Imbalanced C/N - controlled, periphyton-based system has hampered tilapia growth in stagnant experimental tanks

Resumo

The simultaneous use of periphyton and controlled C/N ratio of water may improve water quality and fish growth. The current assay investigated the interaction between periphyton and C/N ratio of water in rearing tanks with Niletilapia juveniles. The study was carried out in 20 outdoor stagnant 250-L tanks. A wooden structure for periphyton development was submerged in five of the tanks. A completely randomized 2 x 2 factorial mode design was employed to evaluate the following factors: (1) substrate for periphyton and (2) the C/N ratio of water. Dry molasses were applied weekly in the tanks to raise C/N ratio of water to 20:1. The addition of molasses to the culture water significantly lowered DO₂ and pH levels of water, and raised nitrite concentration. Fish stocked in the control tanks (no periphyton, no C/N ratio balance) attained a final body weight significantly higher than those observed for other treatments after 6 weeks of culture. In spite of the correction of C/N ratio of water to 20: 1, low DO₂ concentrations avoided the suitable development of bioflocs.