Validating annulus formation and examining the potential use of pectoral spines for age determination in Aristotle's catfish (Silurus aristotelis)
P>The potential use of pectoral fin spines for ageing purposes was examined in Aristotle's catfish (Silurus aristotelis) and validated for growth proportionality and growth mark periodicity. Monthly samples (n = 436, total length range: 11.10-36.70 cm) were collected in Lake Pamvotis, Greece from November 2002 to December 2003. Marginal increment analysis showed that the spine width (SW) radius grew proportionally to total body length (TL) (TL = 9.581 + 6.83SW, r2 = 0.66, n = 431, P < 0.01), and was at a minimum in January and February, indicating a single growth mark formation per year (i.e. annulus). Further analyses showed that the morphometric characteristics of the spines did not differ significantly (r2 > 0.80 in all cases) when removed from one side of the fish or the other. The procedure was based on individuals no older than 5 years of age; extrapolation to higher age classes may be critical.