International Journal of Marine Science 2016, Vol.6, No.42, 1-8
3
1 Material and Methods
The fish specimens of
S. dumerili
(total 267, 66 male, 83 female, 118 unidentified sexes) were collected from
landing site at Gulf of Gabes (Figure1). Southern Tunisia’ between June 2004 to May 2006 by gill and purse seine
nets. The specimens were brought to the laboratory fresh and on ice. The stretched meshes of the nets and their
accessories measured at least 20 mm. Fish were examined shortly after landing while still fresh. Total length (TL),
fork length (FL), standard length (SL), 1
st
predorsal length (PD1); 2
nd
predorsal length (Pre D2); length of 1
st
dorsal
(LD1); length of 2
nd
dorsal fin (LD2); head length ( HL); pectoral fin length (PFL); body depth at pectoral fin
(BDPF); body depth at 2
nd
dorsal fin (BDD2) were measured in mm using digital caliper (Figure 2). Morphometric
characters were recorded and presented in Table 1. The specimens were deposited in the fish collection of the
National Institute of Marine Science and Technologies of Tunisia, Sfax, Tunisia. Sex was determined
macroscopically and data of each sex kept separated. The indices of the morphological characters were calculated
using the following formula:
I = C/TL x 100
Where, I = morphological character index; C = morphological character measurement in mm; TL = total length of
the fish. The relationship between fish total length and different morphometric characters studied was calculated
using the following formula:
Y = a X
b
Where, Y = morphological characters; X = Fish total length; a, b = constants. According to the law of the allometry,
"b" would take a value close to 1. To test this value, Student test "t" was used.
The type of allometry was evaluated by testing the significance of the allometric coefficient “b” (b = 1, b>1 and b<1
for isometry, negative allometry and positive allometry respectively) that used as a measure for the intensity of
differential increase in the morphological characters relative to a specific reference length (Van Snik
et al
., 1997).
Confidence interval (CI) was calculated in order to find out the significance (t-test, p<0.05) of variations between
the means of each character among the male and female.
Meristic characters were counted for each fish specimen. These counts are number of the 1
st
dorsal fin spines and
rays (D1), number of the 2
nd
dorsal fin spines and rays (D2), number of pectoral fin soft rays (P), number of
ventral fin rays (V), number of anal fin rays (A), number of gill rakes on the epibranchial portion of the left 1
st
gill
arch (LGR) and number of scales on the lateral line (LL).
2 Results
In total length, the specimens ranging in total length from 155 to 1660 mm were used in the present study. The total
length of males and females ranges from 294 to 1480 and from 295 to 1480 mm respectively. The total length range
of the undifferentiated specimens was 155 to 311 mm.
Ratios of the different morphological characters to the fish total length are shown in Table 1. For both male and
female, the range and mean of these ratios were not significant (t-test; p>0.05).
For the male specimens, the non-linear power function coefficient ‘b’ of different variable characters (Y) on the total
length (X) was highest in case of LPD2/TL, where the values are 1.03 and for the female was 1.01 in case of PD1
and PD2.
The present study revealed the highest correlation of the percentage on total length for the male (r = 0.99) in cases of
LPD1/TL, PD1/TL and PD2/TL and the lowest value (r = 0.87) in case of LPD1/TL. For the female, the highest
value was in the case of PD2/TL (r= 0.99) and the lowest was in the case of LPD1/TL (r = 0.91)
