Fertility of roach × bream hybrids, <i>Rutilus rutilus</i> (L.) ×<i>Abramis brama</i> (L.), and their identification

Abstract

Adult roach, bream and their presumed F 1 hybrid from an Anglian Water reservoir were identified on the basis of morphological and meristic characteristics. The hybrid was clearly intermediate. Four hybrid breeding crosses were induced to spawn by hypophysis. A bream × roach cross (female named first) failed to produce fertile eggs, whereas F 1 hybrid × roach, roach × F 1 hybrid and F 1 hybrid × F 1 hybrid all produced fry. Fertility (defined as survival of eggs to hatching) was high for the F 1 hybrid × roach back‐cross (56%) but low for the others (&lt;2%), in comparison to the pure species controls (roach 69%, bream 76%). Progeny from these crosses were reared until anal fin rays could be counted. These counts indicated intermediacy between the parents and back‐crossed individuals, and similarity between F 1 hybrids and their F 2 progeny.