Fish silage is a liquid product obtained from the breakdown of fish waste (heads, viscera, bones, etc.) through fermentation, typically with the aid of enzymes or acids. This method has gained attention in recent years as an eco-friendly solution for recycling fish by-products, offering a low-cost alternative to traditional fishmeal.
Fish silage (FS) has been confirmed as a high-quality feed ingredient due to its balanced nutrition, low cost, and environmental friendliness (Shao et al., 2020). By using fish silage, industries can minimize waste while creating a nutrient-rich feed source for livestock and aquaculture.
In this article, we aim to delve into the definition of fish silage, its different types, and its potential use in animal feed, aquaculture, and as an agricultural fertilizer.
What is Fish Silage?
The term “fish silage” refers to the preservation of fish material using acids or microbial fermentation, resulting in a product that can be stored without refrigeration for extended periods. This preservation method breaks down fish proteins, producing a stable and homogeneous mixture of amino acids and peptides, ideal for animal nutrition.
Toppe et al. (2018) define fish silage as consisting of chopped fish by-products or whole chopped fish not suitable for human consumption, with a preservative added to stabilize the mixture. Raziye et al., (2023) highlight that fish silage is “a liquid product made from whole fish or parts of fish to which lactic acid-producing acids, enzymes, or bacteria are added, and the liquefaction of the material indicates the action of enzymes present in the fish.”
Importance of Fish Silage
Fish processing generates between 30% to 70% waste (heads, viscera, bones, etc.) of the total processed fish volume (Toppe y Olsen, 2024), which, if not properly utilized, will end up in landfills, thereby increasing the negative environmental impact of the fishing and aquaculture industries.
In this context, FS presents an important alternative for utilizing fish processing waste. Below is a brief description of the importance of using this technology:
Production of Inputs for Feed Manufacturing
As the global demand for fishmeal continues to rise, finding alternative protein sources is becoming increasingly important.
Fish silage is particularly valuable in regions where fish processing creates large amounts of waste (heads, viscera, bones, etc.), which would otherwise be discarded. In this regard, Murugan et al., (2024) note that fish by-products often include heads (9-12% of the total fish weight), bones (9-15%), scales (around 5%), viscera (12-18%), and skin (1-3%).
Thus, utilizing fish processing by-products not only benefits the environment but also provides a sustainable protein source that contributes to circular economy models in food production.
Reducing Environmental Impact
By utilizing fish waste, fish silage production helps reduce the environmental impact of fish farming. Instead of discarding by-products, they are recycled into valuable feed, supporting a circular economy. This practice not only minimizes waste but also reduces the reliance on wild-caught fish for fishmeal production, contributing to the preservation of marine ecosystems.
Moreover, FS production requires fewer resources than fishmeal production, making it a more environmentally friendly option. Unlike fishmeal, which requires energy-intensive processing, silage can be produced locally using minimal resources. The process does not require heating or drying, resulting in lower energy consumption and a reduced carbon footprint.
Easy Implementation
On the other hand, because the production process for silage is simple, it does not require large investments (Toppe et al., 2018), making the technology suitable for locations where industrial fishmeal and fish oil production plants are not available.
Types of Fish Silage: Which is the Best?
There are three main types of fish silage: acid silage, biological silage, and enzymatic silage. Each type uses a different preservation method, and their effectiveness varies depending on the application.
- Acid Fish Silage: This type is produced by adding organic or inorganic acids to the fish material. The acid lowers the pH, inhibiting bacterial growth and allowing the fish to ferment. The most common acids used are formic acid, propionic acid, and lactic acid. Acid silage is often preferred for its simplicity and reliability, as acids ensure long-term preservation without the need for strict temperature control.
- Biological (Fermentation) Fish Silage: This method involves the use of lactic acid bacteria to naturally ferment the fish material. The bacteria produce lactic acid, which lowers the pH and preserves the fish. Biological silage tends to have a more complex flavor and nutritional profile due to the natural fermentation process but requires more careful control to maintain the proper conditions for bacterial growth.
- Enzymatic Silage: Some processes also incorporate enzymes to break down fish proteins more efficiently. This method can be combined with acid or biological methods and often results in faster protein breakdown, producing a nutrient-rich product suitable for various feeds.
Each type of fish silage has its benefits depending on the specific needs of the producer. Acid silage is known for its stability and long shelf life, while biological silage may be preferred for organic farming practices. The choice often depends on the regulatory environment, costs, and intended use.
How is Silage Made? A Step-by-Step Guide
The process of making fish silage is relatively simple and can be carried out using basic equipment. The goal is to create a stable product that can be stored and used as animal feed without the risk of spoilage.
Steps to Produce Fish Silage
- Collection of Fish Waste: The production of fish silage begins with the collection of fish by-products, such as heads, bones, viscera, and skin. These materials typically come from fish processing plants where large amounts of waste are generated.
- Grinding the Fish: The fish waste is ground into small particles. This step is essential to ensure even fermentation and to prevent large chunks from slowing down the process.
- Addition of Acids or Fermenting Agents: Depending on the type of silage, acids or fermenting bacteria are added to the ground fish. For acid silage, formic acid is commonly used to quickly lower the pH and stop bacterial activity. For biological silage, lactic acid bacteria are introduced, which initiate a slower fermentation process.
- Mixing and Storage: Once the acids or fermenting agents are added, the mixture is stirred well to ensure even distribution. The fish material is then placed in airtight containers for fermentation. It is critical to prevent oxygen from entering the container, as this could spoil the batch.
- Fermentation and Preservation: The fermentation process usually takes anywhere from a few days to several weeks, depending on the method used. During this period, the fish proteins break down into peptides and amino acids, creating a nutrient-rich liquid suitable for animal feed.
- Final Product: Once fermentation is complete, the fish silage is ready for use. The resulting liquid can be stored for several months at room temperature, though refrigeration can further extend its shelf life.
Uses of Fish Silage
The use of fish silage as animal feed has increased. Fish silage is highly popular due to its high protein content and ease of production. It is especially valued in regions where fishmeal is expensive or difficult to obtain. Fish silage can be used to feed a variety of animals, including pigs, poultry, and fish, making it a versatile solution for many aquaculture and agricultural operations.
In Aquaculture
One of the most common uses of fish silage is in aquaculture, where it is incorporated into fish feed. Silage provides a rich source of essential amino acids and fatty acids, promoting healthy growth in farmed fish. Since it is derived from fish, its nutrient profile is well-suited to meet the dietary needs of many aquatic species, including salmon, shrimp, trout, and catfish.
In Livestock Feed
Fish silage can also be used in feed for pigs and poultry. Its high protein content helps increase growth rates and improves feed efficiency. Additionally, the fatty acids present in fish silage contribute to healthier coats and improved reproductive performance in livestock.
One advantage of fish silage over traditional fishmeal is its liquid form, which makes it easier to incorporate into feed mixes. It can be added directly to compound feeds or mixed with other ingredients, providing flexibility in feed formulations.
Agricultural Fertilizer
Fish silage can be used as an agricultural fertilizer when it does not meet the nutritional and quality requirements for animal feed.
According to Toppe et al. (2018), fish silage is a good source of nitrogen (from the protein), phosphorus, potassium, calcium, and magnesium (particularly from the bone structure), as well as most of the trace elements necessary for plants.
Silage for Aquaculture Feed: A Sustainable Solution
Studies have shown that moderate amounts of protein hydrolysate can be included in fish feed, and in some cases, this improves performance (Olsen y Toppe, 2017).
Shrimp
The study by Hernández & Olvera-Novoa (2017) demonstrated that silage from tuna by-products can be used in feeding juvenile Pacific white shrimp. Meanwhile, Shao et al., (2020) reported that fish silage is a viable and beneficial alternative to fishmeal in the diet of Litopenaeus vannamei shrimp at inclusion rates below 25%.
Tilapia
The study by Parvez et al., (2024) demonstrates the potential of fish silage as a valuable alternative to fishmeal in Nile tilapia feed. They report that replacing 75% of fishmeal with fish silage can improve growth performance and enhance protein digestion and utilization. Additionally, Madage et al. (2016) reported a 50% replacement of fishmeal in red tilapia feeds.
Pangasius
According to research by Khan et al., (2021), fish silage can be incorporated (replacing 100% of fishmeal with fish silage) into the diet of Pangasius catfish (Pangasianodon hypophthalmus) fry with better growth and feed utilization, as well as having a positive influence on the fish’s health in terms of general hematology, biochemistry, and antioxidant status.
Nutritional Value of Fish Silage: Is It Better Than Fishmeal?
Fish silage is often compared to fishmeal due to their similar origins and applications in animal feed. However, there are some key differences between the two products, particularly in terms of nutritional value and production methods.
Nutritional Composition of Fish Silage
The nutritional composition and quality of fish silage depend significantly on the type and freshness of the raw materials used (Maksimenko et al., 2024). As a result, the range of protein, fat, and ash content can vary depending on the species, type of waste, and production technology employed.
Fish silage contains a high concentration of essential amino acids, including lysine and methionine, which are crucial for animal growth. It also contains omega-3 fatty acids, which promote healthy development in both livestock and fish. These nutrients are highly digestible, making fish silage an excellent supplement in animal diets.
Table 01: Nutritional composition of fish silage.
| Parameter | Range |
| Protein | 15 to 66% |
| Amino Acid Profile (g/100 g)1 | Essential Amino Acids: histidine (2.11); arginine (8.04); threonine (5.02); valine (1.87); methionine (2.89); lysine (3.70); isoleucine (4.24); leucine (6.12); phenylalanine (4.08). Non-Essential Amino Acids: alanine (5.30); proline (3.62); tyrosine (5.75); serine (5.12); glycine (5.08); aspartic acid (7.10); glutamic acid (14.60); cystine (3.64). |
| Fatty Acids2 | EPA: 6.07% DHA: 21.72% |
| Ash Content3 | 11.9% to 21.5% |
Compared to fishmeal, fish silage generally has a higher moisture content, which can affect its handling and storage. While fishmeal is a dry powder, fish silage is a liquid, which may require different feeding techniques and storage solutions. Despite these logistical challenges, the nutritional benefits of fish silage are comparable to those of fishmeal and, in some cases, superior.
One of the main advantages of fish silage is its ability to preserve nutrients without the need for high-temperature processing. Fishmeal, on the other hand, undergoes heating, which can degrade some of its nutritional components. For this reason, fish silage can retain higher levels of vitamins and certain heat-sensitive compounds.
Fish Silage VS Fishmeal
The following table provides a comparison between fish silage and fishmeal, highlighting the main differences in key aspects such as production process, nutritional value, uses, and environmental advantages:
Table 02: Comparison between the characteristics of fish silage and fishmeal.
| Characteristic | Fish Silage | Fishmeal |
| Production Process | Fermentation of fish using acids or bacteria (cold process) | Drying and grinding of fish by-products (hot process) |
| Form | Liquid | Dry powder |
| Preservation Method | Fermentation with acids or bacteria that stabilize the product | High-temperature drying |
| Moisture Content | High (generally between 65% and 70%) | Low (around 10%) |
| Nutritional Value | High in protein, essential amino acids, omega-3 fatty acids | High in protein, but may lose some heat-sensitive nutrients |
| Digestibility | High, especially for amino acids and lipids | High, but may decrease due to the heating process |
| Shelf Life | Stable for several months if stored properly, but requires special containers | Very long due to low moisture, easy to store |
| Common Uses | Feed for fish, poultry, and pigs; also used as fertilizer | Feed for fish, pigs, poultry, and pets |
| Ease of Transport | Requires special handling due to being liquid | Easy to transport due to its dry, lightweight form |
| Environmental Impact | Lower energy consumption, direct recycling of fish by-products, contributes to the circular economy | High energy consumption for drying, larger carbon footprint |
| Production Cost | Generally more economical, as it uses simpler processes and less energy | More expensive due to drying and processing costs |
| Market Perception | Less known, sometimes perceived as lower quality due to being “liquid” | Established product, highly valued by the industry |
| Versatility in Use | Adapts well to industrial processes where feed is mixed with other liquid ingredients | Used in dry diets and easily incorporated into pre-mixed feeds |
This table highlights that, although both products have similar nutritional value, fish silage offers a more sustainable and economical alternative, albeit with some logistical limitations due to its liquid form. On the other hand, fishmeal is easier to handle and store but has a greater environmental impact due to the drying process.
Challenges and Future of Fish Silage
While fish silage offers numerous benefits, its widespread adoption faces several challenges. One of the main obstacles is the infrastructure required for its production and storage. Since fish silage is a liquid, it requires specialized containers and equipment for handling and transportation, which can be a barrier for smaller producers.
Additionally, the perception of fish silage as a “waste product” can sometimes hinder its acceptance in the market. Educating aquaculturists and feed manufacturers about the nutritional value and sustainability benefits of fish silage is essential to increase its usage.
On the other hand, Patel et al., (2024) summarizes the main issues of fish silage in the following aspects:
- Quality variability: The nutrient content of fish silage can vary depending on factors such as fish species, processing methods, and fermentation conditions. This variability can present challenges for uniform feed formulation.
- Storage and shelf life: Fish silage has a limited shelf life and may require special storage conditions to maintain its quality. Improper storage can lead to spoilage or nutritional degradation.
- Concerns about odor: Fish silage can have a strong odor, which may be an issue in the production of balanced feed.
- Allergy: Some people and animals may be allergic to fish proteins. This could be a problem if fish silage is used in feed for animals like chickens or pigs, which may eventually be consumed by humans.
- Regulatory compliance: The standards or regulatory rules governing the production and use of fish silage as a feed ingredient may vary by region. Meeting these requirements can be challenging.
Looking ahead, advances in fish silage production methods, such as improved fermentation agents and storage technologies, could help overcome these challenges. As awareness of sustainable feeding practices grows, it is likely that fish silage will play an increasingly important role in the global feed industry.
Conclusion
Fish silage is an excellent alternative for efficiently managing waste from fish processing (heads, viscera, bones, etc.) in places where primary fish processing from fishing and aquaculture occurs. Additionally, fish silage can be used for animal feed or as agricultural fertilizer.
References
Banze, J.F.; da Silva, M.F.O.; Enke, D.B.S.; Fracalossi, D.M. Acid silage of tuna viscera: Production, composition, quality and digestibility. Bol. Inst. Pesca 2017, 44, 24–34.
Khan, I., Kaur, V. I., & Datta, S. N. (2021). Effect of fish silage supplemented diets on growth and health status of pangas catfish, pangasianodon hypophthalmus fry. Indian Journal of Animal Research, 55(3), 287-294.
Maksimenko, A., Belyi, L., Podvolotskaya, A., Son, O., & Tekutyeva, L. (2024). Exploring Sustainable Aquafeed Alternatives with a Specific Focus on the Ensilaging Technology of Fish Waste. Fermentation, 10(5), 258. https://doi.org/10.3390/fermentation10050258
Murugan, G., Ahilan, K., Prakasam, V.P.A., Malreddy, J., Benjakul, S., Nagarajan, M. (2024). Fish Waste Composition and Classification. In: Maqsood, S., Naseer, M.N., Benjakul, S., Zaidi, A.A. (eds) Fish Waste to Valuable Products. Sustainable Materials and Technology. Springer, Singapore. https://doi.org/10.1007/978-981-99-8593-7_1
Olsen, R. L., & Toppe, J. (2017). Fish silage hydrolysates: Not only a feed nutrient, but also a useful feed additive. Trends in Food Science & Technology, 66, 93-97. https://doi.org/10.1016/j.tifs.2017.06.003
Parvez, M.S., Biswas, B., Debnath, S., Aktar, S., Rahman, S.M., & Ahsan, M.N. (2024). Zootechnical Performance, Protease Activity and Proximate Composition of Nile Tilapia Fed Diets Containing Fish Silage Produced from Fish Waste. Aquaculture Studies, 24, AQUAST1974. http://doi.org/10.4194/AQUAST1974
Patel, P. K., Sahu, B., Prasad, L. and Kumar, D. 2024. Fish Silage: A Noble Fish Feed Ingredient. Vigyan Varta 5(4): 31-33.
Raziye R, Bahareh SH, and Parastoo P (2023). Use of fish waste to silage preparation and its application in animal nutrition. Online J. Anim. Feed Res., 13(2): 79-88. DOI: https://dx.doi.org/10.51227/ojafr.2023.13
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Shao, J., Wang, L., Shao, X., & Liu, M. (2020). Dietary Different Replacement Levels of Fishmeal by Fish Silage Could Influence Growth of Litopenaeus vannamei by Regulating mTOR at Transcriptional Level. Frontiers in Physiology, 11, 508224. https://doi.org/10.3389/fphys.2020.00359
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