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Ractopamine is a drug used as an additive in animal production to improve growth, body composition, and production efficiency, although its use in fish is still poorly known. This study aimed to evaluate ractopamine hydrochloride (RAC) effects at increasing levels (0, 10, 20, and 40 mg kg-1) in Nile tilapia (Oreochromis niloticus) diets during 40 days by considering growth performance, body composition, and muscle fiber morphometry. One hundred and twelve fish (mean initial weight 518.63 ± 5.49 g) were housed in 16 circular tanks (450 L), following a completed randomized design with four treatments and four replicates. Body composition was significantly affected (P < 0.05), and the content of lipids in fish fillets dropped 26.7% (20 mg kg-1 RAC) and 26.1% (40 mg kg-1 RAC), as well as the amount of unsaturated fatty acids C14:0 and C18:0 in fish fillets (P < 0.05) by treatment with 10 mg kg-1 of RAC. Results demonstrate that fish fed 20 mg kg-1 RAC for 40 days changed Nile tilapia fillet chemical composition, decreasing lipid levels, altering the fatty acid profile, and increasing protein levels. RAC did not affect any productive performance parameters evaluated for muscle fiber morphometry. [ABSTRACT FROM AUTHOR]

Marine microalgae produce extracellular metabolites such as exopolysaccharides (EPS) with potentially beneficial biological applications to human health, especially antioxidant and antitumor properties, which can be increased with changes in crop trophic conditions. This study aimed to develop the autotrophic and heterotrophic culture of Tetraselmis suecica (Kylin) Butcher in order to increase EPS production and to characterize its antioxidant activity and cytotoxic effects on tumor cells. The adaptation of autotrophic to heterotrophic culture was carried out by progressively reducing the photoperiod and adding glucose. EPS extraction and purification were performed. EPS were characterized by Fourier-transform infrared spectroscopy and gas chromatography-mass spectrometry. The antioxidant capacity of EPS was analyzed by the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) method, and the antitumor capacity was measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, showing high activity on human leukemia, breast and lung cancer cell lines. Although total EPS showed no cytotoxicity, acidic EPS showed cytotoxicity over the gingival fibroblasts cell line. Heterotrophic culture has advantages over autotrophic, such as increasing EPS yield, higher antioxidant capacity of the EPS and, to the best of our knowledge, this is the first probe that T. suecica EPS have cytotoxic effects on tumor cells; therefore, they could offer greater advantages as possible natural nutraceuticals for the pharmaceutical industry. [ABSTRACT FROM AUTHOR]