3
The length-weight relationship was established from
1181 data pairs (TL; TW). This relationship in fishes,
considered as an allometric growth model (Le Cren, 1951)
is written as:
TW = a TL
b
where TW: fish total weight (g), TL: fish total length (cm),
b: length-weight factor (slope) and a: constant.
Values of the b factor provide information on fish
growth (Froese, 2006): when b>3 (positive allometric
growth), then there is a significant positive relationship
between weight and length which indicates that weight
will increase faster with the increase in length.
However, when b<3 (negative allometric growth), it
indicates that fish grows faster in length than in weight.
When b=3 (isometric growth), the weight of the fish
increases proportionally with length. The null assumption
of isometric growth (H 0 : b=3) was tested by Student’s
t-test, using the following formula (Schwartz, 1992):
with:
where S b is the standard error of the slope for α = 0.05
to test significant differences among slopes (b and 3)
between two regressions, S y is the standard deviation of
the variable ln TW and S x is the standard deviation of the
variable ln TL.
The instantaneous total mortality rate (Z) was
estimated by length converted catch curve method using
the FiSAT II program (Gayanilo et al., 2005). Natural
mortality (M) was calculated from the empirical formula
proposed for the Mediterranean fishes by Djabali et al.
(1993):
log M = 0.736 - 0.114 × log L ∞ + 0.522 × log K -
0.583 × log T
t =
[b-3]
S b
S b =
n - 2
S y
S x
( )
2
- b
2
where L ∞ and K are parameters from the von Bertalanffy
equation and T is the mean annual bottom temperature
between 0 and 100 m, T= 18°C (MEDAR Group, 2002).
Fishing mortality (F) was obtained with the formula:
F = Z - M and the exploitation rate E was estimated
by dividing fishing mortality on total mortality (Z).
The exploitation rate indicates whether the stock is
underexploited (E<0.5) or overexploited (E>0.5), based
on the assumption that the stock is optimally exploited
when F = M or E = 0.5 (Gulland, 1971).
Results and discussion
Growth parameters
A total of 580 individuals were collected in fall, 388
during spring and 373 in winter. The total length ranged
from 9.3 to 26.2 cm TL and total weight from 10.34 to
221.56 g. The smallest one was sampled in spring and the
largest in winter. Specimens were more abundant in sizes
between 14 and 16 cm TL during most seasons (Fig. 2).
Growth parameters of S. cabrilla are shown in
Table 1. In Bou Ismail Bay, the values of asymptotic
length (L ∞ ) and growth rate (K) were 32.8 cm and 0.41 yr
-1
,
respectively and the value obtained from the growth
performance index (ϕ′) was 2.64 yr
-1
.
The von Bertalanffy equation determined for
S. cabrilla is represented by the following formula and its
curve is illustrated in Fig. 3.
TL=32.8 [1-e
(- 0.41 (t + 0.39))
]
Length-weight relationship
The relationship between total length and total weight
(Table 2 and Fig. 4) was:
TW = 0.012 TL
2.963
According to the t-test, we observed an isometric
growth of this species in Bou Ismail Bay (b = 2.963;
S b = 0.024; r
2
= 0.93; α = 0.05; t = 1.55<1.96): the weight
of this fish increased proportionally with its length.
The growth in weight of S. cabrilla can be described
by the following model:
TW = 372.15 [1- e
- 0.41 (t + 0.39)
]
2.963
Table 1. Growth parameters (L ∞ , K, t 0 ) of S. cabrilla in the Mediterranean Sea and the Atlantic Ocean
Authors
Region
N
*
Length range (cm) L ∞
*
(cm) K
*
(yr
-1
) t 0
*
(yr
-1
) ϕ′
*
(yr
-1
) Method
Bouain (1983)
Tunisia
-
-
31.85
0.095
− 1.48 1.98
Scales
Tserpes and Tsimenides (2001) Cretan Shelf Greece
1004 6.3-19.7
22.29
0.39
− 0.59 2.29
Otolith
Torcu-Koc et al. (2004)
Edremit Bay Turkey
595 8.6-22.3
33.6
0.11
− 3.17 2.10
Otolith
Ilhan et al. (2010)
Aegean Sea
1452 7.4-22.5
23.88
0.298
− 1.58 2.23
Otolith
Gordo et al. (2016)
Eastern Atlantic
471 12-26.5
25.26
0.21
− 1.72 2.13
Otolith
Rachedi and Dahel (2019)
Gulf of Annaba Algeria 1250 11-23.9
24.94
0.38
− 0.45 2.37
ELEFAN I
This study
Bou Ismaïl Bay
1568 9.3-26.2
32.8
0.41
− 0.39 2.64
ELEFAN I
*
N: Number of specimens; L ∞ : Asymptotic total length; K: Growth coefficient; t 0 : Theoretical age when fish has zero length; ϕ′: Performance index
Growth and mortality of Serranus cabrilla
The length-weight relationship was established from
1181 data pairs (TL; TW). This relationship in fishes,
considered as an allometric growth model (Le Cren, 1951)
is written as:
TW = a TL
b
where TW: fish total weight (g), TL: fish total length (cm),
b: length-weight factor (slope) and a: constant.
Values of the b factor provide information on fish
growth (Froese, 2006): when b>3 (positive allometric
growth), then there is a significant positive relationship
between weight and length which indicates that weight
will increase faster with the increase in length.
However, when b<3 (negative allometric growth), it
indicates that fish grows faster in length than in weight.
When b=3 (isometric growth), the weight of the fish
increases proportionally with length. The null assumption
of isometric growth (H 0 : b=3) was tested by Student’s
t-test, using the following formula (Schwartz, 1992):
with:
where S b is the standard error of the slope for α = 0.05
to test significant differences among slopes (b and 3)
between two regressions, S y is the standard deviation of
the variable ln TW and S x is the standard deviation of the
variable ln TL.
The instantaneous total mortality rate (Z) was
estimated by length converted catch curve method using
the FiSAT II program (Gayanilo et al., 2005). Natural
mortality (M) was calculated from the empirical formula
proposed for the Mediterranean fishes by Djabali et al.
(1993):
log M = 0.736 - 0.114 × log L ∞ + 0.522 × log K -
0.583 × log T
t =
[b-3]
S b
S b =
n - 2
S y
S x
( )
2
- b
2
where L ∞ and K are parameters from the von Bertalanffy
equation and T is the mean annual bottom temperature
between 0 and 100 m, T= 18°C (MEDAR Group, 2002).
Fishing mortality (F) was obtained with the formula:
F = Z - M and the exploitation rate E was estimated
by dividing fishing mortality on total mortality (Z).
The exploitation rate indicates whether the stock is
underexploited (E<0.5) or overexploited (E>0.5), based
on the assumption that the stock is optimally exploited
when F = M or E = 0.5 (Gulland, 1971).
Results and discussion
Growth parameters
A total of 580 individuals were collected in fall, 388
during spring and 373 in winter. The total length ranged
from 9.3 to 26.2 cm TL and total weight from 10.34 to
221.56 g. The smallest one was sampled in spring and the
largest in winter. Specimens were more abundant in sizes
between 14 and 16 cm TL during most seasons (Fig. 2).
Growth parameters of S. cabrilla are shown in
Table 1. In Bou Ismail Bay, the values of asymptotic
length (L ∞ ) and growth rate (K) were 32.8 cm and 0.41 yr
-1
,
respectively and the value obtained from the growth
performance index (ϕ′) was 2.64 yr
-1
.
The von Bertalanffy equation determined for
S. cabrilla is represented by the following formula and its
curve is illustrated in Fig. 3.
TL=32.8 [1-e
(- 0.41 (t + 0.39))
]
Length-weight relationship
The relationship between total length and total weight
(Table 2 and Fig. 4) was:
TW = 0.012 TL
2.963
According to the t-test, we observed an isometric
growth of this species in Bou Ismail Bay (b = 2.963;
S b = 0.024; r
2
= 0.93; α = 0.05; t = 1.55<1.96): the weight
of this fish increased proportionally with its length.
The growth in weight of S. cabrilla can be described
by the following model:
TW = 372.15 [1- e
- 0.41 (t + 0.39)
]
2.963
Table 1. Growth parameters (L ∞ , K, t 0 ) of S. cabrilla in the Mediterranean Sea and the Atlantic Ocean
Authors
Region
N
*
Length range (cm) L ∞
*
(cm) K
*
(yr
-1
) t 0
*
(yr
-1
) ϕ′
*
(yr
-1
) Method
Bouain (1983)
Tunisia
-
-
31.85
0.095
− 1.48 1.98
Scales
Tserpes and Tsimenides (2001) Cretan Shelf Greece
1004 6.3-19.7
22.29
0.39
− 0.59 2.29
Otolith
Torcu-Koc et al. (2004)
Edremit Bay Turkey
595 8.6-22.3
33.6
0.11
− 3.17 2.10
Otolith
Ilhan et al. (2010)
Aegean Sea
1452 7.4-22.5
23.88
0.298
− 1.58 2.23
Otolith
Gordo et al. (2016)
Eastern Atlantic
471 12-26.5
25.26
0.21
− 1.72 2.13
Otolith
Rachedi and Dahel (2019)
Gulf of Annaba Algeria 1250 11-23.9
24.94
0.38
− 0.45 2.37
ELEFAN I
This study
Bou Ismaïl Bay
1568 9.3-26.2
32.8
0.41
− 0.39 2.64
ELEFAN I
*
N: Number of specimens; L ∞ : Asymptotic total length; K: Growth coefficient; t 0 : Theoretical age when fish has zero length; ϕ′: Performance index
Growth and mortality of Serranus cabrilla