.±his paper not to bc cited without prior referencc to the uuthor

Transcription

1 .±his papr not to bc citd without prior rfrncc to th uuthor ntrnationul Council for th Exploration 01' th Sa C.H Atlnntic Coitt No. 120 Som Pculinritis 01' th Biology 01' Dntx r&1crophthnlmus in th Arn 01' North-wst Africa by L. N. Domnnvsky This rport is bnsd on th matrial obtaind from May 1963 to Fbruary 1965 during 3 cruiss 01' th scintific vssl 01' AtlantNRO"Chta" und 01' th industrinl vsscls. Cbsrvaticns wr oonductd in th ara 01' Cap-Blunk. Dntx mncrophthnlmus is on 01' th most common bottom-fish spcis in th urn 01' Uorth-"wst Africu. t usually inhabits th dpths from 50 to 350 mtrs ( and probubly dpr). Th most common lngth in th cutchs is cm, wight g Somtims thc lngth is cm, whil th wight rachs 0,6-0,8 kg. Th siz 01' thc fish is diffrnt in th vurious dcpths. n th cours 01' on yar th siz-composition in th diffrnt dpths is not constunt. Th most clar incras in th lngth 01' th fish ulongwith th incras in dpth cun b obsrvd in Novcmbr-Fcbruary. During this priod Dntx mucrophthulmus inhubits th dpth 01' m (Figur 1). n Fbruary-lbrch this dpndnc is not so clur (Figur 2), und,in Muy-July spcimns 01' vurious lngth cun b obsrvd in th sum urus (Figur 3). Jillalysis 01' th siz-rows 01' Dntx macrophthülmus in th sam snsons did not show any substuntiul vuritis in th sum dpth. That is why on cun muk th conclusion thut whil growing th Dntx mncrophthalmus gradually migrats to dccpr layrs. - Th food ccpcsiticn 01' Dntx mucrophthalmus is rathr variabl. ts mouth has rar kn and thin canins, which ur curvd insid and flut-sid tth with kn uppr parts. t has no "molnr" crushing tth. So, th tth 01' Dntx mncrophthalmus ar for sizing und rtaining th "soft" organisms. This is why th lurgr purt 01' its food consists 01' movabl animals, which hav no hard covrs. Th most popular food 01' Dntx Tkcrophthulmus ccnsists 01' rathr snnll fcrms, ccnstituting not mor than 10% 01' its lngth. Th long tapform larvn 01' congr is th only xcption. found:- n th stomahs 01' Dntx macrophthalmus th following groups 01' organisms r 1. Culanuidn, larvn Dcnpodu 2. Euphausiaca 3. Echinodrmutu 4. ljatantia 5. Cphalopoda 6. Brachyura 7. Fishs: Blnnidu Engraulis hcpstus ynagrops microlpis Chlorcphthalmus sp. Dntx maroccanus Dntx mocrophthalmus Con!;ridac

2 - 2 - Th food composition rgulnrly changs whil growing. Th lif-cyl of Dntx rnncrophtbalmus can b dividd intovarious priods aording to th kind of food (Figur 4):- up to 8 cn food mainly onsists of plankton 8-16 cm Euphausiaca cm Natantia und fish 19 cm fish and Ehinodrrnnta othr organisns ar of lss importanc in th food composition and nny b calld "occasional food". Th food composition of th varicus siz-groups indirctly indicats that th young of Dntx macrophthalmus hn.s much mor s trongr inclination of plagi (or, spaking mor xactly, bottom-placic) fish, bcaus th bn.s of its food onsists of plankton n.nd Euphausina. Alongwith th growth of Dntx rnncrophthal mus bottom orgunisns bcom mor and mor importnnt in its food, and gradually it turns to th botton ny of lif. n our colltions th smallst matur nals wr 13 m long, and th fmals 14 m. Th fact that th rlativ prcntag in th sam groups is diffrnt at diffrnt dpths is intrsting. (Figur 5). So, with th incras in th dpth on can obsrv mn.turcd spimns of a snllr siz than thos in th uppr layrs. This can b xplaind by th fact that alongwith naturing, th fish migrat to thc dpr laycrs for spaning. And th fact thnt in th uppr layrs on n.n obsrv larg fish with gonuds in th 2nd stag indiats that spcimns rturn to th uppr layrs aftr spal"ffiing. n ordr to mak th abov-said mor clar, lt us look at Tabl 1 whr th puliaritis of th stat of gonnds of fr.als in diffrnt dptmn.r shown. cmphasizc th fact that hr ar only shovm matur fish. i.. spccinns which had alrady takn part in spawning. W Tabl 1. Stat of ovaris cf rrtur fmals (lngth ubcv 17 cm) in th diffcrnt dyths. Cap-Blank. Fbruury-Mnrch, (in 70). Dpth (m) V V Stag of rnnturity 111 und V Li70-2_4 -'-_5_2_ 2_4 :... 0_. 0. V 75! n th uppr nyrs th fish with conads in th 11 stag prvail. With th incras in dpth th numbr of fully spavmd (V stag) und prrtially spawnd (V- 111 strgs) fish und pr-spaning fish (V stag) rgulrly incrass. At n dpth of 160 m and dpr th fish in th procss uf spn,vninc dominats (V stag). Th fact that hr w cannot at all obsrv fish which hav 0.1 rady spawnd is quit intrsting. Thrfor, alonith th dvlopmnt of its gonnds, Dntx rnncrophthalmus grndually migrats to th dpr layrs, whr it spnwns; aftr spawnin it again rturns to th aras los to th shor. Th spawning of Dntx r.crophthalmus taks plac from Octcbr till April. n this priod fnals with running sxual products ar cauht in th ar of th dg of slop, und oftn on th slops of canyons, at a dpth of 120-3CO m. That th spavming is taking plac in th dpr layrs is quit probabl, but w could not prov it bccaus oe thc linitd trawling dpth oe SRT-R. Sp2wning arcas hav bcn noticd throughout th slop fron 23" to 15" N.l. Spawning is tuking plnc in th aras of upwlling, whr th tmpratur Gradints ur nor distinct.

3 - 3 - spaning Th olour of th spavning fish is bright-rd. stag mor larg onntrations wr obsrvd. During th pr-spaning and spaning Th nrvn of Dntx marophthalmus is of plagi typ with a fat drop. is portional. Th Th yar-yl of th dvclopmnt of th gonuds (nording to visual obsrvations) is in gnral as follows (Figur 6). From April to August th gonnds of th main part of th fish ar in 2nd stag,nnd in August th yolk grovth of ovoitus bgins Th 3rd stag probubly nsts frm August to Dcmbr, und thn th 4th stag prvail. As statd bfor, th spavming taks pl from Otobr to April. Spnvming is of portional typ. Aftr this th gonads turn to 4th nnd thnto th 2nd stag. So, nording to th dat of spawning on an rfr th Dntx Tarophthnlmus to th fish with nutumnwintr spavrning migrnticn. Spnvrning dos not go on throughout th whol ynr. n SUF.mr th gonads rturn to th 2nd stag of maturity. Spnvrning is of portional typ. Lnrvn is plagic with a fut drop. n th nths th numbr of Tals prvuild. As n rul, thy mak up 53-65% of th vmolnumbr of th fish, th sx cf whih nn bc distinguishd visuully. As it s stntd bfor, vmil th growing nnd rnaturing of sxual products tgks plac, th Dntx marophthnlmus migrnts to th dpr plncs. Matur mnl siz is smllr than that of fmals. Thnt is why th dpr th pla, th nrgr th numbr of Tls whih nn b obsrvd. Som nuthors stntd thnt hrmaphroditism is typinl for spnrridn. n in th arn of North-wst Afria about 50 thousand spimns of Dntx mnrophthnlmus wr obsrvd. Howvr, w only D.m2 nross n smnll numbr of hrrrphrcdits. Th ratio cf sxs of th spawning fish is vry los. }fuls mnk up 60-65% of th whol nwnbr of fish. But, if w considr th ratio of mals und fnls of th diffrnt siz-grcups, w obsrvc th smnllr numbr of mals nncng th groups of lrgr siz (Figur<: 7). So, th lif-yl of Dntx marcphthnllfius has th following puliritis: spaning is going on in th nrn of th slop in Uctobr - April los to th cnnycns in n dpth nbov 120 m (mninly l60-25v m), in th Zons of th upwclling of th dp nyr watcr, which brings lni nrvn nnd young to shnllow plns of th shlf. Alongwith th growth, thc young bgins to turn to th bottom-ty,l of i tf. Th minimum lngth in thc nths tkn by bottom-trawls, is 2-2,5 m. Dntx mrohthalmus bin 6-7 cm lng un b obscrvd nt dpths of m. Yfuil th growing nnd mnturin of th sxual produts taks pln, th rish gradunlly migrnts to dpr plns for spnvming. Aftr spnvning Dntx mnrophthnlmus ngain rturn to mor shnllow plos und whil turing or th sxual produts is rnchd, it migrnts on mor to th spnvming nrus. SU.j'l1.RY This ontribution is dvotcd to th problms of th biology of Dntx marophthnlmus. Th lif-yl of Dntx marophthalmus is th following. Spnwning is tuking pla in th arn of th slop in utobr-aril, los to th anyons nt n dpth of 120 m, mninly m, in th zns f uwclling of th dp-lnyrs' wntr, whih brings plngi larvn und young to shqllow plns cf th shlf. Alongwith thir grwth thc young turn to th bttom-typ cf lif. Dntx mnrcphthnlmus of 6-7 m an b obsrvd nt dpths of m in nrgr nllibrs. Vfuil thgrcwing nnd mnturing cf th sxual produts taks pln, th fish grndully migrnts to dpr plns for spnwning. Aftr spnvming th fish rturn to thc shnllw plns.

4 J ," ',' s '-"..c:.p Po< Q) 0 50 J! , Siz.of 2b Fiur 1. fl.sh Siz (mods) of Dsntx macrophthn1mus in Novmbr-Jnnunry. 31() SM in vnrious dpths " '.' '' :0 15 Siz of 20 fish E5 50 SM Figura 2. Siz (modos) qf Dntx macrophtha1mus in vurious dopths in Fobruary-March

5 s _. -...,,-... :S p., 50- (J) 10 5 Siz of 2b fish Figur 3. Siz (mods) of Dntax macrophthalmus in diffrnt dpths in May-July SM 1. 1 : CJ.!) CJ. <:) t-: on tll "" t':> >:: "CJ (J) 'H CJ 'H "N on 'd 'H 0 '0 (J) H co _.-_..._._._._-._._._._--_.., '"", " '.. -"" - o rl >:: o on n tll o < oo 'd oo Pr b d 0 0 (J) co t- (!).!) t':> CJ ""

6 m % 10.' m 150 m > 160 m ,...' SM SizG of fish Figura 5. P0rcntago of matur fomalos in diffront siz-roups in vurious dpths. Figura 6. Schma of tho dovolopmont of S0X products of Dntox macrophthalmus in th8 cours of on yaar. % r 10 "-.._.._ "'.. ---'-- 20 Figura 7.., 25 Si:z:o of fish 30