Restraint, anaesthesia and euthanasia

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Fish find all forms of handling stressful. They struggle during capture both in and out of their natural environment and can easily suffer significant damage to their epidermis (which is external to the scales). This chapter considers physical restraint, sedation and anaesthesia, inhalation anaesthesia, parental anaesthesia, non-chemical anaesthesia and euthanasia.

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Image of Figure 11.1
Figure 11.1 Manual restraint of large koi. Some placid fish can be held out of water for up to a minute, enabling close examination of the external surfaces. Not all koi can be handled in this way, and experience is required. (© W.H. Wildgoose.)
Image of Figure 11.2
Figure 11.2 Sock nets (long tubular nets made of strong fabric and open at both ends) can be used to carry large fish by placing them in the middle and gripping both ends of the net before removing the fish from the water. (© W.H. Wildgoose.)
Image of Figure 11.4
Figure 11.4 The most common stages of anaesthesia: (a) no anaesthetic is present and the goldfish demonstrates a normal posture; (b) light sedation, ataxia and reduced response to stimulation; (c) deep anaesthesia, with loss of muscle tone and total loss of equilibrium; (d) surgical anaesthesia, with lack of response to firm pressure on the peduncle. (© W.H. Wildgoose.)
Image of Figure 11.8
Figure 11.8 Practical anaesthesia of koi. (a) The koi is held in a large storage box containing water from the pond of origin. A stiff polythene bag is filled with a known volume of water (4 litres). Air-stones are present in the box and the bag. (b) A measured amount of anaesthetic agent is dissolved in a small amount of water and mixed with water in the bag. A level quarter-teaspoon measure (equivalent to 0.8 ml scoop) of MS222 contains approximately 650 mg and will produce a final concentration of 160 mg/l when mixed with 4 litres of water. (c) The fish is gently lifted by hand and placed in the anaesthetic solution in the bag until it reaches the desired plane of anaesthesia. This method requires a minimal amount of water and drug but care should be taken to ensure that the fish does not suffocate on the walls of the bag. (© W.H. Wildgoose.)
Image of Figure 11.9
Figure 11.9 Non-recirculating system. A header tank contains a maintenance dose of anaesthetic solution that passes into the fish’s mouth through a plastic tube. A valve mechanism ⊗ controls the rate of flow. Water passes out through the gills and drains away. Fresh anaesthetic solution is added to the header tank when required. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
Image of Figure 11.10
Figure 11.10 Working example of a non-recirculating anaesthetic system. An intravenous fluid bag contains the anaesthetic solution and an air-stone to aerate the water. A control valve regulates the water flow through a shortened giving set. Unrestricted flow will produce about 250 ml/min, enough for fish weighing up to 250 g. (© W.H. Wildgoose.)
Image of Figure 11.11
Figure 11.11 Simple recirculating anaesthesia system. Valves ⊗ control the flow rate and the choice of either anaesthetic solution or untreated water. This passes over the gills and drains from the trough into the sump tank for recirculating to the header tanks. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
Image of Figure 11.12
Figure 11.12 Working example of a recirculating anaesthetic system. The pump is a low-voltage pump for use in garden ponds. It has a valve that controls the output of water that enters the fish’s mouth. Water drains back into the reservoir. To revive the fish, the pump and drain tube are moved into the blue reservoir on the left, which contains anaesthetic-free water. Air-stones are present in both reservoirs. (© W.H. Wildgoose.)
Image of Figure 11.13
Figure 11.13 Restraining device for fish in dorsal recumbency. A block of foam is split half-way through and covered in a waterproof disposable drape. The fish should be positioned with the head free of the holder for the water to pass freely through the opercula. (© W.H. Wildgoose.)
Image of Figure 11.14
Figure 11.14 Modified Higginson rubber enema syringe for emergency resuscitation. The shortened ends contain one-way valves to ensure a unidirectional flow of water when the rubber bulb is squeezed. Gentle pressure is applied to the bulb to produce a flow of water appropriate to the size of the fish. (© W.H. Wildgoose.)
Image of Figure 11.16
Figure 11.16 Veins present on the medial aspect of the opercula in koi. These are easily accessible with fine 25 gauge needles and provide good visibility for intravenous administration of lethal injections. (© W.H. Wildgoose.)
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