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Chapter 6

During recent years the demand for live fish has greatly increased in many markets. Specialization and intensification of freshwater fisheries necessitated the safe transport of live fish. Fish hatcheries have been established which should supply good seed material to national and foreign fish farms. Several countries expect fish to be delivered alive to markets or processing plants, even of species such as trout which are difficult to keep alive during transport. Nowadays, developing countries make efforts to have their own seed producing capability. To run these hatcheries, broodstock of the necessary species and with suitable genetic performance is required. With the exception of locally indigenous fish species, breeders must be imported, sometimes from distant countries. Shipment of valuable broodstock needs special expertise and caution.



The species of fish and its biological characteristics should be considered first. During shipment of different fish species, different appropriate conditions should be ensured. The stress-sensitivity of certain species (e.g., silver carp, pike-perch, trout, etc.) should also be considered. The differing dissolved oxygen demand of the various species determines the fish density possible during shipment.

Health conditions

Only healthy fish can be transported. Parasite-infested fish must be freed of infestation with a bath, and in the case of fungal or bacterial disease transport must be delayed until therapeutic treatment is finished. Otherwise there is not only danger of spreading disease, but also a strong risk of fish death during transport. Fish with damaged or necrotic gills cannot survive conditions of limited oxygen availability during transport. If fish are in poor health, high mortality can be expected even at low population density, especially during long-distance transport; high temperature can increase this loss further.


The size and age of fish to be transported greatly influence the method and technology of transport, especially as regards oxygen supply; for example, 25 kg of rainbow trout of 250 g individual weight have the same oxygen requirement as 20 kg of 18 g individuals, 17 kg of 5.3 g individuals, or 12 kg of 0.5 g individuals (Berka, 1986).

1 Based on material provided by Mr I. Varga, Warmwater Fish Hatchery (TEHAG), Százhálombatta, Hungary

For fry, it is usual to base calculations on the number of specimens per m3, while from fingerling size upwards the total weight per m3 is used. In closed-container or plastic bag transport, the size of fish to be shipped should be taken into account when choosing the type of bag; e.g., during the transport of advanced fry, 2 plastic bags (0.04 mm thick) are sufficient, while during transport of breeders 3 plastic bags (each 0.1–0.15 mm thick) should be used.

Stress and biochemical processes

Stress is closely associated with fishing and transport. It can cause serious losses in sensitive species either during transport or later.

During packing, handling of fish can cause them to become hyperactive, and their oxygen consumption and metabolic excretion increase. The first hour of confinement is especially critical, when oxygen consumption can be increased 3–5 times. Later, fish acclimatize and oxygen consumption decreases. The next critical point of transport is stocking. If fish exposed to stress during transport are stocked in water of different or poor quality (less dissolved oxygen, or more CO2), this extra stress may exceed the limits of tolerance. Further problems can be caused by osmotic shock, especially if fry were nursed in calcium-buffered water and stocked in acid water.

Water quality

Oxygen. Maintenance of dissolved oxygen at a proper level is one of the most important factors during fish transport. The capacity of fish to take up and utilize oxygen depends on their stress-tolerance, water temperature, pH, carbon dioxide concentration, and amount of metabolic products (e.g., ammonia) present in the water.

Total weight of fish and water temperature are decisive factors in oxygen metabolism; whenever water temperature rises by 10°C, oxygen consumption doubles. It is recommended that the total weight of fish be decreased by 5.6% for each 0.5°C temperature increase. The opposite is valid when temperature decreases (Piper, 1982).

Oxygen consumption increases during fish transport due to stress. A fish at rest needs a minimum oxygen level, but during transport fish are not in this state, and thus require oxygen levels higher than in fish ponds. This higher oxygen requirement can last for several hours and returns to normal only after transport is over.

The oxygen consumption of fish depends on the amount of oxygen available. At lower oxygen levels the fish will take up smaller quantities of oxygen to maintain the same muscle activity. The deficit is made up by release of oxygen from stores in the body. This results in an oxygen debt in the body, which is later replaced when conditions return to normal.

At least 5 mg/l of dissolved oxygen are necessary in the water during the transport of most freshwater fish species. This level is high enough to overcome the stress factor.

Higher oxygen levels do not cause any unfavourable effect in fish which are able to control their O2 uptake. For example for rainbow trout, the upper limit of tolerance is 35 mg/l, which is an ideal level with the transport techniques applied at present.

If the oxygen need of common carp is taken as 1, oxygen demand of other fish species can be defined as follows:

rainbow trout2.83pike1.10
pike-perch1.76European catfish0.90
black bass1.46eel0.83

Water temperature. Water temperature is also important, because the intensity of fish metabolism changes in proportion to it. The amount of dissolved oxygen water will hold also decreases with increasing temperature. Optimum temperature values for transport of different types of fish are:

Cold-water fish1–23–56–8
Warm-water fish2–46–812–15

During long transportation in summer, cooling of water is economically worthwhile.

However, the above temperature guidelines cannot be applied to fish larvae. Cyprinid larvae cannot be cooled below 16°–18°C; salmonids cannot be transported above 15°–18°C; 10°C is the optimum transport temperature for coregonids.

pH, carbon dioxide and ammonia. Water to be used in transport should be chemically analysed. The pH value is a good indicator, since the proportion of toxic ammonia and CO2 is closely related to pH.

Prolonged transport will move the water pH into the acid range through increased CO2 content resulting from respiration of fish. A pH between 7 and 8 is optimal for fish, with extreme values of 6.5 and 9. Rapid change in pH stresses fish. Though acidification decreases the ratio of free ammonia, it also decreases the oxygen transfer capacity of water. As a result, when CO2 level is high, fish kills can be caused by lack of oxygen, even if the dissolved oxygen content of water is apparently sufficient. Generally, fish produce 0.9 ml of CO2 from 1 ml of oxygen taken up. With inadequate aeration, therefore, CO2 level can be as high as 20–30 ppm in a closed tank. This can be prevented with aeration, i.e., by an opening at the top of the tank. Foam can also be an obstacle to aeration, leading to CO2 accumulation. Anti-foaming agents can be used to avoid this. If the increase of CO2 level is gradual and slow, fish can tolerate and compensate for it for a while.

Metabolites can also accumulate in the water during transport. Due to protein metabolism of fish and to the activity of protein decomposing bacteria, ammonia level may increase in the water. The highest permissible level of free ammonia is 0.1 ppm; a concentration of 13 ppm is deleterious for trout after 6 hours, and resistance of fish is also impaired. Metabolism can be slowed down by cooling the water. Accumulation of metabolites can be reduced by starving fish for a couple of days before transport.

Chlorine may be present if tap water is used during transport. However, like CO2, this substance can be eliminated with aeration. The highest permissible limit of chlorine is 0.02 mg/l, since even very low levels of chlorine can significantly damage the respiratory system of fish.



To keep stress to a minimum, cautious handling is very important. These guidelines should be followed during harvest:

  1. A net of mesh size suitable for the size of fish should be used.

  2. Seining should be done carefully, especially where there is a large mass of fish in the net.

  3. Oxygen deficiency in the net should be prevented by aeration, so as not to force the fish to mobilize their reserves.

  4. The “from water to water” principle is very important, especially when fry are transported. This means that fish should be kept in water during each stage of transport.

  5. Temperature differences should be kept to a minimum, and physical damage associated with handling (throwing, dropping) avoided.

Sorting, weighing and hygienic treatments

Where fish are reared in polyculture, several species will be caught in the net during harvest preceeding transport. Even in monoculture, fish of different size groups into the net might go together. It is recommended that fish be sorted both by species and size before transport for sale or restocking. Sorting can be done at the pond, or in a sorting/grading place specially constructed for this purpose. The latter is less hazardous for fish and conditions of transport can be better prepared. In both cases, however, fish should be stored in a net (hapa) suitable for their size. For fry, a net made of gauze-like fabric (10–20 m3) is recommended. Nets used for other age groups range from 40 to 50 m3. When fish are to be transported to different places simultaneously, sorted/weighed fish should be kept separately for each destination. To reduce pollution of water by metabolites, fish must be starved for at least one day prior to transport. For Chinese carps two days is better.

After weighing, but before transport, even apparently healthy fish should be treated with a short antiparasitic bath. This not only prevents spreading of parasites to other fish farms, but the extra mucus secretion triggered by the salt solution is also advantageous in increasing tolerance to the handling associated with transport. Chemicals used for baths can be a 3–5% salt solution, commercial insecticides (Flibol E, Dipterex, etc.) at low concentration, or a 5 ppm malachite green solution.


Egg transport

Due to technological and economic factors, transport of eggs is more common with trout, salmon, pike, pike-perch, and sterlet.

Eggs can be transported in one of four developmental stages:

  1. Immature eggs, still in the ovaries of female spawners (see below).

  2. Mature, stripped but unfertilized eggs. Sperm (milt) should then be transported separately in closed aerated plastic bags (10 parts air to one part sperm). Eggs at this stage have no oxygen demand. Both eggs and sperm should be kept cool. With this method, eggs and sperm of Pacific salmon for example retain their fertility for four hours when kept at 8°–11°C.

  3. Fertilized and water hardened eggs. Freshly stripped and fertilized eggs should be transported “shakeproof”. Therefore, no air space should be left in the container.

    Pike-perch spawned in the natural way can lay and fertilize eggs on man-made nests. These egg-loaded nests can be transported for several hours in wet clothes, or for several days on wooden racks, where they are kept cool and wet with moss and ice.

  4. Eyed eggs. Eggs should not be shipped during their first stages of development. They may be shipped over long distances, however, after the eyed stage is reached, provided they are kept cool and shipped in properly insulated boxes.

Shipment of eyed eggs is done in specially prepared boxes which maintain a moist and cool environment without wetting the eggs. These boxes contain several layers of egg trays. Wet cloths can be placed on the trays, and eggs carefully layered onto them before being covered with another wet cloth. The top tray is filled with coarsely crushed ice, ensuring continuous cooling. Melting ice maintains a high humidity. Ice should not be used straight out of the fridge, but instead should be allowed to start melting first.

Shipment in plastic bags under pure oxygen

Shipment in plastic bags is the most widespread, cheap and practical solution used all over the world. It can be used for stocking larvae within the farm as well as for short or long-distance transport. It needs no special vehicle or container, and bags can be transported in cars or by air cargo. All kinds of freshwater fish species can be transported in this way. Some differences in technique are found in different places: the method used in Hungary is described below.

Bags 0.8–1 m long, with 30 cm diameter and an inflated volume of about 60 1 have proved to be the best. For security, several layers of bags are used, depending on the size of fish to be carried. For very small fish, bags with rounded bottoms are preferred to prevent fish from becoming stuck in corners and killed.

Bags can be prepared locally from plastic-sleeve rolls. A double-walled plastic bag is made by cutting double the length required, making a knot in the middle, then pulling one half over the other. The thickness of plastic used should be selected according to the size of fish to be shipped: for larvae 0.04–0.05 mm, fingerlings 0.06–0.08 mm, and larger fish 0.1–0.15 mm.

During shipment, plastic bags are placed in boxes, which protect the bags from mechanical damage and make handling easier. Polyethylene, polystyrene or cardboard boxes can be used. Regardless of the size of the plastic bags used for shipment, the contents are made up of 30% water and fish, and 70% oxygen.

Both safety of shipment and the number of fish per bag can be increased by cooling the water and maintaining a low temperature during transport by using ice. If a polyethylene or styrofoam box is used, ice can be put in the bottom of the box. With a cardboard box, ice should be put directly into the water. The amount of ice necessary depends on the size of the bag, duration of shipment, and upon the temperature difference between the water and the air. If ice is put into the box, it should be approximately 10–20% of the volume of water in the bags; but when ice is put directly into the water 5–10% is sufficient.

It is important to note that larvae must not be cooled with ice for transport. If the temperature of water in which the larvae are to be stocked is similar to that of the hatchery, nothing should be done to change that.

Packing fish in plastic bags. Before the first shipment, or in special conditions (new guide numbers, different size of bags or boxes, water of different quality, etc.) test packing should be done. In shipping live fish, the work should be organized such that fish are packed with the least possible handling and in the shortest possible time. All equipment and tools should be at hand and fish should be put into the storing nets immediately after harvest so that weighing and bagging proceed without delay.

First, water of the best possible quality is poured into the bags. Then fish are gently added. Larvae or fry are measured by volume, while larger fish quantity is determined either by average weight or by counting according to their individual size. If water must be cooled, ice is put in last. After that, air is pressed out of the bags. The opening of the bag is pressed around the outlet tube of an oxygen cylinder with the hand. The cylinder is opened and oxygen allowed to flow until the bag is filled. Then the oxygen tube is quickly withdrawn, and the upper end of the bag twisted several times to close it and ensure overpressure in the bag. Final closing can be made in several ways - with rubber rings, string, adhesive tape, by making a knot in the upper end of the bag, or by soldering it with heat.

Guide numbers for shipment in bags. Transport of fish in bags is economical only up to fingerling size. Therefore, in Tables 6.1 to 6.4 guide numbers for the shipment of larvae, nursed fry and fingerlings only are given. Shipment of valuable broodstock is also economically feasible by this method, usually by air. In this case only one fish is placed in each bag. Even so, a mortality of 10% can be expected with silver carp and 3–5% with bighead carp breeders within one month of stocking.

Table 6.1

(20 1 water and 30 1 pure oxygen)

Fish speciesWater temperature
Duration of transport (in hours)
Brown trout2015105            
Rainbow trout252015102015105151053    
Common carp    20015010050120806040100806030
Tench    1008060306040301560403015
Grass carp        6050403040302515
European catfish        6050403040302515
Asp    10080604080604020    
Barbel    10080604080604020    

Table 6.2

(20 1 water and 30 1 pure oxygen)

Fish speciesWater temperature
Duration of transport (in hours)1
812   24   48812   2448812   2448   8122448
Pike53.53   232.521        
Pike-perch43   2.5132   2121.510.5    
Common carp    1512   1081210   86   10864
Grass carp        108   65   8643
Eur. catfish        86   53   5432
Asp    108   6486   53       
Chub    108   6486   53       

1 Either oxygen should be changed every 12th hour, or half of the fish transferred into other bags

Table 6.3

(20 1 water and 30 1 pure oxygen)

Fish speciesSize of fish
Water temp.
Max. weight of fish per bag
Estim. losses
Maximum time of transport
Brown trout4–610800–1 200-12
Rainbow trout9–12102 000–2 500-12
12–15102 000–2 500-12
Pike4–610800–1 200<324
6–912800–1 200<312
Pike-perch 4–6121 000<112
6–9101 300–1 600<112
9–12102 000–3 000<18
Common carp4–6152 000–3 000<28

Table 6.4

Százhalombatta, Hungary

Number of fish per bag/box for a transport of 12 hours (from packing to stocking) in water at 15°–17°C. Each unit prepared for shipment contains 2–5 kg of fish (18–22 1 water and 32–26 1 pure oxygen)

Fish speciesFish total length (cm)
Pike2 5001 000300250    
Pike perch2 000500250200    
Common carp5 0001 000500300250803010
Silver carp and Bighead carp2508003002008030155
Grass carp3 0001 000500300200803015
Eur. catfish5 0001 5001 0005003001004020
Tench6 0001 5001 0006003001003010
Asp3 000600300150    
Goldfish6 0001 500600500300   
Koi carp5 0001 0005003002501004010
Sterlet2 0001 000500300    

Fish transport in open systems

Transport of fish in open systems has been used for a long time. Many techniques are used, from the conventional Indian “hundi” (earthen vessel) to the complex diesel truck-trailer unit transporting 10–15 t of fish in one load.

General technical considerations. The weight of fish which can be transported safely is determined by the aeration system, temperature and quality of water, duration of shipment, species, size and general state of the fish.

In the past, most of the tanks were of styrofoam, fibreglass or polyurethane. These materials have many advantages: they are light, with good insulating capacity, and durable. Tanks are commercially available in 1 000– 2 700 1 capacity. Most of them are rectangular. In the USA, tanks of elliptical shape are sometimes used, similar to those used in the dairy industry. Their advantage is that mixing and recycling of water, as well as weight distribution, are better.

In special trucks used for transporting fish over longer distances, a recycling system is incorporated. The suction head on the bottom of the tank is covered with a screen. Water sucked from the bottom is pumped back up through sprinkler nozzles.

In most of these systems an oxygen supply is connected, generally at the suction end. Water recycling pumps and compressors can best be independently operated to avoid raising the temperature of water in the transport tank, which can otherwise increase by 2°–4 °C.

Transport facilities. A survey of the technical equipment used for open transport of fish should begin with the classic transport vessel, or “hundi” used in India. This is an earthen vessel made in various sizes. Water should be continuously mixed if high numbers of fry are transported in a hundi, and this must normally be done manually during transport on a train or other vehicle (Table 6.5).

An improved version of the Indian hundi is the special tank for fish transport devised by Gilev and Krivodanova (1984). This is a 39 1 tank with a 2 1 oxygen flask connected via a diffuser. Similar containers of 50–150 1 capacity are used in many countries to transport small quantities of fish.

Transport of fish within the farm can be done more simply and economically. For the transport of breeders over a few hundred metres from the pond to the hatchery, a handcart can be used. Canvas slings on metal or wooden frames are filled first with water. Fish are then added. Open canvas, metal or plastic tanks can be used for 10–30 min transport of fish within the farm.

Transport of fish in closed tanks

Transport longer than half an hour should be done in a closed tank, which is completely filled with water to avoid splashing, and consequent injury to fish. Pure oxygen should be supplied via diffusers. A wide variety of tanks is available for this purpose, together with all the facilities necessary such as compressors, pumps and insulated tanks. Removal of fish from the tank is greatly facilitated by an outlet hopper and tube of appropriate size. Tubes of 30–40 cm diameter are suitable for fingerlings, and 20–30 cm is right for fry.

Special trucks can be used for long-distance shipment. Fish tanks are fixed to the truck chassis.

Quantity of fish carried in closed tanks. Safe loads for various species of fish, fish sizes, and duration of transport are shown in Tables 6.6 to 6.8.

It is a principle in shipment of breeders that no mature spawners may be transported. For fish of large body weight, 10–12 individuals can be placed in one closed tank.

Application of various chemical compounds during shipment

Treatment of carrying water with various chemicals is sometimes done to increase carrying capacity, as well as to prevent health deterioration and stress effects. Chemicals include: anaesthetics, water hardening and antifoaming agents, buffers, agents for ammonia level control, and bacteriostatics.

It is important to note that if conditions are already adequate, in line with those described above, no chemicals should be applied since they might impair the conditions of shipment.

Test packing and shipment should always be made.

Anaesthetics. It is desirable that fish remain quiet during shipment, since the chance of injury is less and CO2 and NH3 production reduced. This state can be created artificially by the application of anaesthetics.

First, it should be noted that the cheapest and simplest tranquillizer is cool (2°– 8°C) water. It has been experimentally proved that there is no difference between cooled and anaesthetized fish during shipment. Thus, the use of anaesthetics is recommended only above a water temperature of 15°C.

No anaesthetics can be used during the shipment of market fish, nor are they recommended when young fish are transported or the distance is short. Anaesthetics are recommended if breeders are transported over long distances.

Two anaesthetics, tricaine methanesulphonate (MS 222) and quinaldine, are the most used during fish transport; MS 222 is a light anaesthetic. Fish generally recover even after long exposure to it. For fish cultured in Hungary, the following dilutions are applied: common carp and grass carp 1:50 000; silver carp 1:100 000; bighead carp and European catfish 1:30 000. At these concentrations fish can maintain their balance, but their movement and respiration are significantly decreased. The amount of fish transported per unit volume can be increased by 50% if an anaesthetic is used.

When broodstock are to be transported in plastic bags, it is recommended to anaesthetize them usually in 1:10 000 MS 222 (10 g/100 1 of water); a concentration of 1:20 000 is preferred for silver carp.

When stocking the fish on arrival, it is very important that the receiving water be rich in oxygen. The main disadvantage of MS 222 is that it is too expensive for everyday use.

Table 6.5

(Alikunhi, 1957)

Length of fry
Max. duration of transport
No. per hundiExpected mortality
12–19241 5002–5
 961 2002–5
19–25201 0002–5
 30    8002–5
25–5124500–800  10
51–77  8    200  10

Table 6.6

AT 4°–15°C

Fish typeDuration of shipment
2–6 hours6–12 hours
(a) Fingerlings (20–30 g) 
Common carp12080
Grass carp13090
Silver carp5030
Bighead carp13090
European catfish140100
(b) Fish averaging 200 g each 
Common carp300200
Grass carp325225
Silver carp12575
Bighead carp325225
European catfish350250

Table 6.7

AT 16°–20°C

Fish typeDuration of shipment
2–6 hours6–12 hours
(a) Advanced fry 
Common carp150 000100 000
Grass carp
     Silver carp
     Bighead carp
120 00080 000
European catfish100 00060 000
(b) Fingerlings of 20–30 g 
Common carp7050
Grass carp8060
Silver carp3025
Bighead carp8065
European catfish8065
(c) Fish averaging 200 g each 
Common carp175140
Grass carp200160
Silver carp7560
Bighead carp200160
European catfish200160

Table 6.8

(Horváth, Tamás and Tölg, 1982)

Fish speciesWeight of fish (kg) to be transported in 1 000 litre water at water temperature of (°C):
Carp and Tench700600450400350280220180
Grass carp750650500450400310250200
Silver carp30025020015010080not suggested
Bighead carp700650500450400300220180
European catfish800700600500400320250200
Pike-perch25020015012010080not suggested

The other anaesthetic, quinaldine, is a toxic solution and must be applied with care. It is worth using only for mass transport in big tanks. Effective concentration ranges between 10 and 30 mg/l according to species. It should not be used with sensitive fish such as trout, pike-perch and silver carp.

Water hardening chemicals. Salt (sodium chloride) or calcium chloride dissolved in transporting water can greatly decrease stress effects and losses after stocking. Naturally, no calcium chloride should be used in hard water which already has high Ca concentration. Dupree and Huner (1984) suggested salt and calcium chloride in concentrations of 0.1–0.3% and 50 mg/l respectively. For species which tolerate higher salinity (striped bass, tilapia, common carp), salt can be used at 0.5–0.7% concentration. Salt concentration should be adjusted according to water temperature: 0.7% at 25°–26°C, 0.5% at 17°–22°C, and 0.3% at lower temperatures.

Anti-foaming agents. Foam production is an inconvenient phenomenon experienced during the shipment of certain fish species such as silver carp. The thick foam develops from mucous and organic matter affected by aeration. It can be very harmful, since the foam covers the water surface, reducing gas exchanges and resulting in accumulation of CO2, acidification of water, and also hindering observation of fish in the bags or tanks. The compound Antifoam AF Emulsion (Dow Corning) can be used to eliminate foaming at a concentration of 0.05 ml/l.

Buffers. Rapid pH change imposes stress on fish during shipment. The pH of water can be stabilized during transport using buffers. The organic compound tris-hydroxyethyl-aminomethane is fairly effective. It is easy to dissolve, has no side effects, and maintains pH in the range 7–8. Recommended concentration is 1–2.5 g/l. During transport in tanks, however, it is not economical due to its high price.

Ammonia control. For transport in bags, the zeolite mineral clinoptiolite at a concentration of 14 g/l of water is suggested to keep ammonia level low during shipment.

Bacteriostatic chemicals. Bactericides can be used to prevent accumulation of bacteria in water during fish transport. The most common are nitrofurazone or furacine (10 mg/l), acriflavin (1–2 mg/l), oxytetracycline (20 mg/l), combiotic (15 mg/l) and neomycin sulphate (20 mg/l).


Alikunhi, K.M. 1957 Fish culture in India. New Delhi. Indian Council of Agricultural Research. Farm Bull. (20): 143 p.

Berka, R. 1986 The transport of live fish. A review. EIFAC Tech.Pap., (48):52 p.

Dupree, M.K. and J.V. Huner (eds). 1984 The third report to the fish farmers. Fort Collins, US Fish and Wildlife Service, pp. 165–76

Gilev, G. and G. Krivodanova. 1984 Container for the transport of fish larvae and fry. Rybov. Rybolov., (11):8

Horváth, L., G. Tamás and I. Tölg. 1982 Special methods in pond fish husbandry. Seattle, Halver Corp., 152 p.

Piper, R.G. 1982 et al. 1982 Fish hatchery management. Washington D.C., US Fish and Wildlife Service, pp. 348–71

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