Assessing the suitability of three purple soils for aquaculture by physiological responses in freshwater bivalves (Hyriopsis cumingii)

Small-scale pond aquaculture is one of the fast-growing land use options in fragmented mountainous regions of southwest China. This study measured the quality of three purple soils from Kaizhou (S1), Bishan (S2), and Tongnan (S3) in the Sichuan Basin and assessed their potentials as aquaculture substrates through overlying water trials. The effects of the substrates on the immunity, metabolism, and thermal resistance of Hyriopsis cumingii were also investigated. Soil properties analysis showed that the three soils varied in pH, total organic matter, macro-nutrient, and micro-nutrient contents. The maximum total potassium and available potassium favorable for phytoplankton growth were observed in S3. The physicochemical parameters of the substrates in the overlying water trials concurred with the soil properties. Furthermore, soil enzymes may be used as indices of soil fishability. However, S1 and S2 soils were prone to leach noxious ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2−-N) in water columns. On the other hand, S3 soil maintained the dynamic balance of the antioxidant system in H. cumingii, activated the relative expression of their immune-related and metabolism-related genes, and improved their resistance to thermal stress. Principal component analysis suggested that NH4+-N and NO2−-N in the soil were key environmental factors that destroyed the antioxidant system and impeded the metabolic process of H. cumingii. Based on the findings, the soils were ranked in terms of their suitability for aquaculture as follows: S3 > S1 > S2. Our study will provide a scientific foundation for building inland aquaculture ponds and developing land use policies in China and around the world.