Adaptive responses of Hyriopsis cumingii to different purple soils under high-temperature stress

Soil sediment constitutes a vital element within pond aquaculture systems, exerting a profound influence on the growth and disease resistance of cultivated animals. In recent years, aquaculture has been under severe threats due to extreme thermal weather conditions. To scrutinize the impact of different sediment types on the high-temperature stress resistance of Hyriopsis cumingii, this study constructed a 28-day aquaculture experiment employing three different purple soils (S1, Feixianguan group; S2, Shaximiao group; S3, Suining group) as sediment. Regular assessments of water quality indicators ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂⁻-N), nitrate nitrogen (NO₃⁻-N), total nitrogen (TN), total phosphorus (TP), active phosphorus (AP), chemical oxygen demand (COD), total hardness (TH) across varied aquaculture systems were conducted. After the completion of the aquaculture phase, H. cumingii in diverse systems were subjected to ambient (23 °C) and high-temperature (33 °C) conditions. Hemolymph antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), immune-related enzymes alkaline phosphatase (AKP), lysozyme (LZM) activities and H₂O₂ levels were measured at 6 h and 12 h after exposure, and the expression of hepatopancreas immune related genes (IAP, IL-17, HSP70) was analyzed. The results revealed differences in water quality indicators among the three aquaculture systems during the cultivation of H. cumingii. The system using S3 purple soil as sediment had the highest TP levels (peak value: 1.13 mg/L) and lower NO₂-N concentrations (peak value: 0.12 mg/L) compared to the other systems, resulting in a more favorable environment for the growth and health of the cultured organisms. Following high-temperature stress, the activities of SOD and CAT in H. cumingii cultured in S3 purple soil increased to 1.2- to 2.0-fold of those in the control group, and the expression of IAP, IL-17, and HSP70 genes was significantly up-regulated (1.2- to 13.0-fold), indicating enhanced thermotolerance. The adaptability hierarchy among distinct bottom sediment aquaculture systems, in terms of resisting high-temperature stress in H. cumingii, was ranked as S3 > S1 > S2. These findings contribute to a more profound comprehension of the influence of aquaculture sediment on the high-temperature resistance of aquatic organisms.