| Summary: | Morphological development of Siberian sturgeon (Acipanser baeri) between hatching and metamorphosis (up to 3 weeks after hatching) was examined in hatchery-reared specimens in order to describe an useful criterion for fish farmers to estimate the quality of young specimens and detect abnormal and unsuitable rearing conditions. Morphological development was described according to morphological traits distinguishable upon external observation of specimens, such as the level of development of sensory, feeding and swimming systems, and the determination of the depletion of yolk sac and onset of exogenous feeding. Two distinct phases were observed in the morphological development of Siberian sturgeon, the prelarval stage which was comprised between hatching (10.4-11.1 mm TL) and first feeding (9-10 days post hatch, 19.7-21.6 mm TL) and the larval stage, which was between the initiation of external feeding and metamorphosis (19-20 days post hatch, 28-32 mm TL). Morphogenesis and differentiation were more intense during prelarval than larval development. Hatchlings and prelarvae had rudimentary sensory and locomotor systems. During prelarval development these systems developed greatly, and at the beginning of the larval stage, their development was almost finished. At the end of the larval phase, specimens resembled a miniature adult. The structure and morphological development of Siberian sturgeon during prelarval and larval ontogeny were quite similar to other Acipenserid species, and some differences were detected in relation with the age at which morphological changes took place, as a consequence of different rates of development and rearing temperatures.
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