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

 Laith Jawad1, Juma Al-Mamry1, Jaifer Al-Busaidi2, Ammar Al-Mamari2, Sami Al-Mamry2, Khadija Al-Owisi2 & Mazin Al-Rubiey2

 

1 Marine Science and Fisheries Centre, Ministry of Fisheries Wealth, Sultanate of Oman, P.O. Box 427, Postal Code 100 Muscat; Corresponding author: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 Department of Marine Science and Fisheries, Sultan Qaboos University, P. O. Box 34, Al-khud 123, Sultanate of Oman.

 

Abstract

Asymmetry analysis has been carried out for six bilateral characters of Sardinella longiceps Valenciennes, 1847 (Family: Clupeidae) collected from the Sea of Oman at the City of Muscat. The results showed that the level of asymmetry of the character number of pectoral fin rays was higher than those of the rest of the characters studied. The possible cause of the asymmetry in this species has been discussed in relation to different pollutants and their presence in the area. An increasing trend in the asymmetry values with fish length was noticed in the pre and postorbital lengths.

Keywords: bilateral asymmetry, Sea of Oman, Sultanate of Oman, Sardinella longiceps.

 

Introduction

The differential development of a bilateral character between the sides of an organism is known as asymmetry (Van Valeen, 1962; Palmer and Strobeck, 1986; Leary and Allendrof, 1989). Fluctuating asymmetry results when a trait present on both sides of the body does not undergo identical development. It is also known that fluctuating asymmetry represents a measure of developmental sensitivity to environmental stress (Moller and Pomiankowski, 1993; Jawad, 2001, 2003, 2004; Jawad et al., 2010).

Asymmetry usually increases under environmental stresses due to the failure of the homeostatic regulatory mechanism. These developmental effects might occur before the concentration of toxicants in the water or food reaches levels high enough to produce morbidity (Bengtsson and Hindberg, 1985). The only published study on the fluctuating asymmetry studies on Omani fish species is that of Jawad et al. (2010), therefore, the present study is considered a quantitative and qualitative addition to the previous studies on Omani fish fauna.

The present work studied fluctuating asymmetry in selected morphological characters of the teleost fish Sardinella longiceps collected from Muscat coastal area on the middle region of the Sea of Oman.

 

 

 

Material and Methods

Fish specimens of Sardinella longiceps were collected from Muscat coastal area, Sea of Oman. The five bilateral characters used to compare asymmetry were as follows: (1) Length of the pre-orbital distance (mm): measured from mouth to the anterior edge of the orbit. (2) Length of the postorbital distance (mm): measured from the posterior edge of the eye to the posterior edge of the operculum. (3) Eye diameter (mm): measured from the anterior to the posterior edges of the eye. (4) Head length (mm): measured from mouth to the posterior edge of operculum. Meristic characters: (5) Number of pectoral fin rays: a count of the total number of pectoral fin ray, including the uppermost ray. Most characters were counted and measured under a binocular dissecting microscope. For specimens too large to fit under a microscope, a magnifying glass was used.

The statistical analysis included calculating the squared coefficient of asymmetry variation (CV2a) for meristic and morphometric characters according to Valentine et al. (1973):

CV2a = (Sr-l x 100/Xr+l)2

where Sr-l is the standard deviation of signed differences and Xr+l is the mean of the character, which is calculated by adding the absolute scores for both sides and dividing by the sample size. To obviate scaling problems associated with growth in morphometric characters, each measurement was divided by suitable general size measurements, e.g. head length was used as the standardizing measurement. Each of the morphometric characters was treated as such before obtaining the signed differences.