7.1 General
7.2 Ambient Temperature
7.3 Capacity
of Boxes and Packing Density
Ice is used in fisheries to chill the fish from surrounding temperature level down to 0°C and to keep it at this temperature.
The weight of ice needed to chill 1 kg fish (0°C) can be calculated theoretically as shown below (in practice Some more ice will be needed):
Table 13 Weight of ice needed to chill 1 kg fish from various ambient temperatures
Starting temperature of fish (°C) |
Weight of ice needed (kg) |
30° |
0.34 |
25° |
0.28 |
20° |
0.23 |
15° |
0.17 |
10° |
0.12 |
5° |
0.06 |
The necessary quantity of ice required to maintain the fish chilled will depend upon the ambient temperature, the insulative properties of the container, the place of the individual box within the load and the length of the storage.
In the following is given an example of ice requirements to chill and maintain in chill condition fish held in individual boxes and within a stack of boxes.
Table 14 Ice requirements for chilling and storage of fish
Melting of ice per box of 50 kg fish |
||||||
1 box |
35 boxes |
|||||
| Surrounding temperature (°C) | +30 |
+20 |
+10 |
+30 |
+20 |
+10 |
| Chilling fish (kg) | 21 |
14 |
7 |
21 |
14 |
7 |
| Keeping chilled (kg/h) | 3 |
2 |
1 |
1 |
0.7 |
0.3 |
For practical purposes the following rules of thumb can be given to calculate ice requirements:
l. Fish boxes: Ice to fish ratio in tropics are 1 kg ice to 1 kg fish, and ice to fish ratio in temperate climate and in insulated van are 1 kg ice to 2 kg fish.
2. Insulated tanks: Water to ice to fish ratio in tropics are 1 kg water to 2 kg ice to 6 kg fish and in temperate climate 1 kg water to 1 kg ice to 4 kg fish.
Necessary volume of ice to chill the fish down to a temperature of 0°C is included in the above mentioned rules. If the fish is already chilled the volume of ice can be reduced accordingly.
The fish carrying capacities of various boxes and containers depend on the density of the mixture of ice and fish.
Table 15 Density of different types of ice
Type of ice |
Bulk weight |
Specific volume |
| Crushed block | 0.690 |
1.45 |
| Tube | 0.565 |
1.80 |
| Plate | 0.570 |
1.75 |
| Flake | 0.445 |
2.25 |
Assumed that density of fish is 0.95 kg per dm³ (1 litre) the density of 1 dm³ (1 litre) of the mixtures of ice and fish in fish boxes, and water, ice and fish in tanks, areas follows:
Table 16 Fish to ice ratio using different types of ice
| Type of ice | Ice to fish ratio |
Water to ice to fish ratio |
||
1:1 |
1:2 |
1:2:6 |
1:1:4 |
|
| Crushed block Tube ice Plate ice Flake ice |
0.82 kg |
0.86 kg |
0.90 kg |
0.92 kg |
From this table the capacity to carry ice and fish in different boxes and tanks can be calculated.
As examples the weight of crushed block ice and fish is calculated for the types of fish boxes described in Section 5.4.
Table 17 Icing using different types of boxes in temperate and tropical climates
Type of box |
Volume (litres) |
Tropics |
Temperate climate |
||
kg ice |
kg fish |
kg ice |
kg fish |
||
A |
26 |
10.7 |
10.7 |
7.5 |
15.0 |
For an insulated tank with a volume of 1 000 litres, the similar calculation gives (crushed block ice).
Table 18 Fish to ice ratio in an insulated tank in temperate and tropical climates
Tropics |
Temperate climate |
||||
water |
ice |
fish |
water |
ice |
fish |
100 kg |
200 kg |
600 kg |
153.3 kg |
153.3 kg |
613.4 kg |
