If the catch is not needed by your family and is to be sold, it is very important to preserve it in a way that is required by customers. Preservation will vary according to:
There is always an advantage in landing fish in the best possible condition, but this must be balanced against the cost of producing this quality. There is no point in landing fish that are in first-class condition if you are spending more to do so than the value of your catch.
In tropical waters, if you want to produce fish of high quality for market, it is important to take special care of your catch. A set of guidelines to ensure that the fish you land are in the best condition possible is set out below. These guidelines are also applicable to catches in temperate areas.
Fish landed from traps and pots are usually very lively and should be taken from the gear as quickly as possible and immediately placed in a large container of fresh seawater. This helps to calm the fish and reduces bruising to the flesh. If fish are landed straight on to the deck they may thrash around violently, causing bruising and scale loss. A gaff should not be used to handle the fish as the injuries provoked will encourage spoilage.
A false bottom or a bag of nylon prawn mesh can be fitted to steel traps to further reduce bruising and scale loss.
To obtain the best quality of product, fish should be processed immediately after capture or as soon as possible. If they are not processed immediately, they should be kept cool using ice, ice water or brine in a wet bag, or at least in the shade, protected from direct sunlight.
To ensure high quality, it is advisable to bleed or spike and bleed fish as soon as they are removed from the trap or from the seawater bin. Effective bleeding will reduce discoloration of the flesh, the start of spoilage and bruising. It can be done by cutting the gill rakers or a main artery. While fish are being bled, they can be either held in seawater contained in plastic bins in the shade or immersed in an ice slurry. The use of an ice slurry is the preferred method.
The best slurry can be made from four parts of freshwater ice mixed with one part of fresh seawater. Slurries should be maintained as close to freezing (0°C) as possible, but not below, as partial freezing will occur and bleeding will not be as effective.
It has been found that partial freezing (between -1°C and
-6°C) will encourage spoilage. This makes it important not to add salt to the slurry, as this will make it freeze. Tests have shown that excessive soak time in the slurry will cause bleaching of the skin, especially in red fish, and cloudiness of the eyes. In tropical areas, if you bleed your catch in an ice slurry, fish of less that 1 kg should be processed within one hour of being placed in the slurry. Fish larger than 3 kg can be left for up to two hours.
Spiking, or iki-jime, will kill the fish instantly and prevent the stress conditions that occur when the fish is left to die in the normal way. There are two main iki-jime methods: from the top of the head or through the gill cover (Figure 64). The first method is used for most medium-sized fish where a sharp spike is driven into the brain from the right side of the head. The position of spiking is diagonal and about 2 cm behind the eye. Smaller fish can be spiked through the gill opening with a sharp knife (Figure 64). This will both spike and bleed the fish. The aim of both methods is to destroy the hind brain of the fish, which is the part of the brain controlling movement. Another iki-jime method is to open a hole to the spinal cord of the fish and pass a stiff nylon fibre down the cord.
Spiking can significantly decrease spoilage if combined with rapid chilling. Spiking is only effective if the fish is alive when it is carried out.
If your market requires gilled and gutted fish, these operations should be carried out as soon as possible after bleeding. All gills, internal organs, gut contents, air bladders and the blood line along the backbone (equivalent to the kidney) should be removed completely. Care should be taken not to cut or damage the inside skin of the gut cavity or to spill gut contents on to any cut surfaces, as this will make the fish spoil more rapidly. A stiff brush or a high-pressure spray can be used to remove the blood line. All excess slime and blood should then be washed from the fish. If necessary, the fish should be placed in a clean ice slurry for a short time to make up for any rise in temperature during processing.
A similar washing and icing method should be used when your market wants good-quality whole fish. Care should be taken not to mark or injure the fish during the washing and cleaning process.
Scales are not usually removed from gutted or whole fish, unless the market requires their removal.
Spiking or iki-jimemethods killing the fish instantly
The cleaned fish should then be packed in ice ready for transportation to market. A good way to pack fish in ice is to use the "soldier" method, in which they are packed in freshwater ice in boxes or the insulated hold of your vessel, with the belly downwards or upwards (Figure 65). Saltwater ice is not recommended as its melting point can be as low as
- 6°C, which can cause partial freezing of the fish.
To chill fish effectively it is important for the ice to be in contact with as much of the surface as possible. Contact between fish should be avoided, as this can cause discoloration.
If the fish are to be landed whole, it is especially important that they are cooled as quickly as possible, so that the internal organs do not start to rot or liquefy.
If the catch is filleted on board, it is still necessary to cool the fish prior to processing so that the quality of the flesh is maintained. After the fillets are removed, they should be thoroughly washed in clean water prior to icing or freezing.
When it is possible, freezing on board is the most effective way to preserve your fish catch, although there is some loss in the quality of the landed product. Whole fish or processed fish can be kept in good condition without serious deterioration for many months if they are snap frozen and kept at temperatures at or below -18°C. However, the installation of a freezer on board is costly and is not possible on all vessels, especially smaller ones. In addition, other factors have to be considered before a decision is taken:
When your fish are unloaded for direct sale on the wharf or transportation to other markets, it is important to minimize temperature changes. Ideally, fish should be unloaded into a well-insulated, refrigerated transport vehicle, but as these may be scarce and are usually expensive, your catch should at least be well protected from the sun. Top up the ice when it melts.
If tropical reef fish are handled as set out above, they can be stored on ice for up to three or four weeks, depending on the species.
Soldier packing in ice