The growth and reproductive biology of the invasive goldfi sh Carassius auratus auratus were studied in Lake Trasimeno, central Italy. The results of the research revealed that the population is made up of eight age-classes. The sex ratio proved to be extremely unbalanced (1 : 19 in favour of females). Growth can be deemed rapid, the von Bertalanffy growth in length function being TL = 43.019{1- e(-0.272(t+0.162) )} for the total sample and Ф’ = 2.702. No sexual dimorphism in growth was observed. Back-calculation analysis suggested the existence of an inverse Lee phenomenon among 1 year-old specimens. The reproductive period covers a broad time-span, from March to June. In females, sexual maturity is reached after the second winter of life (2+ age-class); however, a small percentage (7.55%) of females is able to reproduce at the age of 1 year. Most of the males attained sexual maturity in the fi rst year (60.61%). The reproductive investment of the females is high; the relationship between SL and the number of eggs was Ne = 0.0041 SL4.368. Fecundity varied from 286 to 219104 eggs, with an average relative fecundity of 103 ± 5 eggs g-1; the mean diameter of the eggs was 1.27 ± 0.01 mm. The reproductive investment of the females was not homogeneous across the ageclasses; in addition to absolute fecundity, relative fecundity and egg diameter were seen to increase with the size of the specimens.
The ruffe Gymnocephalus cernuus L. is an introduced species in Italy. In order to assess the impact of exotic species on native fish communities, the ecology and biology of intruders need to be thoroughly investigated. The aim of this study was to analyse the growth and reproductive biology of the ruffe population in Lake Piediluco. From June 1999 to March 2002, and between July 2004 and May 2005, 1 330 specimens belonging to seven age-classes were captured. Sex was determined in 385 individuals: 327 females and 58 males. The SL-TL relationship for the whole sample was TL = 0.923 + 1.075SL. The SL-W relationship was W = 0.0154 SL3.102 for females and W = 0.0157 SL3.106 for males. The parameters of the von Bertalanffy growth curve for length using back-calculated SL were L∞ = 218.29 mm, k = 0.27 y -1, t0 = -0.61 for females and L∞ = 161.54 mm, k = 0.32 y-1, t0 = -0.70 for males. The results showed that in Lake Piediluco ruffe grow as fast as in their original environments. Seasonal growth and back-calculation showed the possible existence of differential mortality prejudicial to small specimens. Moreover, growth analysis revealed marked sexual dimorphism in growth in the Lake Piediluco population. Sexual maturation occurred in both sexes at the end of the first year of life. Reproduction occurred mostly in May and June. The mean diameter of eggs was 1.12 mm. The mean number of eggs produced by each female was 11 961, and increased with the size of the specimens; with regard to relative fecundity, an average value of 239 eggs g-1 was observed. This analysis reveals some important biological characteristics of the ruffe that were not previously well known with regard to the Italian population of the species.