Effect of phosphorus supplementation on cell viability, anti-oxidative capacity and comparative proteomic profiles of puffer fish (Takifugu obscurus) under low temperature stress

The aim of this study was to investigate the effects of dietary phosphorus (P) on the growth and response of obscure puffer under low temperature stress. Six diets were supplemented with graded levels (0, 0.2, 0.4, 0.6, 0.8, 1.2%) of P from Monocalcium phosphate. The analyzed total P contents of the six diets were 0.40, 0.60, 0.81, 0.98, 1.19 and 1.55% respectively. The results showed fish fed diets supplemented with 0 and 0.2% P had significantly lower weight gain, feed efficiency and feed intake than fish fed diets supplemented with 0.6, 0.8 and 1.2% P. After the 8-week feeding trial, puffer fish were exposed to acute low temperature challenge (12 +/- 2 degrees C) and sampled at different time points (0, 3, 6, 12, 24, 48 h). The blood cell numbers were significantly higher in fish fed diets supplemented with 0.6, 0.8 and 1.2% P than in fish fed diets without P supplement at 6, 12, 24 and 48 h. The highest rate of viable blood cells was observed in fish fed diets supplementedwith 0.6 or 0.8% P at 3 and 6 h. At 6, 24 and 48 h, the respiratory burst activities tended to decrease with increasing dietary P supplement up to 0.6, 1.2 or 0.8%, respectively. At 12, 24 and 48 h, plasma CAT activity increased with increasing dietary P supplement up to 0.8%. The highest plasma SOD activity was in fish fed diets supplementedwith 0.6 and 0.8% P at 6 h. At 3, 6, 12, 24 and 48 h, liver GPx activity increased significantly with the increase of dietary P supplement, and GPx activity in the 0.8% feed group achieved the highest. Fish fed diet without P supplement showed the highest plasma MDA level at 3 h and 6 h, highest liver MDA level at 12 h and 24 h. Two-dimensional electrophoresis proteomic approach was used to investigate altered proteins between P deficient (P = 0) and adequate (P = 0.8%) group in liver of puffer fish during cold stress treatment. MALDI-TOF/TOF MS analysis revealed that adequate P diet significantly up-regulated three energy generation related enzymes (ribose-5- phosphate isomerase-like 5, ribulose-phosphate 3-epimerase-like and alpha-enolase-like isoform 2) and two lipid transport proteins (ApoA-I and FABP), and down-regulated an intermediate filament protein (keratin type I cytoskeletal 13-like) of puffer fish during cold stress. These results clearly indicated that dietary P supplement could improve cell viability, anti-oxidative capacity, energy generation and lipid transportation of puffer fish under cold stress. Statement of relevance: This study indicates that dietary P improved cell viability, anti-oxidative capacity, energy generation and lipid transportation of puffer fish under cold stress. The results will contribute to our understanding of the role of phosphorus metabolism in aquatic animals. (C) 2015 Elsevier B.V. All rights reserved.