Adult roach, bream and their presumed F1 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 F1 hybrid × roach, roach × F1 hybrid and F1 hybrid × F1 hybrid all produced fry. Fertility (defined as survival of eggs to hatching) was high for the F1 hybrid × roach back‐cross (56%) but low for the others (<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 F1 hybrids and their F2 progeny.

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