Preliminary data on the study of otolith morphology of five pelagic fish species from the Adriatic Sea (Croatia)

In teleosts, the inner ear is a complicated structure of canals, sacs and ducts filled with endolymph. Each otic sac contains the otoliths of a calcareous structure named sagitta, lapillus or asteriscus (BOND, 1996). The otoliths differ in size and shape. In most species sagitta otolith is the biggest one and mostly used in during the ageing of fish. Even though the otoliths inside the inner ear have similar functions, their form, size, weight, growth, consistency and chemical composition vary considerably among species (LABEELUND, 1988; GAULDIE, 1994; KARLOURIGA, 2000; YOSHINAGA et al., 2000). Nevertheless, otoliths are generally considered as taxonomical and biological archives as they reflect growth and development of species. Due to that, they are routinely used for characterization of events in the fish life history, age and growth estimations, stock discrimination of exploited fish populations as well as permitting the study of food webs from partially digested remains (COTTRELL et al., 1996). As digital technology developed, fishery biologists started using shape analysis in order to identify stocks by means of morphometric characters of fish or otoliths (BOLLES & BEGG, 2000; TORRES et al., 2000; BEGG et al., 2001; MONTEIRO et al., 2005; TUSET et al., 2006; PONTON, 2006; ZORICA et al., 2007) and to study geographical variations in fish populations (GAEMERS, 1984; NOLF, 1985; CASTONGUAY et al., 1991; CAMPANA & CASSELMAN, 1993; PARMENTIER et al., 2001; GAULDIE & CRAMPTON, 2002; TUSET et al., 2003). The purpose of this study was to analyse pelagic fish variations in otoliths shape and their morphometric measurements in species The otolith (sagitta) measurements of five pelagic fish species Engraulis encrasicolus (Linnaeus, 1758); Sardina pilchardus (Walbaum, 1792); Scomber scombrus Linnaeus, 1758; Scomber japonicus Houttuyn, 1780 and Belone belone (Linnaeus, 1761) – were obtained by image analysis of catch samples retrieved from the Croatian part of the Adriatic Sea. Three dimensionless shape descriptors of form factor (FF), roundness (RD) and aspect ratio (AR) were analysed and revealed statistically significant differences between the otoliths of the stated pelagic fish species. Maximum otolith length (LO) and otolith weight (WO) were linearly correlated to total fish length (TL) for each studied fish species; they were increasing proportionally during fish growth.