| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 99 === Four experiments were conducted to assess the feasibility of applying Yucca schidigera extract (YUPE) on the culture of orange-spotted grouper (Epinephelus coioides) and red striped snapper (Lutjanus erythropterus♀ x Lutjanus sebae♂).
Experiment I was aimed to find out the effects of YUPE addition on the reduction of ammonia in water rearing grouper. Water which was collected from a grouper rearing tank, containing 3.5 mg L-1 TAN (total ammonia nitrogen), was diluted for 0, 2, 4 and 8 folds (denoted as D0, D2, D4 and D8) and then added with YUPE at 0, 18, 36, 72 and 108 mg kg-1 (denoted as Y1, Y2, Y3 and Y4). TAN, NO3-N, NO2-N and pH were monitored for 30 h. The higher concentration of YUPE added, the more TAN was reduced. For the two higher dilution or lower initial TAN groups D4 and D8, YUPE was able to reduce their TAN 100% within 30 h. For the highest initial TAN group D0, the highest YUPE addition Y4 could reduce maximum 52.6% TAN at 30 h. NO3-N and NO2-N had same change pattern, their concentration generally increased from 6 h to 18 h and then decreased. It appeared that a nitrification process might occur. The value of pH decreased rapidly from 7.77 to 7.23 within the first 6 h then stabilized.
Experiment II was to assess the effects of dietary supplement of YUPE on ammonia excretion of grouper. TAN in water of grouper (186.5±20.2 g) fed diet containing YUPE at 300 and 150 mg kg-1 was significantly lower than the control 9 h and 15 h post-feeding, respectively. TAN in water at 24 h was inversely related to dietary YUPE concentration.
Experiment III was to compare between liquid and powder YUPE dietary supplement on the rearing and ammonia excretion of snapper. Snapper of initial size 16.86±0.14 g were fed control (C) diet and diets containing YUPE effective concentration equivalent (ECE) at 18 mg kg-1 diets of all liquid (L), all powder (P), and mix (M) of half of L and P. ECE was obtained by estimating ammonia reduction capacity at YUPE addition in water. After 8-week rearing, the sequence in descending order was C≧M=L≧P for survival and C≧M = L≧P for growth. Treatment had no effects on ammonia excretion.
Experiment IV had similar purposes as Experiment III but differed in approach by fish and size, grouper of initial size 122.3±0.54 g and effective YUPE concentration 150 mg kg-1. No fish died in 8-week rearing. Treatments had no effects on growth and blood ammonia. TAN concentrations in water were C≧P≧M=L.
In overall, YUPE reduced TAN 6 h after its addition in water but increased NO3-N and NO2-N until 18-24 h then decreased, depending on concentration of initial TAN and YUPE. The value of pH decreased during first 6 h and then stayed steadily. The effects of dietary supplement of YUPE on rearing performance and water quality can vary with fish species and size and YUPE concentration and forms. The effects of dietary YUPE on digestive physiology require further studies.
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