Care, cleanliness and cooling are the keys to harvesting a catch of good quality. These are the three important ways of preventing fish from going bad too quickly.
Care in handling is essential because unnecessary damage can provide access through cuts and wounds for the spoilage bacteria, thus hastening their effect on the flesh. Fish is soft and fragile and is easily bruised or torn by rough or inexpert handling. Therefore, prompt and proper care of the fish must be taken from the time it is harvested until the time it reaches the consumer. It should always be remembered that fish is food and should therefore be handled as such.
Cleanliness should be observed throughout the fish handling chain. All surfaces with which the fish may come into contact should be scrubbed clean and kept as free as possible from bacteria-laden materials. Fish will keep longer in fresh condition if they are kept as free as possible from contamination with bacteria. Natural sources of bacteria can largely be removed soon after the fish is captured by taking out the guts and washing off the slime from the surface of the fish. Werner A. Janssen invites the attention of the public to the possibility that fish could be infected with and carry human bacterial pathogens causing tuberculosis, cholera, and thyphoid fever due to contamination.2 It is therefore of extreme importance that the fish be handled in hygienic manner so that the chances of contamination are kept to a minimum.
Temperature is the most important factor controlling the speed at which fish spoils, such that the higher the temperature, the faster the bacteria multiply, and the lower the temperature, the slower the bacterial and enzymatic activities. Therefore, the most important step to slow down these activities is to lower the temperature of the fish as quickly as possible. Low temperature in fish can be attained through a number of ways as the use of salt-water ice, freshwater ice, bactericidal ice, refrigerated seawater or through mechanical refrigeration. In the Philippines, however, plain crushed ice is generally used as an effective chilling agent to cool and maintains the temperature of the fish. Proper icing is therefore necessary to attain maximum benefit from the ice.
Ice is the best agent for cooling fish. As a cooling medium it has the following characteristics:
has a very large cooling capacity for a given weight or volume
harmless, cheap and easy to handle
provides rapid cooling through intimate contact between ice and fish
keeps chilled fish cold, moist and glossy
prevents dehydration that could accompany other methods of cooling, such as refrigeration storage without ice.
Ice, in addition to all these characteristics, has another important feature in that it can serve as its own thermostat. This means that ice maintains fish at a temperature just slightly above the point at which the fish would begin to freeze.
Furthermore, ice aids in preservation in two ways: a) the temperature of the fish is lowered to approximately 0°C which slows bacterial and enzymatic changes, and b) the melting of the ice bathes the fish in clean cold water and washes away considerable slime, blood and bacteria.
In order to understand how ice is so useful for chilling fish, it is necessary to know its nature and properties.
Water freezes at a temperature of 0°C as ice. A quantity of heat has to be removed from the water to turn it into ice, and the same amount of heat has to be added to melt it all again. The temperature of a mixture of water and ice will not rise above 0°C until all the ice has melted. Ice needs a large amount of heat to melt it which also means that it has a large reserve of cold. This property of ice makes it so widely used in chilling fish.
Ice made from different sources, i.e., freshwater or seawater ice, tap water ice or distilled water ice has the same cooling power.
When ice is placed in close contact with the fish to be chilled, heat is transferred from the warm fish to ice, thus, lowering the temperature of the fish and melting the ice.
Heat moves from a warm place to a cold place in one or more of these ways: a) by conduction, b) by diffusion, and c) by convection.
In conduction, heat is carried through the structure of a material, for instance, hot air from a warm outside surface of a chillroom is passed through the wall to warm the inside surface of the room. Heat is carried by diffusion when water evaporates from a warm surface and condenses on a cold surface, for example, moisture from humid air condenses on ice transferring heat to the ice. With convection, heat is carried by the movement of a substance, usually a fluid such as air or water, from one place to another; for example, air surrounding warm fish in a chillroom becomes warm and rises to the ceiling where it is cooled by the evaporation coils and falls to the room again.3
In a container of fish with ice, and where all ice has been put on top of the fish, some ice will be melted in chilling the fish, some by heat coming through the container and some by the heat contained in the moist air penetrating the container and condensing on the ice. Therefore, heat comes from many sources and it is very important that sufficient amount of ice is placed between and among the fish in order to attain maximum benefit from the ice.
Ice used for cooling fish may be produced in two main forms, as block and as small ice. In whatever form ice is manufactured, it must be made from water.
Block ice is manufactured by freezing potable water in galvanized steel cans. The size of the block produced may vary from 12 to 140 kg or more.
Block ice is manufactured more rapidly by direct evaporation system. A primary refrigerant is circulated through a jacket around the cans of water passing through the centres of the cans. Blocks are then removed from the molds by immersing the cans in warm water on brine to release the ice.
Block ice, depending on how it is crushed, can either be called large crushed ice or small crushed ice.
Small ice is a general term used to describe the many kinds of ice made in small pieces. These include flake ice, cube ice, ribbon ice and many others.
3 FAO Fisheries Report No. 59, Revision I, Ice in Fisheries, (Rome: FAO, 1975), p. 8.
The two most important types of small ice may be classified roughly as: a) flakes which are smooth pieces that are either flat or slightly curved, and b) cylinders, which are pieces cut from long hollow tubes of ice formed inside refrigerated pipes of small diameter.
Methods used in making ice is based upon the formation of a fairly thin skin of ice on a smooth refrigerated surface, and the removal of that skin is either by mechanical action or by warming of the surface.
| TYPES OF ICE | ADVANTAGES | DISADVANTAGES |
| Block Ice | -Requires less space to manufacture; | -Large pieces of crushed block ice make poor contact with the fish they are meant to cool and may melt less rapidly; |
| -Requires less space during transport. | -Can mark and bruise the fish; | |
| -Melts less during transport. | -Cools fish slowly. | |
| Flake Ice | -The flat shape of flake ice makes transfer of heat from the fish to the ice more rapid; | -Requires more storage and space; |
| -Being smooth and small, does little damage to the fish; | -Melts rapidly during transport; | |
| -There is a closer contact between ice and fish hence, cools fish more rapidly; | -Rate of melting is higher; | |
| -The manufacture of this ice needs less space and needs little maintenance; | -Bridges over the product being cooled, leaving an air space between the ice and top of the fish, thereby reducing the flow of heat from fish to ice. | |
| -Manufacture begins very soon after the machine is started and there's no need to wait several hours before harvesting can begin; | ||
| -No crushing is needed, the ice flows easily and is more easily stored, handled and transported; | ||
| -Melts more rapidly than tube ice and cools the fish more rapidly. | ||
| Tube Ice | -Provides more cooling capacity in a small space than flake ice; | -Larger pieces of tube ice may likely damage and bruise fish than flake ice. |
| -Cools the fish slowly and continuously on a warm atmosphere during transit. |
Fish spoilage sets in after death, hence the need to control spoilage. Some species of fish like tilapia stay alive from four to six hours after they are caught, and this is an advantage specially in places where ice is inadequate or not available at all.
Fish should be chilled as promptly as possible to ice temperature and this temperature should be maintained throughout the distribution chain. It is important to pre-chill fish to ice temperature before packing it in containers for transport because ice melting is reduced, specially if fish are packed in insulated containers or styrene boxes.
Fish deteriorates rapidly and potential keeping time is shortened if they are not properly handled and stored. Much of the fish handled for human consumption is subjected to rough handling treatment.
Fish should not be exposed to direct sunlight or to the drying effects of winds, but should be carefully cleaned and chilled immediately to the temperature of melting ice (0°C) as quickly as possible.5
5 Code of Practice for Fresh Fish, FAO Fisheries Circular No. 318 (Rome: FAO), p. 4
Washing. As soon as the fish are harvested, they should be washed in clean water to remove the mud and debris or any foreign materials that may adhere to the body of the fish.
Pre-chilling. Pre-chilling is usually done by placing the fish in 1:1 ice and fish ratio to cool it immediately to the temperature of melting ice (0°C) as shown in Figure 1. Small pieces of ice are used to make good contact with the fish.
In some places, fish are placed in a chilling tank. The recommended chilling temperature is 0°C (32°F). However, Dolendo, et. al.,6 in their study found no advantage in chilling the fish to 0°C (32°F) over the 4°C (39°F) if chilling is immediately done after harvest. It was also noted that there was no considerable change of temperature during air transport.
Packing. After the pre-chilling process, fish are packed in suitable containers with sufficient ice. For long distance transport, and whenever possible, it is important to pack fish with ice using 1:1 ice to fish ratio. The best method of packing fish in ice is to place a layer of ice in the bottom of the container and in-between the layers of the fish as shown in Figure 2. Enough ice should be placed on top of the container to maintain the temperature close to 0°C until it reaches its destination.
Fig. 1. Pre-chilling
Figure 2.
| ICE TO FISH RATIO | TIME FOR ICE TO FULLY MELT (hr) | TEMPERATURE IN STORAGE (0°C) | ICE MELTAGE (%) |
| 1:1 | 17 | 0 to 1.1 | 30.00 |
| 1:4 | 6 | 2.2 to 4.4 | 85.58 |
| 1:6 | 5 | 6.6 to 7.7 | 90.14 |
From the time the shrimps are caught, there is a continuous and irreversible deterioration in quality. The progress and degree of deterioration depends mainly on the time they are held and the temperature at which they are handled.
The longer the shrimps are left without being washed and iced, the faster they will deteriorate.
It is essential to prevent the temperature of the shrimps from rising. Each degree of rise in temperature increases the rate of spoilage. Even well iced shrimps will not keep longer than seven days without appreciable deterioration in quality.
Sorting. Harvested catch shrimps should be sorted according to kind and species.
Washing. Shrimps should be washed in clean water to remove sediment and iced as soon as possible to prevent the sun and the drying effects of wind.
Pre-chilling. Shrimps should be pre-chilled quickly to the temperature of melting ice (0°C) and maintained in a chilled condition until it reaches the market.
Packing. Shrimps should be packed in ice in shallow layers and should not be overfilled. It should be surrounded by adequate quantities of finely crushed ice. This gives close contact with the shrimps, thus, giving rapid cooling and reducing damage due to pressure.
Fresh shrimps intended for export are handled in a different manner than those intended for local markets. They are usually beheaded and deveined to retard spoilage and “black spot” formation. This “black spot” formation or “melanosis” is a pigmentation defect frequently occurring in shrimp. Such condition may be retarded by the proper application of sodium bisulphite or other related compounds. The usual method is, after sorting, beheading and washing and prior to icing, shrimps are dipped for one minute into a solution of 1.25 percent of sodium bisulphite. The immersion should be taken to insure a thorough treatment. Too short a time will be ineffective while too long exposure will discolor the shrimp.
There are other methods of cooling fish like cooling with cold air or with dry ice, but these methods are not as good as cooling with plain ice.
When using cold air, as in a chill room, the heat taken from the fish will warm the air rapidly and the warm air must be removed by using a fan or blower. However, cold air blown over the fish causes the fish surfaces to dry such that they quickly lose their moist and attractive appearance.
There are a number of reasons why dry ice is less suitable in chilling fish than plain ice. Dry ice cannot be mixed intimately with the main mass of fish. It has to be kept apart from the fish because of its very low temperature which freezes it instead of just chilling it.
In places where ice is not available, fish caught are sometimes packed in rattan/wooden baskets or boxes lined with seaweeds or banana leaves to lower the temperature during transport.
For hardy species like tilapia, they are usually packed in wooden boxes (kaha), tubs (bañeras), or baskets (kaing). Fish, while still alive are transported to nearby markets without icing.
Crabs deteriorate more rapidly after death than most fish and quality can best be maintained by keeping them alive until processing. Live crabs are extremely delicate animals and should be handled at all times with great care. The natural environmental conditions of crabs are quickly changed when they are brought to the surface from the water. Healthy crabs can gradually adapt themselves to these changes but the crab's vitality is considerably weakened, and care is important to avoid heavy losses.
Live crabs should be handled with great care at all times to prevent high mortality.
Live crabs, should be held in clean bags, wet sacks, or boxes since slime or mud suffocates the crab during transport. Crabs may also be transported by packing them with fresh seaweeds.
Transportation of live crabs in lightweight plastic boxes has been found safe and economical.
The commonly used fish containers are made of different materials like galyanized iron sheet, wood, bamboo, rattan or plastic of varying shapes and capacities. However, the most significant difference is their suitability to hold a perishable commodity such as fish.
Bañera. Conical bañeras or tubs made of galvanized iron sheets are the most commonly used fish containers with a capacity of 35–40 kg. It is round with a flat bottom measuring 22 in. (top) and 18 in. (bottom) in diameter and 10 in. height.
Metal boxes measuring 18" × 18" × 24" and having a capacity of 50 kg are used in transporting shrimps by plane.
Wooden fish boxes. These types of containers are of varying kinds and sizes.
Wooden small box with 50 kg. capacity has a dimension of 10" × 30" × 42".
Wooden small box with 70 kg. capacity has a dimension of 18" × 22" × 42".
Kaha (shallow wooden tray). This is rectangular with dimension of 3" × 13" × 24" and has a capacity of 20 kg.
Wooden box used to fish transport by boat and by train has a dimension of 24" × 24" × 48" and with a capacity of 70 kg.
Wooden box for milkfish transport by boat has a dimension of 48" × 48" by 48" and with a capacity of 100 kg.
Bamboo and/or rattan baskets. Like the wooden boxes, bamboo or rattan baskets have varying shapes and sizes.
“Bakol” (medium size bamboo basket). It is round at the top with four corners at the bottom. It has a diameter of 18 in. at the top, 13 in. at the bottom and a height of 6.5 in.
“Tiklis” is a small, big-mouthed bamboo/rattan basket with round sides, flat bottom, with a diameter of 16 in. at the top, 10 in. at the bottom and with a height of 13 in.
“Luelang” is a large, big-mouthed bamboo/rattan basket with round sides, flat bottom, with a diameter of 24 in. at the top, 19 in. at the bottom and a height of 10 in.
Plastic fish boxes. Quality-conscious fishfarmers are now shifting from the traditional fish containers such as tubs and boxes to plastic boxes. These containers have the following dimensions:
outside - 28" × 17-¼" × 11-1/8"
inside - 28-½" × 15-¾" × 10-1/8"
Styrene container. This container is made of styrofoam materials that give an insulating property, thus, having a low thermal conductivity. Styrene container with 30–35 kg. capacity has a dimension of 22-½" × 15-½" × 15-½" (outside) and 20" × 14" × 14" (inside).
Comparative analysis of fish containers is shown in Table 4.
