Summary Atlantic sturgeon (Acipenser oxyrinchus), also known as Baltic sturgeon, is considered extinct in German waters. Fish‐rearing for conservation purposes largely relies on classical hatchery technology focusing on traits like survival and growth in captivity but rarely focusing on subsequent life in the wild, lacking skills such as foraging or anti‐predation behavior. Predation is hence a major factor for mortality in newly stocked individuals. The aim of this study was to evaluate if naïve Baltic sturgeon juveniles were able to recognize a common predator—zander (Sander lucioperca)—by olfactory cues and adapt accordingly. Over a period of 30 days, Baltic sturgeons were supplied with effluent water from a rearing tank with zander (zander unit) and, as a control, carp (carp unit), three tanks each. Distribution within the tank, morphology of the dorsal scutes, stress (glucose, lactate and cortisol) and gene expression of brain plasticity and cognition were studied in comparison to the control group (carp unit). No significant differences between the zander and the carp unit were observed in any of the parameters measured. Thus, we conclude that naïve Baltic sturgeon is not able to innately recognize potential predators by olfaction alone. Therefore, future studies should focus on applying predator odor together with chemical alarm substances.

SUMMARYAtlantic sturgeon (Acipenser oxyrinchus), also known as Baltic sturgeon, is considered extinct in German waters. Fish-rearing for conservation purposes still relies on classical hatchery technology producing fish not well suited for facing life in the wild, lacking behavioural skills such as foraging or anti-predation. Predation is hence a major source of mortality in newly stocked individuals. The aim of this study was to evaluate if naïve Baltic sturgeon juveniles were able to smell and recognize a common predator, sander (Sander lucioperca). Over a period of 30 days, three tanks from each group of Baltic sturgeon were attached to a rearing tank with sander (sander unit) and, as a control, carp (carp unit). Morphology of the dorsal scutes, distribution within the tank, stress (glucose, lactate and cortisol) and gene expression of brain plasticity and cognition were studied in comparison to the control group (carp unit). No significant differences were observed in any of the parameters measured. Thus, we conclude that naïve Baltic sturgeon is not able to innately recognize potential predators and future studies should focus on implementing predator odour together with chemical alarm substances.