Freshwater Ecology Group, Centre for Environmental Management, Central Queensland University, Rockhampton, QLD, 4702, Australia.
Sustainable Regional Development Programme, Centre for Environmental Management, Central Queensland University, Rockhampton, Australia.
Environ Sci Pollut Res Int. 2014 Feb;21(3):1701-1707. doi: 10.1007/s11356-013-2031-0. Epub 2013 Aug 23.
High amounts of humic substances (HS) are commonly found in natural acidic waterways and have been suggested to offer some protection against low pH. This study investigated the ability of HS to decrease respiratory stress in eastern rainbowfish (Melanotaenia splendida splendida) exposed to decreases in pH (range of 7-3.5) in soft and hard water. Repeated measures ANOVA revealed a significant difference in respiration (time taken for ten operculum movements) between pH and HS treatments, with a significant interaction between pH and HS present in 5/6 trials. Respiratory stress was shown to increase with increasing acidity, but significantly decreased in treatments with HS (10 and 20 mg/L) compared to those without. The fish exposed to pH treatments without HS also displayed increased hyperactivity, larger operculum movements and increased mucous production. Increased morbidity was shown in HS treatments at pH 3.5 (soft water) and at pH 4 (hard water) compared to treatment without HS. This indicates that HS is helpful in ameliorating the effects of decreased pH on respiration at sublethal pH levels; however, as pH decreases further, it seems that HS increases the toxicity (morbidity) of the low pH.
高浓度的腐殖质（HS）通常存在于天然酸性水道中，并被认为可以提供一些对低 pH 值的保护。本研究调查了 HS 在软、硬水中 pH 值下降（范围为 7-3.5）时，对东方彩虹鱼（Melanotaenia splendida splendida）呼吸应激的降低能力。重复测量方差分析显示，pH 值和 HS 处理之间的呼吸（十次鳃盖运动所需的时间）存在显著差异，5/6 次试验中存在 pH 和 HS 之间的显著相互作用。呼吸应激随酸度的增加而增加，但在有 HS（10 和 20 mg/L）的处理中显著降低，与没有 HS 的处理相比。暴露于无 HS 的 pH 处理的鱼也表现出过度活跃、更大的鳃盖运动和更多的黏液分泌。与无 HS 的处理相比，在 HS 处理的 pH 3.5（软水）和 pH 4（硬水）中显示出更高的发病率。这表明 HS 有助于缓解亚致死 pH 值对呼吸的影响；然而，随着 pH 值的进一步下降，HS 似乎增加了低 pH 值的毒性（发病率）。
