Best Practices for Handling Wet Fish

Fish is one of the most perishable food products in the world. The moment a fish is taken out of water, a countdown begins – bacterial growth, enzymatic reactions, and oxidation start breaking down its tissues. According to the FAO, unless fish are harvested quickly with minimal stress, properly handled, and chilled, spoilage and quality deterioration accelerate rapidly. This makes proper wet fish handling not just a matter of good practice, but an absolute necessity for food safety, economic returns, and nutrition.

Why wet fish handling matters 🔗

Wet fish handling refers to the entire set of practices involved in managing freshly caught fish – from the moment of capture through cleaning, chilling, storage, and transport to market. The goal is to keep fish in the best possible condition by controlling three key enemies: bacteria, enzymes, and temperature.

Fish flesh contains roughly 80% water and is rich in protein, making it a perfect breeding ground for microorganisms once the fish dies. Bacteria that live on the skin, gills, and gut of live fish begin multiplying rapidly at warm temperatures. The FAO’s fisheries training manual emphasises that temperature is the single most important factor controlling the speed at which fish spoils – the higher the temperature, the faster bacteria multiply. In tropical regions, where ambient temperatures are high, fish can become unfit for consumption within hours if not handled correctly.

The economic consequences are severe. Global post-harvest fish losses caused by spoilage are estimated at 10 to 12 million tonnes per year, which represents roughly 10% of total production from capture fisheries and aquaculture. For small-scale fishers in developing countries, poor handling can mean the loss of 30-40% of a catch’s value.

The three cardinal rules: care, cleanliness, and cooling 🔗

Effective wet fish handling rests on three fundamental principles, often summarised as the three Cs: care, cleanliness, and cooling.

Care in handling 🔗

Fish flesh is soft, fragile, and easily damaged. Rough handling creates cuts and bruises that allow spoilage bacteria to penetrate deeper into the muscle tissue, accelerating deterioration. Every person and piece of equipment that comes into contact with fish must treat it gently. Fish should never be thrown, stepped on, or piled excessively high in containers. Overfilling containers can crush fish at the bottom, causing physical damage that reduces market value and shelf life.

Cleanliness throughout the chain 🔗

All surfaces, tools, containers, and hands that touch the fish must be kept as clean as possible. Natural sources of bacteria – including gut contents, slime, and blood – should be removed promptly after capture through gutting and washing. Sanitation experts recommend that water used for cleaning fish and making ice must come from government-approved potable sources and be regularly tested for contamination. Personal hygiene of handlers is equally important: hand washing before and after handling fish, wearing clean clothing, and maintaining overall cleanliness all help reduce bacterial loads.

Cooling as quickly as possible 🔗

Lowering the temperature of fish immediately after capture is the most critical step. The target temperature is 0°C (the temperature of melting ice), which dramatically slows bacterial growth and enzymatic breakdown. Every degree above this target increases the spoilage rate. Fish that is chilled to 0°C within an hour of capture can last several days longer than fish left at ambient tropical temperatures for even a short period.

Icing techniques and best practices 🔗

Ice remains the most widely used and effective method for chilling fish. It is relatively cheap, widely available, harmless, and provides rapid cooling through direct contact. Beyond cooling, melting ice serves an additional function – it washes away blood, slime, and surface bacteria from the fish.

Proper icing ratios 🔗

The recommended ratio of ice to fish is 1:1 by weight – one kilogram of ice for every kilogram of fish. This ratio ensures that fish are cooled down to 0°C quickly and that sufficient ice remains to maintain this temperature during storage and transport. The FAO notes that at a 1:4 ice-to-fish ratio, all ice melts within about 6 hours and the fish temperature rises to 2-4°C, while at a 1:1 ratio, ice lasts approximately 17 hours and temperatures stay between 0°C and 1.1°C.

Layered icing method 🔗

The best method is to place a layer of ice at the bottom of the container, then a layer of fish, then another layer of ice, and so on. The top layer should always be a generous blanket of ice. This ensures even cooling from all sides. Ice should be made from clean, potable water and crushed into small pieces for better contact with the fish surface. Flake ice is particularly effective because its flat shape creates better surface contact, cools fish more rapidly, and causes less physical damage than large block ice chunks.

Pre-chilling 🔗

Before packing for transport, fish should be pre-chilled – immersed in a 1:1 ice-water slurry to bring their temperature down to 0°C as fast as possible. Pre-chilling reduces the amount of ice needed during subsequent storage and transport, especially when using insulated containers. This step is particularly important in warm climates where the initial body temperature of the fish may be 25-30°C.

Onboard chilling systems for fishing vessels 🔗

For commercial fishing operations, particularly those involving multi-day trips or large catches, ice alone may not be sufficient. Several onboard chilling systems have been developed to address these challenges.

Insulated fish holds 🔗

Modern fishing vessels use insulated fish holds – storage compartments with walls lined with insulation material (typically 50-100 mm of polyurethane foam). Good insulation dramatically reduces the rate of heat leakage into the fish hold, which means less ice is consumed and temperatures stay more stable. The FAO’s technical guidelines on fish chilling show that a well-insulated RSW tank can have a heat leak 10 times lower than an uninsulated one – this translates directly into better fish quality and longer preservation.

Refrigerated seawater (RSW) systems 🔗

Refrigerated seawater (RSW) systems use mechanical refrigeration to cool seawater to just below 0°C. This chilled seawater is then circulated through tanks containing the catch. RSW systems are widely used on commercial fishing vessels because they offer several key advantages over traditional icing: faster and more uniform cooling, reduced physical pressure on fish (since fish float semi-buoyantly), easier handling of large bulk catches, and lower labour requirements compared to manual ice shovelling.

RSW systems are especially valuable for purse seiners, which often land very large catches of pelagic fish (such as mackerel, herring, or sardines) in a short time. These fish can be pumped directly from the net into RSW tanks, where they cool rapidly and uniformly. The tanks on a typical vessel hold about 80% fish and 20% water, and are divided into multiple compartments to maintain vessel stability.

However, RSW systems also have limitations. Prolonged storage in seawater can cause salt uptake in the fish flesh, which may produce an undesirable salty taste. Some species also absorb water, changing their texture and weight. These drawbacks make RSW more suitable for fish destined for canning or industrial processing rather than fresh retail markets.

Chilled seawater (CSW) plants 🔗

Chilled seawater (CSW) systems are similar in concept to RSW, but instead of using mechanical refrigeration, they use ice added directly to seawater to cool it. CSW is generally simpler and cheaper to set up, as it doesn’t require mechanical refrigeration equipment. The key benefit of CSW is that ice-seawater slurry can reach more surface area of the fish quickly and uniformly, providing efficient cooling. The melting ice also helps prevent surface dehydration of the fish.

One practical advantage of CSW is that adding freshwater ice dilutes the seawater’s salinity, which reduces the salt uptake problem associated with full-strength seawater. However, lower salinity also raises the freezing point of the mixture, which may slightly reduce the storage time compared to full-salinity RSW.

Facilities and infrastructure at fish landing centres 🔗

Once the catch reaches shore, the quality chain must continue without interruption. Fish landing centres – the points where fish are unloaded from vessels and prepared for distribution – need specific facilities to maintain the cold chain and prevent contamination.

Ice plants 🔗

A reliable ice supply is the backbone of any landing centre. The FAO recommends that an ice plant at a landing centre should have sufficient capacity for at least the expected daily fish landings, plus additional capacity for a fish collection system if one exists. The ice store should hold at least two days’ worth of production. Flake ice plants are the most popular for industrial use because flake ice has a large surface area for efficient heat exchange, doesn’t clump together during storage, and causes minimal damage to fish.

Cold storage and frozen storage 🔗

Landing centres typically maintain chilled rooms operating at 0-4°C for short-term storage of iced fish, and frozen storage rooms at -18°C or below for longer-term preservation. Chilled room capacity should be calculated based on the expected daily market turnover. Frozen storage is essential when fresh markets are saturated or when fish need to be held for longer periods. Consistent temperature monitoring and backup power systems are critical – a power failure in a cold storage facility is a food safety emergency.

Clean water supply 🔗

High-quality potable water is essential at landing centres for multiple purposes: washing fish, cleaning equipment and surfaces, making ice, and supporting personal hygiene of workers. Many centres require both hot and cold water systems – hot water is particularly important for thorough sanitisation of equipment and work surfaces. The water supply must be tested regularly for bacterial contamination.

Sanitation infrastructure 🔗

Proper sanitation infrastructure includes adequate drainage systems that prevent water pooling (which breeds bacteria and creates slip hazards), handwashing stations with soap and sanitiser, clean and well-maintained toilet facilities separated from fish handling areas, and a systematic pest management programme. All fish-contact surfaces – floors, walls, counters, cutting boards, and equipment – should be made of smooth, non-absorbent, easy-to-clean materials.

Landing platforms and handling areas 🔗

Properly designed landing platforms allow smooth transfer of fish from boats to the handling and processing area. These platforms should have non-slip, easy-to-clean surfaces positioned at heights that minimise heavy lifting. Climate-controlled processing areas, operating at 2-4°C, allow fish to be sorted, graded, and packed while staying within the cold chain. Adequate space for temporary fish storage during peak landing hours is also essential.

Common mistakes that accelerate spoilage 🔗

Even with good infrastructure, certain common errors can undo the benefits of proper handling:

Delayed chilling is the most frequent and damaging mistake. Every minute that fish spends at ambient temperature – especially in tropical climates – accelerates bacterial multiplication exponentially. Fish should be iced or chilled within minutes of capture, not hours.

Insufficient ice is another widespread problem. Using less than the recommended 1:1 ratio means the ice melts too quickly, and fish temperatures rise well above the safe zone. Ice must also be replenished as it melts.

Contamination from unclean surfaces introduces bacteria. Fish placed directly on the ground, handled with dirty hands, or stored in unwashed containers will deteriorate faster regardless of how well they are chilled.

Physical damage from rough handling – throwing, dropping, stacking too high, or using improper containers – creates entry points for bacteria and bruises that lower market value.

Exposure to sun and wind dries out the fish surface, affecting appearance, weight, and quality. Fish should always be kept covered and shaded when not being actively handled.

The role of oxidative and enzymatic spoilage 🔗

While bacteria get most of the attention, two other spoilage mechanisms also affect wet fish quality. Autolytic enzymes – chemicals naturally present in the fish’s digestive system and muscles – begin breaking down tissues after death. These enzymes were used by the living fish to digest food; after death, they start digesting the fish itself, causing softening of the flesh. Gutting the fish promptly removes a major source of these enzymes.

Oxidative spoilage is particularly relevant for fatty fish species such as mackerel, sardines, and herring. The unsaturated fats in these species react with oxygen, leading to rancidity – the development of unpleasant smells and flavours. Keeping fish cold and minimising their exposure to air both help slow oxidation. This is one reason why RSW systems, which keep fish submerged and limit air contact, can be beneficial for oily species during short-term storage.

Maintaining the cold chain from vessel to market 🔗

All the careful handling on the fishing vessel and at the landing centre is wasted if the cold chain breaks during transport to market. Refrigerated transport vehicles, insulated containers, and adequate ice provision are all necessary. Temperature should be monitored throughout the distribution chain, and any deviation should trigger corrective action immediately.

Training is equally important. Fishers, dock workers, transport operators, and market vendors all need to understand why temperature control matters and how their actions affect fish quality. The FAO highlights that one advantage of aquaculture over wild capture fisheries is that producers have greater control over harvesting conditions and timing – but this advantage is only realised when all participants in the chain follow proper handling protocols.

What do you think? In regions where access to ice and cold storage is limited, what low-cost solutions could help small-scale fishers improve their wet fish handling practices? How might better training and awareness at every stage of the supply chain reduce the estimated 10-12 million tonnes of fish lost to spoilage every year?

References

1. https://www.fao.org/flw-in-fish-value-chains/value-chain/aquaculture/handling-after-harvest/en/
2. https://www.fao.org/4/ac061e/AC061E35.htm
3. https://blog.foodsafedrains.com/6-steps-to-maximize-sanitation-in-a-fish-processing-plant
4. https://www.fao.org/4/t0713e/t0713e07.htm
5. https://www.heinenhopman.com/products/rsw-system/
6. https://semcoice.com/pros-cons-chilled-seawater-fish-cooling-on-commercial-fishing-vessels/
7. https://www.fao.org/4/t0388e/T0388E03.htm