The derivation of opposite gender forms in the case of animal names is a peripheral language phenomenon which is not covered by grammars in sufficient detail. Therefore, grammars sometimes contain simplified and inaccurate statements. This article describes occurrences of derived opposite gender forms of animal names in dictionaries and their usage. Some of the statements included in grammars are either disproved or further specified here. For example, this article proves the productivity of the frequently overlooked suffix -ka and points out the complexity of markedness of derived opposite gender forms. Although the article is primarily synchronic, it also deals with historical development where necessary.