Effects of Feed Additive Ulva Reproduced in Feedback Culture System on the Growth and Color of Red Sea Bream, Pagrus major

Abstract

In order to maintain the homeostasis of ecosystem in the water, a feedback culture system was examined for rearing the red sea bream, Pagrus major juvenile.
Six “pan-light” tanks (A: 500l×2; B: 100l×2 & C: 100l×2) were set outdoors at a rearing place with transparency plastic roof. The water recirculated in arrange of tank A→B→C→A by an air-lift pump. The tanks A both in the feedback and control experiments were employed for rearing the red seabream (1.1g in initial average body weight) . The tanks B and C in the feedback experiment were used for reproducing the sterile Ulva pertusa. The U. pertusa harvested from those tanks were powdered and additively feed back to the fish (15.7g w.w. Ulva/84.3g moist pellet) . No Ulva was reproduced in tanks B and C in control experiment.
Results showed that the survival rates were 94% and 62 % in feedback experiment and control, respectively. Daily growth rates of the fish in feedback experiment and control were 44.5% and 31.5%, respectively. The food conversion ratio were 4.21 and 6.16 in feed-back experiment and control, respectively. Body color of the red seabream cultured in the feedback experiment was more reddish than that of the fish in the control. Average NH_4-N and NO_3-N in the water during the experiment were 100.7μg-at⋅l^-1 and 27.3μg-at⋅l^-1 in the feedback experiment, and 284.0μg-at⋅l^-1 and 43.1, 1μg-at⋅l^-1 in the control. Averag e PO_4-P in the water during the experiment were 2.4μg-at⋅l^-1 and 4.9μg-at⋅l^-1 in the feedback experiment and control, respectively.