The Advantages and Uses of Fish Silage in Agriculture

Every year, the global fish processing industry generates millions of tonnes of waste – heads, bones, viscera, skin, and trimmings that typically end up in landfills or get dumped into water bodies. But what if all of that waste could be turned into a valuable, protein-rich product? That is exactly what fish silage does. It is a practical, low-cost, and environmentally sound method of converting fish by-products into nutritious animal feed and organic fertilizer. Whether you run a small coastal operation or manage a large-scale processing plant, fish silage offers a way to turn a disposal burden into an economic opportunity.

What is fish silage? 🔗

Fish silage is a liquid product made from whole fish or fish parts that are broken down – or liquefied – by the action of natural enzymes present in the fish itself, assisted by added acid. According to the FAO, the enzymes break fish proteins into smaller soluble units, while the acid accelerates enzyme activity and prevents bacterial spoilage. The result is a stable, nutrient-dense liquid rich in hydrolysed proteins, lipids, minerals, and free amino acids that animals can easily digest and absorb.

There are two main production methods. Acid silage involves adding organic acids (like formic acid) or inorganic acids (like sulphuric acid) directly to minced fish waste. Fermented silage uses lactic acid bacteria along with a fermentable carbohydrate source such as molasses to produce lactic acid in situ, which then preserves the material. Both methods work by lowering the pH to around 3.5-4.0, creating conditions that suppress spoilage bacteria while allowing proteolytic enzymes to do their work.

Key advantages of fish silage 🔗

Effective utilization of fish by-products 🔗

Fish processing generates enormous volumes of waste. Depending on the species and level of processing, 30-70% of the original fish can become waste material. Fish silage provides a direct route for converting these discarded parts – heads, guts, frames, skin – into a usable product. Even cartilaginous species like sharks and rays, which liquefy more slowly, can be used as raw material for silage production.

Reduction of environmental pollution 🔗

When fish waste is dumped into landfills or water bodies, it creates serious environmental problems – foul odours, water contamination, and attraction of pests. Fish silage production eliminates these issues by channelling waste into a controlled preservation process. As noted by the FAO’s collaborative project with CARDI, silage technology diverts protein-rich fish offal away from landfills and toward productive use, supporting the principles of a circular economy.

Cost-effective protein source 🔗

One of the most compelling advantages of fish silage is its affordability. The production process requires minimal capital investment and can be carried out by unskilled workers using basic equipment. The FAO points out that the capital cost of silage equipment is fairly low compared to a fishmeal plant, and there is no need for engineers or specialised technical staff. Fish silage typically costs significantly less than conventional fishmeal while delivering comparable nutritional value.

Simple technology and scalability 🔗

Fish silage production is remarkably adaptable in terms of scale. A batch can be made in a single oil drum or in large tanks holding several tonnes – the process works the same way. This makes it suitable for small fishing communities with limited resources as well as large industrial processors. Research published in the Brazilian Archives of Biology and Technology confirms that the silage process is virtually independent of scale, requires simple technology, and demands low investment even in large-scale production.

Long shelf life and storage stability 🔗

Properly acidified fish silage keeps at room temperature for extended periods – the FAO reports stability of at least two years without putrefaction when the correct acidity is maintained. Silage produced with organic acids or through fermentation can be stored for years and used on demand. This eliminates the need for refrigeration and allows for flexible distribution schedules, reducing storage and logistics costs considerably.

High digestibility and nutrient availability 🔗

During the ensiling process, fish proteins undergo hydrolysis – they are broken down into peptides, dipeptides, and free amino acids. This pre-digestion makes the nutrients in fish silage highly digestible and easily absorbed by both terrestrial and aquatic animals. The nutritional profile of fish silage is comparable to fishmeal, but its digestibility often exceeds that of fishmeal due to the presence of these pre-hydrolysed proteins.

Minimal odour during production 🔗

Unlike fishmeal production, which is notorious for generating strong, unpleasant odours and often faces community opposition, fish silage production is relatively odour-free. The FAO specifically notes that smell is a major problem when making fishmeal unless specially equipped plants are used, whereas there is essentially no smell when making silage. This makes silage production far more suitable for locations near residential areas or farms.

Uses of fish silage in animal feed 🔗

Poultry diets 🔗

Fish silage has shown strong results as a protein supplement in poultry nutrition. A study published in the AATCC journal found that broiler feed prepared with 5% fish silage replacing soybean meal showed better feed intake and body growth, with a lower feed conversion ratio (1.66) compared to control groups. Importantly, the sensory evaluation of the meat showed no adverse effects – the poultry meat was equally accepted by panelists. Layer hens can also benefit, with fish silage inclusion at moderate levels supporting egg production and shell quality through its rich amino acid profile.

Pig diets 🔗

Pigs are among the best candidates for fish silage feeding because their wet feeding systems can easily accommodate a liquid protein source. Research published in Animal Feed Science and Technology demonstrated that pigs fed diets containing fish silage from formic acid-treated mackerel grew faster than control groups, primarily due to improved feed conversion. The Danish pig industry has used fish silage commercially for decades. One consideration is that very high inclusion levels (above 150 g/kg diet) may lead to soft, yellowish fat in carcasses, so moderation in inclusion rates is important.

Aquaculture feeds 🔗

Fish silage finds a natural application in aquaculture, essentially creating a circular system where fish waste feeds farmed fish. Studies on species including Atlantic salmon, Nile tilapia, catfish, and shrimp have shown that fish silage can partially replace fishmeal in aquaculture diets without negatively affecting growth or protein utilization. Research on Atlantic salmon found that replacing 10% of fishmeal with silage protein hydrolysate actually improved growth. The formic acid present in acid silage may also offer additional benefits by acting as a growth promoter and inhibiting harmful gut bacteria in farmed fish.

Ruminant and other livestock diets 🔗

Fish silage has been successfully tested in diets for sheep, goats, cattle, and even rabbits. The FAO-CARDI project in the Caribbean tested a molasses-based fish silage feed on sheep and found no significant difference in average daily weight gain compared to commercial feed – meaning the silage-based feed performed just as well. The silage feed contained 20.8% crude protein, which was actually higher than the commercial alternative. Dairy cows fed silage produced milk and butter without any undesirable flavour or taint.

Fish silage as organic fertilizer 🔗

Beyond animal feed, fish silage serves as an effective organic fertilizer for crop production. It is a rich source of nitrogen from its protein content, along with phosphorus, potassium, calcium, and magnesium – particularly from the bone fraction. A study published in Scientific Reports found that applying 20 tonnes of salmon silage per hectare to grassland in Chile produced dry matter yields comparable to those achieved with chemical fertilizer. Similarly, research on Chinese cabbage showed that fish silage concentrations of 5-10% delivered results equivalent to commercial fertilizers.

If silage does not meet the quality standards required for animal feed – for instance, if it was made from stale raw material – it can still be repurposed as fertilizer, ensuring that no fish waste is truly wasted. The amino acids in fish silage, particularly in their free form, can be directly absorbed by plant roots and have been shown to promote cell elongation, root development, and stress tolerance in crops.

Fish silage vs. fishmeal: a practical comparison 🔗

Fishmeal has long been the standard animal protein source in feed formulations, but fish silage offers several practical advantages. The capital cost of setting up a fishmeal plant is high, whereas silage production requires minimal equipment. Fishmeal production demands skilled engineers and generates strong odours, while silage can be made by workers with basic training and produces almost no smell.

The main disadvantage of fish silage is its bulk. Because it retains all the water present in the original fish (roughly 80% moisture), it is about four to five times bulkier than fishmeal for the same protein content. This makes long-distance transportation more expensive. However, this limitation can be addressed by drying the silage with agricultural by-products like cereal bran or sorghum, or by using it locally, which is often the most practical approach. In countries like Denmark and Poland, commercial-scale silage production has operated successfully for decades, and nations like Peru and Chile have scaled it up to industrial levels.

Quality factors in fish silage production 🔗

Producing high-quality fish silage depends on a few key factors. The raw material should be fresh – ideally ensiled within a few hours of fish processing. Fresh material liquefies faster and yields a better nutritional product. pH management is critical: maintaining acidity at pH 3.5-4.0 prevents spoilage and ensures long-term stability. If using formic acid, the recommended addition rate is about 3.5% by weight of the fish.

Temperature also plays a role – warmer conditions speed up liquefaction. Silage made from fresh white fish offal at 20°C typically liquefies in about two days, while at 10°C it may take 5-10 days. In tropical climates, the silage process is especially fast. The oil from fatty fish species should be separated and, if possible, protected with antioxidants to prevent oxidation and quality deterioration during storage.

Future potential and emerging trends 🔗

The future of fish silage is closely tied to the growing global emphasis on sustainability and the circular economy. As aquaculture continues to expand – the FAO projects it will supply close to 50% of the world’s seafood by 2030 – the demand for affordable, high-quality feed ingredients will only increase. Fish silage is well positioned to meet this demand by converting processing waste into valuable feed nutrients at low cost.

Researchers are exploring enhanced fermentation techniques using specific bacterial cultures to improve the nutritional profile of silage products. The use of fish silage as a substrate for growing microalgae is another promising avenue, potentially linking waste valorisation with biofuel and feed production. Integration with other agricultural waste streams – blending fish silage with crop residues, for example – is opening new possibilities for creating balanced, complete feed products.

What do you think? Could fish silage become a mainstream practice in your region’s fishing and farming communities? What do you see as the biggest barrier – awareness, infrastructure, or market acceptance – to wider adoption of this technology?

References

1. https://www.fao.org/4/x5937e/x5937e01.htm
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3. https://www.fao.org/americas/news/news-detail/FAO-and-the-Caribbean-Agricultural-Research-and-Development-Institute-(CARDI)-explore-fish-silage-as-a-viable-option-for-animal-feed/en
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6. https://aatcc.peerjournals.net/wp-content/uploads/2025/04/Fish-silage-fortified-poultry-feed-its-effect-on-body-growth-and-meat-quality-of-broiler-chicks.pdf
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