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ABSTRACT In this study we analyzed possible differences among the specimens of the little tunny Euthynnus alletteratus (Rafinesque, 1810) inhabiting Tunisian waters. Our investigation based on the analysis of morphological characteristics of Euthynnus alletteratus from two distant sampling sites (Mahdia and Zarzis) along the Tunisian coast using 11 morphometric and 3 meristic characters in order to investigate the morpholgical variation among them. Uni and Multivariate analysis of variance of 64 adult specimens showed significant differences among the means of the two studied sites for 8 standardized morphometric measurements out of 11 characters. The principal component analysis (PCA), scatter plot of individual component score between PC1 and PC2 showed two morphometric groups. The linear canonical variate analysis (CVA), the overall assignments of individuals into their original groups was 95.13%.
The morphometric and meristic analysis were fully congruent and confirm the occurrence of two potential differentiated groups. This variation of morphometric and meristic characters in specimens from two populations could be caused by differences in genetic structure or environmental conditions.
Key words Euthynnus alletteratus, Morphological characters, Meristic characters, Morphometric differentiation, Tunisian waters.
INTRODUCTION The Atlantic little tunny, Euthynnus alletteratus (Rafinesque, 1810) is the only member of the genus Euthynnus distributed in Atlantic and Mediterranean waters (Collette and Nauen, 1983; El-Haweet et al., 2013). This species is widely distributed in neritic inshore waters about 200 m depth in the both sides of the tropical and subtropical Atlantic Ocean, including the Mediterranean, Caribbean Sea and Gulf of Mexico (Colette et al., 2011). In the Mediterranean Sea, the maximum size attained is about 100 cm fork length and about 12 kg weight whereas in the Atlantic the maximum fork length is 90 cm (Collete and Nauen, 1983; Collete, 1986). This species occurs in schools by size together with other scombridae species, but has a tendency to scatter during certain periods of the year. Usually found in coastal waters with swift currents, near shoals and around the warmer waters of thermal fronts and upwelling.
The information on the migration pattern of small tunny such as E. alletteratus is much scarcer and more fragmented (ICCAT, 2006; di Natale et al., 2009) although its behavior is supposed to be less migratory than other tuna species (ICCAT, 2006). There is little information available to...