Ethyleneglycol mono phenyl ether
It is a colourless oily liquid with a very low solubility in water (2.7wt%), soluble in ethanol, neutral pH 7 (20g/lt. water 20°C) and specific gravity 1.109g/cm3 (20°C). It has a slight aromatic odour.
Phenoxyethanol has an advantage over other anaesthetics, such as MS-222 or benzocaine, in that it does not accumulate in the fish after anaesthesia has been induced; so it can be used for long periods. It is safe and efficacious in most species; certainly the best choice for sea bass and bream, but in few species, e.g. cod, induction of anaesthesia is too slow.
Phenoxyethanol may be used repeatedly on fish of various ages/sizes from young fry to on-growing caged fish. Common handling processes necessitating the use of anaesthetics comprise grading, transportation and vaccination. Most often sedation (stage 1-2 anaesthesia) is sufficient to reduce stress while handling and may last for several hours. Surgical anaesthesia (stage 5) is required for injection vaccination. Fish recovery should be rapid after placing in clean well aerated water. (For example, post injection vaccination requiring stage 5 surgical anaesthesia, sea bass recovers within 3-8 minutes at most.)
Phenoxyethanol should be vigorously mixed with water and added gradually to the fish tank or tarpaulin. Safe dissolved Ο2 levels should be observed to remain between 5.5-8ppm.
For any given concentration the induction time varies according to fish species, size and water temperature which affect the rate of water flow over the gills, which in turn depends on the oxygen requirements.
When a fish is placed in an anaesthetic solution there is an initial phase of excitement followed by erratic swimming and sluggish movements (sedation). Then the fish becomes inactive (surgical anaesthesia).
Shelf injuries are likely during the initial excitement phase, which has to be minimised. The anaesthetic should be already mixed with water and the mix administered gradually in small amounts until the establishment of the desired depth of anaesthesia.
The dose depends in practice on fish species, fish density, but mainly water temperature. Less anaesthetic is required to produce the same result under higher water temperatures.
Indicative phenoxyethanol doses for sea bream and sea bass. Water temperature at 18°-20°C:
Precautions (for the operators):
Moderately toxic if accidentally swallowed. Irritant for skin and especially eyes. Irritates mucus membranes, especially the upper respiratory tract. Avoid direct contact of phenoxyethanol or its water mixtures with skin. Wear gloves and use suitable equipment when handling it. In case of skin or eye contact rinse with plenty clean water for several minutes. Keep away from children.
Packing and storage: Available usually in plastic sealed tubs containing 20-30kg (18-27lt.). Should be stored in a dark, dry, cool environment.
© Dr Panos Varvarigos
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Every effort has been made to ensure that the information above is accurate until the date of last editing. It is based upon the accumulated experience of applied veterinary work. The information may be used as a guide and is not meant to replace professional veterinary guidance for fish treatment. The author cannot take responsibility for incorrect interpretation or any resulting consequences.
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