ZING YANG Kuo

S T U D I E S ON T H E B A S I C F A C T O R S I N A N I M A L FIGHTING: V. I N T E R - S P E C I E S C O E X I S T E N C E I N F I S H *

c / o The SmitAsotrintr Insii iution

ZING YANG Kuo

I n tllis and the following t w o reports, the aim of our study was to discover the main factors which, when not under proper control, mould contribute t o the disturbance of peace among the rnemhers of animals of the sarne species, o r of mixed species living an a communal life. T h r e e classes of vertebrate animals were used, namely, fish, birds, and mammals. T h e experiment< to be described in this paper are mainly concerned wi th environ- mental ant1 dcvclopmcntnl factors affecting the bchavior of fish.

I t will be recalled tha t in the first four reports of this series of investigation on animal fighting, the experi~nents dealt wi th the bchavior of the individual animal (Japancsc grey quail) in its relation wi th another individual, n-hilc in the prcscnt report, ohscroations wcrc made on the bchavior of oric animal in its rclation to a social Kroup ullicll ~ v a s co~nl)osetl of a numlivr of ani~il;~l.; of either the same species, o r a r~ r~ rnbc r of rnixcd specics.

T h e problenis on whicli the experiments reportcd in the follolving pages wcre clcsigncd to investigate may hc stated as fo l lou~s:

1. \.Vhat would be the i tn~ncdiatc and later reactions to each other n-hen a certain number of fish of thc same specics whose past dcveloprnental history is unknown were introduced to live together?

2. TVhxt mould be the immediate and later reactions to each other when a certain nurnbcr of fish of mixed species, developmental history also unknown, were introduced to live together?

3. XYhat and how w o r ~ l d the fo l lo~r ing developmental factors affcct the bchxvior o f an ariirnal n ~ h c n it v a s hrouglit to live togethcr wi th otller individuals of the same species or nlixcd species?

( a ) Living in isolation since hatching or early af ter hatching.

* Accepted for publication by Leonard Carrnichael of the Editorial Board, received in the Editorial Office on J u n e 20, 1960, and given immediate publication as a public service.

IS1

152 JOURNAT, OF GENETIC PSYCIIOLOGY

( b ) Living together witti othcr anitnals of the same species since hatching o r soon af tcr hatching.

( c ) Living togctlicr xvitlr a11i1n:ll o r a n i ~ i ~ : ~ l s of r l i f f c~c~ l t spccics.

( d ) 13eing b ro r~gh t up ant1 trained as fighters. ( e ) Certa in anti-social behavior pnttcrns undcsil-ahlc for a ~>enccful

coexistcncc in an animal society of tlie same specics o r mixed spccics such as aggressiveness o r dominance (namclp pccking ant1 cllasing a n o t l ~ c r fish).

4. C a n such anti-social bcliavior patterns bc eliminatctl? A~itl I1y w h a t means ?

5. H o w would t w o habitual cnc~nics react to cach otlicr \ v l l c ~ ~ they were brought togcthcr into a pcaccful ani~n:tl c o ~ n ~ n r ~ n i t y ?

I n an a t tcmpt t o study the above problems tlic following cxpcriments were carricd out. I t s l i o~~ l t l be riotcd in passi~ig tlint duririg tlie sp:twning season thc beliavior patterns of several specics of fish r~nt lcr invcstig:~tiori change considerably ant1 ret111ir.e n separatc rcport. T h e tlata rcportctl in this papcr a r e rclatcd only to the ltel~avior of tlrc fish ou t of t l ~ c spawning scmon.

T h e purpose of this cxpcri~ncrlt was to invtrstigate l 'roblc~n 1 as statcd abovc wi th reference to fish. 'Thrcc specics of fisl~ wcrc usctl: ( a ) 60 Cliincse fighting fish; (1) 60 Rctl swortl tai ls; ant1 ( r ) 60 Sinincse fighting fish. T h e sizcs of tlic fislrcs a s ~ncasurctl from tip of licad to tail cntl r:tngc from 1%" to 335" in ( c ) ; 255" to 45;;" in ( G ) ; ant1 1?4 to 3>$" i r i ( 0 ) . Tl rc fisl~cs of cach species \l.crc introtlucctl siit~uIt;~nc.or~sly illto a glnss n.:l[c.r t;uik 36" X 12" X 24". T l i c tanks were acratcrl. 'I'he tcmpcraturc was kcpt above 65" F. in thc cold n:catlrcr. 'l'lle fishcs were fed \vitli tlc!rydrated milk-bread sop ground into fine granulc and thoroughly ~ n i s e d xvitli fine multiple vitamin granules. l ' h c bc l l a~~ io r of each fish ton.ard cncl~ other was obscrved immediately af tcr it was rclcasctl into tlic t;~nks. ('1.11~ scxcs of each spccics lvcrc equally divided.) 1,atcr t l ~ c ol)scrv:rtion xras made daily for the first six xvccks and thcn, oncc a ~vcclc t l i rou~lrout tlic yrar.

I t will serve no practical purpctscs to prcscnt t l ~ c stntistic:tl tl:~t:r f r o ~ n thc records of this cxpcrirnent. 'l'llc rcsults coultl I>c very I~ricfly st;~tt.tl t l ~ u s : (a) on the first d:iy tllcre were 12 it~citlcnccs of actual but very brief (one to 5 sccontls only) fighting, 5 of w l ~ i c h occurred it1 tllc t;tlllis con- taining Siamese fish, 2 among thc red sword tailctl fish ant1 5 amorrg tlic Chinese fighting fish. F r o m thc seco~ld d a y on tlit-ougl~out the year not one

Z I N G Y A N G KUO 153

single case of actual fighting was observed although manoeuvres of fighting bctnrcen t w o fish of the same spccies quite frequently occurred. Besides the usual dominance-relationships which havc been extensively stutlicd by othcr investigators among fishcs and otlrcr vertebrates, the life in the tlircc tanks which contained separately the three spccies of fish in this experiment could be described as calm and pcaccful t h rougho l~ t the year. J3omin:lnce took the form of one fish chasing another unti l the runner mas some tlistance f rom the chaser. I n case the victim failed to notice the approaclling ag- gressor, he rcccivctl a "peck" from hi111 hcfore i t started to run. I)ominancc is always one individual over anothcr in any section of the tank both individuals Ilappcnctl to bc. In the rccords of this csperimcnt n-c could not firid a single instance o f dominance o r fighting which could be interpreted as a case of territorial dcfcncc.

Anotlicr important and interesting fact from our obscr\.atiori in this

espcrirncnt is tha t aggression o r domination is almost always encouraged by tlrc non-resistnncc of thc victim of apgression. If tlrc victim mnkcs a stand instcatl of running away, o r mnkcs a counter at tack, the aggrcssor immediately ceascs to chase ant1 ~ v i t h d r a ~ v s f rom it. I n this cxpcrirnent witll thrcc specics of fish m c have recorded 364 incidences of aggressiorl o r dominance. Of tlic 364 incidcnccs, tlicre a r c only 1s instances in ~vlricli the victim of ag- grcssion took a stantl, showing fighting gcsture instead of running awn!-, o r c r c ~ i actually pcckcd back a t tlrc aggrcssor. W e have not observcd a single instancc in which a defensive stand on the par t of the victim of ag- gression o r domination ~ v o u l d result in an actual fighting. I t must be pointed out Ilcrc, liomcvcr, tha t whcn two tmillcd fightcrs meet, a s we shall sce later in this report, a dcfcrlsivc stantl, o r a counter attack is a sure stimulation to initiatc a n actual combat between the two.

?. I his experiment tries to answer I'rvblc111 2 as stated above. S c v r r ~ spccics of fisli, 2 0 racli (half rnalc, half female) were introduced into tlic sanie tank. 'l'hcy wcrc ( 1 ) Cliinesc fighting fish; ( 2 ) Siamcsc fighting fish; ( 3 ) Red Sn.orcl T a i l s ; (4) Angel Fish: ( 5 ) Nco t e t r a ; ( 6 ) Golden fish ; ant1 . .. ( 7 ) l'carl (>or~rnln~. I hc s iws of ( 1 ) , ( 2 ) , a11d (3) n.crc : 1 [~1~ros i lna t~1y

the s:umc as tliosc in E s p e r i ~ n e n t I. T l l c sizcs of ($ ) , ( 5 ) . ( 6 ) . nnrl ( 7 ) lt-cre 2srf to 35/2", 1 to 1 :drr and 2%'' to 4$", and ( 7 ) 245" t o 335 respectively.

'The mrtliods of observation and othcr espcrirncntaI proccdurc were the

same as those in Experiment I.

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185 J O U R N A I . OF GENETIC PSYCFIOLOGY

approaching old inhabitant. I n many cases, "to stand firm" o r "to initiate an attack" was sufficient t o repel the aggressor arid establish almost dominance-rclationship in favor of thc stranger o r newcolncr. I n a few cases, eyen ~ r h c n a counter attack is rnntle by tlie old inhabitant, thc duration of the resulting combat is so brief and tllc battle is almost always cnded in favor of the training newcorner wi th the establishment of a lasting dominance- relationship.

c. P n r t I J I . I n this part of thc experiment an a t tempt was rnadc to find ou t the difference of social behavior in fish bct~vcen fish rnisrtl in isolation and those raised in group life (socialized) (hu t witliout speci;ll training for fighting). A consitlerabl~r large numl~cr of newly hatclicd Chinese and Siamese fighting fish were used in the experiments. Bu t tluc to death, poor health, and incomplete rrcortls, only 20 ~ i i a l r s in r:tch of tlie following

groups will he reported here: G r o u p I , 20 Chincse fighting fish (Ilcrcafter designated as C 1 ) ant1 20 Sizuncse lighting fish (hcrcafter drsign:ltcd as S I ) ; G r o u p 11, 20 Siarnesc fighting fish (S2) ; Group 111, 20 Chinese fighting. fish ( C 2 ) Group IT?, 20 Chinese figl~tinc fish ( C n n ) ; Group V, 20 Chinese fighting fish (Cell,) ; Group V I , 20 Chinesc fighting fish (C:ic).

C , , SI , Cz arid Sz I\-erc socializctl groups. Al l tlie C:, groups w r r e isolatctl ones. Socialization and isolation wcre co~n~nrncc t l soon after h ; ~ t c h i n ~ . CI and S1 were raisctl in tlic same tank. C2 arltl S2 livctl in two separate tanks, each t:ink co~itai~iin:: c.sclusivrly 20 fish of cithcr spccits. Each fish of the C:I groups was kept in a glass jar. I n the soci;~lizrd tanlc fish of both spccies began to chase o r peck each other (dominance o r bullism) when thcy were over

%" in length. Ru t tcsts w r r c not started until they were about two inchcs long. l ' h e tests urerc carried out as follolvs: ( n ) In to the tanlc (hcrcafter desigriatcd as T a n k I ) cont;tining Cl and S1 10 gold fish : ~ n d 10 arlgcl fist1 (both about 2" lorig) were per~ilancntl!r adtlctl. ( b ) Fish I>clongi~ig to Cz , S2, Cg, were introduced into T a n k I. ?'he reaction of tllc fish in the

tarlk lvas ohscrvctl for 3 hours. 'l'llen, thc str;inge fish ~ v ; l s rcmovcd from T a n k I ant1 returned to its own tanlc or glass jar ns the case minht be.

T h i s procedure was repeated for thrce days fo r each fish. ( c ) A l l fish in CRh mere transferred to T a n k I a t the same time instead of irltlividuallj~. T h e y remained in 'I'ank I for thrce days inste;~tl of being returned to their oa:n glass jars evcry day ( fo r threc days) each d;ry after a three hours'

( d ) None of tlie fish in C:<, was cvcr pl;~ccd in 'l'ank I. Instead, fish \vas individu;1ll!: wi th fish in various groups socialized as

\\,ell as isolated. Each pair was observcd for threc hours, then separated.

T h i s was reprated fo r thrce tlnys.

Z I N G YANG KUO 189

T h e condensed results are presented in Tables 2 and 3. T a b l e 2 sutn~naries the tlominance-relationships between the various groups. T h e arrow (+) indicates the direction of domination, which in the case of fish means pecking, attempt a t prcking, o r c l i a s i n ~ hy the do~n inan t fish ~ v l ~ i l e the subrnissivc fish runs :tway f rom the aggressor. T a l ~ l c 3 g.ives the incidences and percrntage of fighting bct~veen indivitluals of the various groups. I t will be noticed: ( n ) that when fighting fish of two different species were raised together in the same tank soon after hatching the trntlrncy of dorninatinn of orie intlividr~nl over ano t l~e r scrnis to cross the sprcics line (sec 'Table 2 tlic columns indicatetl by C1 + S T . C, + S2, Sl -+ Cl and S1+ Cn). 011 the other hand, when fish of tlie two species were raised in scparatc tanI<s, there is only a very Ion. percentage of dominntion which crosses the species line.'

( L ) 'IYli;lt tlic incidcriccs of actual comhat o r fighting betwccn socialized indivitluals a re only slightly more than half of those occurring bctwecn the socializctl and isolated intlividuals, and only 1/12 as many as those oc- curring between isolated individuals. T h i s clearly indicates th:lt the tendency to i~ii t iatc attack o r to make counter attack is very much stronger among thc isolatcd intlividr~als than among the socialized ones. I t rnust be stated here that all isolated animals as 11-ell as trainctl figliters in the previous cxpct.ir~ierlt were later pl:lcetl to live in T a n k I , tlie inter-species tank, resulting in a more o r lcss pcrmancrit cstal~lislimc:nt of domir~ancc-rclatio~~sliip among tliernselves as ~ r r l l as among t l ~ e ~ n ant1 the original inhabitants of the tank. And for five months, not a single instance of fighting was recordcd. ( c ) A n d that fighting took place only bctu,een individuals of the same species. T h e spccies line had nrver bccri crossed in fighting as far as tlie present investigation is concerned.

4. Exper iment IT'

Tliis experi~ncnt deals wi th Problem 4, namely, ways and rneans to cause tlie extinction of the habit of domination of animal over anothcr in an animal community. ' In the case of fish w e employed only one method, namely, selecting much stronger and more aggressive fish to suppress o r subdue those which had already built up a liahit of bullying the weaker ones. W e used thrce species, Siamese fighting fish, Chinese fighting fish, and red sli-ord tails, each spccies consistirig of 40 aggressive fish. Each of thcse 40 aggressive fish was paired by a much strongcr, and much more

1 Exper iments a r e unde r w a y to de termine t he fac tors which make o r break the species b a r r i e r in fish in connection wit11 dominat ion o r fighting. As will he Peen in thc next tvro artic-les in b i rda a n d mammal s , the species l ine ( o r even clags l ine) is often 1,roken no t only in fighting a n d social doinination bu t also in socinble heha\-ionr.

0

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192 J O U R N A L OF GENETIC PSYCIIOI.OGY

fighting fish whose aggressive habit had bcen suppressed by one giant fish of the samc spccics n ~ h i c h \vas almost twice the size of t he suppressed aggressors. T h i s supprcssiori \vent on from S to 10 mont l~s . T h c n , the giant fish was removctl from t l ~ c tank. l ' h c giant fish li\.ctl lvith t l ~ c 10 supprcssed aggressors by rotation. TVhcn the 9 aggressors wcre not living wi th the giant fish, they were kept in isolation. E:ich of the 10 supprcsscd aggressors was tested separately for reappearance of the aggressive habit by placing a weaker and smallcr fisli of its spccies ill the inter-spccics tank. Jn practically every casc it began to bully tlie smaller fish within one hour.

I n this experiment w c wcre concerned wi th the fifth problc~n stated above, namely, w h a t mould the habitual enemies who were brought up to fight whenever they vvcre placcd face to face in a small tank rcact to each other whcn they were put together in a large tank in n ~ h i c h a number of fish of scvcral species wcre living pcaccfully. W e used two g ro i~ps of Cl~inesc fighting fish for this esperinicnt. Group 1 consists of 32 pairs of fish who had fought on a numbcr of occasions, bu t the combat tvas itidccisivc when w e co~nmcnccd to introduce t l ~ c m (onc pair of linbitunl cntrtnics a t a t i~ i ic) into tllc intc:r-spc:cic:s tank. '1'11c:rc w r r c 30 1);lirs o f fisI1 of I~;ll)itr~:rl rnc:mics in G r o u p 2. In this group cacli pair of Ii:~l~itu;tl cncmics was pl:ic.cd in the inter-species tank after their combat had rcacllcd a definite clccisiou. I n both groups, observation ~ v a s made on each pair for two hours. Aftcr two hours, the pair was talcen ou t from the intcr-species tank and put b ;~ck t o thcir original isolation jars. T h i s proccdr~re was repeated for four days. T h e results a r e s11ou.n in ?'able 5.

I t seems notetvortl~y that , of 3 2 pairs of fish n:l~osc p r c v i o ~ ~ s co~r!bats before being i~itroduccd into tllc inter-spccics tank had not rcacllcd a definite decision, 2s pairs (87.5%) stnrtctl to fight in thc intcrsprcics tank. After one to thrcc fig1lts, thc do~lii~~ancc-rrlationsl~ip xvns c?;t:rl~li~hcd in favor of the victors ( 2 6 pairs, o r 81.25%).

T h e r e is not x singlc instance in u-hich the do~nir la~~cc-re la t ionship was established i l l favor of the vanquishers. As almlays was the casc the dorninancc- relationship in ou r study of the fish consisted of chasing o r p c c l i i r ~ ~ the vanquisl:er o r sul?!~!issio~~ by t h c victor or the tlornin;lrlt, and the ruririing away of the fornlcr from the Intter. Such a dominnncc-rcl:ttior1s11ip rcrnailis stable and tlie fighting very rarely, i f cvcr, t:tkel: place for rnanv nlor~t l~c .

I t is of some interest to note also that in this cxpcrilnent, six pairs of fish, from the beginning of introtlnction into tlir inter-spccirs tank, livctl pence-

Z I N G Y A N G K U O

T:IBLE 5 Combat indecisive before introduction

into inter-species tank (Group I )

Dorninance relationchip

Figl~tir~g in estal1li5l1ed inter-species in favor

t a n k of victors No. of p a i r s No. of No. pf

ern ployed l>"rs r~ p n l r s PC

Peaceful Dominance lix-ing rela~ionship \r.itliout in favor of fight o r vanquisher dominance

No., of No. of p a ~ r s PC p a i r s PC

Combat rlrci~ive hrfore introdtlction into inter-species t a n k (Group 11)

No Fighting

Peaceful Figliting Fighting living initiatecl initiated Dominance Dominance xrithont

11). former I>y former Iry f o r m e r hy forrner light or victors vanq~~islier victors vanqr~ishrr dominance

No.of -- pairs No. of No. of No. of No. of No. of

rm~lnyed pair-s I'C pairs I'C pairs P C pairs I'C pair-s PC

fully \v i t l~out c i t l~cr act11:11 figl~ting, or thc CII:IPC-or p rc l i -n r~d- r r~~~-n \vay pl~cnoriicno~l.

W i t h rcfcrcnce to the 30 pairs of prcvious enemirs in Group 2 only four pairs stnrtctl to fight, a11 bcing initiated by thc formcr victor$, ~ rhc rcns in G r o u p 1, 2S pairs had fought in the intcr-specirs tank. On the othcr hand, as to thc tlominancc-relationship ant1 pcaccful living without either fighting o r do~nin:~t ion, the rcsults sccm to be very similar in both groups.

A nurnbcr of cxperinicnts in this report were carricd out to anslvcr several questions rclative to intrrspccies coexistence in fish. T h e f o l l o \ ~ i r i ~ sums up the essential points of our findings:

I . T h e r c a r c certain spccics of fish such as goltl fish and most angel fish, ctc., \vhicli, though living in tlic samc tank are indifferent to each othcr mnd in ~vhic i i the so-c;illcd tlorninance-rclationsllip do not exist. T h e i r relationship with fislics of o t l ~ r r sprcics, even aggressive ones, can aiso be describctl as niutunl indiffcrcncc.

2. 'I'he dotninance relationship rarcl!~ crossc.~ species line. But when t w t ~