Edit: This post was written as a reply to this post. Interestingly, the declension difference between two Croatian dialects is significantly bigger than between Czech and Russian. The Czech declension of ryba looks rather like a transcription of the Russian one into the Latin script. ры́ба - ryba ры́бы - ryby ры́бе - rybě ры́бу - rybu (ры́бо!) - rybo! ры́бе - o rybě ры́бой, ры́бою - s rybou ры́бы - ryby рыб - ryb ры́бам- rybám рыб - ryby (ры́бы!) - ryby! ры́бах - o rybách ры́бами - rybami I see only one difference: in plur. accusative, obviously Russian employs the plur. genitive form (it is possible in Czech, too, but we still call it genitive).