Development of the olfactory organ in the ontogeny of carps (Cyprinidae)

Abstract

Morphogenesis of the olfactory organ is followed with a light microscopy method in silver carp Hypophthalmichthys molitrix, common carp Cyprinus carpio, Eurasian minnow Phoxinus phoxinus, shemaya Alburnus chalcoides, zebra danio Danio rerio, and bitterling Rhodeus sericeus amarus. In these fishes with different reproductive ecology, the olfactory organ develops in a similar way, and it is characterized by a similar structure in the representatives of different species of the same body length. Morphological features revealed in different species are not numerous, and they are not associated with the development of main structures of the olfactory organ. However, the interspecific differences can be connected with different developmental rates of these structures. Based on developmental rate of the olfactory organ, the studied species are divided into three groups with (1) accelerated development (the litophils, Eurasian minnow and shemaya); (2) moderate development (a pelagophil, silver carp, and the phitophils, common carp and zebra danio; and (3) retarded development (an ostracophil, bitterling). The differences in the degree of development of the olfactory organ in the species from various ecological groups are particularly evident to the beginning of the juvenile period. The appearance of all main structures of the olfactory organ is completed in the litophils at the onset of the second juvenile step (XVII); that in the pelagophils and phitophils is by the end of this step, that in ostracophils is substantially later (young of the current year), and that in zebra danio is to the beginning of sexual maturation. In the studied species, olfactory organ becomes differentiated/formed at different age and at various morphological states of the progeny, but at similar body size (29–30 mm). Thus, the body length of carps can be regarded as an indicator of a level of morphological development of the olfactory organ.