~grim,
Lepidorhombus whifJiagonis (Walbaum, 1792).
.iiaki Quincoces & Paulino Lucio
eM 1998/0PEN: 18
wdi Irla sIn 48395, Sukarrieta, Bizkaia, Basque Country, Spain.
INTRODUCTION
Megrim (I.l'pidorlwmlms \I h!ffiagonis, Walbaum, 1792) is a plcuronectiform fish distributed
from Faeroe Isl:mds to Mauritania at depths ranging from 50 to 800 m., more precisely around
100-300 m.(Aubin·011enheimer, 1986). Multispecific fisheries catch this species in ICES Sub·
areas IV to IX. Spain, France, Ireland and Urnted Kingdom take the major proponion of these
catches.
Three stocks have been recognised for assessment and management PUIposes: Megrim in ICES
Sub~area VI. in Div. VlIb.c.e-k and VIIIa,b and in Div. VlIIc and IXa. The calches (landings
and discards) from !he three stocks amOWlted in 1996 for 4,.708 I, 17,183 tand 329trespecr.i.vely
(ICES eM, 1998a,b). Mean annual landings in the Ba5queCoWltry ports from the Bay ofBiscay
(Div. VIlIa,b,d) from 199410 1996 were around 200 t. most of them obtained by "baka"--trawlers.
There is a considerable nwnber of studies about biology, ecology, and grov.1h of Megrim in Subareas VI and VII. However. under ICES Div. VIIIa,.b,d. little is known about the biology of this
species. AJperi (1992) and Landa et aI. (1996) carried out biblogical studies of Megrim in Div.
VIIIc and VlIIa,b respecth·ely.
However, for the first time. a histologiCal study of the gonadal development of Megrim in Div.
VllIa,b,d (Bay of Biscay) is presented.
MATERIALS AND METHODS
During 1996-1997, an imensive sampling program was carried out on a monthly basis to obtain
representative number of L whiffiagonis in order to advance in the reproduction biology knowledge
of the species. Biological samples were collected at the main fishing pats of me Basque Country
from vessels that operate in Div. VIIIa,b,d.
•
Me stain¢d with haematoxilyn-eosin. To do the identification of the structures easier they
o·
1"....
The gonads (ovaries and testes) were collected after fish were brought to the laboratory. For
histological studies, the aim of the sampling was to obtain the gonads ofa maximum of 10
females and 5 males by 1 cm I . range and by month, along a ~biological yearM in the [19961997] period. Gonads were fixed m a 4% fonnaJdebyde buffered sollltion. Later, in the laboratory,
the gonad samples were embedded in glycol methacrylate resin (Tecbnovitt 7100), sectioned
at 2-3 Jim, slHined with Harris haematoxylin and 1% aquose yellowish eosin and mounted willl
Eukitt on slices with a co\'erslip on surface. At the end of the study, a total of 131 histological
samples of male and 489 samples of female Megrim were prepared, examined and described.
The reading of the histological samples were made by means a binocular microscope under
'transmitted light at different magnifications. Some oflbe more representative samples of the
different maturation stages were photographed.
RESULTS
6: advanced atretic
oocyte~
thick black arrow: blood vessel; L: lumen.
A total of 5 gonad development stages for both females and males were considered: I hrunarure
or Virgin, II In Maturation or Resting, III Mature, IV Pre-spawning and Spawning, and V Postspawning. The different development stages of the oocytes (Oogenia. Chromatin nucleolus
stage, Perinucleolus stage, Vitellogenesis, Nuclear migration and Hydratation), and of the
spermatozoa (Spennmoc~1es, Spennatids and Spermatozoa) have been also descnbed. Due to
the rather long period elapsed between the death of the specimina and the ovaries fIXation,
necrotic oocytes were found during the whole cycle_ Post-ovWatory follicles and atretic oocytes
are also described in spent females (see Table 1).
The structures identified for each maturity stage assigned to females and males are shown in
Column ~FEMALES" [(1)-(8)] and Column nMALES~ [(1)-(7)/ respectively. Structures have
been marked with different labels (numbers, leHers, back or white points, etc.)
DISCUSSION
The process of oocyte maturation in L, whiffiagoni$ is similar to other demersal. fish described
in previous works (Marrale, 1990).
Oogonias were observed in all maturity stages. Cltromatin nuclear and perinucleolar stage were
described in inJruttw"e and maturing females. VtteHogenic oocytes appeared in pre-- and spawning
females while hydrated oocytes were observed in spawning females. In almost all the samples,
the rate of neaotic oocytes \vas high. Post-spawning follicles were also observed but, a5 explained
before, because of the rather long time elapsed between the ovary fixation and the death of the
fish, the pictures obtained was only enough for their identification but not for their exposition.
The results of the histological analysis showned a very concrete spawning period for Megrim
in Div. VIlIa,b,d that e,.1ends from January to March with a peak in February-March.The
identification of the different structures observed coincided with the macroscopical analysis
deployed to establish the spawning period. Th1l9, histology appears as the validation method
for ~ maturity stages assigned de visu to Megrim in this sea area
ACKNOWLEDGMENTS
This work was founded by the European Union DO XIV. the Basque Government and by [he
Spanish Ministry of Education and Culture through a fellowship to 1. Quincoces.
stained \.\ itll hill!nllltoxilyn-eosin. To do (he identificati()n (If ilw SlfUt'll1r":S .:"asil.'r they have
I
IPlPlature or '''r)!in
Only ~Ollia. Chrolllll1in IIUdeolus stage.
Spemlilopia and Spc:rm"roc:-1e pmell1.
Spcm1B"'>:l.lld; ablcn,
"
Oo~,mill. Chromatin 1I""lwlus 5tagc.
P"rinudoolus slIlgc. early vildloge ..
Sperma\OilO"i811ILd Spcmul~1e pmmL f<:lO'
Sl"'nn3'l!.lllids.
:
III
\ jreno~rnesis. C1Irly nucleus migration .
J\.blllring
""i...
J\.btu .... o ..
PR-,,'M" ning
Spcmlalozoi\k ptOOuminant Spellnal"~'(lnia
and SI"'II •• al~'tC prest,.1 (lilly 1ft Ihe Ie!",
COI1,'h
, \I,J,1"""'" nudo,us >I~C and n..,:y!C hKlrnlati" .. ,
(~'l"",,a and II ..... IIlher immalun: 5181,"" "'"
l'r~.cr,1..
"
1'''>I''I",,,,"jll~
.1""
1'''''''''nt,ttHf)' li,llides. fi,li~·td~r ~1Il."Sillj; and
311eli< 'k~}1C~.
I ~,v .. ,.." 'mil C'III,"II""n lIud~...,III' "ar.:~.
1';m,'I)' !iCmimli."rdl ,Iu,·t,. l~'o;idu:11
SII<.... ,111l"l'.OId~alld f",,' SI'"llIm1<'~''',ia
Gonad histology and its development in megrim, Lepiu
AZT' j\
Marina Santurtim, Ifiaki
Quincoce~
AZTI. Dept. of Fisheries Resources. Txatxarramendi Irla sin 48395,
FEMALE
Light microscopy photomicrographs of histological structures of L. whiffiagonis ovaries in different stages of maturation. The histological preparations are stained with haematoxilyn-eosin. To
have been marked with different labels (numbers, letters, or black or white points, etc.) and at different magnifications.
I) Ovary in stage I (Inmarure or Virgin). Thin black arrow: Oogenia; 1: chromatin nucleolus stage; L: lumen.
2) Ovary in stage II (In maturation or resting). Thin black mrow: Oogonia; I: chromatin nucleolus stage; :!: perinucleo!ar stage oocyte; L: lumen.
3) Ovary in stage III (Marure). Thin black arrow: Oogonia; 2: perinuc1eolar stage o001e; 3: Vitellogenic oo~te; L: ltunen.
4) Ovary in stage IV (Pre.spawning and spawning). Thin black arrow: OogoOOa; 3: Vitellogenic oocyte; 4: hydrated oocyte; L: Lumen,
S) Ovary in stage V (post-spawning), Thin black arrow: Oogonia; I: chromar.in nucleolus srage;5: early auelic oocyte; L: lumen.
6) Ovary in stage V (post-spawning), Thin black arrow: Oogooia; 6: advanced atretic oocyte; L: Lwnen,
7) Ovary in stage V (Post-spawning), Thin black arrow: Oogonia; 2: perinucleolar stage oocyte; 5: early atretic oocyte; 6: advanced atretic oocyte; thicJ
8) Detail of 0V8IY in stage II (In maturation or resting), Thin black. arrow: Oogama; 1: cltromatin nucleolus stage; 2: perinucleolar stage oocyte.
MALE
Ughl microsC(lpy phowmicrog.r;lphs ol'hislIl1ogit:lli stnH:lurcs of L II'/lfjli(/,~ol1i,\'I,,:-sles in dillcr..:-nt slag..:-~ uf mmumlion. The histologic).!1 rrcpar;Jli(ln~ arc Slmll~d with hacnmtoxilyn-eosin. To do II
been marked \\ilh dilli:rellllllhc1s (11l1l11hcr~. k[[cr~. or black or whill.:' rnints. 1.:'1(, I and at difli:rl'nl magnijic<ltwn~
1) Tcstide in slagc I (lnmallli'c (IT \'irginl, While lhin arrow: spcnnHlngll11ia: hl<l~'h: thin ,ITnI\I: spennaln'~h:"
2l '1L'Sliclc 11) slallc 1/!l1l nmlul'lIlioll nr H":-.'ilinlll, Bl,lt:k Ihin arro\\': spcnnaillt:yl\:5: \Ihilc Sl<1r: ~;pennm<!J:'IIJ.;: IlhilC circle: sell1iniferons l!1hlll ....
3) T ..:Slick in slti!!c III l1>.1al\1r... ). \~'!iil~'lliill ([IT,II\: sp~'nn;jl(\g(lnin: whil~' slar: sp~'mlUllll(\ids.
4) Tl'Slit:1l' in sla~ ... tV (1'l'l.'-~rilll'l1ll1).' and Sp'I\\'l1in~ I, Hlad: 111ill <lml ..,': "pcrl1laln\:~ I~'~: whill' slar' slwm"';"/tl! .. h
5) Delml oj I\:Slldl' Hl ~I,I[!'" II hl~l),jHll" 'H' Vll).'Ull~). Whil~'lhill a('HII\: ~pl'mlal"t:'''ll!a: hlad Ihlll ;111""", 'j"'"'lm,llt'l'yle~,
tJ) Iklail ,)fl\:~1 i~1c ill slag~' I V I l'll'-_r,m Ilill~! ;Il1,1 SP:l\\lIinll), Wllill' 11 IIII ,m """' 'PCflll;I1<I!l"lli;l: wlnle 'I,:: ~I'~'I mal,'J:uids,
7) Teslidl'lIl sial'" J.. . I I'''~II hpa" l'111,~'1 Whllc Ihlll «1'1,11\: sp~'rm;lltl!'''llia' I,hik' ,1:lr :-'Pl'IIlI;lltl..."id,
+-,-.,.