International Journal of Aquaculture, 2018, Vol.8, No.1, 1-7
1
Research Report Open Access
Evaluating Morphological Asymmetry in Three Species of the Genus
Hydrocynus
from the White Nile in Sudan
Elagba H.A. Mohamed , Wigdan A.S. Al-Awadi
Institute of Environmental Studies, University of Khartoum, Sudan
Corresponding author Email
International Journal of Aquaculture, 2018, Vol.8, No.1 doi
Received: 06 Nov., 2017
Accepted: 29 Nov., 2017
Published: 05 Jan., 2018
Copyright © 2018
Mohamed and Al-Awadi, This is an open access article published under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article
:
Mohamed E.H.A., and Al-Awadi W.A.S., 2018, Evaluating morphological asymmetry in three species of the genus
Hydrocynus
from the White Nile in Sudan,
International Journal of Aquaculture, 8(1): 1-7 (doi
Abstract
The present study aimed to determine and evaluate the level of fluctuating asymmetry (FA) of morphological characters
for three species of
Hydrocynus
from the White Nile. In
H. vittatus
41% of morphological characters fluctuated to the right side and
59% to left side. In
H. brevis
50% fluctuated to right and 50% to left side, while in
H. forskalii
34% fluctuated to right and 66%
fluctuated to left side. More scales were recorded along the lateral line on the right side of
H. vittatus
and
H. brevis
compared to
H.
forskalii
, while more gill rakers were recorded on the left side of
H. vittatus
. The smallest asymmetry index was found for PVFL of
the three species and the largest index was found for POL of
H. brevis
. Mean asymmetry index was (3.5%) in
H. forskalii
, (5.1%)
and (4.9%) in
H. vittatus
and
H. brevis
, respectively. Absolute asymmetry values were significantly correlated with character size for
the number of lateral line scales, head length, pectoral fin length and ventral fin length (P>0.05) and highly correlated for snout
length and caudal peduncle length (P>0.001) in the three species. Correlations between means of bilateral characters and body size
were significant (P>0.05) for the head length, pelvic fin length and pectoral spine length of the three species. This study is the first of
its kind in species of the Nile fish. The present result can be a base line for further study of fluctuating asymmetry in fish and as
indicators to detect the level of pollutants in the Nile and the condition of the environment and the organisms.
Keywords
Fluctuating asymmetry;
Hydrocynus
; Meristic; Morphometric; Sudan; White Nile
1 Background
The level of fluctuating asymmetry (FA) is most often used to estimate developmental instability of individuals
and populations of fish, when bilateral traits show some variations in the size or counts of the two sides ‘left-right
asymmetry’, where phenotypic traits of left or right individuals differ asymmetrically (Moller, 1997). When
environmental stressors of the environment affects the total morphology of the organisms, the overall symmetry
and developmental stability will be disturbed (Daloso, 2014). Many zoologists studying fish morphology may
regard fish bodies as being laterally symmetric. However, Palmer and Strobeck (1986) showed that there is a high
index of fluctuating asymmetry in various fish populations under strong environmental pressure. Hence, it can
give rise to decreased developmental stability of individuals, which may result in reduced performance of fitness
components (Clarke, 1995; Moller and Swaddle, 1997). Asymmetry in fishes was first described in scale-eating
cichlids from Lake Tanganyika, in the form of bilateral dimorphism when opening their mouths (Mboko et al.,
1998). Recently, however, asymmetry of morphological traits has been documented (Almeida et al., 2008;
Lutterschmidt et al., 2016). Bilateral asymmetry, in individual and population levels of fish, was found to relate
positively to a wide range of abiotic, biotic and genetic stresses (Allenbach et al., 1999; Franco et al., 2002; Estes
et al., 2006), and could be sensitive to different levels of individual density in captive conditions (Leary et al.,
1991) or increases under genetic stresses such as hybridization, inbreeding and loss of genetic variation (Mazzi et
al., 2002; Dongen, 2006), particularly in reared fishes (Palma et al., 2001; Fessehaye et al., 2007).
Hydrocynus vittatus
(Castelnau, 1861),
H. brevis
(Cuvier and Valencience, 1849) and
H. forskalii
(Cuvier, 1819)
are three species of the Nile fishes in the family Alestidae. These species are abundant in varied freshwater
environments, including the White Nile, Blue Nile and the main Nile and Lake Nubia, but
H. forskaliis
is the
commonest species (Bailey, 1994). The synonymy of
H. forskalii
with
H. vittatus
was revised by Brewster (1986).
However, while examining samples of fish for taxonomic revision of the three species (Elagba and Wigdan, 2015),
