On the populations of roach (Rutilus rutilus), rudd (Scardinius erythrophthalmus), and their hybriin Esthwaite Water, with notes on the distinctions between them

Samples of cyprinid fishes from Esthwaite Water, Westmorland, have been examined and identified as roach ( Rutilus rutilus ), rudd ( Scardinius erythrophthalmus ), with a high degree (37%) of hybridization between these species. The distinguishing features of roach and rudd are discussed in the light of the difficulty of distinguishing the roach x rudd hybrid from the roach. It is concluded that the only reliable characters are the number and external morphology of the pharyngeal teeth.