A DIET ENRICHED WITH TRYPTOPHAN CAN SUPPRESS POST-SHIPMENT STRESS IN Amphiprion ocellaris

Post-shipment stress is a major cause of mortality in the trade of ornamental fish. During transit, fish are subjected to a number of stressors, including deteriorating water quality, crowding, and confinement stress. Dietary supplementation with tryptophan has been shown to reduce crowding stress in fish. In this experiment, we studied the effects that a conditioning diet enriched with tryptophan had on post-shipping stress in the marine clownfish, Amphiprion ocellaris. Stressed and anxious fish prefer swimming in the bottom of a tank, sometimes remaining immobile. We hypothesized that fish fed a diet rich in tryptophan would show less post-shipment stress. A total of 332 juvenile clownfish were divided into ten 76L tanks. All the tanks were connected to our multi-tank 1,113L system. Five tanks were designated as diet A and five tanks were designated as diet B. The experimenters did not know which of the two diets was enriched with tryptophan. The fish were fed their designated diets for a period of seven days. On day 9, approximately 15 fish from each tank were bagged. Each bag was filled with one liter of water and several liters of oxygen, and placed in a covered box at room temperature for 24 hours. On day 10, fish were released into a 38L holding tank following a five-minute acclimation period. After the fish were released, their behavior was recorded with a video camera for 15 minutes. The fish vertical position in the tank was observed every 30 seconds. During the first two minutes of recording, a majority of the fish in both treatment groups stayed in the bottom 1/3 of the tank. Afterwards, more fish in the tryptophan-enriched diet left the bottom of the tank to explore the tank compared to fish in the control diet. During the last two minutes of observation, there were more fish in the bottom of the tank in the control group (p<0.001). Thus, fish fed a diet enriched with tryptophan exhibited less anxiety and stress when moved into a new tank after spending 24 hours in a shipping bag. Considering that 48 hours had elapsed from the time the fish was fed to the time the observations were made, the effects of tryptophan on the stress axis seem to be consistent. Thus, tryptophan-enriched conditioning diets should be considered to minimize shipping and post-shipping mortalities in the marine ornamental industry.