61 Laith Jawad & Zahra Sadighzadeh Water Research and Management, Vol. 2, No. 2 (2012) 61-66 Otolith mass asymmetry in three pelagic ish species collected from the Persian Gulf near Bandar Abbas Laith Jawad 1 and Zahra Sadighzadeh 2 1 Marine Science and Fisheries Centre, Ministry of Fisheries Wealth, P.O. Box 427, Postal Code 100, Muscat, Sultanate of Oman. E-mail: laith_jawad@hotmail.com 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 ish 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 deined 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 ish and the otolith growth rate, although the absolute value of the otolith mass difference decreases with the ish length. This result coincides with the results obtained for the otolith mass asymmetry in other symmetrical ish 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 ish 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 ish 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 ish otolith makes it requisite as a biological model to assess the effect of otolith mass asymmetry on the physiology of ish. Lychakov et al. (2006) recommended that otolith mass asymmetry should be quantiied before any attempt to perform a study of direct acoustic and space experiments on ish. 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 quantiied beforehand (Lychakov et al., 2006). Studies on the otolith mass asymmetry in different ish 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 ish. Such results could be attributed to the otolith mass luctuation (Lychakov and Rebane, 2004, 2005). In most symmetric ish species, the value of the otolith mass asymmetry is well below critical, thus they do not experience functional afliction (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 ish in acoustic environments. UDK: 591.485:597.5(267.35)