Reproductive performance in F1 hybrids of two phytophilous cyprinid fish, the silver bream (Blicca bjoerkna) x the rudd (Scardinius erythrophthalmusl

Reproductive performance including the spawning behaviour and quality of gametes
in cultured F1 hybrids of two phytophilous cyprinid fish species, the silver bream
Blicca bioerkno x rudd Scardinius erythrophtalmus was investigated in this study at
their first sexual maturity. The spawning behaviour was studied in terms of egg
release, courting and mating acts under reproductive conditions between hybrids or
mixed with the silver bream males. Behavioural experiments were conducted in
experimental environments simulating natural reproductive conditions of the
species using the spawning ground, high temperature, mixing of sex, natural
photoperiod and no hormonal injections. The quality of gametes was evaluated by
analysing egg production, sperm density, and F2 and backcross offsprings. For the
egg production, the gonadosomatic index, absolute fecundity and egg diameters
were analysed at spawning. sperm density was estimated by counting spermatozoa
in a hemocytometer. F2 and backcross offsprings were produced from eggs of the
female hybrid fertilised with the sperm of a corresponding hybrid male and a male
silver bream. The results revealed that these hybrids exhibited all the reproductive
behaviours of the parental species with an intense courting activity. Each egg-release
act was accompanied by mating activity, involving simultaneously and successively
all the experimental males, hybrids and silver bream, resulting in fertilised eggs. The
quality of female sexual products was close to that found in parental species.
However, the male sexual products were found more diluted, and F2 generations
produced with a significantly lower hatching rate than backcrosses. This study has
proven that these FL hybrids have the capacity to exhibit all the reproductive
behaviour as observed in the wild population of parental species. These hybrids are
fertile and thus biologically viable. ln rivers, their backcrossed offsprings have a
greater chance of occurring than F2 progeny.