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The present study examines the particular metabolic strategies of the sturgeon Acipenser naccarii in facing a period of prolonged starvation (72 days) and subsequent refeeding (60 days) compared to the trout Oncorhynchus mykiss response under similar conditions. Plasma metabolites, endogenous reserves, and the activity of intermediate enzymes in liver and white muscle were evaluated. This study shows the mobilization of tissue reserves during a starvation period in both species with an associated enzymatic response. The sturgeon displayed an early increase in hepatic glycolysis during starvation. The trout preferentially used lactate for gluconeogenesis in liver and white muscle. The sturgeon had higher lipid-degradation capacity and greater synthesis of hepatic ketone bodies than the trout, although this latter species also showed strong synthesis of ketone bodies during starvation. During refeeding, the metabolic activity present before starvation was recovered in both fish, with a reestablishment of tissue reserves, plasmatic parameters (glucemia and cholesterol), and enzymatic activities in the liver and muscle. A compensatory effect in enzymes regarding lipids, ketone bodies, and oxidative metabolism was displayed in the liver of both species. There are metabolic differences between sturgeon and trout that support the contention that the sturgeon has common characteristics with elasmobranchs and teleosts.

This work analyses the changes in the redox balance in two fish species: Adriatic sturgeon (Acipenser naccarii) and rainbow trout (Oncorhynchus mykiss) during starvation and refeeding period. The starvation period raised the lipid peroxidation (thiobarbituric-acid-reacting substances) levels in liver and blood, while a decline occurred in the antioxidant enzymatic activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR) in both fish species. In liver, after the refeeding period, SOD activity recovered in both species, whereas CAT activity recovered only in trout. Furthermore, in both tissues of the two species, the lipid peroxidation levels remained high after 2 months of refeeding. In white muscle and heart, the lipid peroxidation levels indicate that these tissues did not undergo oxidative stress during the 72-day period. During starvation, in the muscle of both fish the fall in the lipid peroxidation level coincided with a rise in CAT, GPX and GR. The refeeding period in this tissue raised the lipid peroxidation level, and the enzymatic activities reached the values of the first point of starvation. In heart, no oxidative damage was detected during starvation in either species. The CAT and SOD activities increased during the starvation period only in trout. KEY WORDS

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