This paper not to be cited without prior reference to the author International Council for the Exploration of the Sea C.11. 1972/J:6 Pelagic Fish (Southern) Committee A'method for determining the fecundity of the horse mackerel (Trachurus trachurus:(L.)) by C. T. Macer Fisheries Laboratory, Lowestoft Bundesforschun,,' nl!1O t für FisG:her i Homburg Bibliothek • • INTRODUCTION The estimation of fecundity, defined here as the number of eggs which will be released by a female fish in the next spawning season, is an important aspect of the biology of fishes. It can be used, example, to determine stock size (in conjunction with da ta on the ' annual,egg production of the stock) and also as a character far stock separation (Burd ahd Howlett 1971). , _._ . The ease with which fecundity can be determined depends upon whether or not there is a clear size-separation between developing and resting oocytes at any stage prior to spawning. In some spe6ies, such as herring and haddock, 'there is a clear separation but with others, such as hake and pilchard, there is a continuous gradation of oocyte size (Hickling and Rutenberg 1936), and this latter case also applies to the horse mackereI. The .problem, therefore, is to determine which oocytes will develop in the current season • PREVIOUS WORK The simplest aPllroach to the problem has been to decide ona criti- cal size below which all oocytes are considered to be resting. The critical size is chosen by irispection of oocyte.diameter distributions, sometimes coupled with histological examination; 'This method was used oy Andreu (1954)'for Sardina pilchardus, by Petrova (1960) for Sprattus sprattus, by Komarov (1964) for Trachurus trachurus off South-west Africa, and by Rao (1967) for Rastrelliger kanae;urta. -Another method has been to estimate the number of oocytes in a single batch and to determine the number of batches; a 'critical size' is sometimes used in this method also.' Th'e.' batch size is usually deter- mined from the most advanced batch of oocytes, since this is often the ' 1
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This paper not to be cited without prior reference to the author
International Council forthe Exploration of the Sea
C.11. 1972/J:6Pelagic Fish (Southern) Committee
A'method for determining the fecundity of thehorse mackerel (Trachurus trachurus:(L.))
by
C. T. MacerFisheries Laboratory, Lowestoft
Bundesforschun,,' nl!1O tfür FisG:her i Homburg
Bibliothek
•
•
INTRODUCTION
The estimation of fecundity, defined here as the number of eggs
which will be released by a female fish in the next spawning season,
is an important aspect of the biology of fishes. It can be used, ,for,~
example, to determine stock size (in conjunction with data on the '
annual,egg production of the stock) and also as a character far stock
separation (Burd ahd Howlett 1971). , _._ .
The ease with which fecundity can be determined depends upon whether
or not there is a clear size-separation between developing and resting
oocytes at any stage prior to spawning. In some spe6ies, such as herring
and haddock, 'there is a clear separation but with others, such as hake
and pilchard, there is a continuous gradation of oocyte size (Hickling
and Rutenberg 1936), and this latter case also applies to the horse
mackereI. The .problem, therefore, is to determine which oocytes will
develop in the current season •
PREVIOUS WORK
The simplest aPllroach to the problem has been to decide ona criti
cal size below which all oocytes are considered to be resting. The
critical size is chosen by irispection of oocyte.diameter distributions,
sometimes coupled with histological examination; 'This method was used
oy Andreu (1954)'for Sardina pilchardus, by Petrova (1960) for Sprattus
sprattus, by Komarov (1964) for Trachurus trachurus off South-west
Africa, and by Rao (1967) for Rastrelliger kanae;urta.
-Another method has been to estimate the number of oocytes in a
single batch and to determine the number of batches; a 'critical size'
is sometimes used in this method also.' Th'e.' batch size is usually deter
mined from the most advanced batch of oocytes, since this is often the '
used by Clark (1934) and 11aeGregor (1957) for Sardinops eaerulea, but
nei·hi~r 'author was able to givo a definite value for ;the 'numberof :'. ~',·;:.~>,~,,>r:_.l"~~/ ~ ,':'::-':"" ,~ .. '."- .....:~.. ._;.;, '~..::... ~.' '.~:..:batehes.
Most of the studies outlined above have relied primarily upon.\') ~!.... '.' . .;. .., . . . . .'. .:: -,: '
oocyte diameter d~strib~tionsa.s:~"i:ndex 'of the st~ge of. development of... ~. l' ... -,\.' .... ! _..... ...... .... • ••
oocytes but, although such data do provide some useful information, it is
also essential to examine histological material. In this wa:y,. the stage .";': .'. . .~
of development of individual.. oocy'~os:can be relateq to their size.
Chigirinsky (1970) found that, in Traehurus japonicus, the modes in
measurements of whole oocyte diameters did not closely correspond,:.~o:;.. ,;.l
~This suggcsts that the division between resting and developingoocytes .
.~~ ~tage 4 (~he stage ~t Which f~cundi~~S been est~~t~d).~~?~s ;a:~'. •about .0 •.1 .. rom, p'iameter. In Figure .1. the growth of the oocytes up. to .the
'. ... ., '.~: . - .' ". '. '. ....';' '. ..,
ripe stage (5) can be clearly seen•. 'There appear to 1?e at least three.~ '. • t . ' \.
batches of oocytes but the only clear one is the last bateh, which
comprises the hyaline oocytes.
(b) 'The criterion of oocyte development.
Some authors (o.g. Andreu 1954, Clark 1934, Rao 1967) have taken
the prosence or absence of yolk as their cri~erion of whether an oocyte
is resting or will develop in the current~eason. An earlier sign of
development, however, is the appearance of vacuoles in the 'cytoplasm,. .,I. .' ..~ 1 . •
caused by the presence of oil globules w1U:~ are removed in the histologi-
calprocessing (Fulton 1898) •. According to this author, SUCll vacuoles>. -' < • " .~ '.' • ..l. , , ..' ..,' ..• -. •. •
ar~Il~eseI1:t,.'.Qnl..y.~n those specie~.. ~n which the planktonic. eggsalso have •
. c.lil :~~o~ul.?s; however, this is not truefor ..the cod, for ~xample
each ·sizo~hould be determined. ' However,. this would involve an ,enormoust, , •• I. ,. '" . . , '. • • : • ~.' .,. " ........ . . • • '. • • ' ••.•},' ~ :.' •~ .:.. .•~ .;, J • ;
number of meo.surements;. a simpler method, used in the present. work,. is; .....' I : .;, . ' ..:. - , ., . ' , •• ... , ~ . : .' : • .' '. ..: ' •. ' .,; •
to take mean values derived from axamination of a selected number of
ovaries. Table 1 gives the results of the examination of 12 stage. 4·>: :.1 ...... ',.,;
horse D:l.ckerol ovaries • They W'ere used as a 'pool' .fram 'which a .minimum, ',' , ... .:... .... ,~.... . ._', .~'.' ': .~~....:. :.. '. \. i
of 150 oocytes.in.ea"ch 0.02 mm size-class,wero classified as being~ ; .'. • f ~ '. .:..., '. .:, • • • • ;.1.' '. i ~,,' , ~..., ...','
vacuolated.or non-vacuolated~,.Fewer,oocytes were examined in size~ ", . '.;, . . '.. '.' ' ..~ .!.classes in which all oocytes ware of the same type. Only those oocytes
: 4
r-----
•
•
which were seetioned through the nueleus were ineluded in the data.
Vacuoles first appeared in,oocy~es with a diameter of 0.08 mm, andat a
size of 0.16 mm all ooeytes had vaeuoles. Yolk droplets first appeared
in ooeytes measuring 0.24 mm.
':By applying the data in Table 1 to the quantitative estimates gi:ven
by, equation (1), an estimate of the total number of" developing ooeytes,
percvary eould be obtained.
The ooeyte size at whieh vaeuoles first appear is alsothe approxi
mate size at whieh development ean first be detected in oocyte diameter
distributions (Figares 1 and 2). Further supporting evidenee for .the
use of vaeuolation as a eriterion of development is presented in
Figure 3(a), whieh shows "the proportion of vaeuolated,ooeytes bymonths,
per selected maturity stages (usually the most eommonstage). A maxi
mum is reaehed in stage 4/5, after which the proportion falls rapidly.
New oocyt~s do not appear until stage 9, as is, the',ease ,in other fish',
species (Andreu and Pinto 1957, :Bowers and Holliday 1961"Woodhead and
Woodhead 1965), and' so the decrease in the proportion of ,vaeuolated, " ,
ooeytes must be due to an' absolute deerease.
(e) Resorption of ooeytes. ,
As in other fish species' (e.g. Woodhead and W06dhead 1965), both
pre-and post-ovulatory degeneration'of oocytes is obser..:red in thehorse
mackerel. Prior to spawning 'this oeeurs only in oocy'tes 'with advanced
yolk formation, but in latermaturfty stages less advaneed 'o'ocytes may'
also:be affeeted.
Figure 3(b) shows' the p~oportion,~'6f yolky ooeytes undergoing' ,~",
degellerat:ion~ by month arid selected maturity stage. In:'stage 4, the':;
'mean:poi'eentage was 6.31 (SE ±1.15, n= 22) and this is 'aiJ. estimat~ of:'
the e'xten't"of resorption in 'the most"advanced (first) bäteh of' oocyte's. '
No eorrectioll to a fecundity estimate would be:lleeded in 'ihis 'oase, ':,~'
since these ooeytes would almost eertainly disintegrate in Gilson's
fluid. However, some correction would be neeessary if this figure also :;
applied to subsequEmt batehes~'The estiinatetor stage 5 ovaries was
3.73% (SE ± 1.83, n= 11rbut tliis value earlnot be ascribed 'to:aspeci
fic batch, since it has not beeIifotmd possible todetermine how'maiJybatches'have been 'spawned in~ pa;ücuiar ovary. Resorptiori"is, h~wever,
POLONSKII, A. S. and TORMOSOVA, I. D., 1969. The spawning of' the horse
mackerel of the north-east Atlantic and the distribution:ofj,its'
eggs and larvae., Trudy atlant. nauchno-issled. Inst., ryb.', Khoz.
Okeanogr., Vyp. 23, 27-48 lJn Russia:il.
BAO, V. R.,,;·1967. Spawning behaviour and feclUldity of the Indian mackereI,
Rastrelliger kanagurta (Cuvier), at }~galore•• , Indian J. Fish.,
14, 171-186."
vlOODHEAD, A. D. and \.,rOODEElill, P. M. J., 1965. Seasonal changes in the
physiologyof' the Barents Seacod, Gadus morhuaL., in relation
to its environment. I. End~crine changes particularly affecting
migration and maturation. Spec. Publs int. Commn mlAtlant.
Fish., No. 6, 692-715.
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... _" Table.1 .The ..propor.tion of oooytes, in. histological sections .. of.s.tage. 4 horsemackerel. ovaries.__ "which have vacuoles in the cytoplasm. The diameters have been corrected to the ~quiva
lent measurements obtained'from Gilson-fixed material (see'text)
Figure 1 Frequency distributions (on a log scale) of oocyte diameter in the horsemackerel. Each histogram is based on measurements from three ovariesfixed in Gilson 's fluid. The number above each histogram indicates thematurity stage. The vertical broken lines are for reference.
40 (1) 25 (5 )
30
20
10
o
20
15
10
5
o
30
20
10
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0. 0Eoeil
20c
Cl>g15~
cCl>u~ 10
(l...
5
o30
30
20
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o
50
40
30
20
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o30
(8)
•
•
o 3
(9)
02
15
10
5
25
20
(4 )
o002 0·1
15
10
5
25
20
o02 0·3 002 01Oocyte dlometer (m m )
Figure 2 Frequency distributions (on an :l rithmctic scale) of ooc~'te diameter in thehorse mackerei, using the same data as in Figure 1. Oocytes larger than0.3 mm are not -shown. The vertical broken lines are for refercnce.
+ indicates less than 0.3%.
8 9920--0--0-0II,
I,III,
:17
(b)
II
II
4 :p: 74 X 4 I
3 3 "N ....~ ..:n:_ 5/---'c r - 6/:± I ±--'ti..L-.....LI---I_.A--~~--I
Figure 3 (a) Tbc proportion of non-yolky oocytes which contain cytoplasmic vacuoles.(b) Tbc proportion of oocytes with advanced yolk formation which are
undcrgoing resorption+.Each point is based on histologicaI seetions of three ovaries, and shows themean ± one standard error. The number adjacent to each point indicatesthc maturity stage.+for stage 3, in which thcre is no advanced yolk formation, all oocytes withyolk were counted.
7
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130 cm 135cm
o
138cm
10 20 30 40 50
The cube of body length (cm x 10-3 )
Figure 4 The number of developing oocytes related to the cube of the body lengthin stage 4 horse mackerel ovaries. A line fitted by regression und n5%confidence limits are shown.