The chemical methods of treating the transport medium, aimed at increasing the capacity volume of the transport units and preventing physiological and health damage to the fish, constitute an integral part of the complex problem of fish transport. They include the use of anaesthetics, water-hardening and oxygen-producing chemicals, bacteriostatics, buffering and antifoam chemicals.
Figure 49 A fish transport tank wagon (Vollmann-Schipper, 1975) M - technical space and attendant's booth, U - pump and air compressor, T - Transport tanks 1 and 2, S - oxygen cylinders, A -tank drain, F - water aeration (for details see Fig. 50), L - loading space, W - circulating water distribution system, S + D - oxygen or compressed-air distribution system
(a) Water inlet pipe; (b) Water; (c) Air
Figure 50 Water aeration in the tank wagon (Vollmann-Schipper, 1975)
During transport, sedation of the fish is desirable, since oxygen consumption and CO2 and NH3 production are all decreased. However, deep sedation is undesirable because the fish may fall to the bottom, pile up and smother. If pumps are used, the fish may be pulled into the screen, the air may move the deeply sedated fish about and cause a loss of scales. It is best to sedate the fish in the holding facility for 30 min before loading and then to continue exposure to a lower concentration of sedative during transport. The use of anaesthetics should not be relied on for increased load carrying capacity. Other methods are safer and dependable. The use of anaesthetics on food fish that will be consumed soon after exposure is not legal. Consideration should always be given to the legal status of a chemical and possible consequences to the consumer.
Anaesthesia usually applies only to transported brood fish. In practice, the fish are first tranquilized with the normal dose and put into the transport tank, where original concentration is diluted by 50 percent by adding the same amount of fresh water. The brood fish will remain tranquillized well in that diluted solution (Woynarowich and Horváth, 1980). It is advisable to find out the right dose for the fish in question through experimentation. Sensitivity resistance and endurance vary from fish to fish. Even the near related species may differ very much in this respect.
It is not recommended to use anaesthetics on small fish transported on small distances, since in such conditions the space factor has a greater influence on the health of the fish than the accumulation of metabolic products (Shevchenko, 1978).
As Woynarowich and Horváth (1980) assert, fish transport in cold water of 5–10°C is the simplest and best method of anaesthesia; however, this cannot always be done. This view is also supported by Strebkova (1971) who found no differences between the anaesthetized fish and the untreated control fish transported at a temperature of 11–13°C. Horváth, Tamás and Tölg (1984) recommend to anaesthetize the fish for transport only in cases of temperatures above 15°C.
Among the broad spectrum of anaesthetics, tricaine methanesulfonate (MS-222) and quinaldine appear to be used most frequently.
MS-222 is a very mild tranquilizer and fish easily recover from its effects even after a long stupor. Horváth, Tamás and Tölg (1984) recommend to apply MS-222 to water at the rate of 20 mg.1-1 for carp and grass carp, 10 mg.1-1 for silver carp, and 35 mg.1-1 for bighead carp or sheatfish. At these concentrations the fish can still hold their natural position but their respiration and motility are significantly decreased. When applying this anaesthetic, the mass of transported fish in a unit volume can be increased by 50–150 percent, but it is best to test it before application. About the same concentrations of MS-222 are also recommended by Woynarowich and Horváth (1980): the brood fish are first put in a full-strength solution, i.e., 5 g MS-222 in 100 litres of water. After 15–20 min when the fish are fully tranquilized, the solution is diluted by adding water to the concentrations commented on by Horváth, Tamás and Tölg (1984). The applicability of concentrations up to 50 mg.1-1 to carp was verified by Rzanicanin and Balcer (1973, 1974) who found that MS-222 was desorbed within a short time: at the concentration of 50 mg.1-1, MS-222 concentration in fish muscle was as low as 2 mg.kg-1 after 15 h and no traces of the chemical were detected in muscle after 39 h. The MS-222 preparation was also used by Powell (1970) who applied it at the concentration of 7 mg, 1-1 to transported striped bass, and the results were good. Dupree and Huner (1984) recommend to use MS-222 at concentrations from 20 to 200 mg.1-1 (whithout indicating the fish species), and claim that the preparation must be buffered between pH 7 and 8. The majority of authors believe that MS-222 has excellent anaesthetic properties, but - on the other hand - proves to be relatively expensive for everyday use.
Quinaldine (2–4 methylchinolin) is a toxic liquid and must, therefore, be handled with care. The fish are usually treated with it when they are held in a large volume of water, such as a large tank. Woynarowich and Horváth (1980) assert the effective concentration of 25 mg.1-1, Dupree and Huner (1984) 15–30 mg.1-1, nothing that quinaldine appears to be the most practical for warm-water fishes, although it may be damaging to trout and some other species.
Apart from these two tranquilizers, other drugs are to be used. Phenoxyethanol is another chemical that has recently come into use as a fish tranquilizer. It is milder and less effective than MS-222, but it is far cheaper; 30–40 cm3 of phenoxy-ethanol are mixed with 100 litres of water for the treatment (Woynarowich and Horváth, 1980). As to other chemicals, Dupree and Huner (1984) describe the use of tertiary amyl-alcohol at 1.2 to 10.5 ml.1-1, methyl pentynol at 0.4 to 2.6 ml.1-1, and sodium bicarbonate at 0.5 g.1-1.
Fereira, Schoonbee and Smit (1984) recommend to transport Oreochromis mossambicus treated with benzocaine-hydrochloride at a concentration of 25 mg.1-1. A slow-reacting, long-lasting tranquilizing effect on trout is produced also by means of sodium amytal, one of the many hypnotic barbiturates available. The effectiveness of the drug is, to some extent, regulated by temperature. According to Leitritz and Lewis (1976), it appears to decrease when temperature rises above 12°C, the most effective range being from 8 to 12°C at a concentration of 7 mg.1-1. Successful use of sodium amytal in combination with barbital preparations is also commented on by Strebkova (1971). Carbonic acid may also be used for tanquilizing fish. Dupree and Huner (1984) recommend the concentration of 0.1–0.4 mg.1-1, Mishra, Kumar and Mishra (1983) transported fry (0.8 g) of Labeo rohita under the concentration of 0.5 ml.1-1 of carbonic acid. The product called Combelen (Bayer) was found to be effective in the transport of trout; this chemical is a neuroleptic which does not induce direct narcosis, but markedly reduces the effects of stress on the fish during transport (Studnicka et al., 1982); for trout at a weight of 250–300 g kept in 5°C water, a Combelen concentration of 0.2 ml.-1 was found to be effective.
Handling stress and delayed mortality of fish can be decreased by the addition of sodium cloride (NaCl) and calcium chloride (CaCl2) to the transport water. The sodium ion tends to “harden” the fish and reduce slime formation, and the calcium ion suppresses osmoregulatory and metabolic disfunction. Calcium chloride may not be needed in hard water already containing high concentrations of calcium. Dupree and Huner (1984) recommended the addition of 0.1 to 0.3 percent salt and 50 mg.1-1 calcium chloride. Some of the fishes that tolerate wide ranges of salt in the water, such as striped bass, tilapias, carp, can benefit from as much as 0.5 percent salt. Addition of 0.2 percent salt is recommended also by Johnson (1979). Different salt concentrations in dependance on water temperature should be used according to Hatting (1975): for water temperatures of 25–26°C he recommends the concentration of 0.7%, for medium temperatures 0.5% and for low temperatures 0.3%. Powell (1970) even used a salt concentration of 1% with a good result when transporting the fry of striped bass Roccus saxatilis. On the other hand, Carmichael (1984), though admitting that salt affords some measure of protection of the fish during transport, asserts that its function should not be over-estimated. Amend et al., (1982) and Pecha, Berka and Kouril (1983) clearly state that no favourable influence of salt addition was demonstrated during fish transport.
There are contradictory views concerning the use of chemicals as oxygen sources during fish transport. Huilgol and Patil (1975) tested the use of hydrogen peroxide on transported carp fry and found that one drop (1 ml = 20 drops) of hydrogen peroxide (6 percent concentration), applied to 1 litre of water, increased the oxygen content by 1.5 mg.1-1 when the temperature was 24°C. CO2 content and water pH were not influenced by the addition of hydrogen peroxide. Dissolved oxygen was measured by the Winkler method. Astapovich (1974) and Hartman (1976) tested peroxodisulphates for the same purposes; they also obtained a positive result of the enrichment of water with oxygen when measuring its content by the Winkler method. A revision of these results was performed in a detailed study by Máchová (1984) who demonstrated that peroxodisulphates K2S2O8, Na2S2O8, (NH4)2S2O8, in fact, release no oxygen into water and their use in fish transport is entirely useless. The Winkler's method of measurement in the presence of oxidants gives unreliable results; measurements should rather be performed with an oximeter.
Antibacterials are also used to check the development of bacteria in transport units. Among the wide spectrum of bacteriostatic drugs, the following are used most frequently: nitrofurazone (furacin) at 10 mg.1-1, acriflavin at 1 to 2 mg.1-1, oxytetracycline (terramycin) at 20 mg.1-1 Combiotic at 15 mg.1-1 (Dupree and Huner, 1984) and neomycin sulphate at 20 mg.1-1 (Amend et al., 1982). Antibacterials may strengthen the resistance of fish, but they are probably of little value as bacterial checks in transport tanks. Rare exception would be in the case where a superficial infection of an antibacterial-susceptible bacterium was in progress.
Among other chemical additives, buffers such as “tris-buffer” (tris-hydroxylmethyl-amino methane) are helpful in controlling pH at a favourable value of 7 to 8. The accumulation of carbon dioxide in bag transport allows for a decrease in pH, because carbon dioxide is an acid. Since 2.2 to 4.4 g.1-1 (Johnson, 1979; Amend et al., 1982) or 1.1 to 2.2 g.1-1 (Dupree and Hunter, 1984) of tris-buffer are required to control pH in bags with only moderate loads, the use of tris-buffer in tank transport usually is impractical because of cost.
To control ammonia concentration in the transport bags when the transport is expected to be long, it is recommended to use clinoptilolite, a zeolite mineral. Amend et al., (1982) tested with success the dose of 14 g of clinoptilolite per litre, Bower and Turner (1982) tested the doses of 10–40 g.1-1; the concentration of non-ionized ammonia nitrogen never exceeded 0.017 mg.1-1 in bags containing even the lowest dose of clinoptilolite, whereas concentrations as high as 0.074 mg.1-1 were recorded in the control bags left without clinoptilolite.
The formation of foam and scum, especially when drugs are used in transporting fish or on water which is heavily laden with organic material (secretions and excretions, such as mucus and excrements) often becomes quite bothersome. The foam interferes with oxygen exposure at the water surface and also makes it difficult to observe the fish being carried. Water with NaCl foams less than water without NaCl, but NaCl may interfere slightly with the effectiveness of anti-foam chemicals. In some cases, a 10% solution of Dow Corning Antifoam AF Emulsion is used at the rate of 0.05 ml.1-1 of water (Leitritz and Lewis, 1976; Dupree and Huner, 1984). The advantages of using anti-foam chemicals are not so great, but their use does keep the water more clear so that the fish can be observed better.
