A natural anti-A agglutinin in the serum of the brown trout (Salmo trutta).

20% of normal serum samples from adult brown trout (Salmo trutta) possess an agglutinin for human erythrocytes with anti-blood-group A specificity. This agglutinin has properties which clearly distinguish it from the agglutinin with anti-(B+'P') specificity found in ova from fish of the same species and from anti-blood A antibodies found in human serum.