Cairnsichthys bitaeniatus Allen, Hammer & Raadik, 2018

Hammer, Michael P., Allen, Gerald R., Martin, Keith C., Adams, Mark, Ebner, Brendan C., Raadik, Tarmo A. & Unmack, Peter J., 2018, Revision of the Australian Wet Tropics endemic rainbowfish genus Cairnsichthys (Atheriniformes: Melanotaeniidae), with description of a new species, Zootaxa 4413 (2), pp. 271-294 : 279-287

Cairnsichthys bitaeniatus Allen, Hammer & Raadik , sp. nov.

DAIntREE RAInbOwfISH

(fIgS 4–8; tAbLES 2–4)

Cairnsichthys rhombosomoides (non Nichols & Raven, 1928)— Martin & Barclay (2013) (in part): 156.

Holotype: QM I.39335, mALE, 65.6 mm SL, LIttLE COOPER CREEk (16° 10.20'S, 145° 24.84'E), nORtH QuEEnSLAnD, AuStRALIA, 1 m, DIP nEt & tORcH, K. MARtIn, S. BARcLAY & M. HAmmER, 24 JuLY 2015.

Paratypes: AMS I.46950-001, mALE, 56.0 mm SL, cOLLEctED wItH HOLOtYPE; NTM S.17816-001, 7 SPEcImEnS, 35.3–55.3 mm SL, LIttLE COOPER CREEk (16° 10.18'S, 145° 24.81'E), QuEEnSLAnD, 1 m, nEt, K. MARtIn & S. BARcLAY, 10 MAY 2012; NTM S.17821-001, 39.2 mm SL, HutcHInSOn CREEk (16° 12.98'S, 145° 24.90'E), QuEEnSLAnD, 4 m, nEt, K. MARtIn & S. BARcLAY, 10 MAY 2012; NTM S.17932-001, mALE, 63.6 mm SL, cOLLEctED wItH HOLOtYPE; QM I.39336, mALE (SmALLER) & fEmALE, 48.3–50.8 mm SL, cOLLEctED wItH HOLOtYPE; WAM P.34436-001, twO mALES AnD A fEmALE (LARgESt fISH), 38.8–49.7 mm SL, cOLLEctED wItH HOLOtYPE.

Other material examined: DAtA IncLuDED In DEScRIPtIOn. NTM S.17778-001, 9 SPEcImEnS, 34.8–46.3 mm SL, LIttLE COOPER CREEk (16° 10.18'S, 145° 24.81'E), QuEEnSLAnD, 1 m, nEt, K. MARtIn & S. BARcLAY, 10 MAY 2012.

Diagnosis: A SPEcIES Of Cairnsichthys DIStInguISHED bY tHE fOLLOwIng cOmbInAtIOn Of cHARActERS: DORSAL RAYS V–VII, 12–15 (IncLuDIng SLEnDER, fLExIbLE SPInE); tOtAL AnAL RAYS 19–23 (IncLuDIng SLEnDER, fLExIbLE SPInE); PEctORAL RAYS 11–13 (uSuALLY 12); LAtERAL ScALES 38–40 (mODE 39) IncLuDIng 3.5–5 (uSuALLY 4) fROm EnD Of ADPRESSED PEctORAL fIn tO vERtIcAL fROm wItH DORSAL fIn ORIgIn; PREDORSAL ScALES 18–22 (uSuALLY 19–21); cHEEk ScALES 6–9; tOtAL gILL RAkERS On fIRSt ARcH 11–16 (uSuALLY 12–13); vERtEbRAE 37–40 (mODE 39); bODY RELAtIvELY SLEnDER (ESPEcIALLY <45 mm SL), gREAtESt DEPtH 3.8–5.3 (mEAn 4.5) In SL AnD nARROw, gREAtESt wIDtH 2.1–2.8 (mEAn 2.4) In HL; SEcOnD DORSAL fIn bASE RELAtIvELY SHORt 4.5–5.6 (mEAn 5.1) In SL; cOLOuR In LIfE bROwn tO bLuISH gREY On DORSAL HALf, bLuISH wHItE On vEntRAL HALf wItH ExtEnSIvE ZOnE Of PALE YELLOw ImmEDIAtELY bEHInD PEctORAL fIn bASE; nARROw bLAckISH (bLAck wItH SHADES Of bLuE OR bROwn) mIDLAtERAL StRIPE fROm uPPER PEctORAL fIn bASE tO bASE Of cAuDAL fIn, ALSO A SEcOnD, OftEn mORE DIffuSE, bLAckISH StRIPE uSuALLY PRESEnt On LOwER SIDE, ExtEnDIng POStERIORLY tO bASE Of POStERIOR AnAL fIn; SHORt, PROmInEnt bLAck StRIPE AcROSS uPPER OPERcuLum, ItS wIDtH nEARLY EquAL tO PuPIL DIAmEtER, wItH YELLOw AREA ImmEDIAtELY bELOw AnD SOmEtImES ImmEDIAtELY AbOvE; PROmInEnt bLAckISH SPOt On bASE Of PEctORAL fIn AnD ALSO InvADIng AxIL Of fIn; ADuLt mALE fREquEntLY (ESPEcIALLY In nuPtIAL PHASE) wItH YELLOwISH SubmARgInAL StRIPE On SEcOnD DORSAL fIn, YELLOwISH mARgInAL tHIck StRIPE On AnAL fIn, AnD YELLOw cAuDAL fIn, fEmALE fIn cOLOuR PALE wItH A wHItISH AREA On tHE cAuDAL fIn nEAR tHE bASE; mALES tYPIcALLY DEEPER bODIED tHAn fEmALES ESPEcIALLY> 45 mm SL.

Description: bASED On 25 SPEcImEnS, 34.7–65.6 mm SL; cOuntS AnD mEASuREmEntS tHAt APPEAR In PAREntHESES REfER tO tHE RAngE fOR PARAtYPES AnD OtHER mAtERIAL wHERE DIffEREnt fROm tHE HOLOtYPE. DORSAL RAYS VII + 13 (V–VII + 12–15); tOtAL AnAL RAYS 21 (19–23); PEctORAL RAYS 12 (11–13); PELvIc RAYS I,5; bRAncHED cAuDAL RAYS 15; PROcuRREnt cAuDAL RAYS 8 + 9 (7–9 + 8–10); LAtERAL ScALES 39 (38–40); tRAnSvERSE ScALES 11; PREDORSAL ScALES 19 (18–22); PREPELvIc ScALES 16 (14–16); cHEEk ScALES 7 (6–9); cIRcumPEDuncuLAR ScALES 12; gILL RAkERS On fIRSt bRAncHIAL ARcH 2 + 9 (0–4 + 9–13), tOtAL gILL RAkERS On fIRSt ARcH 11 (11–16); tOtAL vERtEbRAE 38 (37–40). FuLL mERIStIc cOuntS ARE SHOwn In TAbLE 3.

First dorsal fin spines (D1) Scales end pectoral fin to dorsal origin (-)

Species 2 2.5 3 3.5 4 4.5 5 Avg. Med. n Species 10 11 12 13 14 15 16 Avg. Med. n C. bitaeniatus sp. nov. 3* 8 7 2 1 1 12.7 13 22 C. rhombosomoides 5 14 16 6 0 1 11.6 12 42 Total vertebrae (Vert)

Species 36 37 38 39 40 Avg. Med. n C. bitaeniatus sp. nov. 1 6* 16 2 38.8 39 25 C. rhombosomoides 4 26 9 * 1 37.2 37 40 HEAD LEngtH 3.8 (3.7–4.2) In SL; bODY DEPtH 3.8 (3.8–5.3) In SL; gREAtESt wIDtH Of bODY 2.3 (2.1–2.8) In HL; SnOut LEngtH 3.1 (2.9–3.6) In HL; EYE DIAmEtER 3.2 (2.5–3.2) In HL; bOnY IntERORbItAL wIDtH 2.5 (2.3–2.8) In HL; DEPtH Of cAuDAL PEDuncLE 2.8 (2.2–2.9) In HL; LEngtH Of cAuDAL PEDuncLE 1.7 (1.4–1.8) In HL.

JAwS AbOut EquAL, ObLIquE, PREmAxILLA wItH An AbRuPt bEnD bEtwEEn tHE AntERIOR HORIZOntAL PORtIOn AnD LAtERAL PARt; mAxILLA EnDS ALmOSt bELOw AntERIOR EDgE Of PuPIL; mAxILLARY LEngtH 2.4 (2.2–2.5) In HL; LIPS tHIn; tEEtH vILLIfORm tO nARROwLY cOnIcAL wItH SLIgHtLY cuRvED tIPS, ExtEnDIng On tO OutER SuRfAcE Of LIPS; tEEtH Of uPPER jAw In AbOut 4–5 IRREguLAR ROwS AntERIORLY, REDucED tO 2–3 ROwS POStERIORLY wHERE cLEARLY ExPOSED wHEn mOutH cLOSED; tEEtH In LOwER jAw In AbOut 3–4 IRREguLAR ROwS AntERIORLY, REDucED tO A SIngLE ROw POStERIORLY.

ScALES Of bODY cYcLOID, RELAtIvELY LARgE, AnD ARRAngED In REguLAR HORIZOntAL ROwS; bEgInnIng wItH AbOut 9tH– 11tH ScALE, REmAInIng ScALES Of mIDLAtERAL ROw wItH SmALL ROunDED tO vERtIcALLY ELOngAtE, SHALLOw PIt At cEntRE; ROw Of SmALL, tRuncAtED ScALES ALOng bASE Of DORSAL AnD AnAL fInS; nO ScALES On mEmbRAnOuS PORtIOnS Of fInS ExcEPt SEvERAL ROwS Of SmALL ScALES bASALLY On cAuDAL fIn AnD mODERAtE-SIZED ScALE mEDIALLY At bASE Of PELvIc fInS; ScALE mARgInS SmOOtH wItHOut cREnuLAtIOnS; PREDORSAL ScALES ExtEnDIng fORwARD tO AbOut REAR EDgE Of IntERORbItAL SPAcE; PREOPERcLE (cHEEk) cOvERED wItH 7 (6–9) ScALES; mAIn bODY Of OPERcuLum cOvERED wItH AbOut 8 (7–13) ScALES wItH ADDItIOnAL SmALL ScALES On IntEROPERcLE AnD SubOPERcLE.

PREDORSAL DIStAncE 2.0 (1.8–2.2) In SL; PREAnAL DIStAncE 1.9 (1.8–2.0) In SL; PREPELvIc DIStAncE 2.6 (2.5–2.7) In SL; LEngtH Of SEcOnD DORSAL fIn bASE 5.3 (4.5–5.6) In SL; LEngtH Of AnAL fIn bASE 2.9 (2.8–3.3) In SL.

FIRSt DORSAL fIn ORIgIn AbOut LEvEL wItH OR SLIgHtLY bEHInD AnAL fIn ORIgIn; LOngESt SPInE (uSuALLY tHIRD) Of fIRSt DORSAL fIn 2.9 (2.3–3.4) In HL, ItS ADPRESSED tIP juSt REAcHIng tO ORIgIn Of SEcOnD DORSAL fIn; LOngESt (gEnERALLY AbOut 5tH) RAY Of SEcOnD DORSAL fIn 2.5 (1.9–2.9) In HL, ADPRESSED POStERIOR RAYS ExtEnDIng AbOut OnE-HALf LEngtH Of cAuDAL PEDuncLE In mALE SPEcImEnS tO AbOut OnE-tHIRD LEngtH In fEmALES AnD juvEnILES; LOngESt (AbOut 8tH) AnAL RAY 2.4 (1.8–2.4) In HL; PELvIc fIn tIPS wHEn ADPRESSED juSt REAcHIng tO AnAL fIn ORIgIn; LEngtH Of PELvIc fInS 2.0 (1.7– 2.1) In HL; LEngtH Of PEctORAL fInS 1.3 (1.2–1.4) In HL; LEngtH Of cAuDAL fIn 1.2 (1.0–1.3) In HL; cAuDAL fIn SLIgHtLY tO mODERAtELY fORkED, cAuDAL cOncAvItY 7.7 (3.6–7.7) In HL. A SummARY Of PROPORtIOnAL mEASuREmEntS ARE SHOwn In TAbLE 4.

Colour in life: gEnERALLY bROwnISH On uPPER HALf Of bODY wItH fInE, DARkER bROwn ScALE OutLInE, fREquEntLY wItH YELLOwISH HuE, ESPEcIALLY tHOSE On uPPERmOSt ROw Of bAck AnD juSt AbOvE mIDLAtERAL DARk StRIPE; RELAtIvELY nARROw bLAckISH mIDLAtERAL StRIPE fROm uPPER PEctORAL fIn bASE tO bASE Of cAuDAL fIn, nARROwER On AntERIOR HALf Of bODY, gRADuALLY ExPAnDIng tO AbOut OnE ScALE wIDtH On cAuDAL PEDuncLE, YELLOw HuE bELOw tHE mID-LAtERAL StRIPE AnD juSt bEHInD tHE PEctORAL fIn bASE; LOwER HALf Of bODY bLuISH tO wHItE wItH LARgE ZOnE Of PALE YELLOw ImmEDIAtELY bEHInD PEctORAL fIn bASE, ALSO A mORE DIffuSE bLAckISH StRIPE uSuALLY PRESEnt bELOw YELLOw ZOnE, ExtEnDIng POStERIORLY tO bASE Of POStERIOR AnAL fIn; HEAD bROwnISH gREY wItH YELLOwISH SuffuSIOn, LIPS DARk gREYISH AntERIORLY; PROmInEnt REctAnguLAR bLAck mARk On uPPER OPERcuLum, ItS vERtIcAL wIDtH nEARLY EquAL tO PuPIL DIAmEtER, wItH YELLOw AREA ImmEDIAtELY bELOw AnD SOmEtImES ImmEDIAtELY AbOvE; IRIS bLuISH On uPPER HALf AnD YELLOw tO bLuEISH bELOw; fInS mAInLY tRAnSLucEnt tO SLIgHtLY YELLOwISH, wItH PROmInEnt bLAckISH SPOt On bASE Of PEctORAL fIn AnD ALSO InvADIng AxIL Of fIn (fIgS 4–6). COLOuR IntEnSIfIES In mAtuRE mALES.

Colour in alcohol: gEnERALLY YELLOwISH-tAn wItH DARk mARkIngS AS DEScRIbED AbOvE unDER LIvE cOLOuRAtIOn. A DEnSE cOvERIng Of mELAnOPHORES IS EvIDEnt On tHE bODY unDER mAgnIfIcAtIOn, PARtIcuLARLY On tHE uPPER HALf Of tHE SIDE ( FIg. 7 ).

Comparisons: ALtHOugH SImILAR In gEnERAL APPEARAncE, tHE nEw SPEcIES DIffERS fROm C. rhombosomoides In SEvERAL cOLOuR PAttERn fEAtuRES, IncLuDIng A mORE RObuSt bLAck StRIPE AcROSS tHE uPPER OPERcuLum, A mORE IntEnSE bLAck SPOt On tHE PEctORAL fIn bASE, A PROnOuncED YELLOw PAtcH On tHE AntEROvEntRAL bODY, AnD uSuALLY A mORE cOnSPIcuOuS SEcOnD DARk StRIPE On tHE LOwER bODY. THE LASt-mEntIOnED fEAtuRE IS gEnERALLY AbSEnt, OR RELAtIvELY DIffuSE, In C. rhombosomoides . FuRtHERmORE, tHE SubmARgInAL DORSAL AnD mARgInAL StRIPES On tHE SEcOnD DORSAL AnD AnAL fIn Of nuPtIAL mALES ( FIg. 6 ) ARE gEnERALLY YELLOw In C. bitaeniatus sp. nov. In cOmPARISOn tO ORAngE-REDDISH In C. rhombosomoides .

THE nEw SPEcIES HAS SLIgHtLY SmALLER ScALES tHAn C. rhombosomoides , wHIcH IS REfLEctED In A HIgHER LAtERAL ScALE cOunt (38–40, mEAn 38.8 vERSuS 36–38, mEAn 37.2), PARtIcuLARLY DIScERnIbLE In tHE AntERIOR HALf Of tHE fISH AS A cOunt bEtwEEn tHE ADPRESSED POStERIOR tIP Of tHE PEctORAL fIn AnD A vERtIcAL LInE fROm tHE DORSAL fIn ORIgIn (3–5, mEAn 4.1 vERSuS 2–4, mEAn 2.9), AnD In DIStInctIvE PREDORSAL ScALE cOuntS, wItH tHE nEw SPEcIES HAvIng 18 OR mORE ScALES (uSuALLY 19–21) vERSuS LESS tHAn 19 ScALES In C. rhombosomoides (uSuALLY 17–18). THERE IS ALSO A mODAL DIffEREncE In tHE tOtAL numbER Of vERtEbRAE wItH tHAt Of C. bitaeniatus sp. nov. RAngIng fROm 37–40 (mEAn 38.8) cOmPARED tO 36–39 (mEAn 37.2) fOR C. rhombosomoides .

SPEcImEnS Of C. bitaeniatus sp. nov. unDER AbOut 45 mm SL tEnD tO bE mORE SLEnDER tHAn SImILAR-SIZED C. rhombosomoides , wItH bODY DEPtH RAngIng fROm 4.3–5.3 In SL, cOmPARED tO A RAngE Of 3.5–4.3 fOR C. rhombosomoides . HOwEvER, tHE DIStInctIOn bEtwEEn tHE twO SPEcIES bEcOmES LESS ObvIOuS In LARgER mALES, IncLuDIng tHE 65.6 mm SL HOLOtYPE (3.8 In SL), wHIcH ExHIbIt A DEEPER bODY SImILAR tO tHAt tYPIcALLY PRESEnt In C. rhombosomoides (DAtA fOR SExAbLE fISH: 10 fEmALES 37.6–50.7 mm SL RAngED fROm 4.0–4.9 In SL; fIvE mALES 35.2– 44.4 mm SL RAngED fROm 4.3–5.3 In SL; fIvE mALES 46.7–65.6 mm SL RAngED fROm 3.7–4.6 In SL). THE gREAtESt bODY wIDtH IS nARROwER In C. bitaeniatus sp. nov. bEIng 2.1–2.8 vERSuS 1.8–2.4 In HL, wItH nO DIScERnIbLE PAttERn wItH SEx. LIkEwISE, tHE nEw SPEcIES tYPIcALLY HAS A SHORtER SEcOnD DORSAL fIn bASE, 4.5–5.6 vERSuS 4.0–5.0 In SL. AnOtHER uSEfuL fEAtuRE, ALtHOugH DIffIcuLt tO ExPRESS In tERmS Of mORPHOmEtRIc vALuES, IS tHE DIStInctLY fLAttER PREDORSAL PROfILE Of tHE nEw SPEcIES In cOmPARISOn tO tHE mORE cOnvEx (I.E. ROunDED) PROfILE Of C. rhombosomoides (fIgS 6–7). FuRtHER tHERE IS A DIffEREncE In tHE SPAcIng Of tHE fIRSt twO AnAL RAYS In RELAtIOn tO tHAt Of tHE OtHER AnAL RAYS ( FIg. 7 ). THE fIRSt twO RAYS Of C. bitaeniatus sp. nov. ARE mucH cLOSER tO EAcH OtHER tHAn tHE SPAcIng bEtwEEn tHE REmAInIng RAYS, wHEREAS In C. rhombosomoides tHE SPAcIng IS mORE OR LESS unIfORm fOR ALL RAYS.

Zoogeography and habitat: knOwn OnLY fROm tHE COOPER CREEk AnD nEARbY HutcHInSOn CREEk SYStEmS Of nORtH-EAStERn QuEEnSLAnD ( FIg. 1 ). THE cOLLEctIvE ExtEnt Of OccuRREncE IS EStImAtED At 16 km 2 AnD AREA Of OccuPAncY LESS tHAn 8 km 2. HAbItAt DEtAILS wERE PROvIDED bY MARtIn & BARcLAY (2013). COOPER CREEk IS A SmALL cOAStAL StREAm APPROxImAtELY 13 km nORtH Of tHE DAIntREE RIvER wHIcH IS HEADwAtERED In tHE THORntOn RAngE AnD DEbOucHES tO tHE SEA At tHE nORtHERn EnD Of ALExAnDRA BAY. THE StREAm IS StROngLY tIDAL At tHE CAPE TRIbuLAtIOn ROAD cROSSIng, wHIcH LIES AbOut 3.5 km uPStREAm fROm tHE SEA. MOSt Of tHE cOLLEctED SPEcImEnS AnD unDERwAtER ObSERvAtIOnS ARE fROm LIttLE COOPER CREEk ( FIg. 8 ), A SmALL tRIbutARY, wHIcH EntERS tHE mAIn cREEk AbOut 500 m uPStREAm Of tHE ROAD bRIDgE At An ELEvAtIOn Of 22 m, AnD AbOvE tIDAL InfLuEncE. FISHES wERE LOcAtED OvER An APPROxImAtELY 600 m StREtcH Of tHE cREEk. HAbItAtS ALOng tHIS cREEk ARE PRImARILY unDIStuRbED RAInfORESt, wItH SOmE PRIvAtE RESIDEntIAL AnD cOmmERcIAL PROPERtIES. THE cREEk fLOwED vERY cLEAR At tHE tImE Of cOLLEctIOnS, wItH InDIcAtIvE wAtER cHEmIStRY vALuES Of PH 7.5, wAtER cOnDuctIvItY 23 µS/cm, AnD wAtER tEmPERAtuRE 20°C. THE cREEk HAD An AvERAgE wIDtH Of 5 m wItH DEPtHS LESS tHAn AbOut 0.5 m . A mIxED SubStRAtE cOnSIStED mAInLY Of ROckS, SAnD, AnD LOg DEbRIS. THE cREEk wAS 50% SHADED bY RAInfORESt AnD LAckED AquAtIc vEgEtAtIOn. THE SPEcIES HAS ALSO bEEn ObSERvED AnD cOLLEctED In SImILAR HAbItAt At SOutH COOPER CREEk, A tRIbutARY tHAt fLOwS IntO tHE mAIn COOPER CREEk EStuARY, wELL DOwnStREAm Of LIttLE COOPER CREEk, AnD HAS ALSO bEEn cOLLEctED fROm An uPStREAm REAcH Of HutcHInSOn CREEk, AbOut 5 km SOutH Of COOPER CREEk. HutcHInSOn CREEk IS A LARgER SYStEm tHAn COOPER CREEk AnD DEbOucHES tO tHE SEA At tHE SOutHERn EnD Of ALExAnDRA BAY. THE LAttER SItES cOnSIStED mAInLY Of PRImARY RAInfORESt wItH StREAmS fLOwIng OvER SAnD AnD cOARSE gRAvEL SubStRAtES. WAtER DEPtHS Of uP tO 4 m wERE REcORDED AnD tEmPERAtuRE AnD PH At tHE ADDItIOnAL SItES RAngED fROm 23–24.5°C AnD 6.5–7.1 RESPEctIvELY, wItH LOw wAtER cOnDuctIvItY AgAIn ObSERvED 27–38 µS/cm . THERE IS OnE PREvIOuS uncOnfIRmED REcORD Of A Cairnsichthys REPORtEDLY cOLLEctED fROm A DAIntREE RIvER tRIbutARY In 2004 (THuESEn 2004), HOwEvER REcEnt ExtEnSIvE SEARcHES At tHIS LOcALItY wERE unAbLE tO fInD tHE SPEcIES ( MARtIn & BARcLAY 2013).

Field observations: LImItED fIELD ObSERvAtIOnS fOR tHIS StuDY HAvE bEEn mADE On C. bitaeniatus sp. nov. At tHE tHREE cuRREntLY knOwn LOcALItIES tHROugH SnORkEL SEARcHIng, nIgHt SPOtLIgHtIng, nEttIng AnD bAnkSIDE ObSERvAtIOn. In tHE cASE Of tHE COOPER CREEk SItES, tHE SPEcIES HAS OnLY bEEn ObSERvED In twO SmALL tRIbutARY StREAmS, AnD HAS nOt YEt bEEn ObSERvED In tHE mAIn cREEk cHAnnEL. In HutcHInSOn CREEk, tHE SPEcIES IS knOwn OnLY fROm twO SPEcImEnS ObSERvED unDER A LOg jAm In An uPPER REAcH Of tHE mAIn cHAnnEL, AnD It HAS nOt bEEn ObSERvED In tHE DOwnStREAm REAcHES OR In OtHER tRIbutARY StREAmS. FuRtHER SuRvEYS mAY REvEAL OtHER LOcAtIOnS but It IS APPAREnt tHAt tHE SPEcIES HAS A PREfEREncE fOR SmALL, tRIbutARY HAbItAtS wItH gOOD fLOw AnD wAtER quALItY.

ALtHOugH tHE SOutHERn SPEcIES Cairnsichthys rhombosomoides HAS bEEn nOtED AS AbunDAnt wItHIn ItS PREfERRED HAbItAt (PuSEY et al. 2004), bY cOntRASt C. bitaeniatus sp. nov. IS gEnERALLY uncOmmOn At ALL knOwn LOcAtIOnS, wItH mOSt EncOuntERS bEIng EItHER AS A SIngLE InDIvIDuAL OR SmALL gROuPS Of twO OR tHREE fISH.

DuRIng tHE DAY, C. bitaeniatus sp. nov. IS gEnERALLY A SuRfAcE tO mIDwAtER SwImmER. It PREfERS AREAS Of HIgH fLOw, AnD PARtIcuLARLY fREquEntS DEEPER POOLS In tHE HIgH fLOw ZOnE ImmEDIAtELY uPStREAm Of RIffLES, wHERE It SwImS vIgOROuSLY IntO tHE cuRREnt tO mAIntAIn A StEADY POSItIOn. THE SPEcIES IS fREquEntLY ObSERvED ScHOOLIng wItH OtHER RAInbOwfISH AnD bLuE-EYE SPEcIES IncLuDIng: Melanotaenia splendida splendida (PEtERS, 1866); Melanotaenia trifasciata (REnDAHL, 1922); AnD Pseudomugil signifer KnER, 1866. HOwEvER, At tImES ADuLt C. bitaeniatus sp. nov. ARE SOLItARY OR In PAIRS POSItIOnED LOw In tHE wAtER cOLumn AnD AvOIDIng LARgE ScHOOLS Of M. trifasciata At LEASt In SOutH COOPER CREEk. At nIgHt, C. bitaeniatus sp. nov. REStS nEAR tHE SuRfAcE In OPEn wAtER POOLS AnD If APPROAcHED wItH A SPOtLIgHt, wILL uSuALLY REtREAt tO A SHALLOw EDgE AREA wHERE It AttEmPtS tO HIDE AmOngSt LEAf LIttER OR EDgE PLAnt ROOt SYStEmS. THE SnAPSHOt Of wAtER quALItY PARAmEtERS PRESEntED In tHE PREvIOuS SEctIOn ( MARtIn & BARcLAY 2013) InDIcAtES cOOL wAtER tEmPERAtuRE RELAtIvE tO tHE tROPIcS (<25°C), LOw wAtER cOnDuctIvItY (<50 µS/cm) AnD vARIAbLE PH vALuES.

NO DAtA ARE AvAILAbLE fOR C. bitaeniatus sp. nov. On REPRODuctIOn OR tROPHIc EcOLOgY. HOwEvER, tHE cLOSELY RELAtED C. rhombosomoides IS knOwn tO HAvE A PEAk SPAwnIng SEASOn fROm AuguSt tO OctObER, AnD EggS ARE gEnERALLY DEPOSItED In bAtcHES wItHIn ROOt mASSES, AnD fEEDIng IS PREDOmInAntLY On tERREStRIAL InvERtEbRAtES wHIcH It cAPtuRES On tHE SuRfAcE (PuSEY et al. 2004). It IS PRESumED tHAt C. bitaeniatus sp. nov. HAS SImILAR REPRODuctIOn AnD fEEDIng HAbItS.

Cairnsichthys bitaeniatus sp. nov. IS A SLEnDER SPEcIES AnD HAS A DIStInctIvE, SInuOuS SwImmIng StYLE, wHIcH mAkES fOR RELAtIvELY EASY bAnkSIDE IDEntIfIcAtIOn fROm cO-OccuRRIng RAInbOwfISHES bY An ExPERIEncED ObSERvER.

Etymology: tHE nEw SPEcIES IS nAmED bitaeniatus (LAtIn: DOubLE RIbbOn) wItH REfEREncE tO tHE twO DARk StRIPES On tHE SIDE, In cOntRASt tO C. rhombosomoides wHIcH gEnERALLY HAS A mORE IncOnSPIcuOuS vEntRAL StRIPE OR It IS AbSEnt.

Figures

FIGURE 1. Location map in the wet Tropics bioregion of northeastern Australia showing Cairnsichthys study collection sites (see Table 1), including locations of other museum material examined, larger cities/townsand major rivers.

FIGURE 6. Comparative life images of sister rainbowfish species, aquarium images unless otherwise stated: (left) Cairnsichthys bitaeniatus sp. nov. (A) adult male from Hutchinson Creek, image reversed (KM), (B) adult female from Little Cooper Creek yawning (KM), (C) group of smaller adults from Little Cooper Creek showing narrow body and double stripes (KM), (D) in situ photograph of adult, Little Cooper Creek (GA), and (right) C. rhombosomoides from Harvey Creek (E) adult male (KM) (F), sparing large adult males, image reversed (Gunther Schmida), (G) group of smaller adults showing deep body and single stripe (KM), (H) in situ photograph of adult (Nathan Litjens).

FIGURE 7. Comparative specimen images of sister rainbowfish species: (left) Cairnsichthys bitaeniatus sp. nov. (A) freshly prepared holotype (QM I.39335), 65.6 mm SL male, Little Cooper Creek, (B) preserved holotype, (C) freshly prepared specimen(NTM S.17778-001), 44.4 mm SL male, Little Cooper Creek,(D) radiograph of holotype with arrow highlightingthe close arrangement of the first two anal fin rays compared to the following rays, and (right) C. rhombosomoides (E) freshly prepared specimen (NTM S.17700-001), 52.4 mm SL male, Smoko Creek, (F) preserved specimen, Smoko Creek (NTM S.17700-001), (G) preservedparatype (AMS IA.4774) 37.5 mm SL, Babinda Creek,(H)radiograph of representative specimen with arrow highlighting different spacing of anal fin rays (NTM S.17930-001), 50.0 mm SL male, Nyleta Creek.

FIGURE8. Typical rainforest fast flowing stream habitat and type locality of Cairnsichthys bitaeniatussp. nov., Little Cooper Creek, wet Tropics bioregion, northern Australia, including adult fish (lower centre of underwaterimage) positioned in area of high velocity (MH).