The authors investigated the growth of straminipiles fungi on the eggs of Adriatic sturgeon (Acipenser naccarii) in water from three trophically different rivers. 170 (32.7%) out of 520 investigated Adriatic sturgeon eggs were infected by straminipiles organisms from 27 species. The largest number of species occurred on the eggs in water from river Biala (more biogenic), and the smallest in water from river Suprasl (poor in biogenes). The most commonly encountered straminipiles species on the Adriatic sturgeon eggs were Achlya polyandra, Aphanomyces irregularis, Saprolegnia ferax, S. parasitica, Leptomitus lacteus and Pythium diclinum. Amino acid, carbohydrate and urease tests were used.