International Journal of Marine Science, 2017, Vol.7, No.21, 200-204
203
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.
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