A five-year-old mature male Red Devil cichlid (Cichlasoma citrinellum) weighing 800 grams presented in May of 1993 to the Veterinary Teaching Hospital of the College of Veterinary Medicine, North Carolina State University (CVM-NCSU) with a two year history of a distended abdomen and inadequate buoyancy control. The fish swam with its head down, but continued to eat and defecate normally. At the time of our examination, the fish rested between a 90 and 120 degree angle to the gravel substrate at the bottom of the aquarium. The fish was able to swim awkwardly when stimulated.

Left to right lateral and right lateral decubitus horizontal beam (dorsoventral) whole body radiographs were obtained without anesthesia. The radiographs revealed the presence of an "I-shaped" radiolucency in the central coelomic cavity which was asymmetrical and larger on the left side. Additional radiographic findings included kyphosis of the central region of the spine, and osseous proliferation of the spine from the level of the kyphosis extending caudally. A normal male Red Devil cichlid was radio graphed for comparative purposes. The affected fish had generalized enlargement of the swim bladder, the caudal compartment septum was not visualized, and the left caudal component was grossly dilated.

To alleviate the fish's buoyancy problem, the fish was anesthetized and a celiotomy was performed to approach the swim bladder and reduce its size. A recirculating anesthesia machine was constructed. Anesthetic water was pumped from a 5 cm flexible tube which was fitted with a "T" adapter. Two 2 cm delivery tubes were attached to the "Y" adapter and placed in the mouth of the fish so that water bathed both sets of gills.

Anesthesia was induced by immersing the fish in a 100 mg tricaine methanesulfonate solution per liter water for 6 minutes followed by the addition of 50 mg tricaine methanesulfonate per liter water for 2 additional minutes. At this time, the fish had only mild opercular movements and the total induction concentration of tricaine methanesulfonate was 150 mg/liter. The fish was placed on the surgery area and the delivery tubes were positioned in its mouth. Anesthesia was maintained with a constant 60 mg/liter tricaine methanesulfonate at a flow rate of 3 liters/minute. Total duration of anesthesia was 71 minutes. The patient was also given an intraperitoneal dose of Enrofloxacin (10 mg/kg) prior to surgery to reduce the possibility of a secondary bacterial infection.

The scales were removed from the area of the planned incision site with forceps. A midline ventral abdominal incision was begun immediately Caudal to the base of the pectoral fins and extended caudally. The incision curved laterally approximately 2 cm cranial to the cloacal opening and ended lateral to the cloacal opening. Small self-retaining retractors were placed to spread the wound edges. The abdominal viscera were retracted cranially. The dorsal abdominal musculature was incised to access the swim bladder. The swim bladder was carefully dissected free from its attachments to the body wall. After an encircling ligature of 4-0 nylon suture material was placed, the Caudal end of the swim bladder was excised (approximately 5 cm x 2 cm). The dorsal abdominal musculature was approximated with 4-0 polyglactin 910 (Ethicon, Inc., Johnson & Johnson, USA). The ventral abdominal incision was closed with simple interrupted 4-0 polyglactin 910 sutures in the musculature and the subcuticular layers and 40 nylon sutures in the skin.

The fish recovered without complication from the anesthesia and surgical procedure, but refused food in the days following surgery. Over the next eight weeks the fish presented several times with buoyancy problems and air was aspirated from the swim bladder using a 23 gauge butterfly catheter. The time intervals between aspirations increased with each procedure until the fish was able to maintain a normal attitude in the water for over 5 months.

The swim bladder is present in most species of fishes where it may perform one or more functions including buoyancy control, respiration, sensation, and sound production.^1,2,3,4 Red Devil fish and other members of the cichlid family are physoclists. Fishes in this category regulate the amount of gas in their swim bladders by utilizing one or more counter-current capillary beds (retie mirabilia) which are located in the wall of the swim bladder. Gasses are exchanged by simple diffusion between the vascular rete and the swim bladder lumen where the partial pressure of a particular gas exceeds the partial pressure of that gas in the bloodstream.¹

Buoyancy problems in captive fishes are not uncommon. Causes include subcutaneous air accumulation due to supersaturation of the water with atmospheric air, swim bladder infection or rupture, and equilibrium disorders related to inner ear disease. The cause of the swim bladder disorder in this Red Devil cichlid is unknown.

Reduction of the volume of the swim bladder improved the fish's ability to maintain a normal posture in the aquarium. Accumulation of air in the weeks following surgery could have been due to small amounts of air leaking from the healing swim bladder. Subsequent aspiration seems to have prevented further accumulation of air.

Tricaine methanesulfonate is a widely used anesthetic for fishes.⁵ Most fish experience an excitatory stage of anesthesia followed by sedation, a loss of equilibrium and finally a loss of any reactivity. It is desirable to maintain an anesthetic plane at this level. Mild opercular movements should be maintained and the gills must be bathed sufficiently with anesthetic water. Anesthetic effects of tricaine methanesulfonate are quickly reversed by placing the fish into a solution of fresh, clean water. This report illustrates the feasibility of radiography, anesthesia, and coelomic surgery in a pet fish patient.

Acknowledgements

The authors thank Drs. Michael Stoskopf, Dr. James Gaines, Dr. Christine Boyd and the owners of the fish, Brian and Wendy Tramm, for their assistance with case management, and Joe Trumpey for artwork and Ree Coan and Wendy Savage for photography.

References

1.  Alexander, R. McN. 1966. Physical aspects of swimbladder function. Biol. Rev. 41. 141-176.

2.  Reyer, HU. 1977. The role of the swim-bladder in vertical movement of fishes (Carassius auratus, Salmo gairdneri, and Tilapia mariae). Biol. Behav. 2. 109-128.

3.  Ross, LG. 1979. The haemodynamics of gas resorption from the physoclist swimbladder: The structure and morphometrics of the oval in Pollachius virens. J. Fish. Biol. 14:261-266.

4.  Stoskopf, MK. 1993. Fish Medicine. W.B. Saunders Co., Philadelphia. 882 pp.

5.  Jolly, DW, Mawdesley-Thomas, LE, and D Bucke. 1972. Anaesthesia of Fish. The Veterinary Record. 91. 424426.