Abstract :
[en] 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.
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