Luminous Organs of Fish Which Emit Light Indirectly

YATA HANEDA1

INTRODUCTI9NTHERE ARE MANY REPO~TS of luminousfishes, all of which, in earlier days, were takenfrom the deep seas. Luminous organs werefound on the sides of the bodies, on the bar­bels, or on the antennae. In ourward 'appear­ance these fishes were strangely shaped andfeebl y developed, with soft bones and loosemuscles, and it was assumed that such 'un­usual fishes belonged exclusively to the deep­sea fauna.

The material examined was invariablydead and damaged. It might have been newly.caught, or else had been preserved in forma­lin or in alcohol for an indefinite period.

There seems to be very little record ofobservations on living material , 'and only the ,morphology of the organs of these fishes wasstudied. The organs were never really under­stood, and were mistaken for sensory organs,electric organs, or secondary eyes, or theywere simply referred to as eye-like organs. ,

In the early days bacteriological knowl­edge, especially knowledge of luminous bac­teria was not far advanced, and fish whichbecame luminous after death as a result ofcontamination by saprophytic luminous bac­teria were mistaken for true luminous fishes.

Recent advances in the study of these in­teresting problems of luminosity have shownthat luminous fishes are not confined to thedeep-sea fauna, but may be found among thefauna of the shallow and coastal waters ofthe sea, and that luminosity may be causedby luminous bacteria. Moreover these studieshave revealed that luminous bacteria play animportant role in the production of light in

"Tokyo Jikeikai Medical College, Tokyo, Japan.Manuscript received January 26, 1949.

some fishes by entering certain ducts pos­sessed,by these fishes, and there settling downto a symbiotic existence. \Vithin the ductthey are cultured and utilized as a source oflight, the fish undergoing some modificationsto create an organization within itself to dis­play the light. Such an association berweena fish and luminous bacteria constitutes whatis known' as luminous symbiosis.

Most known luminous fishes are found indeep oceanic waters and have on the surfaceof their heads or bodies, or on their barbels,or on their antennae, curious arrangementsof luminous organs of varied shapes, sizes,and arrangements. For example the lumi­nous sharks have on the side of their bodiessimple, small luminous dots which consist ofgroups of ,lum inous skin organs. The generaStomias, Chauliodus, and Gonostomias also ,possess numerous luminous dots in the under­lying skin in addition to their regular seriesof luminous organs. A Porichtys species hasrows of many small luminous organs whichfollow the direction of the multiple laterallines. A Pseudoscopelus species has numer­ous minute luminous organs arranged in in­definite rows of a characteristic shape. The 'lantern fishes (Myctophidae ) possess fewerluminous organs , but these are pearl-like andare arranged symmetrically in a series on eachside of the fishes. In some species of Lam-

, panyctus, luminous scales may be presentabove or below the tail base. Luminouspatches or ducts occur on the head of Diaphus,or on the body of Lampanyctus species. TheSternoprychidae and Storniatidae are charac­terized by highly developed luminous organsof a more complex structure, consisting ofaluminous body, reflector, lens, and color fil-

[ 214 }

Luminous Organs of Fish-HANEDA

ter , In addition to the serial luminous organson th~ body there may. be luminous organson the jaws and near the eye. The more com­plex postocular organ of the Stomiatidae isfreely movable, and can be rolled inwardwhen not required.

In the families Stomiatidae and Malacos­teidae there is a barbel which, in Diplolycb­nus, is lumin~us at the end. In many othei:species, however, it is not certain whether thisbarbel is luminous or not.

Deep-sea angler fishes have a luminousantenna. Lamprotoxus has a closed loop ofluminous tissue on each side of the body be­tween the head and pelvic region, whilein Eurypharynx and Saccopharynx there is alooped luminous organ which extends alongeach side of the dorsal fin as far as its poste­rior extremity, beginning either just behindthe skull or just in front of the 'anterior ex­tremity of the fin. There is a half-moon­shaped IU:minous organ which is freely mov­able and which can be rolled inside situatedbelow the. eye in Anomalops. Pbotoble­pharon Can shut off the luminous part of theorgan by.Iowering a black membrane whichfunctions like an eyelid. A species of Do li­chopteryx has a luminous organon the ballof the eye in front of the lens. M onocentrisjaponicus has a pair of luminous organs onthe end of the jaws. Some species of thefamil ies Gadidae and Macrouridae possess aluminous organ ventra lly in front of theanus.

All of these mentioned luminous organsare of the.direct emission rype.. That is, theirluminescence is' emitted directly from thesource ( the luminous body). and remains.more or less concentrated or focused at onepoint without much diffusion.

Some luminous fishes show no outwardpeculiarities in structure or appearance andresemble ordinary non-luminous fish. This isbecause the luminous body lies inside the fishand cannot be seen. Before its light can beseen it must first be directed to a reflecting

215

surface within the body. The light is reflectedto pass through a considerable lateroventraltranslucent area of lenticular muscles whereit appears as a diffused bluish glow. This dif­fusion may be compared with the effect whicha frosted or "opal" bulb of an electric lamphas in screening the glare of the incandes- .cent filament and reducing it to a diffusedglow. As far as is known this indirect emis­sion type is confined to Acropoma and theLeiognarhidae. -

These fishes differ ' from other luminousfish in possessing unu sually large luminousareas. In fact they utilize half the muscles oftheir complicated body structure for this pur­pose. Recently Karo (1947) discovered thatApogon marginatus Doderlein, belonging to

the family. Apogonidae, also possesses thissame type of luminous organ.

I .have made a study of luminous fishessince . 1933, and hav~ collected considerablematerial in Japan and in more southerly re­gions. Subsequent to 1937 I worked at thePalao Tropical Biological Station on severaloccasions during which I took the opportu­nity. to visit the Ph ilippine Islands, NorthBorneo, N ew Guinea, Celebes, Java, Suma­tra, and Malay, where I collected many spec­imens 'of living luminous trop ical fishes andobserved their luminosity.

Acknowledgment: I wish to express myhearty thanks to Dr. S. Hatai, former Direc­tor of the Palao Tropical Biological Stationand to Dr. Y. Tokugawa, Tokugawa Biolog­ical Institute; My'thanks are also due to Mr.W. Birtwistle, former Director of the Fish­eries Department of Singapore and FederatedMalay States, who helped me in many waysduring my stay in Singapore. I must expressmy sincere gratitude to Dr. D. .]. PIetsch,Scientific & Technical Division, ESS, GHQ,SCAP, who assisted me in obta ining publica­tion of this paper.

LUMIN ESCEN CE I N Acropoma japonicumMaterial

Acropoma is a genus of fishes of the family

216

Acropomidae found in the Sea of Japan andthe Philippine Sea. Two species are known:Acropoma japonicum Gunther, and Acropo­ma philippinense Gunther. A cropoma phi­lippinense was found near the Philippine Is­lands by the "Challenger" at a depth of 82to .102 fathoms. Acropoma japonicum isknown as "Hotaru-jako" in Japan, and is con­sidered there to be a single species.

I have examined a large number of these"Horaru-jako" in a fresh condition and be­lieve that there are two species (Haneda,1939 ) but in the absence of confirmation ofthis belief by an ichthyologist, I refer to themas Type I and Type II (Figs. 1 and 2). Theyboth occur in the southern Japan Sea as amid-water dweller in a depth ranging fromabout 80 fms. to 200 fms. They are beauti­fully rose colored and attain a-length 200 mm.

If these two types are examined in detailmany differences are found, not only betweentheir external characters, but also betweentheir luminous organs . For example:

Type I is colored pale red dorsally, andwhitish ventrally.

Type II is a beautiful purple-red dorsally,and ventrally is light purplish-red.

Both possess many chrornatophoreson theventral sides but Type II possesses thegreater number.

The scales of Type I are firmly fixed in thebody, while in Type II they are ex­tremely deciduous; for this reason it isvery difficult to obtain in the publicfish markets specimens of Type II withscales attached.

The anus in Type I is situated approxi­mately under the third spiny ray of thedorsal fin, but in Type II it is situatedbelow' the _hindmost edge of the end ofthe dorsal fin.

The anus in Type I is white and in Type IIit is strongly black pigmented.

Type I is furnished with a pair of canineteeth which Type II lacks.

PACIFIC SCIENCE, Vol. IV, July, 1950

Type I occurs in water of about 80 fms.in depth, while Type II occurs in watersmore than 100 frns. deep. They arevery seldom taken together by trawlingvessels.

The greatest difference, however, lies inthe size of the U-shaped internal lumi­nous gland. That of Type I is short ;with the ends directed posteriorly ; whilethat of Type II is much longer, with thefree ends directed anteriorly.

These differences, I suggest, justify thecreation of a second species, but I prefer . tocall the two kinds of fish Type I and Type II.I have examined many specimens of bothtypes, as well as males and females of eachtype. The gonads of Type I are full in Octo­ber and those of Type II from December toFebruary. All ichthyologists have consideredthem to be the same species, A . japonicum,and Type II only a variety of Type I, but inmy opinion each is a distinct species.

During the winter season they are caughtby trawlers in the Gulf of Tosa off ShikokuIsland, Japan, in depths varying from 80 to200 fathoms , and there is no difficulty inobtaining specimens in the Mimase fish mar­ket near the city of Kechi, Shikoku Island.During each of the winters of 1934 to 19;10I obtained many specimens in this fish mar­ket. In Mimase and Urado near Kechi, theyare called Horaru-jako, meaning "the smallfirefly fish," or Kigane-jako , and the fisher­men who catch them during the night areaware of the luminosity in their ventral re­gions, as are most of the ichthyologists , whostate that the luminosity is due to the numer­ous small black points on the ventral sur­face of the body. These they consider areskin organs similar to those of the luminoussharks ,but they do not describe their structure.

It was not until I had dissected many freshspecimens that I discovered the peculiar lu­minous organs established in them and per­ceived that the small black points which had

Luminous Organs of Fish-HANEDA 217

been believed to be small luminous organswere nothing more than chromatophores.

The luminous organs consist of the fol­lowing five components: a U-shaped lumi­nous filiform body; 'an external opening ofthe canal of the ,luminous body; a reflector;a series of lenses; and a means of controllingthe display of luminescence.

Luminous Organ of A. japon icum Type I(Fig. 1)

Luminous Gland-The luminous gland is '

a whitish-yellow U-shaped filiform body, likea U-tube, lying flat and embedded in the mus­cles of the pectoral and ventral regions. Each"limb" of the tube is sealed at its end. Thebend of the tube lies nearer the head thanthe closed ends of the "limbs" or filaments.This bent filament has an outer layer of lon­gitudinally arranged fibers, an inner layer -ofcircularly arranged fibers, and an innermostfolded glandul ar epithelium, which surroundsa hollow duct or cavity. It is pierced on the

a

e'

d'

lens .. ... --- -lens phot, an lens

FIG. 1. Diagrammatic figure of the luminous organ of Acropoma [aponicurn Type I: phot, lum i­nous gland ; lens, lens; refl, reflector ; a', b', c', d', e ', f-transverse sections at a, b,c, d, e, and f.

218

inner faces of the limbs by numerous capil­lary ducts which enter a larger central canallying between the inner faces of the limbsof the U-tube. This canal is bounded dor­sally and ventrally by concave membranesand has only one opening, which is at theanus. The whole luminous gland from aspecimen 145 mm. long measured 14 mm .,and from a fish 110 mm . measured 13 mm .

External Opening-In the gland, bacteriaoccur in the film of material which lies, onthe inner surface of the epithelial cells. Thesebacteria are present in clusters or else areattached to the surface of the gland cells.They pass from there into the duct or cavityof the U-shaped gland via the gland ducts.Here they remain until they pass through oneof the numerous capillaries or pores into thelarger central canal which opens in front ofthe anus. This is the only external openingof this canal. A luminous organ with anopening of this type is known as an opentype of luminous organ.

Reflector-The reflector is a white , opales­cent, ,opaque membrane lying above the lu­minous duct and extending from the isthmusto the end of the caudal peduncle.' It liesrather low ventrally, and separates the lowerventral or keel muscles from the upper lat­eral and dorsal muscles. It passes below thepericardial and perivisceral cavities; underthe latter it is depressed and forced down­ward into a concavity. Elsewhere it lies flat.

Lens Structure-The lower ventral or keelmuscles below this membrane are lenticularand modified to transmit light. They aretranslucent but cloudy. They lie longitudi- '

, naIly and 'in pairs, i.e., one pair on each side.The first pair extends, one on each side, fromthe isthmus to the anus. The second pair lies,one on each side, from the anus to the endof the caudal peduncle. As they lie extendedthey may touch each other in places,''butwhere they are not in contact they are sepa­rated by non-translucent muscle of ordinarystructure. The luminous gland passes through

PACIFIC SCIENCE, Vol. IV, Jul y, 1950

these muscles, and each limb passes back­ward, one on each side, the bend being in theanterior part of the body of the fish, and theclosedends of the limbs being directed back­ward in the direction of the anus; When Imade complete cross sections of fresh fish, Inoticed that where I had cut through thelimbs of the organ, the luminosity was bril­liant; it was only moderate and diffused inthe muscles which were cut. The light wasscreened by the reflecting membrane above,

' but was reflected downward and laterallythrough the skin of the fish. Where I cut across section of a fish without cutting thelimbs of the luminous gland, the muscles surerounding the limbs appeared to be luminous,suggesting that the muscles themselves wereluminescent.

Light Control Mechanism-This luminousorgan has in itself no regulating mechanismfor controlling the display of light. On theother hand, the ventral area and lower lateralarea below the reflecting membrane are fur­nished with a great number of ' chromato­

phores in the surface of the skin. Above themembrane this particular kind of chromato­phore disappears and is replaced by anotherkind. The former are the chromatophoreswhich at one time were considered to be theactual luminous organs,but by their contrac­tion and expansion they probably control theamount of light emit~ed.

Luminous Organs of A. japonicum Type II(Fig. 2)

The luminous gland is situated in the ven­tral muscle and is long compared with thatof Type 1. It extends from the isthmus toabout the 5th ray of the anal fin, where itbends with a short 'loop on each side of thefin. These loops are directed obliquely down­ward, and continue in a reverse direction fora short distance where the bend is continuedto the center. .In this way the two limbs forma kind of hooked loop, such as would be

Luminous Organs of Fish-HANEDA 21c)

b'

lens-,

lens

c' .a:

e

-lens

FIG. 2. Diagrammatic figure of the luminous organ of Acropoma [aponican: Type II: phot, lumi­nous glandjIens, lens; refl, reflector ; a' , b', c', d', e'-transverse sections at a, -b, c, d, and e.

made if the closed end of a hairpin were bentover to form a hook.

The free ends of each limb of this organlie in the isthmus, and the arrangement is acomplete reversal of that found in Type 1.The gland is reddish-yellow when fresh.Structurally it is similar to that described forthe fish of Type I.

The central canal between the inner loopscontinues beyond the anus and opens into

the cloaca through an ,opening which com­pletely encircles it.

The muscles which form the lenses arecomparatively poor as lenses when comparedwith those of the Type I fish, but are similariri other respects and equally translucent. Thechromatophores are extremely numerous inthe veritral region, and there are many moreof them than in the fish of Type 1.

These two types of luminous organs of

220

Acropoma japonicum are peculiar organs ofa new type. The luminous glands are situ­ated in the muscles, and they may be con­sidered as an indirect or reflecting type of lu­minous organ funct ioning by reflected light.

Remarks on the LuminescenceSince the luminous gland is not visible on

the surface of the body, both types of fish;externa lly and in daylight, have the appear­ance of ordinary non-luminous fish.

In the dark , however, e.g., when caughtalive in a net at night, the ventral area isbrilliantly illuminated. The luminosi ty is con­tinuous, never disappearing completely, butmay be dimm ed by means of the chroma­tophores. .

When the fish are recently dead the lumi­nosity persists in both types, but graduallybecomes dim. One or two days after deaththe muscles become opaque and are no longertranslucent, and then the luminosity is ex­tremely dim. If, however, after this period,the luminous glands are removed it will beseen that their luminosi ty persists as brilli­antly .as before and can even be seen indaylight by shading the glands in the cuppedhands.

PACIFIC SCIENCE, Vol. IV, July, 19 50

Remarks on the Substancein the Luminous Glands. To examine the substance in the glands, I

made emulsions of it in distilled water, in0.5, 2, 3, and 4 per cent N aCl solutions, andin sea water. These emu lsions were kept at18°-23° C. and were examined in the dark.

The sea water emulsion was the most lu­minous; next in order were the 3 per centN aCl, the 4 per cent N aCl, the 2 per centN aCl (which was rather weak), and the0.5 per cent N aCl (w hich was extremely ·weak) . The distilled water emulsion was notluminous.

The temperature of the sea water emulsionwas lowered to 0° c., at which temp eratureir' showed only a weak luminescence, but re­covered its strength when warmed to 18 ° to23° c., within which range it was strongest.At temp eratures above 30 ° C. the luminositydiminished until at 45 ° C. it was no longervisible. When cooled it regained its lumi­nescence, but it was lost again below 0° C;however, luminescence was again recoveredwhen the emuls ion was warmed.

T he Luminous BacteriaWhen the emulsion of the gland was ex-

FIG. 3. Acropoma laponicum Gunther Type I. The lum inous organ is not seen externally, so th atthe fish looks like a common non- luminous one, but the lower part of the fish body is a lightning-likeblu ish-white color. .

Luminous Organs of Fish-HANEDA

amined microscopically a large number ofbacteria and some duct cell fragments couldbe seen. In the latter could be seen whatwere apparently bacteria since they stainedwell with Ziehl's solution and were Gramnegative. ' Bacteria which had been takenfrom the luminous gland and cultured inmedia were tested for luminescence in thesame solution as were the emulsions. "

One hundred different strains of the lumi­nous bacteria were obtained by the usual bac­teriological techniques from 100 of each ofthe two different types of Acropoma japoni­cum. The cultures of bacteria taken fromeach of the types of fish showed some differ­ences, On the basis of preliminary tests itappears that they represent two heretoforeunknown species of bacteria which will bediscussed at ' length in a separate paper. Itested the agglutination reactions of repre­sentative strains of these two new kinds ofbacteria, and they showed a strain specificitysimilar to that of other symbiotic luminousbacteria, (Kishitani 1930,1932; Yasaki andHaneda, 1936).

LUMINESCENCE IN THE FAMILY

LEIOGNATHIDAE

Material

The fishes belonging to the family Leiog­nathidae are true shallow-water forms, andare abundant in the southern Sea of Japanand in tropical seas. When I published myaccount of the luminescence of these fishesin 1940 I was not aware that their lumines­cence was already known, and it was only bychance that 1 found, in 1943, a reference tothe work of J. W. Harmes in BiologicalAbstracts in the Raffles Museum Library. Itis an abstract of a paper which appeared in1928 , entitled "Bau und Entwicklung eineseigenartigen Leuchtorganen bei Equula spec."Unfortunately I have not yet been able to

'see the full account of this discovery. How­ever, while working independently ,on lumi-

221

nous organisms of the South Sea Islands atthe Palao Tropical Biological Station, I dis­covered that Gazza minuta and several otherspecies in this family are also luminescentwhen alive. The Leiognathidae living in shal­low waters are not provided with externallyvisible luminous organs and superficially theyresemble ordinary non-luminous fishes. Forthis reason their luminosity was unexpected.

Besides Gazza minuta I 'collected 15 otherspecies of the Leiognathidae. Investigation ofthese species, reveals that they all possess aluminous organ of a type similar to that ofGazza minuta.

Since the luminescence of these fishes ofthe family Leiognathidae was, I thought, un­

,known, 1 published the results of my investi­gations in 1940. I now present the resultsin revised form.

Gazza minuta occurs in clear water inPalao at a depth of about 30 meters andLeiognathus equulus lives in turbid water inthe vicinity of mangrove trees ata depth of1-2 meters. In Palao and Yap , L. equulusranged in length from 60 to 70 rnm.; in Po­nape it was 180 mm. long; and in Sandakan,200 mm. long. In Sandakan, the Chinesefishermen catch these fishes in nets and bringthem every morning for sale in the Sandakanfish market.

In Japan there are three species, L. argen­teum (Japanese name Uchi-Hiiragi) , L. rivu­latum (Oki-Hiiragi) , and L. elongates (Hirne­Hiiragi) .

L. argenteum and L. rivulatum are com­mon on the southern coast of Japan. Theyare extremely abundant in Nagasaki ' wherethey are called Gira-giraor Gira. In Kochithey are called Nirogi. In the bay of Uradonear the city of Kechi many old men maybe seen fishing for Nirogi on any fine autumnday. L. argenteum is caught almost entirelyby hook and line.. This species lives in ratherturbid water along the shores of the riverestuaries, and it is from this fact 'that the

II

222 PACIFIC SCIENCE, Vol. IV, July, 1950

TABLE 1DATA ON COLLECTIONS OF LUMINOUS LEIOGNATHIDAE

SPECIES

Gazza minuta (Bloch)Koban-Hiiragi (Japanese)Kekek, Kekek labu ( Malay)

Secutor insidiator (Bloch)

Secutor ruconius (H am.-Buch.)Ukekuchi-Hiiragi (Japanese )

Leiognathus equulus (Forsk)Seitaka-Hiiragi (Japanese)Kekek gadabang (Malay)

L. fasciatus (Lacep.)

L. lineolatus (Cuvier & Valenciennes)Ito-Hiiragi (Japanese )

L. splendens ( Cuvier)

L. daura ( Cuvier & Valenciennes)

L. bindus ( Cuvier & Valenciennes)L. berbis (Valenciennes)L. dussumieri ( Cuvier & Valenciennes )L. stercorarlus Evermann & Seale

L. elongatus GuntherHime-Hiiragi (Japanese )

L. rivulatum ( Temminck & Schlegel )Uchi-Hiiragi (Japanese )

L. argent eum ( Lacepede )Oki-Hiiragi (Japanese )

PLACE OF COLLECTION

PalaoYapSandakan, B. N . BorneoPonapeSingaporePenang, MalayBatavia

Sandakan, B. N . Borneo

SandakanSingapore, PenangBatavia

Palao, YapTrukPonapeSandakanItoman , OkinawaSingapore, PenangBatavia

PalaoPonapeTrukSand akanSingapore

PalaoPalaoPalao

SandakanSingaporeSandakanSingaporeDavao, PhilippinesSingapore

.SingaporeSingapore

Izu, Japan

Tosa, Japan

Tosa , Japan

DATE OF COLLECTION

June-1937, Feb. 1938August 19 37March 1938March 1940March 1943, Nov. 1944June 1943March 1945

March 1938

March 1938June 194 3March 1945

June, Aug. 19 37; Feb. 19 38March 1940March 1940March 1938March 1938June 1943, Aug. 1944March 1945

June 1937, Feb. 19 38March 1940March 1940March 19 38Sept. 1943

Oct. 1937March 1940Oct. 1943

March 1938Sept. 194 3March 1938Oct. 1944Aug. 1939Nov. 1943Oct. 1944Nov. 1944 -

Oct. 1938

Oct. 1939

Oct. 1939

species derives its name of Uchi Nirogi-in­shore nirogi. It is always present in the streetmarkets. L. rivulatum occurs in the oft-shorewaters, and is taken only in. nets. It is plenti­ful in the Mimase fish market near the cityof Kochi. Both species are usually .dried for

sale, and are very good to eat.L. elongatus is not common. It is also an

oft-shore species. I obtained my specimensoft Suzukawa-Shizuoka Prefecture.

From the Itoman market, Ryukyu Islands,I obtained two specimens of L. equttlus and

Luminous Organs of Fish-HANEDA 223

the swim bladder forms a parabola, and thata bean-shaped .light spot (one part of theluminous ring gland) is at its focus. We

FIG. 4. a, Diagrammatic figure of the luminousorgan of Gazza minuta (Bloch ). b, Longitudinalsection of the .luminous gland of Gazza minuta.(Bloch): phot, luminous gland; refl, reflector;lens, lens ; vise, internal organ; vesi, swim bladder;chr, chromatophore; memb, membrane; op, open­ing of luminous gland; oeso, oesophagus;. lary,larynx; vent, stomach.

a

b

-+ vent

ono:---~--,..:;.,

~~.l.-_---'-!I

~"~",.,

refl

lary~

Gazza minuta. Both specimens were the sameas those found in tropical seas..

In 1943-1944 I collected in Singapore thespecies as listed in the accompanying table.

Around Singapore and the Malay Penin­sula these kinds of fishes are easily obtainedin all seasons from the fishing trap known asthe Kelong. Fowler (1938) reported 12 spe­ciesof this family in Malaya.

The Luminous Organ

Gazza -minuta: Externally this fish doesnot present any unusual features , and it wasonly by a careful observation of the livingfish by night that the bluish-white lumines­cence of the lower half of the body wasrevealed.

The source of the luminescence is a swol­len ring of gland-like substance which en­circles the oesophagus. It is covered with awhite membrane except at two points, onelocated dorsally and the other ventrally. Theseappear as two small bean-shaped areas of ayellowish-white color. The ring contains agland which has two openings (Fig. 4, op)which lead into the oesophagus. .

The swim bladder arid the thoracic andventral muscles are so modified as to increasethe efficiency of the light-producing rnech­anism. The swim bladder is lined with aremarkably bright silvery reflecting surfaceand the muscles of the thorax and the ven­tral parts of the body are translucent butsomewhat cloudy. The swim bladder has noreflecting surface at its posterior end, whichis translucent. Part of the dorsal silver liningis . continued under the spinal column andacts as a reflector for the light which is trans­mitted backward through the translucent endof the bladder. Light is emitted from thetwO bean-shaped areas only, the dorsal oneilluminating the swim bladder, the ventralone the thoracic and ventral muscles.

If the diagram of the longitudinal sectionof the fish through the swim bladder is stud­ied, it will be seen that the anterior end of

224

have, in fact, a remarkably efficient para­belie .reflector which reflects the emitted lightbackward even as far as the muscles of thecaudal peduncle.

The ventral light spot directs .its lightdownward, and, because of the cloudy trans­lucent muscles of the thorax and abdomen,a diffused luminescence is seen in this area.Because of the presence of a white opaquemembrane extending dorsally from the up­per borders of the abdominal muscles of bothsides, no light reaches the dorsal part of thebody.

The bean-shaped areas are furnished withchromatophores, and it is perhaps due totheir expansion that the light can be shutoff, and by their contraction displayed. Pos­sibly the white membrane which covers thering can be ' contracted to cover the lightspots, but this .Lwas unable to confirm. Nor­mally it is expanded to uncover them .

The complete luminous organ thereforeconsists of three ' components, possibly four:( 1) the luminous 'ring gland; (2) the re­flector; and ( 3) the lenses; with possibly(4 ) , a shutter for the light spots which maybe opened or closed either by the chroma­tophores or by the white covering membraneof the ring working independently or simul­taneously with the chrornatophores. In re­cently dead specimens these spots are closedby the membrane, but the gland materi al isstill luminous.

As previously stated this fish differs fromother luminous fish by its unusually largeluminous area, utilizing in fact half the mus­cles of its extremely complicated body struc­ture. The luminous glands are situated inthe body, and may be considered to be of anindirect or reflecting type, functioning by re­flected light in the same way as describedfor A cropoma japonicum; but Gazz« minutais not only provided with a membrane andchrornatophores for displaying its lumines­cence, it pas a far more complex luminousorgan than A cropoma japonicum.

PACIFIC SCIENCE , Vol. IV, July, 1950

lenslvise

FIG . 5. Diagrammatic figure of the luminousorgan of Secutor insidiator: phot, lum inous gland;refh, refls, reflectors ; lens., lenss, lenses; vise, inter­nal organs.

Secutor spp.: Secutor insidiator ( Fig: 5)and S. ruconius are luminous Leiognathidae,similar to Gazza minuta, but possessing a rel­atively larger luminous gland than does G.minuta. It is yellow in fresh material insteadof white as in G. minuta.

The reflector is very efficiently arrangedand is lined with a bright glossy surface.

The ventral muscles are cloudy and trans­lucent . The ventral cavity walls are 'ex­tremely thin and, because of this, its lumi­nosity is greater than that of any of the othermembers of the family Leiognathidae.

Leiognatbus spp. : There are many speciesof Leiognatbus, varying in length from 50mm. to 200 mm . With the exception of themale L. rivulatum they have comparativelysmall luminous glands . Even when com­pared with Gazza and Secutor, this hasa com­paratively small luminous body and thickventral cavity walls, which are only moder­ately translucent, thus diminishing the bright-ness of the luminosity . '

The species L. equulus, L. fasciatus, L.splendens, L. lin eolatus, L. bindes, L. berbis,L. argenteum, L. dussumieri, L. stercorarius,and L. daura are also only moderately lumi­nous. There is an interesting feature of theJapanese species, L. rivulatum, viz.: the lumi­nous gland of the male is either very largeor else very small. l am ,of the opinion, "though by no means certain, that this differ-

Luminous Organs of Fish-HANEDA

ence in size is due to age. .The luminousgland of the female is smaller and the lumi­nosity of the female is therefore very weakcompared .with that of the male.

The luminous gland of L. rivulatum dif­fers from that of all other Leiognath idae in

225

that it does not surround the oesophagus. comp letely, but occurs as an externa l swell­. ing on the dorsal part only.

L. elongates also possesses a very smallluminous gland with a poor reflector; in con­sequence its luminosity is feeble:

FIG. 6. a, Leiognathus equulus ( Forsk. ) ; b, Secutor insidiator ( Bloch); c, Gazza minuta ( Bloch).The luminous organs are not .seen externally, so that the fish look like common non-luminous fishes, butthe lower half of these fish bodies, namely, the parts .below the black lines, are a lightning-like bluish­white color.

226

R emarks on the Lumin escence

A specimen of Gazza minuta and one ofSecutor insidiator were put into a tank ofsea water in a dark room and their lumines­cence was studied. No luminescence couldbe seen when the fish were viewed dorsally,but if they were viewed laterally a diffusebluish-white luminosity could be seen. If thearea where the transparent scales are ar­ranged was examined directly or obliquelyfrom below, a faint bluish light was seen,emanating from the chest, thorax, abdomen,and tail areas. The light showed uninter­ruptedly in these areas. It did not shine bril-liantly, but was feeble and diffused. .

If the fish received a strong stimulus orwas removed from the water, the lower partof the body lighted up brilliantly, moststrongly in the thoracic and abdominal re­gions. Thi s sudden increase in brilliancy wasaccompanied by a croaking sound, the pro­duction of which is . a peculiarity of theleiognathidae.

If during this .brief period of maximumbrilliancy the fish was enveloped in a cello­phane wrapper and was laid on a photo­graphic film, it would produce a brightimage.

After death the luminous gland was sur­rounded by the membrane and the light wasno longer visible, but if the fish was dissectedand the membrane covering the gland wasremoved, this membrane was found to beluminous and, when kept in an ice box at5-10 0 C , it remained so for 2 days.

Contents of the Luminous Gland

When the substance of the luminous glandis freshly made up as a 3 per cent salt ernul­sion, the whole of the emuls ion will be lumi­nescent , but if it is allowed to stand , onlythe upper layer exposed to the atmospherewill glow while the deeper lower layer be­comes non-luminous. When shaken up inair the whole emulsion becomes luminousagam.

PACIFIC SCIENCE, Vol. IV, July, 1950

Luminescence is greatest at a temperatureof 26 0-30 0 C in the tropics (in Japan atabout 20 0 C ) and becomes feeble at 4 0 CWhen the temperature is raised, it increasesand finally disappears at 450 C , but afteronce attaining this latter temp erature it failsto recover its 'luminosity even when cooledagain .. An ernulsiop in nearly 3 per centN aCl gives the best results; an emulsion indistilled water produces no light. If such adistilled-water emuls ion is centrifuged theupper clear solution is non-luminous but thesediment is luminous. Microscopically thisemulsion is made up of disintegrated parti­cles of gland cells with innumerable bacteria,and it appears from the results of these ex­periments that the contents of the luminousgland consist of luminous bacteria. In orderto test th is, isolation experiments were car­ried out to cultivate them in a 3 per centN aCl agar-agar culture med ium.

Culture of the Luminous Bacteria. A pure culture of the luminous bacteria

from the luminous glands was prepared bythe usual bacteriological techniques. After.8- 10 hours a small , round, transparent andluminous colony appeared. From this starta pure culture which was free from any con­tamin ating bacteria was obtained.

It was clearly demonstrated that the samekind of fishes always had the same kind ofluminous bacteria and that the Leiognathidaeof the tropical sea and those of Japan pos­sessed luminous bacteria of the same group,with only slight variations probably due to

the effects of temp erature. There is a curiousfeature, viz., the bacteria in culture are notas brilliant as are those in the gland, prob­ably because of the unsuitability of the me­dium for greatest luminosity. The details of .the bacteriological work will be presentedelsewhere.

SlJ M M ARY

Some luminous fishes show no outwardpeculiarities in structure or appearance and

Luminous Organs of Fish-HANEDA

resemble ordinary non-luminous fish. This isbecause the luminous body lies inside thefish and cannot be seen from outside.

These fishes differ from other luminousfishes by their unusually large luminous areas,which utilize as much as one half or one thirdof the ,muscles of the extremely complicatedbody structure of the fish.

The luminous fishes hitherto known areprovided with a direct radiating luminousorgan, while the fishes described in this paperpossess an indirect radiating luminous organ. ,These organs of indirect emission are peculiarorgans of a novel type, which appear to beconfined to Acropoma species, the Leiogna­thidae, and Apogon marginatus Doderlein.

REFERENCES

FOWLER, H. W. 1938. A list of the fishesknown from Malaya. Fisheries Bul. [Sin­gapore] 1.

, HANEDA, Y. 1938. Ueber den Leuchtfisch,Malacocephalus laevis (Lowe). Jap. Jour.Med.:Sci. III [Biophysics], 5 (3) : 355-366.

.~,.

--- 1939. New type of luminous organof the fishes. Reiko [Cold Light] I series:48- 55. [In Japanese.]

22 7

1940. On the luminescence of thefishes belonging to the family Leiognathi­dae of the Tropical Pacific. Palao TropicalBiological Station Studies 2 (1): 29-39.

, HARMES, J.W. 1928. Bau und Entwicklungeines eigenarcigen Leuchtorganen bei Equ­ula spec. Zeitscbr. f. wiss. Zo ol. 131: 157­179 [fide Bioi. Abs.].

KATO, K. 19'47. On a new type of luminousorgan in fishes. Zool. Mag. [DobutsugakuZasshi] 57 (12): 195-198. [In Japanese.]

KISHITANI, T. 1930. Stiidien iiber die Leucht­symbiose in Physiculus japonicus Hilgen­dorf, mit der Beilage der zwei neuen Artender Leuchtbakterien. Tohoku Imp. iJniv. ,Sci. Rep. IV [Biol.], 5 (4 ): 801-823.

--- 1932. Stiidien tiber leuchtsymbiosevon Japanischen Sepien [Okajima's] FoliaAnatomica Japonica 10 (3): 317-413.

WEBER, M., andL. F. DE BEAUFORT. 1931.The fishes of the Indo-Australian Archi­pelago. Vol. 6. 448 pp., 81 figs. E. J: Brill ,ltd., Leiden. .

YASAKI, Y ., and Y. HANEDA. 19?6. Uebereinen neuen Typus von leuchtorgan imFische. Imp. A cad. Japan [Tokyo], Proc.12 (2) : 55-57.