Abstract
Early development of the Adriatic sturgeon Acipenser naccarii from its free embryo after hatching (stage 36), until late embryo stage, when the transition to exogenous feeding starts (stage 45) is described. Special emphasis is given to morphological development and description of the different structures that are formed at each life stage. After hatching, free embryos still present embryonic characteristics, little pigmentation and an ovoid yolk sac. The mouth begins to open on the second day post hatch (dph) and is fully open at 3 dph. The head begins to separate from the body at 4 dph and straightens at 6 dph. The first fins to appear are the pectoral fins on the yolk sac and an embryological fin fold that extends from behind the head to the posterior part of the yolk sac. All other fins will develop from this fold. At 7 dph the caudal fin begins to take a heterocercal form and dorsal scutes are observed. This study provides information that will assist aquaculturists by establishing a reference for the normal development of A. naccarii , which may be useful for evaluating the suitability and quality of fish produced for restocking.