Occurrence of Haemogregarina bigemina (Protozoa: Apicomplexa) in Blennius pholis (Pisces: Blenniidae) along the Portuguese west coast

The occurrence of Haemogregarina bigemina in Blennius pholis was studied at four localities on the Portuguese west coast. Prevalence ranged from 2.9 to 78.6% and was significantly different ( P < 0.01) at the various localities. Intensity of infection in individual fish was usually low (< 0.01 % of erythrocytes infected) but one specimen was heavily parasitized (2.8% erythrocytes infected). The smallest infected fish was 3.2 cm long; all 7.0 cm and longer fish were infected. Development was not seen outside erythrocytes or within leucocytes. Some erythrocytes (< 0.01%) in one fish were unusual in containing four mature gametocytes. Circumstantial evidence indicates that prevalence was higher in polluted waters. Possible transmission routes for the parasite are discussed.