Effects of Temperature and Stocking Density on the Ammonia Excretion Rate of Red Seabream, Pagrus major

An experiment was conducted to investigate the effects of temperature and stocking density on daily patterns and rates of total ammonia nitrogen (TAN) excretion in juvenile red seabream Pagrus major (mean body weight: 29.0 g) under fasting and feeding conditions. Fish were acclimated over 7 days under four different temperatures (10, 15, 20, and $25^{\circ}C$) and at two different densities (5.5 and $11.0\;kg\;m^{-3}$). Each treatment had three replicates and a total of 216 fish were used. After 72 hours starvation, endogenous TAN excretion was measured for each temperature and density. To investigate exogenous TAN excretion, fish were handfed a commercial diet containing 51.6% crude protein twice a day for 7 days, at 08:00 and 16:00. Water was sampled from both inlets and outlets of chambers every 2 hours over a 24 hour period. Both endogenous and exogenous TAN excretion increased with increases in temperature and density (P<0.05). Mean daily endogenous TAN excretion rates at 10, 15, 20, and $25^{\circ}C$ were 88.8, 101.1, 125.0, and $143.3\;mg\;TAN\;kg^{-1}\;d^{-1}$ at low density, and 105.2, 119.2, 141.5, and $168.8\;mg\;TAN\;kg^{-1}\;d^{-1}$ at high density, respectively. Mean daily exogenous TAN excretion rates at 10, 15, 20, and $25^{\circ}C$ were 343.5, 403.7, 535.7, and $601.7\;mg\;TAN\;kg^{-1}\;d^{-1}$ at low density, and 391.9, 479.7, 611.9, and $683.4\;mg\;TAN\;kg^{-1}\;d^{-1}$ at high density, respectively. The exogenous TAN excretion rate peaked 10~12 hours after the first feeding under all temperatures and densities. The TAN loss for ingested nitrogen increased with increases in temperature and density (P<0.05), ranging from 27.9 to 50.1% at low density and 31.7 to 56.9% at high density. This study provides empirical data for estimating ammonia excretion and managing the culture of red seabream under the given temperatures and densities.