Abstract
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.
Highlights
Aquaculture has become imperative to cover the demands for dietary animal protein
Liquid Chromatography-Organic Carbon Detection-Organic Nitrogen Detection (LC-OCD-OND) analysis showed, that the carbon-structures consists of 0.1% bio-polymer, 4.2% building blocks, 7.6% low molecular weight substances, and 88.2% humic-like substances with an average molecular weight of 800 g/mol
We showed that persistent free radicals (PFRs) exert stimulation to several parameters including the growth of plants and neuro-behavior of Caenorhabditis elegans when applied at low concentrations and become toxic at higher c oncentrations[28,29]
Summary
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. A long-term application, similar to the use of immunostimulants in feed, has not been studied yet Possible reasons for those lacks are that bath stimulants have to cover several requests: complete water-solubility (excluding high molecular molecules such as ß-glucans from algae and fungi or chitin), non-irritant (excluding many herb extracts), and, due to the required large amounts, they have to be cheap to be economically realistic (excluding many vitamins). Humic substances (HS) are part of natural organic matter and represent up to 95% of dissolved organic matter (DOC) in aquatic ecosystems with concentrations normally ranging from 0.5 mg C/L to 50 mg C/L10–12 They are “complex and heterogeneous mixtures”[13] and their structure can differ greatly depending on their origin: Comparing 20 HS Meinelt, et al.[14] found enormous differences between different lakes and igb‐berlin.de. To compare the effects of different humic substances, the chemical characterization cannot be neglected
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call