Fish SurgeryMichaelJ. Murray, DVM
As the number and value of captive fishes increases, so too will the indications for surgical intervention by the veterinarian. In general, the most difficult aspect of fish surgery is the provision of adequate and safe anesthesia, and several different anesthetic regimens are provided. Once one is familiar with the normal anatomy of the piscine patient, the basic concepts of surgery prevail, including appropriate surgical approach, hemostasis, and gentle tissue manipulation. Specific surgical procedures, celiotomy, liver biopsy, renal biopsy, and laparoscopy are discussed. Finally, successful outcome of a surgical manipulation often rests in the postoperative management of the surgical patient. Suggestions for appropriate postoperative management are also discussed. Copyright 2002, Elsevier Science (USA). All rights reserved. Key words: Fish, surgery, anesthesia, laparoscopy, celiotomy, biopsy.
increased. Public aquaria have increased in b o t h n u m b e r and complexity and often exhibit fish with substantial financial and genetic value. As a result, advances in fish surgery have b e c o m e commonplace. A n u m b e r of excellent reviews of surgery in the piscine patient have b e e n published recently in the veterinary literature. 1,2 Much of the earliest work published was directed towards and written by fish pathologists and biologists with particular emphasis on diagnostic sample collection and transmitter implantation. ~-7 An a t t e m p t will be m a d e within this review to present a m o r e traditional veterinary a p p r o a c h to fish surgery that includes discussion of anesthesia, patient preparation, instrumentation, surgical procedures, and postoperative m a n a g e m e n t .
g g V o u can do that?" is probably one of the At most c o m m o n l y e n c o u n t e r e d responses to clinicians advocating a surgical m a n i p u l a t i o n of a piscine patient. O n the surface, one should not be terribly surprised at such a response; however, one n e e d only look m o r e carefully at the demographics associated with captive fish to u n d e r s t a n d some of the driving forces b e h i n d "pet" fish medicine. Although the exact numbers are difficult to ascertain, the results of the 2001 p e t ownership survey posted on the American Pet Product Manufacturers Association Web site indicate that there are approximately 160 million pet fish. Many of these fish are dear pets to their owners, a n d the h u m a n - a n i m a l b o n d definitely influences the level of veterinary care expected. As life support systems for captive fish have i m p r o v e d and decreased in cost, b o t h the value and longevity of m a n y specimens has
AnesthesiaDebate still occurs regarding the ability of fish to feel pain. W h e t h e r or not they feel pain, it is i n c u m b e n t u p o n the veterinarian to err on the side of caution, assume pain can be experienced, and offer anesthesia during painful procedures (Table 1). T h e r e can be no doubt, however, regarding the often violent reaction that fish have to noxious stimuli. O n e must always recognize the potential for idiosyncratic problems with anesthetics in fish. For that reason, there are circumstances in which painless procedures, such as skin scrapings, may be carried out with gentle physical restraint. This does not imply, however, that physical restraint is appropriate for procedures that may be painful to the fish. Many elasmobranches are adequately sedated following immersion in a water column that is supersaturated with oxygen. Still other species may be adequately immobilized by physically holding t h e m in dorsal r e c u m b e n c y via a process of tonic immobility. This practice should be used with caution because some species may experience adverse effects to e x t e n d e d periods of tonic immobility.
From the Monterey Bay Aquarium, Monterey, California. Address correspondence to Michael J. Murray DVM, Monterey Bay Aquarium, 886 Cannery Row, Monterey, CA 93940. Copyright 2002, Elsevier Science (USA). All rights resemed. 1055-937X/02/1104-0007535.00/0 doi:10.1053/saep. 2002.126571
Seminars in Avian and Exotic Pet Medicine, Vol 11, No 4 (October), 2002: pp 246-257
Table 1. Anesthetic DosesAnesthetic Agent Inhalant anesthetics Tricaine methanesulfonate Induction Maintenance Eugenol Induction Maintenance Injectable anesthetics Ketamine Teleost Elasmobranch Ketamine/ medetomidine Immobilization Reversal, atipamezole Ketamine/xylazine (sharks) Ketamine Xylazine Dose
100-200 mg/L 50-100 mg/L 100-120 mg/L 40 mg/L 66-68 mg/kg IM 12-20 mg/kg IM Ket, 1-2 mg/kg IM Medet, 50-100 /xg/kg IM 200/,g/kg IM 12-20 mg/kg IM 6 mg/kg IM
Abbreviation: IM, intramuscularly. Table reprinted with permission,s
Inhalant AnestheticsNot to be confused with the traditional inhalant agents used in terrestrial animal anesthesia, inhalants include those c o m p o u n d s added to the water that sedate or anesthetize the fish. Although a n u m b e r of c o m p o u n d s have b e e n ' e m p l o y e d in the past, the most c o m m o n l y used agents currently in use are tricaine methanesulfonate (MS-222 or Finquel; Argent Chemical Laboratories, R e d m o n d , WA) and eugenol. Both c o m p o u n d s are readily available and have b e e n evaluated for b o t h efficacy and safety. Generally, fish are initially placed in an induction c h a m b e r that contains the p r o p e r levels of anesthetic, with the a p p r o p r i a t e temperature, pH, a n d oxygen levels, and is large e n o u g h to prevent excessive struggling but not so large as to p e r m i t concussive injury. Once the fish reaches an a p p r o p r i a t e level of anesthesia, it may be r e m o v e d f r o m the induction c h a m b e r for out-of-water procedures. For p r o c e d u r e s that are expected to be shorter in duration, such as gill or fin biopsies, no further chemical restraint may be required. In general, the time that the fish is held out of water should be less than 5 minutes, s In m o r e
p r o l o n g e d procedures a m e c h a n i s m for maintaining respiratory support and acceptable anesthetic levels must be provided. Inhalant anesthesia as described in this context may be maintained in one of t w o fashions. In smaller specimens, a non-rebreathing system may be used. Anesthetic- and oxygen-laden water appropriately p r e p a r e d for the fish may be placed in a reservoir bag, such as an e x p e n d e d IV bag. Anesthetic-laden water may then be delivered via gravity flow through an appropriately sized tube through the oral cavity directed over the gill filaments. Flow rates are easily controlled with clamps on the tubing. Water that accumulates may be drained into a n o t h e r reservoir but is not recycled over the fish's gills. In larger specimens a rebreathing system is r e c o m m e n d e d . A variety of anesthetic delivery systems have b e e n described. In the author's experience, the design described by Lewbart and H a r m s is p r e f e r r e d and may be modified to anesthetize large specimens (Fig 1). sq~ In this system, anesthetic-laden water is p u m p e d f r o m a reservoir across the fish's gills f r o m where it drains back into a reservoir for recirculation to the patient. Such a system permits a p r o l o n g e d out-of-water p r o c e d u r e yet still maintains adequate respiratory support and anesthesia. It is i m p o r t a n t that the flow be directed over both gill arcades and in a n o r m o g r a d e fashion. Retrograde flow may c o m p r o m i s e the n o r m a l counter-current m e c h a n i s m of the gills and may actually h a r m the structures.
Figure 1. Piscine rebreathing anesthetic system. A side port off the power head (white arrow) is used to provide a trickle of water to keep the fish moist (black arrow). Reprinted with permission. 1~
Despite the a p p a r e n t "bullet-proof' nature of these systems, there are areas of concern. First, one must be ever cautious of water quality. Prolonged p r o c e d u r e s may result in water that becomes increasingly c o n t a m i n a t e d with nitrogenous waste. Additionally, one should be certain that adequate gas exchange is occurring at the water's surface. In some circumstances it may be necessary to percolate oxygen t h r o u g h the anesthetic reservoir. In most cases, a dissolved oxygen concentration of 6-10 p p m is adequate since p r o l o n g e d exposure to high oxygen levels may be d a m a g i n g to the respiratory system (the gills). Finally, such a system has limits to varying the "anesthetic setting." O n e may modify the anesthetic concentration of the reservoir by adding a known concentration of anesthetic or a known volume of clean water to the system to either raise or lower the anesthetic concentration, respectively. Mternatives to such manipulations include multiple reservoirs of varying concentration or the use of an alternating system of anesthetic provision at a steady level, followed by use of anesthetic-free water when the anesthetic d e p t h becomes excessive.
nature of the solution, buffering of anesthetic systems should occur just before their use on fish. An oily residue n o t e d on the surface of the stock solution indicates that desulfonation has occurred and that the solution has lost potency and should be replaced. As a general guideline, MS-222 induction is carried out at concentrations of 100-200 m g / L . Anesthetic m a i n t e n a n c e may then be accomplished at 50-100 m g / L . It is imperative that the clinician develops a familiarity with the effects of the agent u p o n the species in question. Varying degrees of sensitivity to MS-222 have been observed, and margins of safety may vary depending u p o n the water-quality parameters. In most cases, the rate of recovery is directly related to the length of anesthesia, anesthetic depth, and water quality. O n e would typically anticipate rapid recovery of less than 15 minutes in shorter procedures and p r o l o n g e d recover?, periods (hours) in procedures of a longer duration.
Eugenol (Clove Oil)T h e phenolic c o m p o u n d eugenol is the active ingredient in clove oil, which has long b e e n advocated as a safe and effective anesthetic by fish hobbyists and commercial fish farmers. 1~ Because eugenol is not water-soluble, it must be diluted in 95% ethanol before use. Generally, it is diluted 1:10 in 95% ethanol to p r o d u c e a stock solution of 100 m g / m L . A concentration of 100120 m g / L is generally used for induction, 40 m g / L for maintenance. W h e n c o m p a r e d with MS-222, both compounds were f o u n d to contribute to hypoxemia, hypercapnia, acidosis, and hyperglycemia. 11 Eugenol typically results in a m o r e rapid induction and a m o r e p r o l o n g e d recovery period than MS222. Eugenol has a m o r e narrow range of safety and may in fact cause respiratory failure at higher doses. As with MS-222 one must be cognizant of the idiosyncratic reactions to eugenol, such as the cardiorespiratory depression and death n o t e d anecdotally with Acanthuridae (tangs and doctorfish). 1
Tricaine Methanesulfonate (MS-222)MS-222 is probably the most c o m m o n l y used fish anesthetic at this time. It is a water-soluble benzocaine derivative that is FDA-approved for use in food fish that require a 21-day withdrawal time. In aqueous solution, tricaine is acidic, with a p H of nearly 3.0. T h e r e f o r e buffering is necessary, typically with sodium bicarbonate, especially in freshwater systems. Marine systems typically contain adequate i n h e r e n t buffering, but the p H should always be evaluated before the induction of fish with MS-222. Tricaine is generally recognized to cause hypoxia, hypercapnia, and acidosis. 11 Secondary to these effects hyperglycemia and elevations of potassium, magnesium, hemoglobin, and hematocrit may also be noted. An increase in urinary o u t p u t a n d subsequent electrolyte loss may be n o t e d for up to a week postanesthetic, lz It is r e c o m m e n d e d that an aqueous stock solution (10 g i n / L ) of MS-222 be p r e p a r e d for dosing anesthetic systems. Such stock solutions are unstable in light, necessitating storage in dark containers, and can be refrigerated or frozen for increased shelf life. Because of the acidic
Injectable AnestheticsT h e r e are circumstances in which inhalation anesthesia is inappropriate for use. It may not be possible to provide anesthetic induction cham-
bers for very large specimens. Some species such as Scombridae do n o t tolerate confinement, a n d "capture" of individuals in large aquaria may preclude induction with tricaine or eugenol. In those instances, parenteral administration of agents may be indicated. Intramuscular injections are typically given in the dorsolateral musculature dorsal to the lateral line. Although intramuscular injections are not the ideal m e t h o d , they may be necessary, particularly when injection with a pole syringe or Hawaiian sling is necessary in larger aquaria. W h e n administering intramuscularly, a deep injection may aid in minimizing the retrograde drainage of the material f r o m the injection site. If possible, the needle should be directed cranially to minimize d a m a g e to the integument.
KetamineAn injectable, short-acting, dissociative anesthetic agent, ketamine hydrochloride is rarely used alone, but rather in combination with other agents, such as the ~-agonists m e d e t o m i dine or xylazine hydrochloride. In most teleost fish, a relatively high dose is required for immobilization and therefore is often used as an "induction" agent. Elasmobranchs are typically m u c h m o r e sensitive to the effects of ketamine and may require addition of an o~-agonist for adequate sedation, s
PropofolT h e intravenous sedative/hypnotic agent p r o p o f o l has some potential use as an anesthetic despite its obvious limitation as an intravenousonly c o m p o u n d . O f particular interest is its application in tonically immobilized fish such as elasmobranchs. It has several advantages when used, including rapid, s m o o t h induction, relatively short duration of effect, and n o n c u m u l a tive effects. It has b e e n used in sharks at a dose of 2.5 m g / k g administered intravenously over a 30-second period into the caudal vein. TM Following administration, righting reflex is lost within 5 minutes and returns in approximately 75 minutes.
the procedure. O n e may attribute a series of stages, planes, and descriptions to the events that occur as the fish proceeds f r o m its n o r m a l state to the deepest state of anesthesia--sedation followed by narcosis a n d finally anesthesia. 12 Care should be taken to prevent iatrogenic injury to the fish as it passes t h r o u g h the excitability phase of anesthesia. Duri...