Otolith mass asymmetry in three pelagic fish species collected from the Persian Gulf near Bandar Abbas

 Laith Jawad1 and Zahra Sadighzadeh2

 

 

1 Marine Science and Fisheries Centre, Ministry of Fisheries Wealth, P.O. Box 427, Postal Code 100, Muscat, Sultanate of Oman. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 Marine Biology Department, Faculty of Marine Science & Technology, Islamic Azad University, Hesarak, Tehran, Islamic, Republic of Iran.

 

 

Abstract

The mass asymmetry in the otolith of the three pelagic fish species, Encrasicholina punctifer (Family: Engraulidae), Sardinella sindensis (Family: Clupeidae) and Sillago sihama (Family: Sillaginidae) collected from the Persian Gulf near Bandar Abbas was calculated. Saccular otolith mass asymmetry, x, can be defined as the difference between the mass of the right and left paired otoliths divided by the average otolith mass. The results showed that the absolute value of x in these three species does not depend on the length of the fish and the otolith growth rate, although the absolute value of the otolith mass difference decreases with the fish length. This result coincides with the results obtained for the otolith mass asymmetry in other symmetrical fish species. The value of x for the three species did not exceed the range of -0.2 and +0.2.

Keywords: Otolith, Mass Asymmetry, Persian Gulf, Iran, Pelagic Species

 

Introduction


Otolith mass asymmetry can cause several adverse types of behaviour in fish when they experience weightlessness (Egrov and Samarin, 1970; Hoffman, 1977; Von Baungarten et al., 1982; De Jong et al., 1996; Hilbig et al., 2002; Rehman and Anken, 2002; Takabayashi and Ohmura-Iwasaki, 2003; Lychakov and Rebane, 2004). Acoustic functionality of fish might be changed and severely hindered due to changes in the otolith mass asymmetry (Lychakov and Rebane, 2005; Lychakov, 2006). In such changes, the otolith mass asymmetry directly affects the vestibular and auditory functions, however, the exact quantitative morphological and physiological bases of the otolith asymmetry are still unclear (Lychakov, 2006). The lateral compact shape of the fish otolith makes it requisite as a biological model to assess the effect of otolith mass asymmetry on the physiology of fish. Lychakov et al. (2006) recommended that otolith mass asymmetry should be quantified before any attempt to perform a study of direct acoustic and space experiments on fish.

The compact shape of the otolith is always the preferred shape to be used as a biological model through which the physiological role of otolith mass asymmetry can be assessed quantitatively. The natural patterns of otolith mass asymmetry should be quantified beforehand (Lychakov et al., 2006).

Studies on the otolith mass asymmetry in different fish groups showed that the value of this phenomenon falls within the range of -0.2< x < +0.2 or < 20% (Lychakov 1992; Lychakov et al. 1988; Lychakov & Rebane 2004, 2005; Takabayashi and Ohmura-Iwasaki, 2003). The previous authors have also concluded that the value of the otolith mass asymmetry did not correlate with the length or weight of the fish. Such results could be attributed to the otolith mass fluctuation (Lychakov and Rebane, 2004, 2005).

In most symmetric fish species, the value of the otolith mass asymmetry is well below critical, thus they do not experience functional affliction (Lychakov and Rebane, 2005; Lychakov et al., 2006). Several authors (Egorov and Samarin, 1970; Lychakov, 1992; Samarin, 1992; Lychakov, 2002; Scherer 2001) have suggested that the mass of right and left paired otoliths are generally not equal and it is this difference that might be considered among the important factors that impaired the quality of reception of fish in acoustic environments.

The objective of the present study is firstly, to quantify and compare the value of the otolith mass asymmetry range in three pelagic fish species in question, secondly, to assess the variability of this asymmetry during the growth of these species. No previous work has been done on Iranian fish with regard to otolith mass asymmetry. Thus, the present work is considered as additional information in this field for Iranian fish fauna.

 

 

Materials and Methods

Fish specimens (30) of E. punctifer, S. sindensis and S. sihama were collected on 13 June 2007 from the Persian Gulf near Bandar Abbas. Standard length was measured following the procedure of Lychakov et al.( 2006) prior to the removal of otoliths. Otoliths from both sides of the head of fish were dissected out from the auditory capsules, then rinsed in distilled water and air dried at room temperature for several days. The weight of the otoliths was then measured using a Sartorius TE 313S analytical balance to the accuracy of 0.0001g.

The otolith mass asymmetry (x) was calculated from the formula: 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.

In theory, the x value can vary between -2 and 2, and x = 0 represents the absence of mass asymmetry (MR – ML), whereas x = -2 or x = 2 represents the maximum asymmetry (absence of one otolith). The positive value of x means that the right otolith mass is larger than the left paired otolith mass and a negative sign means the opposite.

The relationship between the species' absolute value of x and the species' otolith growth rate was studied. The absolute value of the species' otolith mass asymmetry is calculated as the average individual value.

Results

For E. punctifer, the mean value of x is 0.0068+ 0.0407, n = 30 (Fig. 1) and the value of IXI is 0.0348+ 0.0191, n = 30 (Fig. 2). For S. sindensis, the mean value of x is 0.0063+ 0.0654 (Figure 3) and the value of IXI is 0.0499 + 0.041762, n = 30 (Fig. 4) and for S. sihama, the mean value of x is -0.0013 + 0.0248, n = 30 (Fig. 5) and the value of IXI is 0.0184 + 0.0163, n = 30 (Fig. 6). According to the regression analysis there was no relationship between fish length and both IXI (y = 0.0028x + 0.015) (P > 0.05, R2 = 0.0043) and x (y = 0.0415x - 0.2818) (P > 0.05, R2 = 0.2012) for E. punctifer, (y = -0.0064x + 0.1017) (P > 0.05, R2 = 0.0139) and x (y = -0.0047x + 0.0317) (P > 0.05, R2 = 0.0031) for S. sindensis and (y = -0.0026x + 0.0587) (P > 0.05, R2 = 0.094) and x (y = -0.0009x + 0.0122) (P > 0.05, R2 = 0.0046) for S. sihama.

For the three species in question, the relation between the otolith mass difference (MR – ML) and fish length was more complex than the relation between x and fish length (n = 30, for E. punctifer, total length = 64-77 mm, P > 0.05, y = 0.258x - 1.7459, R2 = 0.2055) (Fig. 7), for S. sindensis, standard length 72-107 mm, P> 0.05, y = 0.0533x - 0.1198, R2 = 0.0269 (Figure 9) and for S. sihama, standard length= 127- 201 mm, P>0.05, y = -0.0132x + 0.1821 + 0.0295 (Figure 9). The saccular otolith mass difference decreases with fish length.

 

Fig1

Figure 1: Saccular otolith mass asymmetry x in Encrasicholina punctifer as a function of the total length of the fish

 

Fig2

Figure 2: Absolute otolith mass asymmetry in Encrasicholina punctifer as function of the total length of the fish

 

Fig3

Figure 3: Saccular otolith mass difference in Encrasicholina punctifer as a function of the total length of the fish

 

Fig4

Figure 4: Saccular otolith mass asymmetry x in Sardinella sindensis as a function of the standard length of the fish