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245
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2.
The Redfish; Gametogenesis and Migrations of the Sebastes marinus (L.)
and S ebastes m en tella Travin
By
V. P. SOROKIN
PINRO, M urm ansk, U.S.S.R.
T h e redfish Sebastes marinus (L.) and Sebastes
mentella T ravin, are of great im portance to the trawl
fishery by their abundance an d the size of concentra­
tions they form. It is therefore easy to understand why
so great and so fully justified an interest in the behavi­
our of this fish has developed.
W ithin recent years a significant p a rt of the life
history of the redfish, inhabiting the Barents Sea and
the Norwegian Sea, has been the subject of study. Age
and rate of growth have been studied by N. P. Smaragdova (1936), V. V. Veshchezerov (1941), A. K otthaus (1952), and E. I. Surkova (1957). Its distribution
and its fisheries have been investigated by V. V. Vesh­
chezerov (1941), N. A. Maslov (1944), V. I. Travin
(1949, 1951, and 1957), and A. S. Baranenkova
( 1957). G. V. Boldovski ( 1944) reported on the redfish
feeding behaviour.
V. F. Schm itt (1944) studied the development of
the ovaries, embryonic developm ent of the eggs, and
the larval distribution after “spaw ning” . Sim ilar studies
have been carried out by K. H. Lüling (1951), who
did not seem to know about the work of Russian inve­
stigators (Schm itt and others), concerned with the life
history of the redfish, as is seen from this quotation
from the introduction to his paper: “We may say th a t
we know almost nothing about the reproductive biology
of the redfish Sebastes marinus.” D r. J. Magnüsson
(1955) and Sorokin (1956) m ade histological gametogenesis studies independently of each other.
T h e present p ap er is not aim ed at a critical analysis
of all the d a ta on the biology of the redfish. However,
it was thought useful to try to assess how fa r the m igra­
tions of redfish in the Barents and Norwegian Seas are
inter-related w ith the processes going on in the gonads.
T h e distribution and m igration areas of S. marinus,
as described by N. A. Maslov ( 1944), still rem ain valid
(see Fig. 1). R ecent investigations have only completed
an d defined this general scheme.
In the Barents and Norwegian Seas, to the east of
Figure 1. D iagram of S.marinus (L.) migrations according to
N. A. Maslov.
1 = “spawning” areas
2 = areas of autum n/w inter concentrations of males and
females
3 = areas of spring concentrations of males
4 = migrations of females
5 = migrations of males
the continental slope, S. marinus females liberate their
larvae in the Lofoten Islands area and along the slope
fu rth er north, as fa r as approxim ately 71°N. Liberation
of larvae starts in the second half of April. I t is a t its
height in M ay and comes to an end in the first half
of June.
T h e spent S. marinus females m igrate to the feeding
grounds. A t least three such areas are known: the
eastern Barents Sea as far as Goose Bank (T ravin
reports S. marinus being caught incidentally a t 73°N,
50°E) ; the Demidov Bank (Norwegian fishermen call
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246
it “T h o r Iversen Banken” ) and adjacent northern and
eastern areas; the third area includes the slopes of the
Bear Island Bank and the continental slope of West
Spitsbergen. S. marinus is sometimes found north-east
of H ope Island (7 8 °N ; T ravin, 1949).
A fter liberation of the larvae, the ovaries become
reduced in size and w eight (m aturity factor — 0-2-1-1
% ),* an d become flabby; the m em brane is shrunken.
C u t sections show connective tissues of the follicular
m em branes to be partly degenerate. Sometimes unfer­
tilized eggs in the process of resorption occur in the
ovaries. T h e strom a of such an ovary contains sex cells
of several generations, beginning with oogonia and
including oocytes with a follicle of one or two layers.
In Jun e certain females have oocytes in the ovaries,
with yolk accum ulating in the plasma. Yolk deposition
in the oocytes of older generations is not simultaneous,
i.e. the vitellogenesis is of an asynchronous nature.
Vitellogenesis does not app ear to be very active
during June, July, and August, and the m.f. does not
show a significant rise (1-2 % on average) ; by August
it increases to 1-8 % . T h e diam eter of the older genera­
tions of oocytes varies from 200 to 300 ju during this
period.
T h e shoals of males and females, formerly separated,
unite during these three m onths of the feeding m igra­
tion, an d S. marinus disperses on the feeding grounds
m entioned above.
C u t sections of ovaries suggest th a t in September
vitellogenesis becomes m ore active; the yolk granules
increase in size (12-19 ju), as also does the ovary-mass.
M.f. averages 2-3 % and in some cases even reaches
2-6 % . D uring N ovem ber/D ecem ber S. marinus leaves
the feeding grounds, this being concurrent w ith and
probably due to the beginning of w inter cooling of the
w ater.
Yolk accum ulation is com pleted in Ja n u ary -F eb ru ary, sometimes in M arch. T h e oocyte is filled with large
yolk granules; the nucleus loses its round form and
becomes am oebiform ; the nucleoli disappear and zona
rad iata begin to form. D iam eter of such (living)
oocytes varies from 900 to 1100 u. T h e follicular m em ­
brane is stretched and epithelial cells are stretched out
and flattened. T h e ovaries increase m ore in size and
become heavier; the m em brane stretches an d becomes
thin an d transparent, so th a t oocytes can easily be seen
through it. M .f. increases to 4 -6 % , whilst some females
have been found to possess a m.f. of 10-2 % ; such fish
occur from M u rm an Bank to Finnm ark Bank; in the
N orw egian D eep; in the Dem idov Bank and Bear
Island Bank areas.
L a te r on, w hen the album en com ponents of the
oocyte have taken up w ater, hom ogenization begins
in
* T he gonad weight, relative to the total weight of the fish, expressed
is called the “m aturity factor” or briefly m.f.
%
-
and the oocyte becomes transparent. Meiosis takes
place, followed by ovulation and fertilization (gametic
syngam y). T h e diam eter of the oocyte in the ripe condi­
tion attains 1500 ju. T h e ovaries are of a greenish-gray
colour. T h e eggs lie free in the ovary-cavity and, if the
belly of the fem ale is lightly pressed, are discharged
from the oviducts. T h e ovaries grow larger still and
occupy m ore th an half of the body cavity. M.f. averages
7 % , some specimens attaining a m.f. of 12 % .
Females bearing ripe (and fertilized) eggs are found
in February and M arch on the Finnm ark Bank and
westwards, in the K opytov area, and in the W estern
Deep. Females w ith eggs already fertilized are rarely
found east of the K ola m eridian or on the slopes of the
Bear Island Bank. T he author, at least, has never h ad
an occasion to observe them .
Egg ripening and fertilization are followed by an
active m igration of females to the “spaw ning” places.
T his is also the period of form ation of unisexual shoals.
A fter fertilization the period of em bryonic develop­
m ent begins, also characterized by an increase in the
size of the eggs an d of the ovary as a whole. T h e eggs’
spherical form changes into an elliptical one. T h a t is
why V. F. Schm itt adopted the value of half the sum of
diam eters for characterizing the eggs’ growth. T h e
largest egg size so m easured (in fixed m aterial) varied
from 1980 to 2150 ju.
As the eggs tend to be discharged from the ovaries
when they have reached the embryonic stage, the
w eight of the ovaries cannot be determ ined exactly.
Despite this fact ovaries were weighed an d it was found
th a t the m ean m.f. of the great m ajority of specimens
was not lower th an 11-3 % . Figure 2 shows the varia­
tion of the m.f. of S. marinus during the year.
H ere a reservation m ust be m ade, in th a t observa­
tions from this m aterial do n o t agree w ith Liiling’s
opinion, th a t copulation would affect the grow th-rate
of oocytes.
Observations m ake it possible to suggest th a t the
copulation period does not affect the rate of vitello­
genesis an d the period of fertilization of the oocytes. In
the case of some females w hich rem ain unfertilized,
vitellogenesis is not ham pered an d ovulation takes place
in the norm al way. U nfertilized oocytes become de­
generate or, eventually, abortive spawning takes place.
Females w ith ripe b u t unfertilized oocytes have been
found relatively often, b u t this problem will be dis­
cussed elsewhere.
A t the tim e when the females start liberating larvae,
active spermatogenesis is observed in the testes of the
males. In April num erous cells in the testes of most of
the males are observed in the process of division, a t the
m etaphase or prophase of prim ary meiosis. Spermatids
are already present in almost 50 % of the spermatocysts, being especially num erous in the gonads of males
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247
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fem ales
fertilization
m ales
sPawnin9
m ales
fe m a le s
2-
June J u ly
Gugust SeptemS. October NovemberDecemb.January February March Qprit
M ay
June
Figure 2. Changes in the maturity factor of the redfish (Sebastes marinus (L .)) males and females during the year (% ).
caught during May, while in April they are rarely
found. In Jun e general transform ation of the sperm a­
tids into spermatozoa is observed. T h e spermatocysts
begin discharging sperm into the lumen of the am pullae
and ductuli efferentes. T h e num ber of spermatocysts
with fully formed spermatozoa increases continually;
the am ount of sperm in the lumen of the am pullae and
ductuli efferentes also increases. By August sperm ato­
genesis has ceased. All sperm atogonia, which have
begun to divide, are transform ed to spermatozoa. D uc­
tuli efferentes and ductus epididymidis are filled with
sperm ; the m ale is capable of copulation. Insemination
takes place on the feeding grounds between August and
October. T h e period of copulation indicated above
does not coincide fully w ith the period reported by J.
Magniisson. I t m ay be th a t the two populations obser­
ved were of a different ecological character. T h e copul­
ation period varies, probably owing to the circum ­
stances obtaining at the time of spermatogenesis.
T h e spermatozoa lie in the ovaries in the condition
of physiological rest, influenced — as J. Magniisson
supposed — by a secretion produced w ithin the bladder
of the male. Sperm atozoa rem ain in this resting state
until the oocytes have ripened and ovulated (February/
M a rc h ). R ipening and ovulation are effected by
changes in the p H of the ovarian fluids. According to
the m easurem ents of p H obtained from this m aterial,
p H changes from 6-5 to 7-0. As a result the resting sper­
m atozoa become active, and the oocytes are fertilized.
A cross-section cf a testis during the period following
copulation clearly shows two zones, a peripheral and a
central one. T h e peripheral zone contains the empty
am pullae after the discharge of sperm. In the central
zone the ductuli efferentes, ductus epididymidis and
p a rt of the am pullae still contain sperm. Several speci­
mens at this period (Septem ber) show the presence of
some mitosis of sperm atogonia undergoing division, but
such testes occur only rarely. T h e rem ainder of the
sperm atozoa in the testes undergo phagocytosis. T h e
role of phagocytes is played by epithelial cells lining the
ductuli efferentes and ductus epididymidis. O n the cut
sections plasmatic bulges can be seen “seizing” the
spermatozoa w ith which the ductuli are filled. T he
duration of phagocytosis of the sperm atozoa varies. It
coincides to some extent w ith the feeding period, but
occurs mainly during the w inter migrations. In the
m ajor p a rt of the testes observed, phagocytosis was
found to end by Jan u ary /F eb ru ary . But there were
some testes (M ay, 1954) in which spermatozoa of a
new generation had been formed ; at the same time the
ductus epididymidis contained “old” sperm, u nder­
going phagocytosis.
By early O ctober, secondary and later sperm atogonia
have already appeared in the spermatocysts, first in the
peripheral zone of the testes. In N ovember testes sec­
tions sometimes show spermatocysts containing sperm a­
tids. T hus, during the w inter m igrations of the males,
two processes are going on simultaneously in the testes :
phagocytosis of the “old” sperm and a new wave of
spermatogenesis. In D ecem ber/January, intensity of
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248
rt
11lllllll}
Figure 3. D iagram of migrations of S. mentella Travin.
1 = females
4 = migrations of females
2 = males
5 = migrations of males
3 ~ “spawning” areas
sperm atogonal division increases an d over all the testis
sperm atogonia of later stages can be observed. Sperm a­
tocysts with sperm atids are by no m eans infrequent. In
February sperm atid form ation intensifies, an d by
M arch it reaches its height. Figure 2 shows how the
relative w eight of the testes (m.f.) changes during
the year.
Investigations have also been m ade into the history
of gametogenesis of the S. mentella. Com parison of the
d ata obtained showed th a t gametogenesis and m.f. are
very similar for both species. I t has been possible, how ­
ever, to discover th a t the duration of gametogenesis is
influenced by the ecological differences of the species
reported by T rav in (1951). I t has been found th a t
spermatogenesis and oogenesis term inate earlier in S.
mentella (Bear Island-Spitsbergen populations) than
in S. marinus (inhabiting the Barents S ea). In 1959
this difference was at least one m onth.
As has been shown by T ravin, the habitats of S.
marinus and S. mentella are different an d so are their
routes of m igration. A schematic chart of S. mentella
m igrations (Fig. 3) has been draw n, based on the d ata
collected by scientific workers of P IN R O since 1946,
(V. I. T ravin, N. A. K haldinova, T . S. Berger, A. S.
B aranenkova, V. P. Sorokin). T h e feeding areas of S.
mentella include deep-w ater areas of the W estern Deep
(to the east an d south-east of Bear Islan d ), the south­
ern an d western slopes of Bear Island Bank, and the
area northw ards along the continental slope, including
the W est Spitsbergen area. H ere S. mentella lives from
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Ju n e /A u g u st until February/A pril. In A ugust/Septem ber insem ination of the females takes place; during
Ja n u a ry /F e b ru a ry and partly in M arch, the oocytes
ripen and are fertilized, and this coincides w ith the
beginning of the active “spaw ning”m igration of females
to the “spawning” areas. T h e m igration of males begins
approxim ately a m onth later than of females.
In 1959 the m igrations of females reached their
height by February, whereas mass m igrations of males
were observed only a t the end of M arch. A t this time
the form ation of unisexual shoals takes place.
From the Spitsbergen area and the western slope of
the Bear Island Bank, S. mentella moves southw ard
along the slope; from the W estern D eep area the fish
move in a westerly and south-westerly direction,
keeping to depths greater than 350 m. “ Prespaw ning”
female concentrations of S. mentella are already being
formed at the beginning of M arch in the south-west
p art of the K opytov region. This area lies between
7 1°50'-72°20'N , 15°00'-16°30'E . T h e ovaries of
females caught in this area contain embryos w ith the
eyes pigm ented; the body is segmented and there are
chrom atophores on the ventral and dorsal side of the
caudal p a rt of the body. T h e latest stage of embryo
developm ent observed in the area of “prespaw ning”
concentrations can be characterized as follows: body
length, 7-7 m m ; eye pigm entation is com plete; num er­
ous chrom atophores are present on the dorsal and
ventral sides of the body; the alim entary canal and
the occipital region are pigm ented. T h e pectoral fins
are form ed and the rays of the caudal fin can be seen.
T h e embryo lies in the egg m em brane. Females with
such embryos pass to the areas of liberation of larvae.
M aterial collected over several years by Baranenkova
an d others (1956) on the distribution of redfish larvae,
as well as th e samples taken in 1959, indicate th at
liberation of larvae by the females of the B ear Is la n d /
Spitsbergen populations of S. mentella takes place in
the area between 7 0 °-7 1 °N and 11°-16°E .
In 1959 the liberation of larvae belonging to this
population began between 25. A pril an d 2. May.
D uring liberation S. mentella females are not found in
concentrations suitable for com mercial fishing. A fter
liberating the larvae the females m igrate to the feeding
grounds via the same route.
T h e S. mentella males do not undertake such long
migrations. T hey rem ain in the n orthern p a rt of the
K opytov area, n o rth of 72°20'N. In early spring
(M arch) shoals of males are observed at 25°E. In due
course they move to the west, an d by Ju n e reach 15°E.
W ith th eir advancem ent to the west their concentration
increases; the greatest density of shoals of males is
observed in April. T hro u g h o u t the whole m igration
period the concentrations of S. mentella males are
fished intensively by the traw l fishery.
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?
/ c^ '
S,
Figure 4. Sex ratio dynamics of the S. mentella Travin
population during the 1959 spring migration.
1 = males
2 — females
3 = locality of capture
T h e m igration dynamics can be clearly traced by the
changes in the sex composition of the m igrating stock.
T his is illustrated by Figure 4, w here the results of
three m onths’ observations on the sex ratio variations
during the spring period of the m igrations (M arch,
April, M ay) are summarized.
Summary
Redfish oogenesis and spermatogenesis take place in
different seasons. Spermatogenesis is completed by
August; then copulation takes place, resulting in the
females’ insemination. T h e spermatozoa are m aintained
in the ovary in a state of physiological rest until the
m om ent of ripening of the oocytes, which occurs in
F eb ru ary /M arch . Ripening and ovulation are accom ­
panied by a p H change of the ovarian fluid, which
results in an intensification of the sperm atozoan activ­
ity and fertilization.
T h e extent of migrations of S. marinus and S. mentella is different. T h e spring migrations of females have
a “spawning” character, the m igrations of males are
249
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w inter migrations. T h e su m m er/au tu m n m igrations of
both are associated w ith feeding. T he form ation of
unisexual shoals takes place in F eb ru ary /M arch .
T h e bulk of S. marinus m ature males inhabit the
area eastw ard of the N orth Cape. S. mentella males
generally inhabit the area north of 72°20'N. T h e males
and females re-unite, after the liberation of larvae, in
Ju n e-Ju ly , during th eir m igrations to the feeding areas.
T h e small num ber of males observed by Liiling in the
Andenes, Langanes, M alangen areas (i.e. area of larval
liberation by females, or the areas of prespawning con­
centration) does not signify, as Liiling thought, th a t
males are in the minority in the S. marinus population
b u t is the result of differential distribution brought
about by different behaviour of males and females in
the period of spring migrations.
T h e tim e of the m igration of females to the “spaw n­
ing” areas depends on the period of ripening of oocytes,
their fertilization and subsequent embryonic devel­
opment.
T h e duration and rate of m igrations of males are
determ ined by therm al conditions of the w ater masses
in which they spend the winter. T h e tim e of the begin­
ning of the males’ and females’ migrations may change;
it is not necessarily the same in different years.
These investigations perm it the conclusion th a t the
sex ratio in a redfish population, not subjected to fish­
ing, is unity ( LI ) .
T h e actual redfish fishery results in an upsetting of
the m ale : female ratio. M any years’ exploitation of the
shoals of female S. marinus in the Lofoten Islands
area has resulted in a reduction of females. T h e inten­
sive fisheries for m ale S. mentella belonging to the Bear
Island/Spitsbergen population has resulted in a reduc­
tion of m ale S. mentella.
T h e general biological timing of the annual cycle of
the redfish, as established w ith respect to S. marinus
an d S. mentella populations of the Barents and N or­
wegian Seas, is apparently also valid for other Sebastes
species accomplishing seasonal migrations.
References
Baranenkova, A. S., 1957. “Materialy k raspredeleniu morskykh okunei roda Sebastes. (D ata on the distribution of
redfish, Sebastes).” Dokl. Akad. Nauk S.S.S.R., 113 (2):
468-71.
Baranenkova, A. S., Khokhlina, N. S., & Yudanov, I. G., 1956.
“Raspredelenie lichnok morskogo okunia roda Sebastes v
Norvezhskom more. (The distribution of larvae of Sebastes
in the Norwegian S ea).” Dokl. Akad. Nauk S.S.S. R., Ill
(2) : 489-90
Boldovski, G. V., 1944. “Pitanie morskogo okunia Barentsova
moria. (Feeding of Redfish from the Barents S ea).” T rudy
P IN R O , 8: 307-30.
Kotthaus, A., 1955. “Age and growth in redfish (Sebastes
m a r i n u s ) Biol. Anst. Helgoland. Fischereibiol., Bremer­
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250
Liiling, K. H., 1951. “Z ur intraovarialen Entwicklung und
Embryologie des Rotbarsches (Sebastes marinus L.). Zool.
Jahrb., Abt. Anat., 71: 145—288.
Magnüsson, J., 1955. “Mikroskopisch-anatomische U ntersuch­
ungen zur Fortpflanzungsbiologie des Rotbarsches (Sebastes
marinus L .).” Z. Zellforsch., 43: 121-67.
Maslov, N. A., 1944. “ Promysel morskogo okunia v Barentsovom more i u severo-zapadnogo poberezhia Norvegii. (T he
fishery for Redfish in the Barents Sea and the Northwest
coast of N orw ay).” T rudy P IN R O , 8: 271—79.
Schmitt, V. F., 1944. “O razmnozhenii morskogo okunia. (O n
the reproduction of the redfish).” T rudy PIN R O , 8: 280306.
Smaragdova, N. P., 1936. “Rost Sebastes marinus L. v Barentsovom more. (Growth of Sebastes marinus h. in the Barents
S ea).” Biul. Mosk. obshch. ispyt. prirody, otdel biol., N.S.,
45 (5) : 331-37.
Sorokin, V. P., 1958. “O biologii razmnozhenia morskikh
okunei Sebastes marinus i Sebastes mentella Travin v Barentsovom i Norvezhskom moriakh. (O n the reproductive
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biology of Redfish, S. marinus and £. mentella in the Ba­
rents and the Norwegian Seas).” T rudy Soveshchanii, Vyp.
8 (T rudy Soveshchaniya po Fiziologii Ryb, 1956), pp.
158-70.
Surkova, E. I., 1957. “ Polovoi i vozrastnoi sostav okuniakluvacha (Sebastes mentella Travin) rayona Kopytova. (Sex
and age composition of S. mentella in the Kopytov a re a ).”
T rudy P IN R O , 10: 172-85.
Travin, V. I., 1951. “Novy vid morskogo okunia v Barentsovom more (Sebastes mentella sp. T rav in ). (A new species
of redfish in the Barents Sea, S. m e n t e l l a ) Dokl. Akad.
N auk S.S.S.R., 77: 741-44.
Travin, V. I., 1957. “ Promysel morskogo okunia v yuzhnoi
chasti Barentseva moria i rayonie Kopytova. (T he redfish
fishery in the Southern Barents Sea and the Kopytov a re a ).”
T rudy P IN R O , 10: 161-71.
Veshchezerov, V. V., 1944. “ Materialy po biologii i promyslu
morskogo okunia v Barentsovom more. (D ata on the biology
and fishery of Redfish in the Barents S e a ).” T rudy PIN R O ,
8: 236-70.