EFFECT OF RATION LEVELS ON NITROGEN BUDGET IN JUVENILE BLACK PORGY (SPARUS MACROCEPHALUS)

Four feeding-growth experiments on juvenile black porgy (Sparus macrocephalus) were carried out during August-November in 1994 at a mean seawater temperature of 26.8℃, 24.4℃,20.1℃ and 14.8℃, respectively. The fish, reared in 801 aquarium (pH = 8.0, salinity = 32), were fed Ammodytes personatus at 4 ration levels from starvation to ad libitum The introgen intake,faeces and retention were measured and the nitrogen excretion were calculated using the nitrogen balance equation (CN = FN + UN + GN ). The nitrogen intake [mg / (g. d)] increased with ration levels (%). Nitrogen fasces [mg / (g. d)] also increased with ration levels at 26.8℃ and 24.4℃, but a maximum appeared in the second highest ration levels at 20.1℃ and 14.8℃. The relationships between the nitrogen excretion and ration levels are similar to those between nitrogen intake and ration levels. At the maximum ration, nitrogen intake, fasces and retention [mg / (g. d)] decreased with decreasing temperture and increasing body weight. At starvation the nitrogen excretion [mg /(g d)] changed a little and ranged 1.04-1.41 mg / (g d).The nitrogen budget for the black porgy changed with ration levels. The nitrogen excretions as percentage of nitrogen intake are the highest among the compopents in the nitrogen balance equation,At the maximuxn rations the nitrogen excretion decreased with decreasing tempebe and increasing body weight. The nitrogen excretion (%, nitrgen intake) was positively correlated with ration levels at 26.8℃ and 14.8℃. The nitrogen retention (%, nitrogen intake) efficiency decreased with decreasing ration levels, but a maximum appeared at 4.07% of ration level, not the maximum ration,at 24.4℃. At the maximum ration, the nitrogen retention efficiencies changed in the range of 5.81%34.20%. The nitrogen retention (mg / d) was positively cormlated to nitrogen intak (mg / d) and nitrogen absorption (mg / d).