floor of the mouth, but the lower jaw remains intact-projectingin front like an old-fashioned Ames-made shovel. That this may beclear to the reader, a figure of a pug-headed brown trout (Salmo fario) isreproduced from a previous paper of mine. This fish, seen in lateral viewin Fig. 3, should be compared with those shown in Figs. 1 and 2.Figures 3 and 2 then emphasize very strongly what has taken placein the little silver perch. Not only has the anterior part of the head2 [No. 6131933] A ROUND-HEADED BAIRDIELLA CHRYSURAfailed to develop, but the lower jaw has likewise failed in exactly thesame degree. The lower jaw is slightly longer than the upper-a merefraction of a millimeter-but so it is in the normal young fish shown inFig. 2, and also in the adult fish. In brief, the shortening of the headhas taken place equally in both jaws, producing that deformity in fishesknown as round-headedness.Along with the shortening of the snout has come a marked humpingup in the region over the eye and over the operculum. The shorteningof the snout has brought the steep forehead close to the eye and hasapparently reduced the nasal openings to one. Compare here the normalfish with the deformed one.As to the causes of this deformity, one cannot speak with too muchconfidence. In the round-head as in the pug-head, it is clear that theFig. 3. A pug-headed brown trout (Salmo fario) drawn to show the steep fore-head and the fully developed projecting lower jaw.After Gudger, 1929.basal bone of the skull, the parasphenoid, has failed to develop and theanterior part of the skull has failed to elongate. As a result of thisdevelopmental failure all the bones forming the anterior part of the skullhave become tied down in front giving the snub-nosed appearance seenin Fig. 1.In some pug-heads the parasphenoid buckles up into the spacebetween the eyes causing these to bulge noticeably. This I found in apug-headed sea-bass (Roccus lineatus) which I described some years ago.No exophthalmia is found in the silver perch under consideration.For the shortening of the lower jaw, I have no particular explanationto offer. It has simply failed to develop along with the other parts ofthe head. However, for the whole head it may be said that it has re-mained in the embryonic condition. This explanation is offered because3AMERICAN MUSEUM NOVITATESit is well known that all embryonic fishes are round-headed. Hilde-brand and Schroeder's figure (not reproduced herein) of an 11-mm. speci-men of Bairdiella chrysura shows this very distinctly. The body andhinder two-thirds of the head of the teratological little silver perchdeveloped, but the anterior part of its head never did-it remained inthe embryonic condition. As to the cause of this retarded development,one can only conjecture that it was due to a failure in the hormonicbalance. It is known that such achondroplastic disturbances (possiblya failure of the pituitary) in dogs bring about pug-headedness. Pre-sumably the same thing holds for fishes.Since this is presumably the latest round-head fish on record(March, 1933), it may be of interest to reproduce the earliest knownfigure of such a deformity and briefly to describe it.This oldest account is found in Conrad Gesner's 'Liber IIIF'Fig. 4. Gesner's round-headed carp, the earliest published figure, in which theartist's imagination had free play.After Conrad Gesner, 1558.('De Piscium & Aquatilium Animantium Natura') of his encyclopedic'Historia Animalium' (Tiguri, 1558). Gesner had seen Rondelet'sfigure of a pug-headed carp (1555-the first figure of such a fish everpublished) and had data for four carp with abnormal heads; he haddrawings of two of these fish, and had two specimens of these deformedfish, or their dried skins, which had been sent to him. Whether his speci-mens were pug-heads or round-heads cannot be said from his text. Buthis figure (No. 4 herein) would indicate that it was drawn from a round-headed specimen. Rondelet's figure is a well-drawn and scientificallyvaluable representation of a pug-headed carp. Gesner's drawing-in themaking of which his artist took great liberties-is of interest from ahistorical and antiquarian standpoint only. It is apparently the firstdrawing ever attempted of a round-headed fish.[No. 613419331 A ROUND-HEADED BAIRDIELLA CHRYSURA 5Few other round-headed fish have been figured and described. Sofar as known to me, these comprise: one other carp, a bream, a mullet,and three gadoids. I have photographs of such a round-headed codfishand of a pollack which I hope later to publish with descriptions. Appar-ently this deformity is more often found in the Gadidae than in fishesof any other family.

Round-headed Bairdiella chrysura

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