The age and quality of pond bottom soil affect water quality and production of Pangasius hypophthalmus in the tropical environment

Pangasius hypophthalmus is the most cultured freshwater fish by smallholder farmers in Indonesia. One of the main challenges in the production is the highly weathered and infertile soils on the bottom of a pond that influences aquaculture productivity. This work investigated the effects of pond age on soil quality, water quality, benthic algae population, and P. hypophthalmus production. We carried out a field experiment in a randomized design with pond age of 4 levels: Ponds aged 0–5 years (P1), 6–10 years (P2), 11–15 years (P3), and 16–20 years (P4). The soil is a Typic Palaeudult (Ultisol), and fish were grown for three months. The results showed that the chemical soil quality parameters and soil organic matter content increased linearly with pond age, resulting in the enhancement of water quality parameters. The increase in nitrate and phosphate directly affected benthic algae richness. These, in turn, in the highest fish production in P3, 6.4 kg/m2, specific growth rate was 3.76 %/d, survival rate of 66.7%, and feed conversion ratio of 1.8%. Linear correlation coefficients indicated that the contents of total N, total P, and organic carbon in the bottom soil of the pond were related to the increase in phosphate, nitrate, and organic matter content in pond water. Total N content, total P, carbon organic matter, C/N ratio, and CEC value in pond bottom soil significantly correlated to Pangus fish production. C/N ratio, CEC value in pond bottom soil, and CO2 concentration in pond water significantly correlated to fish survival rate. Multiple linear regression indicated that fish production was significantly related to the pond age, water NH3, total alkalinity, and soil total P and C/N ratio (R2 = 0.99, P < 0.001). Increased soil C/N ratio caused a negative effect on fish production. The results suggested that old-aged ponds, with proper management, act as a nutrient sink, resulting in increased aquaculture production. The implementation of the best practices will benefit the Pangus culture in the tropical environment.