Natural growth, otolith shape and diet analyses of Odontesthes nigricans Richardson (Atherinopsidae) from southern Patagonia

M.E. LATTUCA; I. E. LOZANO; D. BROWN; M. RENZI; C.A. LUIZON

ESTUARINE COASTAL AND SHELF SCIENCE

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Año: 2015 vol. 166 p. 105 - 114

0272-7714

Age and growth, otolith shape and diet of Odontesthes nigricans were analysed in order to provide an insight into the life history of the species and furthermore, to assess their possible use as a tool for discriminating silverside populations from the South Atlantic Ocean (Punta María) and Beagle Channel waters (Varela bay). The age and growth analysis was performed by counting daily increments and annual marks in sagittae otoliths. Length-at-age data of individuals < 65 mm standard length (SL) were fitted to the Laird-Gompertz model (SLt= 6.22 exp 2.45 [1-exp (-0.02 t)]), which explained properly the daily growth for O. nigricans juveniles from Varela bay. The spawning period was also assessed through back-calculation of hatching dates and it extended from November to February. The count of annual marks in larger individuals allowed identifying 7 year classes (0+ to 6+) in Varela bay and 6 year classes (0+ to 5+) in Punta María. The von Bertalanffy growth model explained more than 95% of the growth pattern observed in O. nigricans from Varela bay (SLt = 245.49 [1 ? exp ?0.24(t + 0.46)]) and Punta María (SLt = 345.09 [1 ? exp ?0.15 (t + 0.31)]). Particularly, k and L∞ varied significantly between sampling sites; reaching Punta María population a larger L∞ value at a lowest rate. Otolith shape variation was also explored using elliptical Fourier analysis and it showed significant differences between Varela bay and Punta María populations. Furthermore, the gut content analysis allowed characterizing O. nigricans as an invertebrate predator, being benthic organisms the most important components of its diet, which also showed significant site dependence. The use of all these analyses contributed to a holistic approach which maximized the likelihood of correctly defining the fish population structure in the southernmost limit of the species distribution.