The article presents the principles of the program to restore the Atlantic sturgeon Acipenser oxyrinchus in Poland and the results obtained to date. Since 2004, various life cycle stages (fertilized eggs, hatchlings, fingerlings) obtained through the controlled reproduction of wild spawners caught in the St John River in Canada have been imported. Broodstocks are held in three facilities, two of which were built specifically for the Atlantic sturgeon restoration programme. From each group of the initial imports from Canada, 50-100 individuals are being held for further rearing. Additionally about fifty individuals from the 1997 and 2001 year classes were transferred from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (Berlin, Germany). These are also the offspring of earlier imports from Canada. Juvenile sturgeons are used for experimental stocking and studies aimed at increasing rearing effectiveness. Rearing early life cycle stages of Atlantic sturgeon was a difficult task, the final results of which remained unpredictable in early trials. The highest losses of larvae are incurred when the fish begin exogenous feeding. Feeding studies focus on the selection of appropriate diets and feeding strategies. The latest results indicate that during the initial feeding period, the fish can be fed once daily. Studies on sturgeon migration were conducted in the Drwęca River, and the results indicated that migration rates vary significantly among juvenile sturgeon, with the mean migration rate in spring being lower than in autumn. Currently, the Polish efforts to restore the Atlantic sturgeon focusses on (i) building broodstocks at specialized facilities, (ii) improving hatching and early rearing techniques, (iii) performing experimental stocking with hatchery-reared juveniles, and (iv) acquiring knowledge on the basic elements of the Atlantic sturgeon life history under local conditions. Fertilized eggs of A. o. oxyrinchus will still have to be imported from Canada for several years before self-sufficient production from raised ex-situ brood stocks will become available. The formation of a Polish ex-situ founder population is imbedded in an overall restoration approach in close cooperation with the neighbouring country having shared sturgeon waters and this is in line with the respective international recommendations for sturgeon species conservations.

Bromelain is a proteolytic enzyme extracted from Ananas comosus and has great potential to affect several physiological functions. The current study examined the effect of bromelain added to commercial feed at concentrations of 0 g (control), 10 g (B1) and 20 g (B2) per kg diet on growth, feed utilization, intestinal morphology, digestive enzyme and immune response of juvenile Sterlet (Acipenser ruthenus) for 56 days. At the end of this experiment, the highest final body weight was detected in fish fed diet of B2 compared to control. The protein content of whole fish was higher in fish fed diet of B1 and B2, but the content of calcium, iron, copper and zinc was noted lower in fillets of fish fed diet of B1 and B2. Supplementation with bromelain significantly increased the height of mucosal folds, enterocytes and the supranuclear zone of the epithelial cells compared to control diet. The enzymatic activity of lipase and pepsin was significantly (p < 0.05) higher in fish fed diet of B1 and B2. The highest activity of lysozyme, total protein level and total immunoglobulin and the proliferative activity of T and B cells were detected in fish fed diet of B2 compared to control, where no significant (p > 0.05) difference was found in ceruloplasmin, metabolic activity of spleen macrophages and potential killing activity of spleen phagocytes between different treatments.

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Abstract. The aim of the study was to determine the retention rates of visible implant elastomer (VIE) and coded wire tags (CWT) and the impact tagging had on the growth of Atlantic sturgeon, Acipenser oxyrinchus Mitchill, during an eight-week rearing period under laboratory conditions. Two size groups of young-of-the-year (YOY) sturgeon were used in the study. The tagging was not found to have a significant impact on the final total length or body weight or the condition coefficient of the sturgeon from either size group. Sturgeon survival in the different groups ranged from 90.6 to 100%. Mortality was not noted until two (CWT) and four (VIE) weeks following tagging and was probably not linked to tagging. The retention rate for VIE tags implanted in the rostrum in both size groups was 100%, while for tags implanted at the base of the pectoral fin was 93.5%. The retention of CWT in the smaller fish was 90%, and in the larger sturgeon it was 100%. Tagging small sturgeon with CWT and VIE is minimally invasive, and it did not impact the growth or condition of the tagged fish.

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