Introduction

One of the major factors that causing modification in the behaviour of the fish is the case of lightness due to the weight difference of the otolith between the two sides of the head 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). Variation in the weight of the fish may be due to the otolith weight differences, which might cause acoustic inadequacies (Lychakov et al., 2006), consequently, the fish cannot avoid the impairment in the function of the sense of hearing.

In fishes, the otolith weight asymmetry is usually 0.2< X < +0.2 or <20% (Lychakov et al., 1987; Lychakov, 1992; Takabayashi, 2003), and the otolith mass asymmetry and length or weight of the fish were not related to each other (Lychakov and Rebane, 2004). Results of several investigators have revealed the function of hearing in the fish will be affected if otolith weight asymmetry becomes lower than the standards stated above for the symmetric fish species (Lychakov et al., 2006). Samarin (1992), Scherer (2001) and Lychakov (2002) have recommended that the mass non-symmetry of otolith might change the quality of reception, which could affect in return the navigation of the fish.

Numerous studies on the weight difference of the otolith of fishes from the Omani waters were published in the recent years (i.e., Jawad et al., 2010; Jawad et al., 2011; Ambuali et al., 2011; Jawad et al., 2012; Jawad, 2013), but there is no such study on L. ehrenbergii. Therefore, the present work is a significant addition to the knowledge of otolith mass asymmetry in the area of Sea of Oman. The objective of the work at hand is to determine and to evaluate the discrepancy of this asymmetry of L. ehrenbergii. Habits of the fish might show deviation from that of the normal pattern once the weight in the otolith is started (Gagliano et al., 2007; Gagliano and McCormick, 2009). The endurance of the juveniles will be endangered with the increasing inability to locate an appropriate place to inhabit and hence noteworthy alterations to the population of the species will yield.

1 Materials and Methods

Otolith mass and fish length were obtained from 50 samples of L. ehrenbergii fished from the Sea of Oman, the City of Muscat, Sultanate of Oman between May and June of 2017 from the commercial artisanal catch. Fish were measured for their standard length was recorded preceding to otolith removal. The otoliths were extracted, washed in 70% ethanol and left to dry in the room temperature for few hours. Analytical balance to an accuracy 0.0001 g was used to record the weight of the otolith. The otolith non-asymmetry (x) was measured using following the formula:

Where MR and ML are the otolith weights of the right and left otoliths and M is the mean mass of the right and left otoliths. Theoretically, x value can take any value between -2 and 2, and x = 0 indicates the absence of mass asymmetry (MR – ML), while x = -2 or x = 2 denote the maximal asymmetry (absence of one otolith). The x positive value indicates that the weight of the otolith on the right is larger than that on the left, while the negative sign denotes the opposite. The association of the species absolute value of |x| and the increase in the growth of the otolith was investigated. The absolute value of the species otolith weight non-asymmetry is estimated as the average individual value. To assess otolith growth rate, the relationship between otolith mass and fish length, m = a x l + b, was determined, where “l” is the length of the fish, “a” is the coefficient illustrating the growth rate of the otolith, and “b” is a constant.

2 Results

The x mean value is 0.0049 + 0.0237 SE, n = 45 (Figure 1) and the value of |X| is 0.0156 + 0.0134 SE, n = 45 (Figure 2). Absence of association between fish length and both |X| was revealed (y = 0. 0006 x + 0.0222) (P > 0.05, R² = 0.1107) and x (y= -0.0001 x +0.0328) (P > 0.05, R² = 0.0219).

The correlation between otolith mass difference (MR – ML), and fish length was more intricate than the relation between x and fish length (n = 45, standard length = 210-230 mm, P > 0.05, y = -2E- 05x + 0.0051, R² = 0.0177) (Figure 3).The saccular otolith mass difference increases with fish length.

3 Discussion

The results have shown that the value of x falls in the range -0.2 and +0.2, which is comparable to what is normally given for other marine fish species (Lychakov, 2013) and it is found that the mass asymmetry in the otolith is less than 0.05. An agreement with the value of weight asymmetry observed in marine fishes (Lychakov et al., 2006) and did not depend on otolith growth rate. Moreover, the absolute value of the otolith non-asymmetry with the fish length and this is a characteristic of the littoral fishes (Lychakov, 2013).

The function of the ear of the fish can be disturbed because of the difference in the weight of the otolith (Lychakov and Rebane, 2004; 2005). As in the previous cases on several fish species, including the lutjanid fish observed, otolith weight non-asymmetry is low (|x| < 0.5), irrespective of fish size. This low level of otolith asymmetry is one of the features of both the hearing organs. Lychakov and Rebane (2005) have indicated that fishes with large otoliths and |x| > 0.2 may, in theory, develop difficulties with sound processing due to inconsistency and peculiarity of the movement of the two otoliths in the head of the fish. Consequently, large number of fish species can avoid the loss in hearing ability of their otolith mass non-asymmetry is ranging below the value (0.2< X < +0.2).

This study showed results support those acquired for a number of fish species, where otolith mass non-asymmetry dissociate with the fish length (Jawad et al., 2017). Nevertheless, the relationship of the otolith mass difference and fish size is complicated. This study showed that this correlation is very ineffectual and near non-absence. Lychakov and Rebane (2004) have revealed comparable results on a number of fish species and suggested that the minimal correlation or non-appearance of such association may because to the small number of samples studied, with specimens are very close in their sizes.

The results obtained for Beryx splendens and Lutjanus bengalensis (Jawad et al., 2012) and Rhynchorhamphus georgi (Jawad et al., 2011) appeared to be species specific due to their high inconsistency in weight of the left and right otolith. In the analysis where a large number of specimens is used with clear differences in the fish size, such discrepancies in the otolith weight between the two sides of fish head become minimal (Lychakov et al., 2006).

Authors’ contributions

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

Acknowledgments

Our sincere thanks are due to Oman Animal & Plant Genetic Resources Centre (OAPGRC), Scientific Research Council, Muscat, Sultanate of Oman, for giving us the opportunity to work on the fish specimens.

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