Nutritional Benefits of Fish Silage in Animal Feed

Every year, the global fishing industry generates millions of tonnes of waste – heads, bones, viscera, and other by-products that often end up polluting water bodies or filling landfills. But what if this waste could be turned into a high-quality, protein-rich animal feed? That’s exactly what fish silage achieves. Fish silage is a liquid product made from whole fish or fish parts, liquefied through enzymatic action in the presence of added acids. It retains most of the nutritional value of the original fish, making it a powerful and cost-effective feed ingredient for livestock and aquaculture species alike.

What makes fish silage nutritionally valuable? 🔗

Fish silage stands out among animal feed ingredients because of its impressive nutritional profile. The composition of fish silage closely mirrors that of the raw material used to produce it. According to the FAO, a typical analysis of white fish offal – and therefore the silage produced from it – shows approximately 80% water, 15% protein, 4.5% ash, and 0.5% fat. When produced from whole fatty fish like sprats or sand eels, the protein and fat content are higher, with correspondingly lower water and ash levels.

On a dry matter basis, these numbers shift significantly. Dried fish silage can contain crude protein levels ranging from about 40% to over 69%, depending on the raw material. For instance, acid silages produced from whole saltwater fish have shown protein levels as high as 69.91% on a dry weight basis, as documented in research published in Animal Feed Science and Technology. When fish silage is prepared from fish viscera alone, protein content on a dry matter basis typically hovers around 12%, while lipid content can be significantly higher – above 59% in some formulations.

The fat and ash content in fish silage can vary considerably based on the type of raw material used. Silages made solely from fish viscera tend to have lower ash content because viscera contain fewer bones and scales. By contrast, silages produced from whole fish waste – including heads, fins, bones, and scales – can have ash levels ranging from about 12% to over 21%. This variability means that producers can somewhat control the nutritional composition of their silage by selecting appropriate raw materials.

Protein quality and amino acid profile 🔗

What truly sets fish silage apart from many other protein sources is not just the quantity of protein, but its quality. During the ensiling process, enzymes naturally present in the fish tissue break down large protein molecules into smaller peptides and free amino acids. This hydrolysis is a key reason why fish silage is considered one of the most bioavailable protein sources available for animal feed.

Fish silage is rich in essential amino acids – those that animals cannot synthesize on their own and must obtain through diet. Research published in the journal Fishes found that leucine and lysine were the predominant essential amino acids in both acid and fermented fish viscera silages. Lysine is particularly significant because it is often the first limiting amino acid in cereal-based animal diets. Fish silage contains substantial amounts of lysine, making it an excellent supplement to correct this common deficiency.

Beyond lysine, fish silage provides generous amounts of methionine, threonine, and other sulphur-containing amino acids. These are frequently deficient in plant-based protein sources like soybean meal. A study examining ileal amino acid digestibility in broiler chickens found that fish silage had significantly higher digestibility coefficients for all amino acids compared to both soybean meal and fish meal. For methionine, the digestibility coefficient was 0.94, compared to 0.90 for soybean meal. For lysine, it was 0.95 versus 0.88, and for threonine, 0.88 versus 0.79.

Why hydrolyzed proteins matter 🔗

The process of ensiling essentially “pre-digests” the fish proteins. The enzymatic breakdown produces short-chain peptides and free amino acids that are much easier for animals to absorb compared to intact, complex protein structures. As noted in a comprehensive review published in the journal Fermentation, these smaller molecules can be absorbed directly without requiring prior digestion by pancreatic proteases, which is why fish silage often surpasses fish meal in terms of digestibility.

This pre-digestion effect is especially beneficial for young animals – piglets, chicks, fry, and fingerlings – whose digestive systems are not yet fully developed. Feeding hydrolyzed proteins from fish silage allows these young animals to extract maximum nutrition from their feed, supporting faster growth and better overall health.

Digestibility: how fish silage compares to fish meal 🔗

Digestibility is one of the most critical factors when evaluating any feed ingredient. A feed may be protein-rich on paper, but if animals cannot efficiently digest and absorb those nutrients, the value is limited.

Fish silage consistently performs well in digestibility trials across multiple animal species. The nutritional properties of fish silage are comparable to those of fish meal, but the digestibility of silage often exceeds that of fish meal due to its hydrolyzed protein content. According to ScienceDirect, the enzymes released during ensiling break down proteins into easily digestible and highly absorbable nutrients for animals. Research on tambaqui juveniles, for example, demonstrated that the apparent digestibility coefficient for crude protein from fish viscera silages was comparable to that of Peruvian fish meal, while the digestibility for gross energy exceeded 82% across all formulations tested.

For pigs, research compiled by the FAO shows that the energy and nitrogen in fish silage are highly digestible – in some cases, digestible energy and nitrogen were actually higher in diets containing fish silage than in those based on fish meal. Feeding trials have consistently shown that pigs fed fish silage grow at comparable rates to those fed fish meal, with no negative impact on meat quality or flavour.

Essential fatty acids and lipid content 🔗

Fish silage is not just about protein. It also serves as a valuable source of essential fatty acids, particularly the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). These long-chain polyunsaturated fatty acids play critical roles in animal health, including supporting cardiovascular function, reducing inflammation, and promoting healthy cell membranes.

Research on fish viscera silages has revealed EPA content ranging from 5.4 to 17.8 mg per gram of lipids and DHA content from 1.7 to 8.9 mg per gram of lipids. Interestingly, silages showed higher levels of polyunsaturated fatty acids (PUFAs) and omega-3 fatty acids compared to the original fish viscera. This enrichment makes fish silage a particularly useful ingredient for aquaculture feeds, where many plant-based formulations lack these essential fatty acids.

However, the fat content of fish silage does require careful management. In warm climates, the oil in silage will float to the surface and can rapidly oxidize if antioxidant substances are not added during production. Oxidized fats reduce the nutritional quality of the silage and can even be harmful to animals. Producers typically either separate the oil for use as a standalone feed ingredient or add antioxidants like butylated hydroxytoluene (BHT) to prevent lipid degradation.

Minerals and micronutrients 🔗

The mineral content of fish silage varies significantly based on the raw material. Silages produced from whole fish waste, which includes bones and scales, tend to be high in calcium and phosphorus – minerals essential for skeletal development and metabolic function in livestock. However, excessively high ash content is not always desirable. In aquaculture feeds, for instance, many of the mineral requirements of fish can be met directly through the water they inhabit, making high-ash feeds less necessary and potentially wasteful.

Fish viscera silages, on the other hand, typically have lower ash content, which can be advantageous for certain feed formulations. The organic acids present in fish silage – whether added during production or produced through fermentation – also contribute to animal health. These acids have antibacterial properties within the animal intestine, supporting gut health and potentially reducing the need for antibiotic growth promoters. As highlighted in research from ScienceDirect, formic acid present in fish silage hydrolysates may function as a growth promoter, particularly under unfavourable microbiological conditions.

Applications in livestock feeding 🔗

Fish silage has proven its value across a wide range of livestock species, each with its own optimal inclusion rates and feeding strategies.

Swine 🔗

Pig farming remains one of the most natural outlets for fish silage, primarily because its liquid form integrates easily into the wet feeding systems common in modern pig production. Feeding trials across multiple countries have confirmed that pigs fed on fish silage-based diets grow at rates comparable to those on fish meal diets, with no adverse effects on meat quality. In Denmark, fish silage has been used commercially in the pig industry for decades. In Cuba, the production of acid fish silage reached 20,000 to 25,000 tonnes annually between 1968 and 1990, largely to provide a protein-rich feed for livestock.

Poultry 🔗

In poultry production, dried fish silage has been shown to effectively replace both fish meal and soybean meal without significant differences in weight gain or feed conversion efficiency for broilers. Replacing up to 50% of the fish meal in layer diets with fish silage had no negative impact on egg flavour or quality. However, it is worth noting that thiamine (vitamin B1) may not be present in adequate amounts in fish silage to support normal growth in certain poultry species like ducks, so supplementation may be necessary.

Dairy and beef cattle 🔗

Ruminants also benefit from fish silage supplementation, especially during periods when pasture quality declines. In tropical and subtropical regions, forage digestibility and protein content drop significantly during dry seasons, leading to reduced milk production. Adding even small amounts of fish silage – as little as 1 kg per day – to the diet of dairy cows during these periods has been shown to maintain milk production at levels comparable to the wet season, without any taint in the milk or butter.

Applications in aquaculture 🔗

Perhaps the most fitting application of fish silage is in aquaculture – feeding fish to grow fish, creating a truly circular system. Research has demonstrated that fish silage can effectively replace a significant portion of fish meal in diets for various aquaculture species.

Studies on species like tilapia, catfish, sea bass, and shrimp have shown that replacing 15-50% of fish meal with fish silage in aquafeed does not compromise growth performance. In fact, moderate inclusion levels have sometimes led to improved growth, likely due to the higher bioavailability of hydrolyzed proteins and the growth-promoting effects of organic acids. However, excessive replacement – above 75% – typically leads to reduced growth performance, as noted in research published in Frontiers in Physiology.

Fish viscera silage is particularly interesting for aquafeed because its essential amino acid content improves the overall nutritional value of diets, especially when combined with plant-based ingredients that may be deficient in lysine and methionine. Furthermore, peptides and free amino acids resulting from protein hydrolysis have been shown to stimulate non-specific cellular immunity in fish, contributing to disease resistance as well as growth.

Limitations and considerations 🔗

Despite its many advantages, fish silage is not without limitations. The most notable challenge is its high water content – typically 75-80% – which increases transportation costs significantly. Transporting silage is roughly four to five times more expensive per unit of protein compared to fish meal, which is a dry, concentrated product.

Another concern is the potential loss of certain heat-sensitive amino acids during storage. Tryptophan, in particular, tends to degrade under acidic conditions and at temperatures exceeding 30°C. Methionine and histidine can also decompose under these conditions. For this reason, proper storage management – including temperature control and the use of antioxidants – is essential to maintain nutritional quality.

The variability in composition depending on raw materials can also be a challenge for feed formulators who need consistency. Establishing standardized production protocols and regular quality testing helps overcome this issue. Drying the silage – by co-drying with ingredients like soybean meal or wheat bran – can address both the transportation and consistency problems, though drying adds cost and energy requirements to the production process.

Why fish silage is a sustainable choice 🔗

From a sustainability perspective, fish silage offers compelling advantages. Fish processing generates enormous volumes of waste – the edible flesh of most fish species represents only about 40% of the total body weight, meaning up to 60% ends up as by-product. Converting this waste into a valuable feed ingredient through ensiling reduces environmental pollution, decreases reliance on wild-caught fish for fish meal production, and provides an additional income stream for fishing communities and processors.

The production process itself is simple, requires minimal capital investment and technical expertise, and produces no offensive odours – unlike fish meal manufacturing. A silage operation can be set up in a single plastic drum or scaled up to handle several tonnes per batch, making it accessible to small fishing communities and large processing plants alike.

What do you think? Could fish silage help reduce the environmental impact of your local fishing industry while simultaneously improving the quality and affordability of livestock and aquaculture feeds? In a world where sustainable protein sourcing is becoming increasingly critical, how might the wider adoption of fish silage technology reshape animal agriculture?

References

1. https://www.fao.org/4/x5937e/x5937e01.htm
2. https://www.sciencedirect.com/science/article/abs/pii/S0377840103000567
3. https://www.mdpi.com/2410-3888/8/2/111
4. https://www.cabi.org/Uploads/animal-science/worlds-poultry-science-association/WPSA-turkey-2009/27_marzooqi_mps2009.pdf
5. https://www.mdpi.com/2311-5637/10/5/258
6. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/fish-silage
7. https://www.fao.org/4/v4440t/v4440T0d.htm
8. https://www.sciencedirect.com/science/article/abs/pii/S092422441630348X
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC7232572/