3. CLOSED SYSTEMS OF FISH TRANSPORT

The closed systems are represented by polyethylene bags and other sealed transport units. They are used mainly for the transport of the early fry, but also brood fish. The transport of fry in polyethylene bags with oxygen is particularly widespread in the world, being used as a very effective method. It substantially reduces the total volume and weight of transport water, enables public transport to be used for fish-transport purposes, makes it possible to prolong the transport time, and is economically advantageous.

The methods of fish transport in sealed medium are described in detail in several general studies (Orlov et al., 1974; Kozlov et al., 1977; Pecha, Berka and Kouril, 1983; Vollmann-Schipper, 1975; Woynarowich and Horváth, 1980) and in a number of separate specific studies (Bogdan, 1972; Hamman, 1981; Lusk and Krcál, 1974; Snow, Brewer and Wright, 1978; Garádi and Tarnai, 1983; Varga, 1984; Ioshev, 1980; Amend et al., 1982; Popov, 1975; Kruzhalina, Averina and Vol'nova, 1970, 1984; Orlov, 1971, 1973, 1975; Orlov et al., 1973, 1974). Soviet authors prevail because this method of stocking fish transport from hatcheries is used particularly frequently in the USSR.

3.1 Polyethylene Bags

The bags used for fish transport in water with oxygen atmosphere are produced in a number of modifications. They are manufactured from a thin (soft) or thicker (hard) transparent polyethylene foil and usually have the shape of sack or sleeve.

The bags of the traditional shape (sacs) usually have the dimensions of 0.8–1.1 × 0.35–0.45 m. The upper end is usually fully open. The bottom either has a seam in the middle or consists of a rectangular piece of foil; the latter variant is better because it helps avoid losses of the fish squeezed in the corners. For safety reasons, the bags are sometimes duplicated: a thin (soft) bag is inserted in another thin bag, or a thin bag forms a lining in a thicker (harder) bag.

The other type of bags has the form of a sleeve. Its width usually is 0.4–0.5 m. The final length of the sleeve depends on where the sleeve is cut. One of the ends has to be completely closed, sealed: a suture is welded, or the folded end of the sleeve is fused in, after tightening with a rubber seal or a plastic adhesive tape, or binding with a rope. The welding is done with a special device, whereas for the fusing (sealing) the flame of a candle will suffice (Fig. 5). Another possibility is to bind a knot on the end of the sleeve. It is important to make the knot as tight as possible. One sleeve equalling about 2.5 times the length of the future bag suffices, after binding a simple knot, to make a duplicated bag.

During transport the bags with fry are placed in outer cases protecting the bags against mechanical damage, mainly punching or tearing in contact with the ground. The case keeps the bags in the desired position, enables easier handling and/or provides thermal insulation of the bags.

These cases can be cardboard boxes, suitable plastic containers, wide polyethylene cans, polystyrene boxes. The kind of outer casing depends on the number of bags transported, length and method of transport, requirements for further handling (transloading), and on the differences between ambient temperature and the temperature of water inside the bag.

Figure 5 Procedure of closing the bottom end of a polyethylene sleeve (Woynarowich and Horváth, 1980)

If water with transported try is to be cooled, bags with ice should be placed under the fish-transport bags on the bottom of the polystyrene box (Fig. 6). It is not recommended to put the ice inside the transport bag. The amount of ice depends on the size of the bag with water, transport time and difference of temperature. The volume of ice placed under the bag with transport water is usually 10–20% of the transport water. This method of packing enables transport by public transport routes.

The water to be used for fry transport in a bag should comply with all requirements. It is best to use water of the same quality as that in which the fish were kept before transport, but there should be no organic pollutants and no dispersed mud of mineral origin. Sac fry, in particular, need transport water with air bubbles, i.e., released air contained in water in oversaturated condition.

Before putting the fry in the bag, the procedure of catching, counting and distributing the fry in the bags should have been thoroughly prepared to finish the operation as quickly as possible.

The polyethylene sac, or sleeve with a closed bottom end, is first put in the outer transport case; if a double bag is to be used the inner bag is to have been inserted in the outer one. Then, water is poured in the bag, about 20 litres if the volume of the bag is 50 litres, and the fry are placed inside. Air is displaced from the space above water in the bag and a hose, connected to the pressure regulator of an oxygen cylinder, is introduced in the bag, the upper end of the bag being held tight around the hose by hand. Then, technical oxygen from the pressure cylinder is left to blow via the pressure regulator to the upper part of the bag. If the volume of water with fry is 20 litres, the volume of oxygen atmosphere should be 30 litres. The supply of oxygen is stopped when the bag is filled: the hose is quickly drawn out of the bag and the upper end of the bag is twisted to prevent oxygen from leaking and to produce some overpressure by reducing the volume. If the bag if to be transported in a horizontal position, the pressure should be 0.05 to 0.06 MPa but for vertical transport the pressure should be 0.02 to 0.04 MPs (Pecha, Berka and Kouril, 1983; Orlov et al., 1973). In practice, this means that after filling the bag is tight: when pressed with thumb the foil quickly returns to its original position. During air transport the pressure in a vertically kept bag reaches -0.01 MPa (Orlov et al., 1973), owing to the lower outside pressure. Finally the opening of the bag is closed. There are several ways of closing the bag; the simplest way is to tighten the end of the plastic foil with rubber, preferably duplicated. Rope or adhesive tape can also be used. The bag can also be closed with a metal screw cap. The procedure of bag filling is described in Fig. 7.

In hatcheries or fry rearing farms with regularly repeating mass dispatching of the fish, it is recommended to build a dispatching line (Fig. 8).

After transport, or during control on a longer journey, the condition of the fry should be checked before release. The fry are examined for position, i.e., swimming, lying on the bottom, staying in physiological position or turning to one side, for motility, readiness of reaction to light, touch, and/or number (proportion) of dead individuals.

Figure 6 Transport of a bag in styrofoam case (Vollmann-Schipper, 1975)
1 - lid, 2 - insulation filling, 3 - oxygen atmosphere,
4 - water with fish, 5 - insulation lining, e.g., foam rubber,
6 - ice

The fish are released only when the temperature of the water in the bag reaches the same level as that of the receiving water. For sac fry the difference in water temperature should not be greater than 1°C, for older fry 2°C in both directions. To balance the temperatures it is best to put the closed bag on the surface of the receiving water. When the temperature difference is reduced to 2–3°C at the maximum, the bags are opened step by step and the receiving water is slowly added to the transport water. Releasing can start when about 50% of the receiving water has been added to the bags. The behaviour of the fry should be constantly examined (Fig. 9).

If the bags are handled with maximum care, if they are closed in the most careful manner and transported in suitable outer cases, they can be used repeatedly. However, this is not a general recommendation because damage to the bags, however tiny it may seem, can never be avoided during fish release.

As Kruzhalina, Averina and Vol'nova (1970) assert, it is also possible to use bags - tanks, made of 4–12 layers of polyethylene foil (“sleeve” 80 cm in width), having a total volume of 300 litres. However, these types of bags are hard to handle and are used only for individual transports of large and broad fish.

3.2 Other Sealed Containers

Containers similar to polyethylene bags may be sealed. Generally made of cured plastics (Fig. 10) they can do the same job as bags and do not require as much care during handling, despite repeated use. However, their unit price is much higher.

3.3 Fry Densities in Plastic Bags

Calculation fromulae were worked out for the theoretical determination of fish densities in plastic bags (Orlov, 1971; Orlov et al., 1974, 1975); they take into account factors such as changing environment, transport time, volume of water and coefficient of free space. Nevertheless, for practical purposes, it is simpler to use the guide data published by some authors, either individually or as fish-transport tables.

Figure 7 Procedure of filling the bag with water, stocking with the fish, displacing the air, introducing oxygen and closing the upper end (Woynarowich and Horváth, 1980)

For instance, the recommended numbers of fry to be transported in polyethylene bags according to Czechoslovak Instructions for fish-farming practices (Pecha, Berka and Kouril, 1983) are shown in Tables 3–5.

About the same standard densities of transported fish are indicated in the West German recommendation for fish transport (1979) - Tables 6–8.

Figure 8 Dispatching line of the pike hatchery of the Czech Angler's Union at Tábor (Pecha, Berka and Kouril, 1983) 1- water tank with the float system of water filling, with water aeration and tempering, 2 - filling valve, 3 - calibrated vessel with a turning joint, 4 - handling banch with rollers for carrying the boxes, 5 - cardboard box, 6 - polyethylene bag, 7 - valve for filling the bag with oxygen, 8 - rubber band magazine, 9 - packing table, 10 - cylinder pressure regulator, 11 - pressure cylinder with oxygen, 12 - oxygen atmosphere in bag, 13 - water in bag, 14 - oxygen supply from pressure cylinder to filling valve 7

Hungarian experience with specialized transport of pike-perch in closed bags is interpreted by Horváth, Tamás and Tölg, (1984). The conditions of transport are documented in Table 9.

The standards of fish fry transport published in the instructions by Orlov et al., (1974) for Soviet conditions can also be considered as practically verified. The data apply to fish densities in bags, volume 40 litres, including 20 litres of water and 20 litres of oxygen, from the point of view of the possible total weight and number of fish transported; the standards are indicated for cyprinids (Tables 10 and 11), salmonids (Tables 12 and 13), for fish of the perch family (Tables 14 and 15), and for Soviet sturgeons.

Similar details concerning the transport of fish fry in polyethylene bags are given in the monograph by Kozlov et al., (1977) on the acclimatization of aquatic organisms in which fish transport forms an inseparable part of the acclimatization processes.

As to other commercially important fish not separately referred to in the above tables, it should be mentioned that Snow, Brewer and Wright (1978) transported sac fry of largemouth bass. The transport distances were up to 2 500 km. The fry were kept in polyethylene bags containing 7.57 litres of water with a supply of oxygen, and the bags were protected in insulated polystyrene containers. The transport density of the fry was 3 000 per litre. To ensure that the fry would be ready to begin feeding when they were released into rearing ponds, they were shipped at 1, 2 or 3 days of age, depending on the distance of their destination. Shipments were made by commercial airline or bus, but automobiles were also successfully used.

Literature also contains other data on the transport capacity of polyethylene bags, e.g., Ioshev (1980), Kruzhalina, Leis and Ovchinnikova (1984), Bogdan (1972), and others. But a large proportion of these data lack detailed documentation on all the aspects that can substantially affect the results of transport.

3.4 General Notes on the Transport of Juvenile Fish in Bags

In the final comments on fry transport in polyethylene bags, some findings and information should be mentioned, as given generally in the relevant literature. Emphasis should be laid on the requirements to transport the fry after the absorption of food: when the fry are freshly fed the amount to be transported should be reduced by at least 50%. The water in which sac fry are transported should be kept as still as possible (the fry could be damaged in the bags). On the other hand, advanced fry and fingerlings are not affected by increased movement of the transport water. When oxygen is replaced in the bag during shipment survival increases by 20–40%; when half the water and all oxygen are replaced survival increases by 50–60%. and when all water and all oxygen are replaced the increase in survival is by 90–100% (Orlov et al., 1973). Differences in the nature of each group of fishes also have a marked influence on the results of shipment: in the case of the sac fry of cyprinids the losses highly increase when temperature during transport is under 20°C, and the transport time should never be longer than 24 h; when salmonid fry are transported, longer stops during transport threaten to create an oxygen deficit. Adherence to the recommended standards of the transport of different fish groups would keep the losses of larvae below 5%, fry 3%, and yearlings 1%. There is one exception still waiting for satisfactory explanation: at temperature above 15°C the yearlings of big head may suffer up to 50% losses, despite a comparatively low transport density (Orlov et al., 1973).

Figure 9 Transport of young fish packed in plastic bags (Woynarowich and Horváth, 1980)

	(a) Aerator with screw cap; (b) Water;
	(c) Water inlet with screw cap;
	(d) Tight cover; (e) Tightening ring;
	(f) Plastic pipe; (g) Plastic container

Table 3

Numbers of sac fry, in thousands, to be transported in a polyethylene bag with a volume of 50 litres, i.e., 20 litres of water and 30 litres of oxygen

Note: Water of 15°C is the minimal temperature level for cyprinid fishes

Table 4

Numbers of advanced fry 2–3 cm long, in thousands, to be transported in a polyethylene bag with a volume of 50 litres, i.e., 20 litres of water and 30 litres of oxygen

Note: Every 12 h the oxygen should be replaced or the amount of fish should be reduced to 50%

Table 5

Numbers of young fish to be transported in a polyethylene bag with a volume of 50 litres, i.e., 20 litres of water and 30 litres of oxygen

Note: Transport should not be interrupted for longer than 15 minutes

Table 6

Numbers of sac fry, in thousands, to be transported in bags containing 30 litres of water and 30 litres of oxygen

^a Minimal temperature level. After 12 h of transport, the oxygen should be replaced or the amount of fry should be reduced by 25–50% according to the duration of transport

Table 7

Numbers of advanced fry 2–3 cm long, in thousands, to be transported in bags containing 30 litres of water and 20–30 litres of oxygen

Note: Every 12 h, the oxygen should be replaced or the amount of fish should be reduced to 50%

Table 8

Numbers of young fish to be transported in oxygen-filled bags, volume 50 litres, oxygen:water ratio from 3:1 to 3:2

Note: Transport should not be interrupted for longer than 30 minutes

3.5 Transport of Large Fish in Bags

Individual shipments of large brood fish can also be made in polyethylene bags. This possibility is suggested by several literary sources. The transport of brood carp and herbivorous fish from Hungary to Egypt and Iran is commented on by Varga (1984) and by Varádi and Tarnai (1983); however, it is only Orlov who published tables (Table 16) with values of the survival of large carp, herbivorous fish, pike-perch and also some sturgeons, enabling to derive some guide parameters for shipment.

3.6 General Notes on the Transport of Brood Fish in Bags

Naturally, when large fish of these species are transported for introduction or acclimatization, it is not recommended to apply the theoretical critical possibilities. The main requirement is to keep the fish healthy and physiologically intact throughout the transport, because brood fish are of a high potential value and their transport is to pay off in future. With respect to this, the safe transport densities of these fish, as recommended by Orlov et al., (1974) are 5 to 10 times lower than those of the fish of the same size transported to market.

Table 9

Transport of pike-perch fry in polyethylene bags

Note: It is not recommended to transport large fish in bags due to the possibility of bag damaging by fin rays

Table 10

The amounts in kg of cyprinid juveniles to be transported in 40-litre bags containing 20 litres of water and 20 litres of oxygen

Table 11

The numbers of cyprinid juveniles to be transported in 40-litre bags containing 20 litres of water and 20 litres of oxygen

Table 12

The amounts in kg of salmonid juveniles to be transported in 40-litre bags containing 20 litres of water and 20 litres of oxygen

Table 13

The numbers of salmonid juveniles to be transported in 40-litre bags containing 20 litres of water and 20 litres of oxygen

Table 14

The amounts in kg of juveniles of the perch family to be transported in 40-litre bags containing 20 litres of water and 20 litres of oxygen

Table 15
The numbers of juveniles of the perch family to be transported in 40-litre bags containing 20 litres of water and 20 litres of oxygen