On the formation of the pike otoliths

Abstract

The purpose of the work is to describe the morphological features and time frame of otolith formation in pike embryos for subsequent use of otolith marking for juveniles released to the nature habitats. Observations of the development of eggs were carried out in aquarium conditions. The recirculating aquaculture system was used for incubation of pike eggs. The development of embryos and larvae, as well as preparations of otoliths, were examined using light microscope equipped with digital camera. The sizes of developing embryos, larvae and otoliths were measured in photographs, the scale of the images was determined using reference scale. It was found that the beginnings of hearing organs in form of otic vesicle are formed in pike embryos at the stage of organogenesis on the 6th day of development at the temperature of 9–13 °С. The detectable sign of the processes is the beginning of pigmentation of the embryo’s eyes. The formation of otoliths such as sagittae and lapilluses due to the fusion of primordial spherules and enlargement of globules continues throughout the entire period of embryonic development. By the moment of pre-larvae hatching (on the 10th day after fertilization), they have two pairs of otoliths (sagittae and lapilluses), the average size of which is 66,3±5,1 microns and 53,3±5,3, respectively. The appearance of diurnal rings on otoliths is observed before hatching, at the stage of the mobile embryo or on the first day after hatching. The data on the age of formation of otoliths and appearance of diurnal rings will be used to develop techniques of marking of pike juveniles in the hatcheries.