Anaesthesia

Induction

Fish are most commonly caught and then immersed directly into a container with suitable concentration of anaesthetic. Induction should be rapid, and handling time minimal. For fish that are too large, direct application to the gills by way of syringing concentrated anaesthetic solution through the fish's mouth.

Anaesthesia Maintenance

For short procedures, gills can be irrigated manually by way of drawing solutions with syringe intermittently. For prolonged procedures (>30 minutes), continuous gill irrigation is recommended. A contraption can be made to allow water to flow by gravity to the fish, or a circuit (flow-through or recirculating) powered by a water pump.

It is important to maintain aeration of the anaesthetic solution, or oxygenation. Additionally, all exposed parts of the fish should be kept moistened throughout the procedure.

If the depth of anaesthesia is excessive, increase the flow of irrigation with clean water to trigger the buccal-heart reflex (water passing faster through the buccal cavity will increase heart rate). Doxapram may be used to counteract respiratory depression at 1–5 mg/kg IP or IV. Adrenaline may be used at 0.2–0.5 ml/kg IM [1:1000].

Recovery

To regain consciousness, drug-free water is passed over the gills until spontaneous ventilation returns. Fish may then be returned to clean water to recover unassisted (but continue to monitor) until they are free swimming.

Recovery facilities should be provided with adequate filtration and heating if necessary. The water parameters should be similar to the pond or aquarium water that the patient is normally kept in.

Preanaesthesia Considerations

 Do not attempt to anaesthetise fish if water quality is poor (e.g., low pH, high ammonia or nitrite). Correct water conditions and schedule a revisit to perform other procedures. Ensure good water quality - ensure pH and hardness are improved and within 85% of values of the original water.

 Do not attempt to anaesthetise fish that are infested with ectoparasites. Routinely examine gill biopsies and skin mucus scrapes as part of the preanaesthetic protocol.

 Fast fish for 24–48 hours prior to procedure.

 Plan carefully and have contingencies (premeasured doses of doxapram to counteract respiratory depression).

 Anaesthetic doses - add slowly to effect, as there are few indicators of depth of anaesthesia.

 Where appropriate, the salinity may be altered (increasing by 1–5 g/L NaCl in freshwater fish or decreasing it in the case of marine fish) to reduce osmoregulatory stress.

 Adjust the water temperature to within the species' optimal range (in my experience, the optimum temperature for koi and goldfish is 20–24°C). If it is possible to wait for the correct season, this is suggested. Then, maintain water temperature within 2°C of source water temperature. Performing surgery in conditions near or outside thermal optimal ranges can exacerbate stress, reduce immunity, and increase complications.

 Consider species and size - large, active fish need less anaesthetic than small, sluggish ones; and fishes with accessory breathing apparatus (e.g., anabantoids, catfish, lungfish) will take longer to induce or will need higher dose rate.

Post-Anaesthesia Considerations

 Some fish, especially sharks, can regurgitate food upon recovery. Such fish should initially be recovered in a separate tank, such that it will not contaminate its resident tank.

 Lights should be dimmed in the recovery aquarium.

 Diazepam may be used if the fish becomes distressed during the recovery phase at 0.1–0.2 mg/kg IP or IM (up to 4–5 mg/kg in whale sharks).

Fish Surgery

Introduction

Surgery of ornamental fish is an exciting and pioneering field for veterinary practitioners. With the right equipment, anaesthetic setup and skills, surgery is a feasible option for ornamental fish. Most of the surgical requests in private practice involve goldfish, koi, or large tropical fish such as cichlids - although smaller fish can be operated on with the right equipment and preparation.

Patient Preparation

Once the patient is anaesthetised, the fish is removed from the water and placed on a smooth, padded platform. Patient positioning for surgery can be optimised using a polystyrene foam (Styrofoam) block with a custom-cut U- or V-shaped groove. Disposable sterile plastic drapes are ideal and should be transparent to allow visual monitoring of the patient throughout the procedure. The edges may be secured via sutures in large patients or via applying a thin layer of wound gel (e.g., SoloSite or Intrasite) on the edges that can be rinsed off easily after the surgery.

Care must be taken to avoid desiccation of the fins and skin during the procedure. Wrap the remainder of the fish body in plastic bag or cling wrap to retain moisture, or remember to moisten with water regularly. Note that fish eyes do not adapt to bright light rapidly, and therefore surgical patient's eyes should be shielded from any bright surgical light.

Skin Preparation

Aseptic techniques and maintaining asepsis is challenging. Gentle irrigation is performed to remove gross contamination from the site to be incised. The skin can be irrigated with one of the following:

 Clean, dechlorinated water

 Sterile 0.9% saline

 Dilute 1:10–1:20 povidone-iodine solution (dilute in sterile water or sterile 0.9% saline solution) followed by sterile 0.9% saline

Initial removal of scales makes suturing easier at closure. Large scales covering the incision site can be removed gently with sterile rat tooth forceps (pulling the scale in the direction of its growth; i.e., caudally) - this is not necessary for fish with small scales.

Analgesia

Depending on the procedure, post-operative analgesia may be necessary. This should be given prior to recovery from anaesthesia). A selection of medicines includes:

 Meloxicam at 0.1–0.2 mg/kg IM

 Flunixin 0.25–0.5 mg/kg IM

 Carprofen 2–4 mg/kg IM

 Morphine 0.1–0.3 mg/kg IM

 Methadone 0.1–0.3 mg/kg IM

 Butorphanol 0.1–0.4 mg/kg IM

Common Surgical Procedures

Wound Debridement and Closure

Wounds in fish may be the result of an attack by another fish or in some instances by a cat or bird gaining access to the tank or outdoor pond. Powerful filters can sometimes injure fish via their suction inlets. Provided the water quality is optimal, small lacerations exposing muscle usually heal without surgical intervention. However, the patient would need to be monitored closely for any bacterial or fungal infection of the wound. In cases where wounds are initiated or complicated by bacteria, the lesion should be debrided and any scales that are damaged or in the lesion should be removed. Systemic antibiotics may be indicated and should be based on bacterial culture and antibiotic sensitivity testing.

Removal of Cutaneous Tumours

Cutaneous growths may occur quite commonly, especially in goldfish and koi. The tumour can be surgically excised with a scalpel blade and cryosurgery (e.g., Wart-Off Freeze spray) may be applied to the excision site to destroy remnant neoplastic cells.

Fish skin defects after tumour removal can be difficult to close due to the lack of elasticity in the skin and muscle. Large defects are therefore left to heal by second intention. If there is significant bleeding, haemostasis can be achieved by applying direct pressure, 2.5% phenylephrine hydrochloride ocular drops or ferric sulphate lightly. The use of silver nitrate and potassium permanganate are not recommended because they are too harsh. Electrocautery may also be used to cut and cauterise vascular skin tumours. Histopathology should be performed on the lesion resected, and the fish owner should be warned of potential recurrence especially in the case of neoplastic lesions.

Trimming of the 'Wen' in Oranda Goldfish

The wen (a 'normal' myxomatous growth on the head of this variety of goldfish) can sometimes grow so large that it starts obstructing their eyes. Fortunately, the wen does not actually grow on the eyes or adhere to the cornea. The patient should be fully anaesthetised, and careful surgical technique is required to avoid damaging the eyes. Trimming of the wen involves using a pair of forceps to locate the pore that remains in the tissue which is usually over the eye. Gently pull the growth away from the eye as you excise the growth with a scalpel blade. Ensure no loose tags of tissue remain; otherwise these will grow excessively. The excision site does not usually bleed, and there is no need for haemostasis.

Correction of 'Gill Curl' in Arowanas

Due to water flow, developmental or dietary problems, the opercular membrane may 'curl' outward. Cosmetic correction of this problem includes trimming of the membranous portion of the gill along the bony opercular margin with a pair of sharp scissors or scalpel. The bony edge is then sanded down to smooth over using P1000 sandpaper (average particle size 18.3 µm). The opercular membrane should regrow normally. To prevent recurrence, attention needs to be paid to the underlying cause.

Correction of 'Droopy Eye' in Arowanas

This condition is thought to arise because these fish are designed to look up. Many aquaria are set at human eye level and filled to capacity. As such, the eyes of these fish become 'lazy', their retractor bulbi muscles atrophy and their eyes 'droop' as a result.

There are several methods to prevent this occurring, and they include floating table tennis balls in the water to give them something to look at, positioning aquaria lower to the ground and lowering the water level in aquaria. Surgically, this can be rectified by scarifying the tissues around the dorsal aspect of the orbit and placing a temporary suture to hold the eye in place until it heals.

Eye Exenteration

Eye exenteration may be indicated in severe or refractory pop-eye syndrome, ocular infections, trauma and neoplasia. The reason for exenteration (complete surgical removal of the eyeball and other contents of the eye socket), rather than enucleation (removal of an eye, intact from its supporting tissues), is because the supporting structures consist mainly of adipose tissue, and, if these are left behind, will become infected. A pair of curved tenotomy scissors is required to transect the muscular attachments and the optic nerve and vessel. Gentle technique is required to avoid damage to the multiple branches of cranial nerves V and VII that traverse the retrobulbar space. It is very important to remove all the periorbital adipose tissue to prevent delayed healing and infection. Bleeding can be controlled using direct pressure or 2.5% phenylephrine hydrochloride ocular drops. Once the bleeding has been controlled, the empty orbit is left to heal by second intention. Note that the defect will be large, deep and pale, so you will need to manage the owner's expectations prior to surgery. The concavity of the defect will become shallower over time.

Laparotomy/Coeliotomy

A laparotomy may be indicated for the removal of an ovarian tumour (e.g., spindle cell sarcoma, ovarian carcinoma), space-occupying impacted eggs, abscess and foreign body. A ventral-midline or paramedian incision can be made, depending on the type of fish. Ventral-midline incisions should be avoided in fish that rest on the tank floor. In fact, in stingrays, incisions are made in the dorsolateral aspect. Scales should be removed for ease of making the incision and for suturing. The incision should be as short as possible; however, the removal of scales must account for the necessity to extend the incision. Three to four rows of scales can be removed by firmly grasping the free edge of the scale with forceps (rat tooth may be necessary) and tugging in a caudal direction with quick, sharp movement. The scales will regrow.

For closure, swaged-on needles with cutting tips are recommended to facilitate ease of use through piscine skin and scale. Non-cutting tips are recommended in instances where tissues are more friable (e.g., juveniles and smaller fish). Synthetic non-absorbable monofilament suture material should be used to the abdominal wall, using a simple, interrupted pattern. Make sure the internal bones of the pelvic fins are used to secure the suture.

Beware that there is a higher risk of wound dehiscence compared to mammalian surgery.

Correction of Positive Buoyancy Problem in Cyprinids

From time to time, some fish may succumb to swim bladder disease. The affected fish is unable to maintain equilibrium and become positively buoyant. Death can occur within hours to days after the onset of signs if the condition is left uncorrected.

Fine-needle aspiration of the swim bladder is a good first-line treatment and will be curative if the fish is attended to within the first 24 hours of clinical signs. Here, an appropriate gauge needle is inserted from a caudocranial approach and guided toward the swim bladder to remove the excess gas.

A life-saving laparotomy procedure has been described by Erik Johnson for the rapid correction of buoyancy issues in goldfish and koi with swim bladder disease. A sterile (autoclaved) quartz stone is implanted intracoelomically to act as a ballast, to correct the imbalance.

The heaviness of the weight is proportional to the degree of positive buoyancy. To estimate the weight necessary, the anaesthetised fish can be placed in a plastic bag to float in the water. Weights are then placed on the bottom of the plastic bag to determine the amount required to weigh down the fish.

Microchipping

The recommended microchip implantation locations for fish are:

1.  Deep implantation in the midline, anterior to the dorsal fin (British Veterinary Zoological Society guidelines).

2.  Large fish >30 cm in length - on the left side at the anterior base of the dorsal fin (World Small Animal Veterinary Association guidelines).

3.  Smaller fish <30 cm in length - on the left side into the coelomic cavity (World Small Animal Veterinary Association guidelines).

Conclusion

With the right medicines and equipment, surgery on fish is within the scope of traditional veterinary practice.

References

1.  Brattelid T, Smith AJ. Methods of positioning fish for surgery or other procedures out of water. Laboratory Animals. 2000;34:430–433.

2.  Harms CA, Wildgoose WH. Surgery. In: Wildgoose WH, ed. BSAVA Manual of Ornamental Fish. 2nd ed. Quedgeley, UK: BSAVA; 2001:259–266.

3.  Harms CA. Surgery in fish research: common procedures and postoperative care. Laboratory Animals. 2005;34(1):28–34.

4.  Johnson EL. Surgery in Koi Health and Disease. 1997:102–108.

5.  Loh R. Fish Vetting Essentials. Perth, Australia: Richmond Loh Publishing; 2011.

6.  Loh R. Fish Vetting Techniques and Practical Tips (DVD). Perth, Australia: Richmond Loh Publishing; 2014.

7.  Murray M. Fish surgery. Seminars in Avian and Exotic Pet Medicine. 2002;11(4):246–257.

8.  Raidal SR, et al. Surgical removal of an ovarian tumour in a koi carp (Cyprinus carpio). Australian Veterinary Journal. 2006;84(5):178–181.

9.  Ross LG. Restraint, anaesthesia and euthanasia. In: Wildgoose WH, ed. BSAVA Manual of Ornamental Fish. 2nd ed. Quedgeley, UK: BSAVA; 2001.