Age, growth and reproduction in creole perch (Percichthys trucha) in the Negro River, Argentinean Patagonia

P>Age, growth and reproductive characteristics of creole perch, Percichthys trucha, were investigated in the Negro River, southern Argentina from samples collected seasonally, December 1994-December 1995. Age was estimated via scale and whole otolith reading methods. Total length (n = 413) ranged from 103 to 432 mm, and weight from 12 to 1042 g. Significant differences between the length-weight relationships of males and females were detected (P < 0.05). Isometric growth was observed in juveniles and males, whereas total population and females exhibited positive allometric growth. The marking pattern in scales and otoliths followed an annual rhythm, with the formation of only one annulus in scales and only one hyaline band in otoliths during autumn-winter. The oldest males were 5 years old whereas maximum age in females was 12 years from scales and 15 years from otoliths. Because scales were found to underestimate age in individuals older than 4 years, otoliths were considered to be the best structures for creole perch age determination. Gompertz growth parameters based on otolith data were L infinity: 428.0 mm, k = 0.46 and t(0) = 0.43 for total population (r = 0.90), L infinity: 410.7 mm, k = 0.42 and t(0) = 0.46 for males (r = 0.91), and L infinity: 434.1 mm, and k = 0.49 and t(0) = 0.43 for females (r = 0.91). Lengths at first maturity (TL(50)) were 260 and 241 mm in males and females, respectively, both of which corresponded to ages between 1 and 2 years. Macroscopic gonad inspection and the high percentage of juveniles captured during summer indicated that spawning begins at the end of spring.