FEATURES OF EARLY STAGES OF DEVELOPMENT OF ANCHOVY SPRAT (CLUPEONELLA ENGRAULIFORMIS BORODIN)

For more than 50 years anchovy sprat fishing in the Caspian Sea has been a leading trend. Yearly sprat catch reached 440,000 tons. The main fishing object was anchovy sprat represented in the Caspian Sea by a single population consisting of a large number of non-separated reproductively biological groups occupying the area of the Middle and Southern Caspian at a depth more than 15-20 m. Studying the size of population in sprat generations is impossible without knowing embryonic and post embryonic periods of species development, because main elimination of generations takes place in early ontogenesis. This problem has not been studied thus far and requires further investigation. The study is based on the results of scientific surveys made in 2010-2017 in the Middle and Southern part of the Caspian Sea by the researchers of Caspian scientific institute of fisheries. The study of early stages of development was carried out at water temperature of 19-20°C, samples were taken every hour. Fecundation was made by dry method in Petri dishes; impregnated roe was transferred into aquariums. Early stages of impregnated eggs development: processes of swelling and forming a plasma knob, blastomeres, stages of forming morula, blastula, gastrulation turning into organogenesis (from segmentation up to emerging prolarvae from membrane). Post-embryonic development is characterized by forming rudimental fins, mouth opening, movements that precede swimmability, pigmentation of eyeballs, orientation to light. For 11th-14th day after hatching there takes place the change of mixed nutrition to food taken from the water, which means qualitatively new, larval stage of development.