ANNALES · Ser. hist. nat. · 30 · 2020 · 1
43
received: 2020-02-05                 DOI 10.19233/ASHN.2020.07
SPAWNING PERIOD, SIZE AT FIRST SEXUAL MATURITY AND SEX RATIO 
OF THE ATLANTIC HORSE MACKEREL TRACHURUS TRACHURUS 
FROM BÉNI-SAF BAY (WESTERN COAST OF ALGERIA, SOUTHWESTERN 
MEDITERRANEAN SEA)
Khaled RAHMANI & Fatiha KOUDACHE 
University Djillali Liabes, Ecodeveloppement of spaces Laboratory, Sidi Bel Abbès 22000, Algeria 
e-mail: khaled46310@gmail.com
Nasr Eddine Riad MOUEDDEN
University center Belhadj Bouchaib of Ain Temouchent, 46300, Algeria 
Lotfi BENSAHLA TALET 
University Oran 1 Ahmed Benbella, Faculty of Natural Sciences and Life, 31000 Oran, Algeria
Roger FLOWER
Department of Geography, University College London, Pearson Building, Gower Street, London WC1E 6BT, UK
ABSTRACT
Reproduction characteristics of the Atlantic horse mackerel, Trachurus trachurus (Linnaeus, 1758), from Béni-
Saf Bay were investigated. A total of 355 specimens were sampled between November 2015 and October 2017, 
comprising 47.04 % males, 44.79 % females and 8.17 % undetermined. The length of individuals ranged between 
7.2 and 35.4 cm, and the weight from 5.28 to 312.7g. The length at first sexual maturity was evaluated at 15.6 cm 
for males and 14.9 cm for females. Variations in gonado-somatic index (GSI) showed that gonads of both sexes 
started to develop in late February and reached sexual maturity in May-June, which marks the spawning period of 
the species. T. trachurus from Béni-Saf Bay uses nutritional reserves mainly accumulated in spring to develop their 
sexual products for spawning in early summer. 
Key words: Atlantic horse mackerel, Trachurus trachurus, reproduction, Béni-Saf Bay, Algeria
PERIODO DI RIPRODUZIONE, DIMENSIONE ALLA PRIMA MATURITÀ SESSUALE E 
RAPPORTO TRA SESSI NEL SUGARELLO TRACHURUS TRACHURUS NELLA BAIA DI 
BÉNI-SAF (COSTA OCCIDENTALE ALGERINA, MEDITERRANEO SUD-OCCIDENTALE) 
SINTESI
Gli autori hanno studiato le caratteristiche della riproduzione del sugarello, Trachurus trachurus (Linnaeus, 
1758), proveniente dalla baia di Béni-Saf. Un totale di 355 individui sono stati campionati tra novembre 2015 e 
ottobre 2017, con il 47,04 % di maschi, il 44,79 % di femmine e l’8,17 % di indeterminati. La lunghezza degli 
individui variava da 7,2 a 35,4 cm, e il peso da 5,28 a 312,7 g. La lunghezza alla prima maturità sessuale è stata 
valutata a 15,6 cm per i maschi e 14,9 cm per le femmine. Le variazioni dell’indice gonado-somatico (GSI) 
hanno mostrato che le gonadi di entrambi i sessi hanno iniziato a svilupparsi a fine febbraio e hanno raggiunto 
la maturità sessuale a maggio-giugno, il che evidenzia il periodo di riproduzione della specie. I sugarelli della 
baia di Béni-Saf utilizzano le riserve nutrizionali accumulate principalmente in primavera per sviluppare i loro 
organi sessuali per la deposizione delle uova all’inizio dell’estate.
Parole chiave: sugarello, Trachurus trachurus, riproduzione, baia di Béni-Saf, Algeria
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INTRODUCTION
The Atlantic horse mackerel, Trachurus trachu-
rus (Linnaeus, 1758), is a gregarious species of the 
Carangidae family. It can be found in circa-littoral 
bottoms and even in the higher horizon of the bath-
yal zone (Athanassios & Konstantinos, 2015). This 
species is common in shallow coastal waters off the 
north-eastern Atlantic, from Iceland to the Islands of 
Cape Verde. It is also found in the Mediterranean, 
the sea of Marmara and more rarely in the Black 
Sea (Polonsky, 1969; Arneri, 1983), in the Eastern 
Channel and the North Sea. T. trachurus is a migra-
tory species; it lives and hunts in shoals. Usually, it 
migrates towards the coasts in summer and returns 
to offshore waters in winter; it can be found close 
to the bottom where it can live between 50 and 400 
m depth with a capacity to adapt to brackish water 
(Santic et al., 2003). In the Mediterranean Basin T. 
trachurus is very common (Fezzani et al., 2006), liv-
ing in open water and near sandy bottoms; it feeds 
primarily on fish such as gobies, anchovy, sardine 
and only on certain shellfish (Ameri, 1983; Kerstan, 
1985).
The study of the reproductive activity through 
the analysis of certain parameters such as variation 
of some biological indexes can help us better char-
acterize the reproduction cycle by indicating the 
spawning period and the strategy of these fish. Several 
works have dealt with T. trachurus (Polonsky, 1969; 
Sedletskaya, 1971; Macer, 1974; Arneri, 1983; Ar-
ruda, 1984; Kerstan, 1985; Korichi,1988; Eaton,1989; 
Hecht,1990; Ben Salem & Ktari, 1994; Abaunza et 
al., 1995; Kerstan,1995; Karlou-Riga & Economidis, 
1996, 1997; Viette et al.,1997; Fezzani et al., 2002; 
Abaunza et al., 2003; Šantić et al., 2008; Tahari, 2011; 
Aydin & Karadurmuş, 2012; Carbonara et al.,2012; 
Wahbi et al., 2015; Aydin & Erdoğan, 2018; Gherram 
et al., 2018; Azzouz et al., 2019; Ferreri et al., 2019). 
The present paper focuses on the reproductive biol-
ogy of T. trachurus of Béni-Saf Bay, with an emphasis 
on the reproduction period and the size at first sexual 
maturity to complete gaps in the life cycle of this 
carangid species and to better manage this resource 
in this Mediterranean area.
MATERIAL AND METHODS
A total of 355 specimens of Trachurus trachurus 
were collected from Béni-Saf fishery, fished by trawlers 
operating between 30-130 m depth, from November 
2015 to October 2016 (Fig. 1). For each individual, to-
tal length (TL) was measured to the nearest millimetre, 
total weight (TW) and gonads weighed to the nearest 
0.01 g. Fish lengths were classified in 1 cm group inter-
vals (Fig. 2), and sex was determined macroscopically 
based on the morphology and the colour of the gonads 
(Mahdi et al., 2018).
Sex ratio
Sex ratio is defined as being the proportion of the 
male or female individuals compared to the total num-
ber of individuals. It also gives an idea regarding the 
balance of the sexes within the population. The sex 
ratio generally relates the rate of femininity or mascu-
linity of the population: 
SR = F / (M + F) x 100 
F= number of females,
M = number of males.
 
 
Fig. 1:  
 
Fig. 1: Map showing the exact location where the estimated 
500-cm TL female shortfin mako shark was observed on 28 
June 2018.
Sl. 1: Zemljevid obravnavanega območja z označeno loka-
liteto, kjer so avtorji 28. junija 2018 opazovali na 500 cm 
dolžine ocenjeno samico atlantskega maka.
 
Fig. 2:  
 Fig. 2: Trachurus trachurus length frequency distribution of 
males and females caught in Béni-Saf Bay.
Sl. 2: Porazdelitev dolžine pri samcih in samicah navadnih 
šnjurov, ujetih v zalivu Béni-Saf.
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Khaled RAHMANI et al.: SPAWNING PERIOD, SIZE AT FIRST SEXUAL MATURITY AND SEX RATIO OF THE ATLANTIC HORSE MACKEREL TRACHURUS ...., 43–52
Gonado-somatic index (GSI)
In order to understand the sexual cycle and 
determine the spawning period the gonado-somatic 
index (GSI) was calculated monthly for both females 
and males, according to the equation below. The 
description of the reproductive cycle of this species 
and the determination of the spawning period were 
figured by tracking the monthly variations of this 
index. 
GSI = GW / TW × 100 (Ferreri et al., 2019)
GW: gonads weight in g,
TW: total weight in g.
Coefficient of condition 
The coefficient of condition K is defined by the 
relationship between the weight and the size of fish 
according to the equation: 
K =  × 1000 (Crim et al., 1990; Ferreri et al., 2019) 
TW: total weight,
TL: total length.
Size at first sexual maturity
The size at first sexual maturity (Lm 50 %), 
which corresponds to the length at which 50 % of 
the individuals are mature, was calculated for our 
specimens. When considered ripe, the gonads oc-
cupy, or almost so, the totality of the visceral cavity. 
For males, the testes are milky white; for the females, 
the ovaries are bulky and pink, with oocytes visible 
through the ovary walls. For each size class (1 cm) 
previously defined, we counted mature individu-
als on one hand and immature individuals on the 
other. Consequently, we determined the relative 
proportions of each group in relation to the total 
size of each size class. We determined the values 
corresponding to the sizes at first maturity from an 
equation (1) whose curve is sigmoid:
P =    (1) (Wahbi et al., 2015) (1)
P: proportion of mature individuals,
TL: total length in cm,
The constants a and b are determined by the 
method of least squares transforming the equation (1) 
into linear type: 
Ln (  ) = b + aL (2)
RESULTS
Sex ratio
In total, 355 specimens of Trachurus trachurus were 
collected, 167 males (47.04 %), 159 females (44.79 
%) and 29 unsexed (8.17 %). The length frequency 
distribution of the entire population is shown in (Fig. 
2). Male length range was 12 to 33.5 cm; female 
length range was 8.8 to 35.4 cm. Male weight varied 
from 14.36 to 292.83 g and female weight varied from 
5.28 to 312.78 g. 
Of the 355 individuals sampled sex ratio was in 
favour of males 1:0.95 and the χ2 test did not reveal 
any significant difference (p<0.05). In addition, the 
variations of sex ratio according to the size (Fig. 3), 
revealed by khi2 test significant differences in favour of 
females for length classes between 9.5 to 11 cm of TL 
(χ2=11 > χ2t ,0.05=3.84); beyond 16.5 cm of total length, 
males have the advantage but without significance 
(khi2). Beyond 34.5 cm of TL females are dominant.
 
 
 
Fig. 3:  
 
0%
25%
50%
75%
100%
9.5 11.5 13.5 15.5 17.5 19.5 21.5 23.5 25.5 27.5 29.5 31.5 33.5 35.5
Fr
eq
ue
nc
y 
(%
)
Total length (cm)
Males Females
Fig. 3: Sex ratio of Trachurus trachurus by length size.
Sl. 3: Delež spolov pri primerkih navadnega šnjura glede na 
telesno dolžino.
 
Fig. 4:  
0%
25%
50%
75%
100%
D J F M A M J J A S O N
Fr
eq
ue
nc
y 
(%
)
Months
Males Females
Fig. 4: Monthly evolution of sex ratio of Trachurus trachurus.
Sl. 4: Delež spolov pri primerkih navadnega šnjura po 
mesecih.
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Khaled RAHMANI et al.: SPAWNING PERIOD, SIZE AT FIRST SEXUAL MATURITY AND SEX RATIO OF THE ATLANTIC HORSE MACKEREL TRACHURUS ...., 43–52
Monthly variations of sex ratio (Fig. 4) reveal that 
females dominate during the months of November, 
October, December, January, March and July. Males 
outnumbered females during April, May, December, 
June and September, with numerical equality in August 
and February. 
Evolution of sex ratio related to seasons (Fig. 5) 
showed that females outnumbered males during the 
autumn-winter period, while males outnumbered 
females during the spring-summer period (χ2=5.54 > 
χ2t ,0.05=3.84) corresponding to the spawning period of 
T. trachurus in Béni-Saf Bay.
Gonado-somatic index (GSI)¶
The monthly changes of the gonado-somatic index 
(GSI) allowed the determination of the spawning period 
during an annual cycle (Fig. 6); the monthly values of 
this index varied between 0.47 and 5.69 for females 
and between 0.37 and 4.98 for males. From February, 
this index increases for both sexes to attain a maximum 
in June, after which values begin to gradually decrease 
until they reach their lowest value in October for males 
and females. 
Gonado-somatic index related to size classes
To investigate the role of small specimens and their 
contribution to the renewal of the resource we linked GSI 
to the total length of individuals (Fig. 7) and it was estab-
lished that GSI increased simultaneously with length. 
For males, we recorded a maximum GSI at 5.94, 
corresponding to a size 26.5 cm TL, and a minimum of 
GSI with 12.5 cm TL. For females, the GSI maximum 
value was recorded at 4.89 corresponding to a size of 
22.5 cm TL, while the GSI minimum was recorded for 
a size of 13.5 cm TL.
 
Fig. 4:  
0%
25%
50%
75%
100%
D J F M A M J J A S O N
Fr
eq
ue
nc
y 
(%
)
Months
Males Females
Fig. 4: Monthly evolution of sex ratio of Trachurus trachurus.
Sl. 4: Delež spolov pri primerkih navadnega šnjura po 
mesecih.
 
 
Fig. 5:  
0%
25%
50%
75%
100%
winter spring summer autumn
Fr
eq
ue
nc
y 
(%
)
Season
Males Females
Fig. 5: Evolution of sex ratio of Trachurus trachurus by 
seasons.
Sl. 5: Delež spolov pri primerkih navadnega šnjura po 
sezonah.
 
Fig. 6:  
 
0
1
2
3
4
5
6
N D J F M A M J J A S O
G
on
ad
os
om
at
ic
 in
de
x 
G
SI
 %
Months
Males Females
Fig. 6: Monthly evolution of gonado-somatic index for 
males and females of Trachurus trachurus.
Sl. 6: Gonadosomatčni indeks pri samicah navadnega 
šnjura  po mesecih.
 
 
Fig. 7:  
0
1
2
3
4
5
6
7
9.5 12.5 15.5 18.5 21.5 24.5 27.5 30.5 33.5
G
on
ad
os
om
at
ic
 in
de
x 
G
SI
 %
Total length (cm)
GSI Females GSI Males
Fig. 7: Evolution of gonado-somatic index related to total 
length of males and females of Trachurus trachurus.
Sl. 7: Gonadosomatčni indeks pri navadnem šnjuru glede 
na celotno dolžino samcev in samic.
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Condition factor K
Evolution of the condition factor coefficient K 
seems to be closely related to the gonado-somatic 
ratio GSI, but the two indices tended to be inversely 
proportional. In fact, during the spawning period, the 
condition factor of the specimens is recorded at its 
lowest values (7.05) and in rest period the same factor 
records its highest values (8.54). The maturation of the 
sexual products and their emissions requires relatively 
high energy expenditure, and as a consequence the fish 
weight during spawning period is reduced (Figs. 8 and 
9), corresponding to a reduction in condition factor of 
~14 and 20 % for males and females, respectively.
Size at first sexual maturity
The proportion of mature individuals in each size 
class (Fig. 10) showed that first maturity was attained 
at 14.9 cm TL where 50 % of the females were mature, 
whereas 50% of males attained this proportion at 15.6 
cm TL.
DISCUSSION
The sex ratio is slightly in favour of the males. The 
evolution of this index does not have phrenological 
regularity and is close to 1 for the March-June period, 
whereas females dominate in July. The Atlantic mack-
erel is a pelagic fish living in dense fish benches. It 
is possible that certain fish populations are predomi-
nantly males or females. According to Carbonara et al. 
(2012) and Wahbi et al. (2015) fluctuations of the sex 
ratio are due to ethologic phenomena (stray species, 
demographic segregations) responsible for the over-
dispersion and segregated distribution of the sexes. 
The difficulty in interpreting the fluctuations of this 
ratio is due to several factors, such as the behaviour of 
the species, the spawning period and mortality, sam-
pling procedure, aggregation of the of the same sex 
individuals, etc. The change in weight of the ovaries 
and the testes during the cycle of maturation shows 
that the gonads develop at stage II, increased at stage 
III then regress at stage IV. The weight of the testes is 
higher than that of the ovaries during this last phase; 
this could indicate intense expulsion of the sexual 
products of females.
The monthly evolution of GSI follows a similar 
pattern for the two sexes, the spawning starting at 
the beginning of February to continue until July. 
The period of reproduction (Tab. 1) extends from 
February to July with a peak in June, while in central 
Algerian waters (Bousmail Bay), the reproduction is 
during summer and at its maximum in July-August. In 
ccertain areas (Spain, Portugal, France and Morocco) 
T. trachurus has an early spawning period beginning 
in spring with a maximum around March and all 
 
 
Fig. 8:  
 
 
0.06
0.07
0.08
0.09
N D J F M A M J J A S O
C
on
di
tio
n 
fa
ct
or
 K
Months
K Males K Females
Fig. 8: Annual evolution of condition factor K of Trachurus 
trachurus males and females.
Sl. 8: Letna dinamika kondicijskega faktorja K pri samcih in 
samicah navadnega šnjura.
 
Fig. 9:  
 
 
0.07
0.07
0.08
0.08
0.09
0.09
Winter Spring Summer Autumn
C
on
di
tio
n 
fa
ct
or
 K
Season
K males K Females
Fig. 9: Seasonal evolution of condition factor K of Trachurus 
trachurus males and females.
Sl. 9: Sezonska dinamika kondicijskega faktorja K pri sam-
cih in samicah pri primerkih navadnega šnjura.
 
 
 
 
Fig. 10:  
 
 
 
 
 
 
 
 
 
 
 
 
Lm50%=15.6 cm 
Lm50%=14.9 cm 
Fig. 10: Length at sexual maturity of males and females of 
Trachurus trachurus.
Sl. 10: Dolžina, pri kateri samci in samice navadnega šnjura 
dosežejo spolno zrelost.
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Khaled RAHMANI et al.: SPAWNING PERIOD, SIZE AT FIRST SEXUAL MATURITY AND SEX RATIO OF THE ATLANTIC HORSE MACKEREL TRACHURUS ...., 43–52
Tab. 1: The spawning period and length at first maturity obtained for Trachurus trachurus by various authors.
Tab. 1: Obdobje drstitve in dolžina, ko šnjur Trachurus trachurus doseže spolno zrelost po različnih avtorjih.
Authors Area Lm50% (cm) Spawning period
Polonsky, 1969 North Sea and English Channel 20 - 24 * -
Sedletskaya, 1971 North Africa 16 - 23 -
Macer, 1974 North Sea and English Channel 20 - 24 March to August
Arneri, 1983 Adriatic 15 - 18 -
Arruda, 1984 Portuguese coast
Western coast
16 - 19 M
21 - 24 F
November to May
Matosinhos Bay April to December
Southern coast Whole year
Kerstan, 1985 North -East Atlantic (British water) 24.2 - 24.6 -
Korichi, 1988 Algiers Bay (Bou-Ismail bay) 14.2 * -
Eaton, 1989 West of the British Isles March to July
Hecht, 1990 South-East coast of South Africa 32 - 33 June to November
Abaunza et al., 1995
North-west of Spain
Galician and Cantabrian shelf
20.9 M
21.9 F
February to May
Kerstan,1 995
Southwest coast of Irland
19.8 M
25 F
-
Northern biscary
19.4 M
24.6 F
-
South of biscary
19 M
25.3 F
-
Karlou-Riga & Economidis, 1996 Aegean Sea 22 -
Karlou-Riga & Economidis, 1997 Saronikos Gulf (Greece) - December to April
Viette et al.,1997 Italy  Gulf of Trieste
15.6 M
16 F
May to August
Abaunza et al., 2003 Northwest Atlantic 16 - 25 February to August
Šantić et al., 2008 Eastern Adriatic Sea - December to May
Tahari, 2011 Oran Bay (Algeria) - October to March
Aydin & Karadurmuş, 2012 Ordu Black Sea (Turkey) - May to August
Carbonara et al., 2012 Central-Western Mediterranean Sea
GSA 10
17.8 M
18.9 F
GSA 18
17.8 M
18.9 F
GSA 19
17.8 M
18.9 F
Aydin & Erdoğan, 2018 Northern Aegean Sea between (Turkey) 13 F April to August
Gherram et al., 2018 Oran Bay (Algeria)
18.42 M
18.28 F
January to May
Azzouz et al., 2019 Gulf of Skikda (Algeria)
14 M
13.65 F
December-April
Ferreri et al., 2019
Central Mediterranean Sea: Strait of 
Sicily: Tyrrhenian Sea
16.1
17.6
-
Present study Béni-Saf Bay
15.6  cm M
14.9 F
February to July
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Khaled RAHMANI et al.: SPAWNING PERIOD, SIZE AT FIRST SEXUAL MATURITY AND SEX RATIO OF THE ATLANTIC HORSE MACKEREL TRACHURUS ...., 43–52
the authors attribute this to the temperature of the 
medium. An increase in the temperatures beyond 11 
°C conditions the development of the eggs (Villamor 
et al., 1997; Wahbi et al., 2015). Our study shows 
that Trachurus trachurus females reached their sexual 
maturity at 14.9 cm, earlier than males, which attain 
this maturity at 15.6 cm TL. 
To indicate the importance of our results regarding 
size at first sexual maturity (Lm 50%), the comparative 
study sets out with different research groups (Tab. 1). 
Firstly, it is clear that our (Lm 50%) value was much 
higher than those reported by Aydin & Erdoğan (2018, 
Northern Aegean Sea near Turkey) and Azzouz et al. 
(2019, Gulf of Skikda, Algeria). On the other hand, the 
obtained (Lm 50%) value comported fairly well with 
Viette et al. (1997, Italy, Gulf of Trieste), Arneri (1983, 
Algeria; 1983, Adriatic), and Korichi (1988, Algiers 
Bay). We found no significant differences compared 
with research groups of Arruda (1984, Portuguese 
coast), Abaunza et al. (2003, Northwest Atlantic) and 
Ferreri et al. (2019, central Mediterranean Sea), etc. 
(see Tab. 1).
T. trachurus from Béni-Saf Bay reaches sexual ma-
turity at an earlier size, and this suggests that the fish 
has changed its sexuality strategy to ensure its sustain-
ability. The species changes the size of its first sexual 
maturity and reproduces very early.
ACKNOWLEDGMENTS
The authors are grateful to coast guards of Béni-Saf 
for their precious help and also grateful to the review-
ers who improved the manuscript with their helpful 
advices and directives.
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OBDOBJE DRSTENJA, SPOLNA ZRELOST IN SPOLNI DELEŽ ŠNJUROV TRACHURUS 
TRACHURUS IZ ZALIVA BÉNI-SAF BAY (ZAHODNA OBALA ALŽIRIJE, JUGOZAHODNO 
SREDOZEMSKO MORJE)
Khaled RAHMANI & Fatiha KOUDACHE 
University Djillali Liabes, Ecodeveloppement of spaces Laboratory, Sidi Bel Abbès 22000, Algeria 
e-mail: khaled46310@gmail.com
Nasr Eddine Riad MOUEDDEN
University center Belhadj Bouchaib of Ain Temouchent, 46300, Algeria 
Lotfi BENSAHLA TALET 
University Oran 1 Ahmed Benbella, Faculty of Natural Sciences and Life, 31000 Oran, Algeria
Roger FLOWER
Department of Geography, University College London, Pearson Building, Gower Street, London WC1E 6BT, UK
POVZETEK
Avtorji so raziskovali razmnoževalne posebnosti pri navadnem šnjuru, Trachurus trachurus (Linnaeus, 1758), 
iz zaliva Béni-Saf. V obdobju med novembrom 2015 in oktobrom 2017 so analizirali skupno 355 primerkov, od 
katerih je bilo 47,04 % samcev, 44,79 % samic in 8,17 % nedoločenih primerkov. Šnjuri so merili med 7,2 in 
35,4 cm v dolžino in tehtali od 5,28 do 312,7 g. Spolno zreli samci so merili v dolžino 15,6 cm, spolno zrele 
samice pa so dosegle 14,9 cm v dolžino. Spremembe v gonadosomatskem indeksu (GSI) so pokazale, da se 
gonade pri obeh spolih pričnejo razvijati konec februarja, spolno dozorijo pa v maju in juniju, kar opredeljuje 
obdobje drstenja pri vrsti. Primerki T. trachurus iz zaliva Béni-Saf porabljajo prehranske rezerve, pridobljene 
spomladi, za razvoj spolnih produktov za zgodnje poletni drst. 
Ključne besede: navadni šnjur, Trachurus trachurus, razmnoževanje, Béni-Saf Bay, Alžirija
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