On June 8, 1994, a client phoned the NCSU-CVM with a complaint of acute high morbidity and mortality among the koi in her pond. The client related that she was out of town on vacation and had received a call from her landscaper who informed her that when he arrived to check on the fish the pond contained only a few inches (vertical measurement) of water. The client asked the landscaper to fill the pond slowly with tap water and instructed him to add a commercial dechlorinator. The landscaper reported stressed and dying fish shortly after the pond had been filled.

Upon our arrival we noted 5 dead koi (3 tancho, 1 shusui and 1 ogon), 1 large sanke koi with minimal opercular movements floating on the surface, and 3 koi (2 tanchos and 1 hi-bekho) that were swimming but appeared "stressed." There was a strong chlorine-like smell around the pond. Pond and tap water samples were collected for evaluation upon return to the veterinary college. There were no gross lesions present on the dead koi, and based on gill coloration, it was estimated that they had been dead less than 4 hours. Attempts to resuscitate the sanke koi were unsuccessful. Once the dead fish had been removed, a commercial dechlorinator was added to the pond. Shortly thereafter, the 3 surviving fish were removed from the pond and placed in large coolers where they could receive more intensive care. Despite our efforts, one of the tancho koi died within the hour. The hi-bekko's condition improved and after several hours of observation it was sent to a neighbor's koi pond. The surviving tancho was estimated to weigh 400 grams and was given 1 milligram of dexamethasone intravenously. The fish was transported back to the NCSU-CVM where it was placed in a plastic bag containing approximately 7 liters of water and 20 liters of 100% oxygen for 3 hours. Analysis of the pond and tap water samples collected 4 hours earlier revealed chlorine levels of 0.2 ppm and 1.8 ppm respectively.

The tancho was placed in a 75 liter aquarium containing de-chlorinated tap water and 1.0 parts per thousand (ppt) artificial sea salt. Oxygen was bubbled from a cylinder into the aquarium at a rate of 0.5 liter per minute through two 2 inch glass bead air stones. Dissolved oxygen levels were closely monitored and were maintained close to 12 parts per million (ppm). Room air was also pumped into the tank via a single air stone as a safety precaution. Reusable ice-packs were floated in the aquarium to lower and maintain tank temperature at 60 degrees Fahrenheit (F). The fish's condition was unstable and appeared to be deteriorating. The fish was given 1.0 mg prednisolone intravenously. The following day the fish was given 1.0 mg dexamethasone intramuscularly, a 50% water change was performed, and the aquarium was covered because the fish became stressed by human activity in the area of the tank. By late afternoon the fish's condition had stabilized. The owner was contacted and updated on the situation. Later that evening the fish's condition again deteriorated and the fish lost equilibrium and was in respiratory distress. The blood vessels in the Caudal fin appeared injected. One ma. of prednisolone was given intraperitoneally (1P) and 2.0 mg of dexamethasone were given IM. The next morning the fish was noted to have regained some of its equilibrium capacities although it still had difficulty maintaining a normal position in the water column. By late evening on the third day the fish appeared stable and no longer exhibited signs of respiratory difficulty. The fish's condition improved over the next day and on day 5 the Caudal fin injection had resolved as had the equilibrium deficits. It was noted that the fish appeared to`tire quickly' after periods of manipulation and evaluation. At this time the oxygen flows were reduced to 0.25 liters per minute, ice pack therapy continued, and the tank remained covered. On day 6 the fish appeared normal and the oxygen was turned off and the tank was uncovered. The fish was kept one more night and discharged on day 7 to the neighbor's pond where the hi-bekko had been taken. The owner was asked to monitor the fish closely for respiratory distress, anorexia, or loss of equilibrium. The owner was also instructed to keep the tancho in as cool and quiet an environment as possible. To date the fish is doing well.

Upon further discussion with the owner it was determined that the landscaper had not added the dechlorinator to the pond before he filled it with the tap water. We believe the relatively low level of chlorine in the pond water sample was a result of aeration and exposure to sunlight between the time the pond was filled and the time the sample was obtained (approximately 4 hours).

Acknowledgements

The authors would like to thank Adriana Doi, Lecia Johnson, and Debbie Whitt for their help with this case.