Growth of black bullhead Ameiurus melas (Rafinesque, 1820) in Corbara Reservoir (Umbria – Italy)

摘要

The age and growth of the invasive black bullhead Ameiurus melas (Rafinesque, 1820) were studied in the Corbara Reservoir, an artificial lake located on the River Tiber in central Italy. The results of the research revealed that the population was made up of eight cohorts, the oldest specimens being spawned in 1999. The sex ratio appears to be balanced, although females predominate in the younger cohorts, while the percentage of males increases among older specimens. The differences between sexes in the slope of the length-weight relationship were not statistically significant; the slope for the whole sample (b = 3.055) was significantly greater than 3, indicating an allometric growth pattern of the black bullhead. There were no significant differences in mean back-calculated lengths at age between the sexes. Analysis of Lee’s phenomenon revealed the existence of differential mortality among younger individuals (1 and 2 years old) that favours larger individuals. The Von Bertalanffy growth function was TLt = 35.69 {1 – exp[–0.18 (t + 0.27)]}. The specimens caught displayed mean relative weight (Wr) values distinctly below 100 at all ages, while no significant difference emerged between the sexes with regard to condition.