Asymmetry in Some Morphological Characters of Indian Oil Sardine, Sardinella Longiceps Valenciennes,1847 Collected from Muscat Waters on the Sea of Oman - page 03

 

Discussion

There is some variation in the asymmetry values among the six morphological characters studied in S. longiceps. In the present time it is impossible to evaluate the level of asymmetry of these characters and to determine if they are higher or lower than the average due to the lack of data regarding natural asymmetry in this part of the world. However, characters such as pectoral fin ray count showed higher asymmetry value than those of the remaining characters. High asymmetry value for this character was also recorded in several freshwater and marine fish species (Al-Hassan et al., 1990; Al-Hassan and Hassan, 1994; Jawad, 2001, 2003; Jawad et al., 2010). The consistency of asymmetry results might indicate the vulnerability of this character to the immediate changes in the environment. It is not possible at this stage to confirm such effect as the correlation between different environmental pollution and the morphology of the fish species in question is not available. However, based on previous studies in this field, it is possible to conclude that there is a direct correlation between environmental stress due to pollution and asymmetry in this species. Such environmental factors are present in the waters of the coastal area of the Sea of Oman. On the other hand, the low asymmetry values displayed by the remaining four characters such as pre- and postorbital lengths, head length and eye diameter might be explained on the basis that these characters are less vulnerable to environmental stresses.

This may be the case when the developmental period of these characters does not coincide with adverse environmental events (Jawad, 2003; Jawad et al., 2010). Other factors, including genetic ones, might be responsible for the asymmetry in these characters, but these cannot be discussed at this stage due to the lack of genetic data on the ichthyofauna of Oman.

The origin and cause of asymmetry in fishes can depend on several factors, one of which is environmental stress which leads to an increased level of asymmetry, but might occur at low levels before causing wide spread death (Bengtsson and Hindberg, 1985).

Pollution of sea water and sediments by hydrocarbons, heavy metals, pesticides and organic matter are considered the main cause of environmental stress. This state of pollution is not unusual for the coastal environment of Omani waters where different pollutants have been reported to be affecting its water over the past twenty years (De Mora et al., 2004; De Mora et al., 2005; Al-Darwish et al., 2005; Tolosa et al., 2005; Abdel Gawad et al., 2008; Khan, 2008).

The environmental causes might be natural events, and several factors are known to produce nutritional deficiencies such as various pathogens and various population phenomena (Bengtsson and Hindberg, 1985), and it is highly possible that these factors may be in action in Omani waters as they seem to be common in the aquatic environment.

 

Table 2: Squared coefficient of asymmetry and character means (Xr+l)  by size class of Sardinella longiceps

Size Class

n

CV2a

character mean Xr+l

% of individuals with asymmetry

Preorbital length

16-16.9

13

157.3

15.4

92.30

17-17.9

30

162.6

15.8

96.66

18-18.9

19

176.8

16.52

94.74

19-19.9

2

171.5

18.27

100

21-21.9

4

179.2

17.32

100

22-22.9

3

183.0

19.14

100

Total

71

Postorbital length

16-16.9

13

73.5

22.44

92.30

17-17.9

30

76.2

22.50

96.67

18-18.9

19

81.5

23.16

100

19-19.9

2

89.2

24.51

100

21-21.9

4

98.3

26.74

100

22-22.9

3

99.4

26.98

100

Total

71

Eye diameter

16-16.9

13

121.7

1.91

92.31

17-17.9

30

105.4

1.60

76.92

18-18.9

19

110.7

1.63

78.95

19-19.9

2

109.3

2.03

50.00

21-21.9

4 0

2.02

0

22-22.9

3 0

2.40

0

Total

71

Head length

16-16.9

13

8.5

43.93

92.30

17-17.9

30

84.9

45.07

90.00

18-18.9

19

134.6

46.37

94.74

19-19.9

2

116.5

45.92

100

21-21.9

4

6.2

52.33

100

22-22.9

3

2.68

54.76

66.67

Total

71

Number of pectoral fin ray

16-16.9

13

158.6

12.19

92.30

17-17.9

30

104.1

12.15

90.00

18-18.9

19

163.44

12.52

83.33

19-19.9

2

168.6

12.75

100

21-21.9

4

42.67

12.50

75.00

22-22.9

3

19.72

12.50

66.67

Total

71