Best Practices for Handling and Preserving Fish Meal Raw Materials

Fish is one of the most perishable food commodities on the planet. It begins to deteriorate almost immediately after being caught, driven by enzymatic activity, bacterial growth, and oxidation. For the fish meal industry, this rapid spoilage poses a serious challenge – because the quality of the final fish meal product is directly linked to how well the raw material was handled and preserved before it ever reached the processing plant. Whether you are dealing with whole fish caught specifically for reduction, by-catches, or offcuts from the consumption industry, using fresh raw material consistently yields the highest product quality and the best processing output. But freshness is not always easy to maintain, especially when fish must travel long distances from remote fishing grounds. That is where proper handling and preservation techniques become essential.

Why handling and preservation matter in fish meal production 🔗

Fish destined for meal production can come from a variety of sources. These include fish caught exclusively for reduction (as in Peru, Chile, Norway, and Denmark), by-catches from other fisheries, and offcuts or offal from the food fish processing industry. Regardless of the source, all raw material shares one common trait: it spoils fast.

The breakdown of fish protein and oil happens through both autolytic (enzyme-driven) and microbial processes. In small pelagic species like sardines, anchovies, and herring, digestive enzymes can cause severe softening of the flesh, rupture of the belly wall, and loss of protein and oil into liquid form – a process worsened when the fish have been actively feeding before capture. Microbial spoilage adds to this, producing volatile compounds like ammonia and trimethylamine that degrade quality further.

If raw material quality is poor at the time of processing, no amount of advanced equipment can produce premium-grade fish meal. The protein content drops, free fatty acid levels rise, and the nutritional value of the finished product declines. This is why the period between catch and processing – and what happens during that window – is so critical.

Physical preservation methods 🔗

Physical methods rely on controlling temperature and moisture to slow down the biological processes that cause spoilage. They are the most widely used approaches in the fish meal industry globally.

Draining 🔗

Draining is the simplest and most cost-effective first step in raw material preservation. Proper drainage – both on the fishing vessel and at the shore facility – reduces the free water that carries body slime, gut contents, and bacteria, thereby limiting how quickly spoilage organisms can spread and multiply. On board vessels, good drainage also reduces physical damage to the fish caused by the rolling and pitching motion of the boat. While draining alone cannot preserve fish for extended periods, it meaningfully extends short-term storage life and should be standard practice on every fishing operation.

Chilling 🔗

Chilling is among the most effective methods for preserving bulk-stored fish, particularly in tropical and temperate regions where catches are made at high ambient temperatures. The rate of spoilage caused by bacteria and digestive enzymes roughly doubles with every 4°C increase in temperature. By bringing the fish down to near 0°C, chilling dramatically slows both microbial and autolytic activity.

There are two primary approaches to chilling raw fish for meal production:

Refrigerated or chilled water systems: These involve circulating cooled water through the mass of fish in the hold. Advanced systems pump chilled water upward from the bottom of the hold to ensure even cooling throughout the catch. However, prolonged storage in sea water can cause salt absorption, which is undesirable in fish meal. Using diluted sea water or fresh water helps mitigate this issue.

Ice mixing: Mixing fish with ice in the correct proportion to reach 0°C is a highly effective preservation technique. Melt water drains from the bottom, leaving the fish dry and compact. For industrial-scale fishing, automated systems that mix fish and ice at high throughput rates have been developed. In Scandinavian countries, particularly Denmark, such systems have been installed in over 100 vessels.

A newer development in this area is pumpable ice technology, which creates a homogeneous slurry that cools fish faster than traditional freshwater ice and eliminates freeze burns. This technology complies with international food safety standards and uses less energy than conventional solid ice methods.

Freezing 🔗

Freezing remains one of the most common onboard preservation methods, capable of extending shelf life to several months when done correctly. By lowering temperatures below −18°C, microbial activity effectively stops and enzymatic reactions slow to a negligible pace.

However, the freezing process needs careful control. Whole frozen fish generally retain quality longer than gutted or filleted fish. Rapid freezing is preferred because it creates smaller ice crystals that cause less damage to cell walls, preserving the texture and structural integrity of the fish. Superchilling – where only a small fraction of the water content is converted to ice – can extend shelf life by 1.5 to 4 times compared to standard chilling, while causing less structural damage than full freezing.

For fish meal production specifically, the key concern with freezing is the energy cost and the logistics of thawing large quantities before processing. Freezing is best suited for situations where the raw material must be stored for extended periods before reaching the processing plant.

Chemical preservation methods 🔗

When physical preservation alone is insufficient – for instance, during long transport from remote fishing grounds – chemical preservatives can be used to further extend the storage life of raw fish. Chemical preservatives act immediately on surface bacteria, though there is a delay in their action on the interior of the fish depending on the rate of penetration.

Salting 🔗

Salt (sodium chloride) is one of the oldest and most widely understood preservatives. It works by reducing water activity in the fish tissue, making the environment inhospitable for most spoilage bacteria. Salting can be done as dry salting (rubbing salt directly onto the fish) or brine immersion (soaking the fish in a salt solution).

For fish meal applications, the concentration of salt must be carefully calibrated. Too little salt provides inadequate preservation, while excess salt ends up in the finished meal product, reducing its quality and suitability for animal feed formulations. Salt-preserved raw material also requires consideration during the pressing and drying stages of meal production, as residual salt can affect the final product’s composition.

Formaldehyde 🔗

Formaldehyde is one of the most widely used chemical preservatives in the fish meal industry. Beyond its antimicrobial properties, it provides a beneficial firming effect on the raw material, making the fish more amenable to pressing after cooking for oil removal. This is particularly useful for species like sand eels that quickly turn semi-liquid after capture.

Formaldehyde works by combining with protein through a mechanism similar to tanning, and the reactive amino acid lysine is involved in this interaction. At small concentrations – for example, around 0.05% formalin based on the weight of the fish – there is no detectable negative effect on protein quality. However, higher concentrations can reduce the availability of lysine, an essential amino acid, which lowers the nutritional value of the finished meal.

Research has shown that formaldehyde had no significant effect on lysine levels at moderate concentrations, but it did reduce tyrosine in a dose-dependent manner. This means that while formaldehyde is effective and practical, its dosage must be precisely controlled to balance preservation benefits against potential nutritional losses.

Sodium nitrite 🔗

Sodium nitrite has shown particularly favourable preservation properties for species like herring, significantly slowing the growth of spoilage microorganisms and reducing the formation of free fatty acids. It also helps inhibit the growth of dangerous bacteria such as Clostridium botulinum.

However, sodium nitrite carries serious safety concerns. Unless added in strictly controlled small amounts, nitrites can react with other components in the fish to form nitrosamines – harmful carcinogenic compounds. Because of this risk, its use is tightly regulated. In Norway, for instance, nitrite addition is permitted only under strict supervision with carefully controlled dosages.

Special measures must also be taken during meal manufacturing when the raw material has been preserved with nitrite. The general recommendation from organizations like the FAO is that nitrite use should be permitted only under careful supervision and should not be broadly encouraged.

Other chemical preservatives 🔗

Several other chemicals – including sodium sulphite, ascorbic acid, and benzoic acid – have been evaluated for fish preservation, but they see only very limited use in practice. Each has specific advantages and drawbacks related to penetration rate, cost, and impact on the final product’s quality. The choice of chemical preservative ultimately depends on the fish species, expected storage duration, and regulatory requirements in the country of operation.

Factors that determine fish meal quality and shelf life 🔗

The effectiveness of any preservation approach depends on several interconnected factors. Understanding these helps processors make better decisions about which methods to use and how to combine them.

Freshness of raw materials 🔗

This is the single most important factor. Raw material is transported to factories either fresh or preserved in sodium nitrate or formaldehyde. Freshly caught fish have lower levels of microbial contamination and minimal enzymatic breakdown, giving processors the best starting point for producing high-grade meal. Even something as basic as the rapid deterioration caused by anaerobic conditions in bulk storage can lead to significant protein losses through ammonia production. The shorter the time between catch and processing, the better the outcome.

Preservative concentration 🔗

Getting the dosage right is critical with every chemical preservative. Insufficient concentrations fail to prevent spoilage, while excessive concentrations can degrade protein quality, introduce safety hazards, or cause regulatory non-compliance. For formaldehyde, the threshold is around 0.05% formalin by fish weight for safe and effective use. For sodium nitrite, even small deviations from the approved concentration can lead to nitrosamine formation. Regular testing and standardised application protocols are essential.

Storage conditions 🔗

Even well-preserved fish can deteriorate if storage conditions are poor. The three key environmental factors to manage are:

Temperature: Storage temperature is one of the most important determinants of shelf life. Fish should be maintained at the target temperature for the chosen preservation method – near 0°C for chilling, below −18°C for freezing. Even brief temperature fluctuations can accelerate spoilage.

Humidity: High humidity promotes microbial growth on fish surfaces, while excessively low humidity causes dehydration and texture changes. Storage facilities need to maintain balanced humidity levels appropriate to the preservation method being used.

Light exposure: Exposure to light accelerates lipid oxidation, leading to rancidity and off-flavours. Raw fish should be stored in dark environments or opaque containers whenever possible.

Best practices for handling fish meal raw materials 🔗

Based on the principles covered above, here are practical recommendations that fish meal producers and handlers should follow:

Minimise the catch-to-processing interval: Process fish into meal as quickly as possible after landing. Every additional hour of delay increases the risk of quality loss.

Implement proper drainage on vessels: Ensure fishing vessels are equipped with adequate drainage systems to remove free water from fish holds during transit.

Use chilling for short-to-medium transport: Ice mixing or refrigerated water systems should be standard for any voyage or storage period exceeding a few hours, especially in warm climates.

Reserve freezing for long-term storage: When raw material cannot be processed within a few days, freezing is the most reliable option for maintaining quality over weeks or months.

Apply chemical preservatives judiciously: Use formaldehyde or other approved preservatives only when physical methods alone are insufficient, and always within recommended concentration limits.

Monitor storage conditions continuously: Install temperature logging equipment in holds and storage facilities. Conduct periodic quality checks using indicators like total volatile basic nitrogen (TVB-N) to detect early signs of spoilage.

Train handling crews: Everyone involved in the catch-to-factory chain should understand how their actions affect raw material quality. Poor handling – rough treatment, delayed icing, contaminated surfaces – undoes even the best preservation strategy.

The bigger picture: preservation and fish meal economics 🔗

Preservation is not just a quality issue – it is an economic one. The composition and degree of deterioration of raw material are frequently used to set purchase prices in countries where the fishing fleet and the fish meal industry are separate commercial entities. Better-preserved raw material yields more meal and oil per tonne of fish, commands higher prices, and produces a product with superior nutritional value for aquaculture and animal feed applications.

Conversely, poorly preserved fish leads to lower protein recovery, higher free fatty acid levels in the oil, increased odour problems during processing, and a finished product that may not meet quality standards for premium markets. The investment in proper handling and preservation equipment – from ice-making machines on vessels to temperature-controlled storage at shore facilities – almost always pays for itself through improved yields and product quality.

What do you think? Given the trade-offs between cost, practicality, and safety, which preservation method do you think is most suitable for small-scale fish meal operations in tropical regions? And how do you think emerging technologies like superchilling might change preservation practices in the fish meal industry over the coming years?

References

1. https://en.wikipedia.org/wiki/Fish_preservation
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC7825328/
3. https://www.fao.org/4/x6899e/X6899E03.htm
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC7760111/