Research Report

Otolith Mass Asymmetry in Two Parrotfish Species, Chlorurus sordidus (Forsskål, 1775) and Hipposcarus harid (Forsskål, 1775) from Hurghada, Red Sea Coast of Egypt  

Laith A. Jawad1 , Sahar F. Mehanna2 , Mohamed A. Abu El-Regal3 , Yassin A. Ahmed4
1 Flat Bush, Manukau, Auckland, New Zealand
2 Laboratory of Population Dynamics, Fisheries Division, National Institute of Oceanography and Fisheries, Suez Branch, Suez, Egypt
3 Marine Science, Department, Faculty of Science, Port Said University, Port Said, Egypt
4 Laboratory of Population Dynamics, Fisheries Division, National Institute of Oceanography and Fisheries, Red Sea Branch, Hurghada, Egypt
Author    Correspondence author
International Journal of Marine Science, 2017, Vol. 7, No. 21   doi: 10.5376/ijms.2017.07.0021
Received: 08 May, 2017    Accepted: 31 May, 2017    Published: 09 Jun., 2017
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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:

Jawad L.A., Mehanna S.F., El-Regal M.A.A., and Ahmed Y.A., 2017, Otolith mass asymmetry in two parrotfish species, Chlorurus sordidus (Forsskål, 1775) and Hipposcarus harid (Forsskål, 1775) from Hurghada, Red Sea coast of Egypt, International Journal of Marine Science, 7(21): 200-204 (doi: 10.5376/ijms.2017.07.0021)


The asymmetry in the mass of the sagitta of the parrotfish species, Chlorurus sordidus and Hipposcarus harid collected from Hurghada, Red Sea coast of Egypt was investigated. In the present study, the weight of the difference between the weight of the sagitta from both the left and right sides was divided by average otolith mass. The results shown that the value of x in the two-species studied does not related to the length of the fish, though the value of otolith weight difference has shown a trend of increase with the fish length. The value of x was calculated to fall between -0.2 and +0.2.

Otolith; Weight asymmetry; Parrotfish; Red Sea; Acoustic and vestibular functions


The condition of weightlessness due to the mass asymmetry in the otolith might cause changes in the behaviour of the fish (Egorov and Samarin, 1970; Hoffman, 1977; Von Baungarten et al., 1982; De Jong et al., 1996; Hilbig et al., 2002; Rehman and Ankan, 2002; Takabayashi and Ohmura-Iwasaki, 2003; Lychakov and Rebane, 2004). The inconsistency and incongruity of the otolith from both sides of the head can be due the otolith weight asymmetry that could lead to acoustic imperfections in fishes (Lychakov and Rebane, 2005; Lychakov, 2006). Therefore, the damage in the tasks of the vestibular and auditory sense are unavoidable, but Lychakov et al. (2006) suggested that the certain measureable morphological and physiological outcomes of otolith asymmetry are uncertain at this stage.


To evaluate quantitatively the physiological role of the otolith weight asymmetry, a compacted form of otolith is considered the ultimate shape and since fish otolith has such configuration, then it is preferred for such studies (Lychakov et al., 2006).


In fish, the otolith mass asymmetry is usually having a value of 0.2< X < +0.2 or <20% (Lychakov et al., 1988; Lychakov, 1992; Takabayashi, 2003; Lychakov and Rebane, 2004; 2005). In addition, the previous authors reach to a conclusion that the otolith weight asymmetry and length or weight of the fish were not related to each other (Lychakov and Rebane, 2004; 2005). Additionally, no functional damage will be detected as the otolith mass asymmetry drops well below the values stated above as in the symmetric fish species (Lychakov and Rebane, 2005; Lychakov et al., 2006). The mass asymmetry of otolith might affect the quality of reception as proposed by Egorov and Samarin (1970), Lychakov (1992), Samarin (1992), Scherer (2001) and Lychakov (2002).


There are no studies on the asymmetry in weight of fishes from Egypt. Therefore, the work at hand is regarded the pioneer work in this field and will add further information on the asymmetry in weight in fish fauna of Egypt. The goal of this study is to calculate and to assess the inconsistency of this asymmetry of Chlorurus sordidus and Hipposcarus harid. In having mass asymmetry in the otolith, fish might change its habit (Gagliano et al., 2007; Gagliano and McCormick, 2009). The survival of young individuals will be threatened as it will be difficult for them to find a proper place for settlement and hence a pronounce changes to the stock of the species will result.


1 Materials and Methods

Hurghada is located at the northern part of the Red Sea between latitude 270 10'N- 270 33'N and longitudes 330 70'E – 330 85'E (Figure 1). It is situated 500 km south-east of Cairo, and extends for about 36 kilometres. Hurghada is bounded by Ras Gareb in the north, Safaga in the south, Red Sea coast in the east and Sohag and Asyut Governorates in the west. Hurghada was selected as a study area in this work due to its importance as a main fishing ground for the two species in question.


Figure 1 Map showing sampling locations


The fish landings at Hurghada fishing harbour is used to obtain specimens of parrotfish samples during two fishing seasons June-August, 2012-2013. The nets used consist of one layer in gill nets and three layers in trammel nets, the first and third layers have large mesh size while the second (middle) one with narrow openings. The fishing net used are with length range of 60 to 100 m with mesh size of 2 – ¼ mm. A single population of the two species was used in the analysis presented in this study. Total length was measured to the nearest 0.1 mm. Sagittae were extracted and then cleaned and stored dry in glass tubes. The left and right otolith were dealt with separately. Sagittae specimens were collected from different fish length groups and several specimens from each length group were collected. The weight of each otolith was taken using Sartorius TE 313S analytical balance to an accuracy 0. 0001 g.


The otolith mass asymmetry (x) was calculated from:

x = (mR – mL) m-1


Where mR and mL are the otolith masses of the right and left paired otoliths and m is the mean mass of the right and left paired otoliths. The x value can fall between -2 and +2, and x = 0 represents the absence of mass asymmetry (mR = mL), whereas x = -2 or x = 2 represent the maximal asymmetry (absence of one otolith). The positive value of x means that the right otolith mass is larger than the left otolith weight and a negative sign means the opposite. The absolute value of the species otolith mass asymmetry |x| is calculated as the average individual value. To assess otolith growth, rate the association between otolith mass and fish length, m = a. l + b, was calculated where, l is the length of the fish, “a” is the coefficient illustrating the growth rate of the otolith, and “b” is a constant for the species studied.


2 Results

The mean value of m is mean = 0.0078 ± 0.002 (n = 30, total length = 17.0-24.8 cm) for C. sordidus and 0.0067+ 0.004 (n = 30, total length = 17.0-36.8 cm) for H. harid (b = 0.0027, a = -0.0473). The relationship between otolith mass and fish total length is m = a l + b, (b = 0.0027, a = -0.0473) for C. sordidus and (b = - 0.0024, a = -0.0698) are shown in Figure 2 and Figure 3.


Figure 2 Saccular otolith mass asymmetry x in Chlorurus sordidus as a function of fish length


Figure 3 Saccular otolith mass asymmetry x in Hipposcarus harid as a function of fish length


The mean absolute value of the otolith mass asymmetry |x| for C. sordidus and for H. harid are 0.44 and 0.03 respectively.


The regression analysis has shown that the fish length and |x| were not related in the two-species studied (Figure 4 and Figure 5). However, the qualitative results of absolute value of otolith mass difference |mR– mL| in both species showed to be increased slightly with the fish length (Figures 6 and Figure 7).



Figure 4 Absolute otolith mass asymmetry of Chlorurus sordidus as function of fish length



Figure 5 Absolute otolith mass asymmetry of Hipposcarus harid as function of fish length


Figure 6 Saccular otolith mass difference in Chlorurus sordidus as a function of fish length



Figure 7 Saccular otolith mass difference in Hipposcarus harid as a function of fish length


3 Discussion

In both species studied, the value of x is found to be between -0.2 and +0.2 a case is similar to what is usually found in the remaining marine fish species (Lychakov et al., 2008) and the weight asymmetry in the otolith was less than 0.05. This value corresponds with the value of weight asymmetry gained for a large number of marine species (Lychakov et al., 2006) and did not rely on otolith growth rate. Additionally, the absolute value of the otolith weight difference increases with the fish length and this is a distinctive of the littoral and bottom fishes and not the pelagic fishes (Lychakov and Rebane, 2004; Lychakov, 2013).


The functionality of hearing of the fish ear can be affected and reduced due to asymmetry in otolith weight (Lychakov and Rebane, 2004; 2005). As in the most of the fish species studied (Lychakov et al., 2006; Lychakov, 2013), including the two parrotfish species studied, otolith mass asymmetry is very low (|x| < 0.5), regardless of fish length. Such a low level of otolith asymmetry is characteristic for utricular and lagenar otolith organs. Lychakov and Rebane (2005) have stated that only fishes that contain the largest otoliths and |x| > 0.2 could, in theory, develop problems with sound processing due to discrepancy and oddness of the movement of the two otoliths on both sides of the head of the fish. As a result, most fish species can evade functional inability as they have otolith mass asymmetry below critical value (0.2< X < +0.2).


The present results agree with those obtained by other investigators on several fish species where this asymmetry does not depend on fish size (Lychakov and Rebane, 2004; 2005; Lychakov et al., 2006; Jawad et al., 2010; Lychakov, 2013). Though, the relationship between otolith mass difference and fish length is intricate. The present work, this relationship is very low and near non-existence for both species studied. Lychakov and Rebane (2004; 2005) have shown similar results on several fish species and proposed that the low relationship or absence of such relationship could be due to small sample used in the study and when the specimens do not differ markedly in size.


The difference between the otolith masses was investigated in Beryx splendens and Lutjanus bengalensis and found to increase with the increased fish length (Jawad et al., 2012), but practically did not change in Rhynchorhamphus georgi (Jawad et al., 2011). This difference seems to be connected with that in many fish species because of their high variability of the left and right weight difference and the fish length is clearly revealed in analysis of the sufficiently large sample when individuals significantly differ in size (Lychakov et al., 2006).


Investigation this type of study in a large number of specimens with wide range of body length is necessary to assess the relationship between the otolith mass difference and the fish length.


Authors’ contributions

All authors have contributed equally toward the publication of this paper.



We would like to thank D. Lychakov, Russian Academy of Science, Institute of evolutionary Physiology and Biochemistry and D. G. Pazhayamadom, School of Biological, Earth and Environmental Sciences, University College Cork, Ireland for reading the manuscript and for their valuable advice and suggestions.



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