EFFECT OF PHYTASE ON GROWTH PERFORMANCE, MINERAL COMPOSITION, AS WELL AS PHOSPHORUS AND NITROGEN EXCRETION OF JUVENILE RED DRUM Sciaenops ocellatus

A 9-week feeding trial was conducted to evaluate the effects of  dietary  phytase on  phosphorus  (P) utilization of juvenile red drum (Sciaenops ocellatus) .  Two control diets were designed to contain 40% crude protein primarily contributed by menhaden fishmeal and  plant-protein feedstuffs. One diet without extra monocalcium P supplementation was the negative control diet and contained 0.56% available P (0.77% of total P ). The positive control diet was supplemented with monocalcium P to achieve the  previously established  minimum  dietary P requirement (0.7% of dry diet) . Another four experimental diets were formulated by adding phytase (Quantum Blue Phytase, AB Vista) at 1000, 2000, 4000, or 8000 FTU/kg to the negative control diet.  A total of 480 fish (initial weight 4.99 ± 0.09 g/fish) were assigned  as groups of 20 fish  to 24, 110-L glass aquaria connected as a closed-recirculating system maintained at 7 ppt salinity. E ach dietary treatment  was  randomly assigned to  quadruplicate aquaria. Fish were fed twice daily at representative percentage of body weight that approached apparent satiation and was adjusted weekly after group weighing .  In addition, at the end of the trial, P and nitrogen  (N)  excretion of fish  after feeding was quantified at different time intervals as well as disappearance of N and P from different sections of the gastrointestinal tract .

After the 9-week feeding period, there were no significant (P < 0.05) differences i n survival, hepatosomatic index, or intraperitoneal fat  ratio  among  fish fed with  various  experimental diets. However, c ompared to fish fed the negative  control  diet,  those  fed  all other diets had significantly increased weight gain and feed efficiency (Table. 1) . In addition, fish fed  the  diet supplemented with 8000 FTU/kg of phytase had significantly higher weight gain and muscle yield than fish fed  the  positive  control diet. More results will be supplied after remaining samples are analyzed.