Aquaculture often requires transporting live animals from one place to another. A large shipment of the same type of fish can be delivered via a hauling tank and truck if the distance is not too great.
But for long distances, or when the shipment is not large enough to justify a truck with hauling tanks, shipping fish in boxes is a feasible and more economical alternative. For international shipments, air freight in boxes is the only true option.
The ornamental fish trade has a long and successful history in using air freight. Today, more and more aquaculture products such as eggs, fry and fingerlings are shipped by air freight in boxes.
With modern air transportation, fish can be transported almost anywhere in the world and arrive in healthy condition. Many factors are involved in successfully preparing, packing and shipping fish in boxes.
It is important to keep in mind that once the bags and boxes are sealed, the fish must be able to survive in the container with a minimum amount of stress until they reach their final destination.
This publication addresses the major considerations involved in making successful shipments, but because of extreme variations in species, sizes and durations of transport times, it should be used only as a guide.
Limiting environmental factors:
The following environmental factors must be within an acceptable range for success. If they reach a critical, limiting level they can cause stress, disease and even mortality. Consider each of these when planning a shipment so that problems can be prevented.
Always start with good quality water. However, as soon as the boxes are sealed many key water quality parameters will begin to change—temperature can go up or down, pH typically will fall, oxygen will be consumed, carbon dioxide will increase, etc. While fish can tolerate some change in their environment, especially for short periods, they do not handle rapid changes well.
Water quality parameters can reach critical levels if not managed properly. The goal is to prevent these parameters from changing, or at least manage the rate and degree of change to ensure that fish will arrive in good condition.
Temperature:
Fish are cold-blooded animals that cannot regulate their own body temperature. They will be the same temperature as the water they are in. This affects their health in two ways. First, all fish have a defined temperature range in which they thrive and limits at which they can survive.
If water temperature deviates from the optimum range, the fish can become stressed; if it deviates beyond their tolerance levels, they can die. Second, fish metabolism goes up as temperature increases and down as temperature decreases.
If metabolism increases, many of the other limiting environmental factors will deteriorate more quickly. If possible, fish should be shipped at their lowest optimal temperature to slow their metabolism and decrease the rate at which other environmental factors deteriorate inside the box.
Dissolved oxygen:
Dissolved oxygen is often the most important limiting factor in shipping fish. The only source of dissolved oxygen during shipment is the diffusion of oxygen from the air overlying the water within the bag.
Because the amount of oxygen in the bag is limited to the volume of the bag, it is essential to maximize the amount of oxygen available during shipment.
The main ways to achieve this are to reduce the biomass of fish in the bag, increase the amount of oxygen in the bag by using pure oxygen instead of atmospheric air, decrease the length of the shipment time, and decrease the metabolism of the fish by keeping water temperature at the lower level for the given species.
Carbon dioxide:
Carbon dioxide is produced by respiration. In a closed bag, carbon dioxide can reach harmful levels that can have a narcotic effect and interfere with the absorption of oxygen by the gills. If the dissolved oxygen level is high when fish are packed it should not be a problem during shipping.
Because carbon dioxide in water acts as an acid, it also decreases the pH level, which can be stressful or lethal if allowed to progress unchecked.
The main ways to manage carbon dioxide are to reduce the biomass of fish in the bag, increase the amount of oxygen in the bag by using pure oxygen instead of atmospheric air, decrease the length of the shipment time, and decrease metabolism of the fish by keeping water temperature at the lower level for the given species.
In addition, buffers can be added to lessen the effect of carbon dioxide on the pH of the water.
Nitrogenous waste/ammonia:
Fish excrete ammonia across the gill membrane to rid themselves of nitrogenous waste. Ammonia in water exists in two forms—ionized (NH4+) and un-ionized (NH3). Un-ionized ammonia is toxic to fish at very low levels, while ionized ammonia is relatively harmless.
The ratio of the two types of ammonia in water is directly related to the water pH and temperature. As pH and temperature decrease, so does the portion of the ammonia that is in the toxic, un-ionized form.
During production, ammonia and other nitrogenous wastes can be managed with tools such as biological filtration. In a sealed bag other methods must be used.
The main ways to manage ammonia during shipment are to reduce the biomass of fish in the bag, withhold food from the fish for 24 hours before shipment to reduce the amount of waste they produce, decrease the length of the shipment time, decrease the metabolism of the fish by keeping water temperature at the lower level for the given species, and add a substance to the shipping water to remove ammonia. A combination of methods can be used.
Authors:
Craig Watson, Kathy Heym Kilgore and Carlos Martinez
