Interactive effects of short-term temperature and density stress on growth, physiology, endoplasmic reticulum stress, and apoptosis of juvenile Megalobrama amblycephala

To examine the interactive effects of temperature and density on short-term growth and stress responses, juvenile Megalobrama amblycephala (30.18 ± 0.60 g) were reared for four weeks under two temperatures (22 °C, 32 °C) and three stocking densities (1.5, 3, and 6 kg/m³). Two-way ANOVA revealed that FBW, WGR, and SGR were significantly influenced by temperature, density and their interaction, with density being the stronger effect. The reduced growth observed at lower temperature and higher density. Plasma GLU, TC, and HDL were significantly influenced by the interaction between the two factors, with temperature being the stronger effect. The elevated temperature increased plasma lipids levels (TC and LDL), while higher density elevated plasma GLU and reduced plasma lipids levels (TC, HDL and LDL). Hepatic GSH content declined with increasing density. Temperature markedly affected hepatic genes related to ER stress and apoptosis ( ire1 , vdac1 , nf-κb , il-6 ), which were upregulated at low temperature, whereas hsp90 expression was higher at high temperature. The expression of perk , grp75 , and hsp70 increased with density. Temperature also significantly influenced intestinal metabolites, with 13 common differential metabolites identified among the 22 °C-1.5 kg/m³ group, 32 °C-1.5 kg/m³ group, 32 °C-6 kg/m³ group. In conclusion, both rearing temperature and stocking density exert significant and strong effects, with density exerting the dominant effect on growth performance of juvenile M. amblycephala , while temperature primarily affected plasma parameters. Furthermore, rearing temperature playing a dominant role in regulating physiological status, ER stress, and intestinal metabolites. • Stocking densities of 6 kg/m 3 inhibited growth and caused stress of M. amblycephala . • Rearing temperature of 32℃ promoted growth, while 22℃ caused stress. • Density and temperature exert the dominant effects on growth performance and plasma physiology. • Intestinal metabolites involved in antioxidant, anti-inflammatory, and lipid metabolism changed.