Sudden mass mortalities of fish reared in recirculating aquaculture systems (RAS) have occurred in recent years. High total dissolved sulphide (H₂S + HS^- + S^2-) levels in the rearing water have been suggested as an underlaying factor for such mass mortalities. However, limited information is available regarding H₂S dynamics in commercial aquaculture production facilities. In this case study, we present H₂S dynamics in the rearing water of two commercial salmon post-smolt (150–250 g) RAS facilities equipped with different biofilters: one RAS with fixed bed biofilters (fRAS) and the other RAS with moving bed biofilters (mRAS). The farms operated at different water exchange rates and cumulative feed load but were otherwise comparable in terms of biomass and feed loading throughout the monitoring period. Self-calibrating, automatic gas-phase H₂S sensors were installed at three locations per farm: after the fish tanks, after the biofilters and after the degassers and operated for a period of approximately 70 days in both farms. H₂S was observed at maximum daily average of 0.6 µg/L in all locations monitored in the two RAS facilities and no significant fish mortality was reported during the monitoring period. In the fRAS, H₂S concentration dynamics showed that there was a net concentration increase after the fish tanks and after the biofilters, and a net concentration decrease after the degassers. Furthermore, in the fRAS, backwashing of fixed bed biofilter chambers caused a slight increase in H₂S after the biofilters. In the mRAS, there was a net positive increase in H₂S after the fish tanks, and a net concentration decrease after the biofilters and degassers. Moreover, generally, H₂S concentration in RAS seemed to be unrelated to feeding or fish biomass. Thus, this study suggests that the main contributing factors to H₂S dynamics in RAS are biofilter design, system, and tank water exchange rates and, and potentially aeration and turbulence within each compartment.

近年来，循环水养殖系统（RAS）养殖的鱼类突然大量死亡的情况时有发生。饲养水中的高总溶解硫化物 (H ₂ S + HS ^- + S ^{2- ) 水平被认为是造成这种大规模死亡的潜在因素。}_{然而，关于商业水产养殖生产设施中H 2} S动态的可用信息有限。在本案例研究中，我们展示了两个配备不同生物过滤器的商业鲑鱼后幼鱼（150–250 g）RAS 设施的饲养水中的 H ₂ S 动态：一个 RAS 配备固定床生物过滤器 (fRAS)，另一个 RAS 配备移动生物过滤器。床生物过滤器（mRAS）。这些农场在不同的水交换率和累积饲料负荷下运营，但在整个监测期间的生物量和饲料负荷方面具有可比性。自校准、自动气相 H ₂ S 传感器安装在每个养殖场的三个位置：鱼缸后、生物过滤器后和脱气器后，并在两个养殖场运行了大约 70 天。在两个 RAS 设施监测的所有地点，观察到的H ₂ S 最大日平均值为 0.6 µg/L，并且在监测期间没有报告显着的鱼类死亡。在fRAS中，H ₂ S浓度动态表明，鱼缸和生物过滤器之后的净浓度增加，而脱气器之后的净浓度下降。此外，在fRAS中，固定床生物过滤室的反冲洗导致生物过滤器后的H _{2 S略有增加。}在mRAS中，鱼缸后H ₂ S净浓度正增加，而生物过滤器和脱气器后净浓度下降。此外，一般来说，RAS中的H ₂ S浓度似乎与摄食或鱼生物量无关。因此，这项研究表明，RAS 中 H ₂ S 动力学的主要影响因素是生物过滤器设计、系统和水箱水交换率，以及每个隔间内潜在的曝气和湍流。