Department of Ecophysiology and Aquaculture, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, 12587, Germany.
Faculty of Life Sciences, Humboldt University of Berlin, Berlin, 10115, Germany.
Sci Rep. 2021 Jan 8;11(1):174. doi: 10.1038/s41598-020-80449-0.
Aquaculture has become imperative to cover the demands for dietary animal protein. Simultaneously, it has to overcome prejudices from excessive use of antibiotics and environmental impacts. Natural supplements are traditionally applied orally. In this study, we demonstrated another pathway: the gills. Humic substances are immunostimulants and a natural part of every aquatic ecosystem, making them ideal to be used as bath stimulants. Five and 50 mg C/L of a fulvic acid-rich humic substance was added for 28 days to the water of juvenile rainbow trout (Oncorhynchus mykiss). This fulvic acid is characterized by a high content of phenolic moieties with persistent free radicals and a high electron exchange capacity. The high concentration of the fulvic acid significantly increased growth and reduced the food conversion ratio and the response to a handling-stressor. Phagocytosis and potential killing activity of head kidney leukocytes were increased, as well as the total oxyradical scavenging capacity (TOSC) and lysozyme activity in the gills. In conclusion, immunostimulation via gills is possible with our fulvic acid, and the high phenolic content improved overall health and stress resistance of fish.
水产养殖对于满足人们对动物蛋白的需求变得至关重要。与此同时，它还必须克服过度使用抗生素和对环境产生影响的偏见。传统上，天然补充剂是通过口服来使用的。在这项研究中，我们展示了另一种途径：通过鳃。腐殖质是免疫刺激剂，是每个水生生态系统的天然组成部分，因此非常适合用作沐浴刺激剂。将富里酸含量高的腐殖质以 5 和 50 mg C/L 的浓度添加到幼虹鳟（Oncorhynchus mykiss）的水中 28 天。这种富里酸的特点是含有大量的酚类部分，具有持久的自由基和高电子交换能力。高浓度的富里酸显著增加了生长，降低了食物转化率和对处理压力的反应。头肾白细胞的吞噬作用和潜在的杀伤活性增加，鳃中的总氧自由基清除能力（TOSC）和溶菌酶活性也增加。总之，我们的富里酸可以通过鳃来实现免疫刺激，而高酚含量提高了鱼类的整体健康和抗应激能力。
