Using ammonia nitrogen excretion rates as an index for determining stress conditions in sea bass (Dicentrarchus labrax)

A time-course study was conducted in order to evaluate the recovery time of juvenile Sea bass (Dicentrarchus labrax) from transport and handling stress. Among metabolite indices, ammonia nitrogen excretion rates were used as stress indicator. The measurements were carried out in water ambience of 13±1 ºC under natural light conditions (16L/8D photoperiod). Juveniles were transported for about 2 hours in a fish transporting tank with an oxygen supply. Handling stress was due to the netting at the outlet site during stocking the fish into the transport tank and due to netting at the experimental facility while transferring fish from transport tank into the experimental tanks. At the end of transportation, rates of ammonia nitrogen excretion of sea bass juveniles in the transport tank became about 4 times higher when compared to that in sea water at the outlet facility. Ammonia nitrogen concentrations in fish exposed to transport and handling stress reached a peak 10 hours after stocking the fish to the tanks, and then declined to the initial values 24 h after stocking. In fish under normal condition and without stress, the postprandial trend of ammonia nitrogen excretion was similar however a peak was reached 6 hours after feeding, and then decreased to the initial values 24 h after feeding. Based on the duration for recovery of ammonia nitrogen excretion in fish, it is suggested that sea bass juveniles may completely recover from stress caused by transportation and handling, and return to normal feeding conditions in 24 hours after truck transportation for 2 hours.Keywords: Sea bass, Dicentrarchus labrax, stress recovery, ammonia concentration, nitrogen excretion, fish transport