Application of a Single-Tank Sequencing Batch Reactor for Long-Term Zebrafish Care

Abstract

Sequencing batch reactors are efficient wastewater treatment systems, however, they are not adapted to treat aquaria. We aimed to compare the efficacies of a modified single-tank sequencing batch reactor (SSBR) and a regular overflow filtration system. Zebrafish were maintained in an acrylic aquarium connected to an SSBR or in a tank connected to a regular overflow filtration system for 27 weeks. Water change or aeration using air stone was not performed. The water quality in both groups was within the normal range until 26 weeks, after which the nitrite and nitrate levels increased. The average temperature was, 29.46 ± 0.71°C and 29.78 ± 0.70°C; pH, 8.22 ± 0.14 and 8.20 ± 0.12; ammonia levels, 0.1 ± 0.001 and 0.01 ± 0.005; nitrite level, 0.04 ± 0.06 and 0.05 ± 0.09 mg/l; and ammonia removal rate, 0.12 and 0.12 mg/l/h, in the control and SSBR groups, respectively. The average dissolved oxygen concentration was 5.81 ± 0.48 and 6.18 ± 0.50 mg/l; and the average nitrate level was 5.59 ± 6.47 and 10.17 ± 15.31 mg/l, in the control and SSBR groups, respectively. Beneficial microorganisms such as bacteria, diatoms, nematodes and ciliated protozoa were found in the biological reactors. The SSBR provides a long-lasting, healthy aquarium environment with optimal aeration and a diverse microbial community, while enabling the culture of a small number of fish. Zebrafish are common experimental animals in clinical research, especially in veterinary and medical science. This modified system could be beneficial for small-scale animal laboratories with limited budgets.