The Importance of Standardized Raw Materials for Organic Hydroponic Nutrients – Part III: Fish-based Fertilizers


This is part III of a 3-part article series on the importance of standardized raw materials when manufacturing organic hydroponic nutrients. Part III focuses on the trouble that soilless farms tend to face when using fish-based fertilizers as a nutrient input.

The Benefits of Fish-based Fertilizers

Fish emulsion fertilizer

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Fish Emulsion is made from fish waste, including fish renderings, fish offal, and spoiled fish. Fisheries’ wastes can be converted into organic fertilizers through composting as well as through the manufacturing of fish-based fertilizers such as fish emulsion, fish hydrosylate, and fish solubles. For a multitude of reasons, fish emulsion, as a fertilizer, has gotten increasingly popular over the years. As a quick-acting organic liquid fertilizer, it’s used by diluting the product with water and then applying it to the crop or plant. While there are fish-based fertilizers that have a strong, fishy odor, over the years many companies have begun producing deodorized versions – thus eliminating the smell issue. Generally, fish emulsion plant fertilizers have a macronutrient or “NPK”, representative of Nitrogen, Phosphorus, and Potassium, ratio of 5-2-2 or 5-1-1. These liquid organic fertilizers may provide the ingredients which your soil might lack and are necessary for a rich and balanced growth in your soil garden.

The reason many farms have gravitated towards fish-based fertilizers ranges. For some, it’s an organic, closed-loop option because it’s produced from unused fresh fish parts, and are natural resources which will otherwise be wasted. Some farms like that it contains a good amount of NPK, with most having a ratio of 5-2-2 or 5-1-1. Others tout that because it’s mild, the possibility of it damaging plants reduces significantly. For farms that are resourceful, they may even opt to use the fish emulsion as a foliar spray without the need for any synthetic mineral salts.

The Risks of Fish-based Fertilizers for Soilless Farmers

  1. Highly putrescible - The fish waste that these fertilizers are made from quickly gets decomposed by microorganisms, making it highly putrescible. What this means is that they can quickly begin to produce an odor if not handled properly. Anaerobic conditions increase the potential for putrefaction, causing the decomposition of compounds that cause malodors, including ammonia, hydrogen sulfide, dimethyl sulfide, mercaptans, indoles, skatoles, and phenols. In addition, highly putrescible organic wastes combined with anaerobic conditions create a ripe environment for the development of pathogenic microorganisms such as salmonella and E. coli. Thus, there are special considerations for handling fish waste to avoid putrefaction, malodors, and pathogenic contamination.
  2. Requires microbes in soilless or hydroponic system to work harder - When attempted to be used as a nutrient in a soilless or hydroponic system, the microbes that work to decompose the abundant source of organic matter will cause the water temperature in the reservoir to rise, alongside an increasing pH level. This is due to the increased energy from the microbes needed to digest the fish waste into plant-available nutrients. This tends to also produce a tremendous amount of bubbling action from the build-up of protein due to the high level of proteins and amino acids found in fish-based fertilizers. Once again, for this to become available to the plants, it requires a bacterial breakdown process. In other words, the protein needs to be transformed to ureum, to ammonia, to nitrite, and finally to nitrate. If we go back to what hydroponics is all about, in many ways, this process defeats the process of a more efficient and sustainable growing method that drives the soilless farming industry. Now, this can be mitigated by diluting the product prior to applying to one's reservoir. However, it doesn't remove the constant battle of needing to balance microbes, temperature, and pH, therefore creating a high-maintenance nutrient routine not experienced in soil-based farming.
  3. Fish-based fertilizers are messy, smelly and difficult to manage based on a recirculating solution’s EC and pH – The typical composition of fish-based fertilizers is such that the protein has been “enzymatically” digested. This produces a viscous liquid which is akin to chocolate pudding, but with an odor of fresh fish and vinegar. However, understanding the breakdown of the components of a fish fertilizer pre-processing is also useful to be mindful of. An example of this is salmon hydrosylate.

Breaking Down Your Nutrient Input

Having broken down the advantages and challenges of each nutrient input, we hope this gives soilless or hydroponic farms some food for thought (pun intended) when selecting nutrients for their crops. By taking the time to tear apart every single aspect of the input, soilless farms will be able to produce more high quality crops which will then feed into a healthy ROI for the farm. So, which one will it be for your farm? Manure and molasses, food waste and compost, fish-based fertilizer, or closed-loop food waste?