Short-term dietary teprenone improved thermal tolerance and mitigated liver damage caused by heat stress in juvenile largemouth bass (Micropterus salmoides).

Heat stress seriously threatens fish survival and health, demanding immediate attention. Teprenone is a gastric mucosal protective agent that can induce heat shock protein expression. This research investigated the effects of teprenone on largemouth bass (Micropterus salmoides) subjected to heat stress. Juvenile fish were assigned to different groups: group C (control group, 0 mg teprenone/kg diet), T0, T200, T400, and T800 (0, 200, 400, and 800 mg teprenone/kg diet, respectively), which were fed for 3 days, followed by a day without the diet. All groups except group C were subjected to acute heat stress (from 24 °C to 35 °C at 1 °C per hour and then maintained at 35 °C for 3 h). The results were as follows: The critical thermal maxima were significantly higher in the T200, T400, and T800 groups compared with the T0 group (P < 0.05). Heat stress caused severe damage to the tissue morphology of the liver, while teprenone significantly reduced this injury (P < 0.05). Serum cortisol concentration decreased gradually as teprenone concentration increased, and the lowest concentration was observed in the T800 group (P < 0.05). Compared with the T0 group, the serum activities of aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transferase were significantly lower in the T200, T400, and T800 groups (P < 0.05). The liver activities of catalase, total superoxide dismutase, and peroxidase were significantly higher in the T200 group than in the T0 group (P < 0.05). Transcript levels of the heat shock proteins (hsp90, hsp70, hspa5, and hsf1) and caspase family (caspase3 and caspase9) in the liver of the T200 group were significantly higher than those of the T0 group (P < 0.05). Western blot results showed that HSP70 and HSPA5 in the liver were significantly upregulated in the T200 group compared with the T0 group (P < 0.05). In summary, dietary teprenone improved thermal tolerance, alleviated heat stress damage in the liver, enhanced antioxidant capacity, and upregulated heat shock proteins in juvenile largemouth bass. This study offers theoretical support for applying teprenone in aquaculture to reduce financial losses caused by abiotic factors.

Effect of enzyme-assisted fermentation on quality, safety, and microbial community of black soldier fly larvae (Hermetia illucens L.) as a novel protein source.

Considering the significance and scarcity of quality protein, this study aims to obtain a novel safe protein source through fermenting the black soldier fly larvae (BSFL). Lactobacillus crispatus M1027 and Pichia kudriavzevii DHX19 were added as starters together with neutral protease for enzymolysis during fermentation. The results showed that the low pH value (from 6.60 to 3.99), generated by lactic acid accumulation, created an environment where the pathogen could hardly grow. During fermentation, the flavor compound ethyl acetate content reached up to 406.55 mg/L, and the melanization was effectively inhibited by the starters. The increase of trichloroacetic acid-soluble protein content (from 8.73 % to 17.96 %) contributed to improving the absorbability of product by animals after feeding. Notably, the contents of detrimental substances, including total volatile basic nitrogen and histamine, were both below specified limits after fermentation. Simultaneously, the malonic dialdehyde content remained stable during fermentation. Relative abundance of Lactobacillus and Pichia gradually increased and finally dominated in the culture during fermentation, accompanied by pathogens decline below detection limit (1.0 Log cfu/g). Moreover, there was a close relationship between the dynamics of physicochemical indices and microbial succession. Overall, our studies explored a new process to ferment the BSFL paste which would improve the quality and safety of fermented BSFL paste. This research provided theoretical support for fermented insect as a novel protein source.