Not all fish eggs can be transported over long periods of time. The soft eggs with their wide perivitelline space can be transported successfully over a time span of 1–1½ hours during the swelling time when their oxygen consumption is very low. Hard eggs with thick shells and narrow perivitelline spaces, and eggs with double shells can be transported successfully over longer periods (even one day) and distance by packing them between soft and moist layers of cotton or soft wet moss. The most unsuitable stages, from the point of view of transportation, are the morula and blastula. Eggs can also be transported in small numbers if they are placed in plastic bags under oxygen pressure.
The transportation of fish seeds usually takes place from the hatchery to a farm which has rearing facilities. Fish larvae and just feeding fry can be transported in plastic bags with oxygen under pressure, putting 5 000–8 000 larvae or fry in one bag containing 5–7 l of water and 15–20 l of oxygen under pressure. It is important to prevent water splashing in the bag, since it may prove lethal to the fry. Advanced fry and fingerlings, however, are not very much affected by splashing.
The procedure for making plastic bags is shown in Figure 68, while that for packing fish seed in bags with oxygen under pressure and their transport by different means are shown in Figures 69 and 70.
Millions of just feeding fry can also be transported at one time in 1–2 m3 containers provided with a lid and with the provision of oxygen supply (see Figure 66). Such a container is half filled with clean water of the same temperature as the water in which the fry are held. The estimated number of fry are then carefully introduced into the container. After this the container is completely filled with water and its lid closed. A sheet of foam rubber is fixed around the rim of the container to ensure that the container remains water tight. A 10–15 cm long plastic tube of 1–2 cm diameter is tightly fitted into a hole on the top of the container to enable excess compressed oxygen to escape.
About 100 000 just feeding fry can be transported in 100 l of water. This would mean that 2 million fry can be transported in a 2 m3 container. It is advisable to cover the container with a wet rug or grass mat or to use an insulated or partly insulated container in the tropics, to prevent water temperature from rising.
Three to four week-old fingerlings can be transported in plastic bags; about 500–2 000 of them can be placed in one bag. The number of fingerlings to be put inside the bag depends on the size of the fingerlings and the length of time spent in transport.
By using the previously mentioned containers for transporting fingerlings, about 10 000 fingerlings can be transported per 100 l of water (Figure 71a). The fingerlings are packed in the same way as the just feeding fry; i.e., container must be completely filled with water and provided with a continuous oxygen supply. A drain pipe can be fitted into the bottom of the container as shown in Figure 71b.
The same transportation technique is not applicable to the fingerlings of all species. It is advisable to determine through experimentation the optimum number of fingerlings in a consignment relative to transportation time and prevailing temperature and with respect to the species in question.
The transportation of brood fish is a delicate operation. They must be tranquillized before transportation, otherwise they may dash against the wall of the transporting container and injure themselves. The least expensive method of tranquillizing them is the use of cold water (5°–10°C) as a transportation medium. Unfortunately, this method cannot be used for all fishes, and it certainly is a questionable method for tropical and sub-tropical regions.
If cold water is not suitable, tranquillizers should be used. Most fishes cannot tolerate full strength tranquillizers for more than an hour. However, in a diluted solution, they can be maintained for a longer time.
The procedure for tranquillizing brood fish before transportation is the following:
The brood fish are first put in a full strength (1:20 000) solution of MS 222 (i.e., 5 g MS 222 in 100 1 water), which very soon puts them to “sleep”. After 15–20 minutes when the fish are fully tranquillized, the solution is diluted by adding water, the quantity of which depends on the hardiness of the fish. The dilution is two times (1:40 000) for hardy fish such as common carp and bighead, 2½ times (1:50 000) for mildly sensitive fish such as grass carp, and five times (1:100 000) for very sensitive fish such as silver carp (Figure 72a).
During long transportation, the water in the container must be oxygenated and care taken to see that the temperature does not rise beyond 28°C; 20°–24°C is the best temperature range for transportation in the tropics.
One or two small-sized brood fish can be transported in tranquillized condition in a plastic bag under oxygen pressure. However, in the case of fishes with sharp spines, it is necessary to first cut off the spines otherwise they may puncture the plastic bag.
Simple devices such as hammocks and bags made of half sack can be conveniently used for transporting brood fish over very short distances (Figure 72b).
Figure 68 Making plastic bags for fish seed transportation
Figure 69 Packing young fish in plastic bags with oxygen
Figure 70 Transport of young fish packed in plastic bags
Figure 71a Estimating the number of fingerlings
Figure 71b Container fitted with drain pipe. Used for transporting young fish
Figure 72a Long distance transportation of brood fish
Figure 72b Devices for catching and transporting brood fish over short distances