Age, growth and otolith morphometry of Atlantic bonito (Sarda sarda Block, 1793) from the eastern Mediterranean Sea /Mado Kotsiri, Ioannis E. Batjakas, Persefoni Megalofonou.
Sažetak

The otoliths of the Atlantic bonito, Sarda sarda (Bloch, 1793), were examined with the aim to estimate the age and growth of the species in the eastern Mediterranean Sea and to reveal possible relationships between otolith shape or size and age. All specimens used in this study, ranging from 7.2 to 70.4 cm in fork length and from 20 to 4889 g in total weight, were caught in the Aegean and Ionian Seas during the period 1997-2010. Otolith morphometry was studied using image analysis techniques for all intact sagittae ranging in weight from 0.6 to 11.3 mg and four shape indices were calculated. No statistical significant differences between left and right otolith morphometric variables were found. The age of fish was estimated by counting the pairs of opaque and translucent bands in transversal thin sections of otoliths. The estimated ages ranged from 0+ to 7 years and the von Bertalanffy growth parameters were determined \((L∞=79.9 cm, k=0.261 and to=-1.230 years)\). The examination of the type of growth bands at the outside margin of each otolith per month showed that one translucent band is formed annually during the cold season. The results revealed statistically significant relationships between otolith morphometric variables and fish length or age. Among the variables, otolith weight was the one that showed the highest correlation with age (R=0.77). Therefore, otolith weight could represent a valuable criterion for age estimation in Atlantic bonito that is objective, economic and easy to perform compared to annuli counting method in hard parts.; Kako bi se odredila starost i rast palamide Sarda sarda (BLOCH, 1793), koja obitava u Sredozemnom moru, analizirani su njeni otoliti. Isto tako se analizom morfometrijskih parametara otolita palamide pokušala utvrditi korelacija između oblika samog otolita i očitane starosti. Vilična dužina i masa svih analiziranih jedinki palamide, koje su prikupljene na području Jonskog i Egejskog mora u razdoblju od 1997. god. do 2010. god., kretala se u rasponu od 7.2 cm do 70.4 cm odnosno od 20 g do 4889 g. Morfometrijske značajke neoštećenih otolita, čija masa je bila od 0,6 mg do 11,3 mg, su definirane preko četiri parametra oblika istih. Nije utvrđeno da postoji statistički značajna razlika između lijevog i desnog otolita. Starost palamide, dobivena očitavanjem i brojanjem zona prirasta na otolitu, istraživanih jedinki je kolebala od 0+ do 7 godina starosti te su definirani von Bertalanffy parametri rasta \((L∞=79.9 cm, k=0.261 i t_o =-1.230 god.)\). Analizirajući zone prirasta na otolitu uočeno je da tijekom jedne godine nastaje jedan hijalini (proziran) prsten i to u hladnijem dijelu godine. Utvrđena je statistički značajna korelacija između morfometrijskih parametara otolita i dužine ribe kao i starosti. Osobito značajna korelacija (R=0,77) je uočena između mase otolita i dužine istraživane jedinke, što upućuje na to da bi se u budućnosti navedeni parametar – masa otolita, mogla koristiti kao indikator starosti s obzirom da se radi o metodi koja bi u svakom slučaju bila dosta ekonomičnija i jednostavnija.