Effects of dietary Sargassum horneri on resisting hypoxia stress, which changes blood biochemistry, antioxidant status, and hepatic HSP mRNA expressions of juvenile black sea bream Acanthopagrus schlegelii

Abstract

Aquatic hypoxia is a frequent event and a complex set of physiological and biochemical alterations are employed to cope with this environmental stress in fish. This study aimed at evaluating the protective effects of Sargassum horneri on hypoxia stress in black sea bream Acanthopagrus schlegelii. Four hundred and eighty fingerlings with approximate mean body weight of 12.0 ± 0.1 g were randomly distributed into four experimental groups in triplicate. Each group was stocked with 40 fish and fed with isonitrogenous (42% crude protein) and isolipidic (12% crude lipid) experimental diets containing either 0% (control), 3%, 6%, or 9% S. horneri in the feed. At the end of 8 weeks of experimental feeding, fish were exposed to hypoxia (dissolved oxygen 2.5 mg L−1) conditions for 12 h and subsequent recovery to normoxia (dissolved oxygen 7.2 mg L−1). Fish samples were collected after hypoxia stress at 0, 6, 12 h, and 12 h recovery to normoxia, respectively. Hypoxia stress caused a significant increase in the serum concentrations of cortisol, glucose, and lactate at 6 h after hypoxia, as well as the activities of hepatic superoxide dismutase (SOD) and MDA content at 12 h after hypoxia compared with 0 h after hypoxia. Moreover, the fish exhibited a significantly higher level in the mRNA expressions of hepatic Cu/Zn-SOD, HSP70, and HSP90 at 12 h after hypoxia. However, dietary S. horneri supplementation could significantly improve antioxidant capacity and resistance against hypoxia stress, particularly in the 6% S. horneri group. Therefore, the optimal dietary S. horneri level based on increasing the resistance of hypoxia for juvenile black sea bream in the present study was estimated to be approximately 6% dry diet.