Reproductive behaviour and sexual production in the first-generation hybrids of roach Rutilus rutilus L. x common bream Abramis brama L

English. peer reviewed

English. The aim of this study was to further test the viability of the roach Rutilus rutilus · common bream Abramis brama hybrid in terms of reproductive behaviour and sexual production. Egg release, mating and aggressive acts in reproductive behaviour, as well as absolute fecundity and sperm density in milt for sexual production were examined in the first generation of these hybrids at their first sexual maturity. The F2 and backcrosses of hybrids were also studied. The results revealed that these hybrids expressed a normal and typical mating behaviour, producing viable gametes. Under experimental reproduction between hybrids (hybrid reproduction), the number of egg-release acts (range, 21–66) was nearer (v2 test, P > 0.05) the number of mating acts (11–65). Moreover, hybrid males exhibited territorial and aggressive behaviours. However, in experimental reproduction of female and male hybrids mixed with parental males (mixed reproduction), the egg-release act and the mating act were inhibited by the intense territorial and aggressive activities of the common bream male. Absolute fecundity values (median, <2.2 · 103 eggs) and sperm density (<7 · 109 spermatozoa ml)1) of hybrids showed a greater decrease (U test, P < 0.05) than in parental species (median, >6.0 · 103 eggs and >14 · 109 spermatozoa ml)1, respectively). Nevertheless, these hybrids were fertile. F2 and backcross generations were produced, although with a significantly lower viable hatching rate (FEP test, P < 0.05) in F2 individuals from the female and its corresponding hybrid male (<6%), indicating a very low chance of survival in rivers.