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 6 Saccular otolith mass difference in Chlorurus sordidus 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.

Acknowledgments

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.

References

De Jong H.A.A., Sondag E.N.P.M., Kuipers A., and Oosterveld W.J., 1996, Swimming behaviour of fish during short periods of weightlessness, Aviation Space Environ Medicine, 67: 463-466

Egorov A.D., and Samarin G.I., 1970, Possible change in the paired operation of the vestibular apparatus during weightlessness, Kosmicheskaya biol I Aviakosmicheskaya Medicine, 4: 85-86 (in Russian)

Gagliano M., Depczynski M., Simpson S.D., and Moore J.A.Y., 2008, Dispersal without errors: symmetrical ears tune into the right: frequency for survival, Proceedings of the Royal Society B, 275: 527-534

https://doi.org/10.1098/rspb.2007.1388

Gagliano M., and Mc Cormick M., 2004, Feeding history influences otolith shape in tropical fish, Marine Ecology Progress Series, 278: 291-296

https://doi.org/10.3354/meps278291

Hilbig R., Anken R.H., Bäuerle A., and Rahmann H., 2002, Susceptibility to motion sickness in fish: a parabolic aircraft flight study, Journal of Gravity Physiology, 9: 29-30

Hoffman R.B., Salinas G.A., and Baky A.A., 1977, Behavioural analyses of killifish exposed to weightlessness in the Apollo-Soyus Test Project, Aviation Space Environmental Medicine, 48: 712-717

Jawad L.A., Al-Mamry J.M., Hager M., Al-Mamari M., Al-Yarubi M., Al-Busaidi H.K., and Al-Mamary D.S., 2011, Otolith Mass Asymmetry in Rhynchorhamphus georgi (Valenciennes, 1846) (Family: Hemiramphidae) Collected from the Sea of Oman, Journal of the Black Sea/Mediterranean Environment, 17(1): 47–55

Jawad L.A., Al-Mamry J.M., Al-Mamari D., and Al-Hasani L., 2012, Study on the otolith mass asymmetry in Lutjanus bengalensis (Family: Lutjanidae) collected from Muscat City on the Sea of Oman, Journal of FisheriesSciences, 6: 74–79

Lychakov D.V., 1992, Morphometric studies of fish otoliths in relation to vestibular function, Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 28, 531-539 (in Russian)

Lychakov D.V., 2002, Otolithic membrane: structural and functional organization, evolution, ecomorphological plasticity and tolerance to extreme conditions (Doctorskaya Dissertaziya), Vol 1. Sechenov Institute, St.-Petersberg (text, tables), pp.1-266, Vol. 2 (illustrations), pp.1-107 (in Russian)

Lychakov D.V., 2013, Behavioural lateralization and otolith asymmetry, Journal of Evolutionary Biochemistry Physiology, 49: 441-456

https://doi.org/10.1134/S0022093013040099

Lychakov D.V., and Rebane Y.T., 2004, Otolith mass asymmetry in 18 species of fish and pigeon, Journal of Gravity Physiology, 11: 17-34

Lychakov D.V., and Rebane Y.T., 2005, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hearing Research, 201: 55-69

https://doi.org/10.1016/j.heares.2004.08.017

Lychakov D.V., Boiadzhieva-Mikhaĭlova A., Khristov I., Pashchinin A.N., and Evdokimov I.I., 1987, Changes in the otolithic apparatus of rats and fish after long-term rotation with increased acceleration, Kosmicheskaia biol i aviakosmicheskaia Med, 22: 27-33

Lychakov D.V., Rebane Y.T., Lombarte A, Fuiman L.A., and Takabayashi A., 2006, Fish Otolith asymmetry: morphometry and modelling, Hearing Research, 219: 1-11

https://doi.org/10.1016/j.heares.2006.03.019

Lychakov D.V., Rebane T.Y., Lombarte A., Demestre M., and Fuiman L., 2008, Saccular otolith mass asymmetry in adult flatfishes, Journal of Fish Biology, 72: 2579-2594

https://doi.org/10.1111/j.1095-8649.2008.01869.x

Rahman H., and Anken R.H., 2002, Gravitational biology using fish as model systems for understanding motion sickness susceptibility, Journal of Gravity Physiology, 9: 19-20

Samarin G.I., 1992, Study of the labyrinth asymmetry and its possible role in the motion sickness genesis (Tezisy Kandidatskoi Dissertazii), Institute for Biomedical Problems, Moscow, pp.1-33 (in Russian)

Scherer H., Helling K., Clarke A.H., and Hausmann S., 2001, Motion sickness and otolith asymmetry, Biological Sciences in Space, 15: 401-404

https://doi.org/10.2187/bss.15.401

Takabayashi A., 2003, Functional asymmetry estimated by measurements of otolith in fish, Biological Sciences in Space, 17: 293-297

https://doi.org/10.2187/bss.17.293

Von Baumgarten R.J., Wetzig J., Vogel H., and Kass J.R., 1982, Static and dynamic mechanisms of space vestibular malaise, Physiology, 25: 33-36