P>The life history characteristics of Aristotle's catfish, Silurus aristotelis (Agassiz 1856) were studied in Lake Pamvotis (northwestern Greece). Samples were collected on a monthly basis using gillnets, trammel-nets and traps. Total lengths ranged from 11.1 to 36.7 cm. Sex ratio was biased toward females (F : M = 1.8 : 1) and was statistically different from unity (KH2 = 46.94, P < 0.001). Spawning is from April to June. The relationship between total length and total weight showed positive allometric growth for males (TW = 0.0035 x TL3.21, r2 = 0.93, n = 198, P < 0.001) and females (TW = 0.0066 x TL3.02, r2 = 0.95, n = 363, P < 0.001). Age was determined on the annual growth marks formed on the spine of the pectoral fin. Based on cross-section readings of the spine, lifespan of the Aristotle's catfish was 5 years. Age classes 1 and 2 dominated the catches (39.1 and 40.0% of the total sample, respectively). Back-calculated lengths at age showed a rapid increase in fish size during the first year of life, reaching 61.1% of maximum attainable length, and a declining growth rate thereafter. Growth parameters were calculated as L-infinity = 36.12 cm, K = 0.37 year-1, t(0) = -0.76 year based on the observed lengths at age and as L-infinity = 28.19 cm, K = 0.53 year-1, t(0) = -0.62 year based on the back-calculated lengths at age. It seems that some of the life history traits (longevity, growth pattern, reproductive period) are influenced significantly by adverse effects of pollution and eutrophication on the lacustrine ecosystem.
