THE INTERACTION BETWEEN GROWTH AND REDOX SYSTEM IN DEVELOPING ATLANTIC SALMON Salmo salar SMOLT

Introduction and objective

Reactive oxygen species (ROS) are becoming increasingly appreciated as signaling molecules, regulating varying cellular processes, such as proliferation and differentiation, beyond the role as damage signal 1, 2. The key mechanism of redox signaling and control involves is impacting the structures, functions, activities or trafficking of associated proteins via the reversible or irreversible redox modifications of redox-sensitive amino acids 3, 4. Accumulating evidence indicates a strong relationship between increased oxidative stress and periods of high growth rates in fish 5-7. However, whether and how the redox system changes during the growth stimulation seen in Atlantic salmon, and do the growth hormone (GH) signals interact with redox signaling directly to increase metabolism or is the oxidative stress a secondary function of a higher metabolic rate and oxidative phosphorylation in the mitochondria caused by growth hormone stimulation remain unclear.

The objective in this study is to elucidate the relationship between growth stimulation and redox environment of Atlantic salmon and the potential role of ROS in contribution to the effects on GH.

Material and methods

This study had two sequential experimental phases (EP) termed EP1 and EP2, both lasting for 6 weeks. Atlantic salmon (initial weight: 38.7 ± 0.6 g) were divided into two groups and reared in 6 replicate tanks at stable temperature (around 12°C) and continuous light. We provided salmon with a diet low vitamins (L) with 230mg/kg ascorbic acid as stay C and 120mg/kg α-tocopherol using the acetate form, while diet high vitamins (H) had 380mg/kg ascorbic acid and 210mg/kg α-tocopherol, respectively. At the beginning of EP2, half of the fish from each group was implanted with formulation of recombinant bovine GH (Posilac®), while the other half was sham-implanted with same volume of the sesame-seed oil vehicle. We evaluated the liver and muscle redox environment and health condition of Atlantic salmon via accessing the total glutathione (tGSH) levels, the redox potential (Eh), ascorbic acid (AA), α-tocopherol (α-TOH), malondialdehyde (MDA) concentrations, the activities of antioxidant enzymes including superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferase (GST) and catalase (CAT) and cataract score compared between treatments in EP1 and EP2.

Results

Here we show that redox-related parameters measured in the EP2 were influenced by growth hormone and diet to varying degrees. Notably, GH-treated salmon had lower levels of reduced glutathione, a more oxidized redox potential of muscle, and higher MDA concentrations of liver. We found that fish fed diet H had higher ascorbic acid and α-tocopherol of liver and muscle than those fed diet L, whereas implantation GH significantly decreased their concentrations. The activities of antioxidant enzymes of liver and muscle were differently regulated by GH implantation, which may be associated with the difference in tissue antioxidant capacity and regulation. There were interactive effects between GH and diet on GPX of liver, and SOD and GR of muscle. Furthermore, we found GH-treated salmon had higher cataract score in the EP2, which suggested cataract is more severe in fish implanted with GH.

Conclusion

Our results demonstrated GH has an oxidative effect on liver and muscle of Atlantic salmon and that there is an interaction between the effects of antioxidant and GH on redox signaling. The present study is intended as a starting point to further understand the potential interactions between growth and redox signaling of fish. 

References

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