وحید مرشدی

Background. Fish may experience periods of food deprivation or starvation in nature and under culture conditions. Because of the wild stock reduction of some sturgeon species, Siberian sturgeon, Acipenser baerii Brandt, 1869, has been used as a biological model of physiological and nutritional studies since the 1980s. There are no published records on the physiological responses of Siberian sturgeon to starvation. Hence, in this study the effect of shortterm starvation (0, 2, 4, and 8 days) on plasma thyroid hormones (T3 and T4), total protein levels, and hepatosomatic- (HSI), viscero-somatic- (VSI), and digestive-somatic (DSI) indices in juvenile Siberian sturgeon was investigated. Materials and methods. The experiment was conducted at the International Sturgeon Research Institute of Rasht (Iran) in October 2009, using a semi-natural environment (natural photoperiod and natural water temperature fluctuations). After a period of adaptation (10 days on a formulated diet), 180 juvenile Siberian sturgeon individuals (mean weight ± standard error at start of experiment: 19.32 ± 0.43, n = 15) were randomly distributed among twelve circular, 500-L, fibreglass tanks with a flow-through system. In this trial, control (C) was fed a formulated diet to apparent satiation four times daily throughout the experiment. The other three groups were deprived of feed for 2- (2S), 4- (4S), and 8 (8S) days, respectively. At the end of the starvation periods, blood samples were collected to analyze biochemical and physiological parameters. Results. Plasma T3, T4, and total protein levels did not significantly vary between the fed and the starved fish. In comparison to the starved groups, after 8 days of starvation, plasma total protein in group 8S (3.43 ± 0.20) was markedly higher than in 2S (2.67 ± 0.07) and 4S (2.37 ± 0.12) groups. In the presently reported study, a decrease in the measured morphometric indices was observed with an increase in the length of the starvation period. Conclu