Best Practices for Storing Fish Meal to Maintain Quality

Fish meal is one of the most valuable protein-rich ingredients used in animal feed – particularly for poultry, pigs, and farmed fish. But here’s the catch: if stored carelessly, this nutrient-dense product can lose its quality rapidly, become contaminated with harmful toxins, or even pose a fire risk. Proper storage isn’t optional – it’s essential to protect both the nutritional value and safety of fish meal throughout its shelf life.

Why fish meal is so vulnerable during storage 🔗

Fish meal is a biologically active product even after processing. It contains residual oils, proteins, and moisture that continue to interact with the surrounding environment. Three main threats drive quality loss during storage: moisture absorption, lipid oxidation, and microbial contamination. Each of these can occur silently and cause significant damage before any visible signs appear.

What makes fish meal especially tricky to store is its hygroscopic nature – it readily absorbs moisture from the surrounding air. Once the moisture content rises beyond safe levels, it creates ideal conditions for bacteria and fungi to thrive. At the same time, the natural oils present in fish meal are prone to oxidative degradation, which not only destroys essential fatty acids and vitamins but can also generate enough heat to become a fire hazard.

Moisture: the primary enemy 🔗

Fish meal typically has a moisture content between 6% and 12% after processing. Maintaining this range during storage is critical. When fish meal absorbs additional moisture from humid air, it triggers a chain of problems – bacterial and fungal growth accelerate, proteins begin to degrade, and the overall nutritional profile deteriorates.

Aflatoxin contamination 🔗

One of the most serious consequences of moisture absorption is the growth of Aspergillus mold species, which can produce aflatoxins – highly toxic compounds that pose serious health risks to livestock and can enter the human food chain through contaminated animal products. Research on stored commodities has shown that products kept in polyethylene bags at 65% relative humidity had significantly lower aflatoxin levels compared to those stored in porous jute bags at higher humidity. The same principle applies to fish meal: controlling moisture is the front line of defense against mycotoxin contamination.

Salmonella risk 🔗

Beyond molds, Salmonella bacteria present another major concern. These pathogens can survive in dry conditions for extended periods and multiply quickly when moisture levels increase. Animals consuming Salmonella-contaminated fish meal can develop infections that reduce productivity and potentially transmit to humans handling infected animals. Good storage hygiene, combined with moisture control, is essential to keep this risk in check.

Packaging: your first line of defense 🔗

The choice of packaging material directly determines how well fish meal is protected from moisture, oxygen, and pests during storage. Not all bags are equal – the material, lining, and seal quality all matter.

Polyethylene-lined bags 🔗

The gold standard for fish meal packaging is the multi-layer paper bag with a polyethylene lining. According to the FAO’s technical guidelines on fish meal production, these bags effectively block insects and microbes while significantly reducing the penetration of oxygen and water vapor. Data from FAO testing shows that oxygen passage through a polyethylene bag is roughly 1,510 ml/m²/day, compared to 18,360 ml/m²/day through a 6-ply paper bag – a dramatic difference that directly impacts meal stability.

Standard jute or unlined paper bags are porous and allow moisture to pass through freely, making them unsuitable for fish meal storage in most climates. When using polyethylene-lined bags, ensure that sealing is complete – any gaps or tears compromise the moisture barrier entirely. Double-lining offers extra protection in high-humidity environments.

Solid polyethylene bags 🔗

Solid sheet plastic bags made from low-density polyethylene or PVC offer even better protection. These bags can be customized for short- or long-term storage needs. However, they tend to be less rigid when filled and have a lower coefficient of friction, which can make stacking and transport more challenging. Drop testing by FAO researchers indicated that 0.25 mm polyethylene bags are physically stronger than multilayer paper bags, though they are more susceptible to puncture damage during handling.

Warehouse conditions: controlling the storage environment 🔗

Even the best packaging won’t compensate for a poorly managed storage facility. The warehouse environment plays a critical role in maintaining fish meal quality over time.

Temperature and humidity control 🔗

Fish meal storage facilities should maintain consistent temperatures, ideally between 15°C and 25°C. Relative humidity should be kept below 65% to minimize moisture absorption, even through packaging. Storage areas must be cool, dry, and protected from rodents and birds. Roof insulation or false ceilings may be needed in some climates to prevent nighttime condensation from dripping onto stored bags.

Ventilation 🔗

Adequate ventilation is one of the most important – and often overlooked – aspects of fish meal storage. Good airflow serves two purposes: it prevents heat buildup from residual oxidation reactions, and it inhibits moisture migration within stacks that can lead to localized condensation and mold growth.

FAO guidelines recommend that bulk storage units should not exceed about 5 meters in width, and bag stacks should incorporate channels or “chimneys” to allow residual heat to dissipate. Freshly made oily fish meal, in particular, should be stored in ventilated stacks – especially in hot climates – until it has fully cooled and stabilized.

Stack management 🔗

How bags are arranged within the warehouse matters significantly. Proper stacking prevents excessive pressure on lower bags (which can stress polyethylene linings and cause tears), allows air to circulate, and provides firebreaks between storage areas. Many guidelines recommend leaving at least 15-20 cm gaps between tiers, supported by cross dunnage, to maintain airflow and prevent heat accumulation.

Oxidation and the risk of spontaneous combustion 🔗

The residual fish oils in fish meal are rich in polyunsaturated fatty acids, which are highly susceptible to oxidation. When these oils react with atmospheric oxygen, the process generates heat. Under normal conditions, this heat dissipates harmlessly. But in large, poorly ventilated stacks where heat cannot escape, temperatures can rise progressively until the meal reaches its ignition point.

This isn’t a theoretical risk. The IMDG Code classifies untreated fish meal as a Class 4.2 substance – meaning it is liable to spontaneous combustion. Ships have historically caught fire and even sunk due to fish meal cargo fires. The risk is highest with oily meal from species like anchovy and pilchard, which have highly reactive oils.

Antioxidant treatment 🔗

The most effective way to prevent oxidation-related problems is the addition of antioxidants during or immediately after production. Ethoxyquin is the most commonly used antioxidant in the fish meal industry, typically applied at rates of 200-1,000 mg/kg depending on the oil reactivity of the species. Other approved antioxidants include BHT (butylated hydroxytoluene) and tocopherol-based compounds. According to UN safety guidelines, stabilized fish meal must contain minimum residual levels of these antioxidants at the time of shipment – at least 50 ppm of ethoxyquin, 100 ppm of BHT, or 250 ppm of tocopherol-based antioxidant.

Fish meal not treated with antioxidant must undergo a curing (weathering) process for at least 28 days before bulk storage or transport. During curing, bags are arranged in single rows or small units to allow the oxidation reaction to proceed slowly and safely, with heat dissipating naturally.

Light exposure 🔗

UV light and general light exposure can accelerate oxidation reactions. Storage areas should be dark or have windows treated with UV-filtering materials. This simple precaution helps slow down fat degradation and preserves the nutritional quality of stored fish meal for longer periods.

Pest and rodent control 🔗

Fish meal is a protein-rich product that attracts insects, rodents, and birds. These pests don’t just consume the product – they contaminate it with droppings and can introduce pathogens like Salmonella. Screens on doors and windows, regular pest control measures, and clean storage floors are all essential. Some facilities also use foot dips to prevent workers from carrying harmful bacteria into storage areas.

Monitoring and quality checks 🔗

Even with all the right precautions in place, regular monitoring is non-negotiable. Storage facilities should implement routine checks for temperature, moisture content, and any signs of heating, discoloration, or off-odors in stored fish meal.

Temperature monitoring is especially important for detecting early-stage oxidation problems. Any unusual heat generation in a stack should be investigated immediately. Laboratory testing of stored samples at regular intervals – covering moisture, protein, fat quality, and microbial load – provides objective data on product condition and helps determine optimal storage duration.

A first-in, first-out (FIFO) inventory rotation system ensures that older stock is used before newer arrivals, minimizing the time any batch spends in storage and reducing the cumulative risk of quality degradation.

Summary of key storage precautions 🔗

Maintaining the quality and safety of stored fish meal comes down to a few critical practices. Use polyethylene-lined or solid polyethylene bags to create an effective moisture barrier. Store bags in well-ventilated, cool, dry warehouses with temperatures between 15-25°C and humidity below 65%. Ensure antioxidant treatment is applied during production, or allow proper curing before bulk storage. Manage stack height and spacing to prevent heat accumulation and allow airflow. Implement pest control and maintain strict hygiene standards. Finally, conduct regular quality monitoring and follow FIFO inventory rotation.

When these measures are followed consistently, fish meal can retain its nutritional value and remain safe for animal consumption over extended storage periods – sometimes lasting several years without significant quality loss.

What do you think? Given that fish meal storage requirements are so demanding, how might climate change – with rising temperatures and humidity – affect storage practices in tropical fish-producing countries? And could newer biodegradable packaging materials ever match the moisture protection offered by polyethylene?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC8066737/
2. https://www.sciencedirect.com/science/article/abs/pii/S0022474X23000073
3. https://www.fao.org/4/x6899e/x6899e04.htm
4. https://www.fao.org/4/x5926e/x5926e01.htm
5. https://www.cargohandbook.com/Fishmeal
6. https://unece.org/DAM/trans/doc/2016/dgac10c3/UN-SCETDG-50-INF24e.pdf