| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 99 === The indoor rearing of Grouper fingerlings has received tremendous attention nowadays. In order to increase feed intake and avoid cannibalism in the indoor rearing, net cage culture has been widely practiced. However, it cuts off water flow and brings feces to sewage drainage holes in the center at the bottom of tanks, which consumes more manpower and time in changing the water and cleaning the bottom. In addition, feces in the bottom results in water pollution. Consequently, reduction in the amount of residues at the bottom of Grouper net cage nursing tanks is a major issue in the rearing of Grouper fingerlings.
The current study designs an apparatus, called solid substance（SS）collector, which can automatically clean the bottom residues. This apparatus is to set up extra tubes external to the drainage pipes of the nursing tanks. The top of the tubes is equipped with leaves whereas its bottom close to the bottom of the tanks is installed with two horizontal syphon tubes. Given both the use of water flow facilitated by pouring water into the tanks to rotate the tubes and the disturbing activities by the syphon tubes, the bottom residues easily come off, float and are suched into the tubes along with the water flow through syphons, which are, in turn, discharged out of the pools through the drainage pipes. This design cleans the bottom residues. To gain a full understanding of the workability of this apparatus, the parameters for water quality and the amount of collected bottom residues are considered as criteria for assessing the removing effect of residues of this apparatus.
In the present study, three experiments were conducted to test the residues removal effect of the apparatus. The first one is to investigate a difference between the use of a cage rotation SS collector (System A) and the nonuse of a SS collector (System B) in 48hr fixed quantity feeding (210g/3 times a day) with the aim of testing whether the use of the collector has any influence on the improvement of water quality. A distinction between groupers reared in the net cage and that reared without cage, the second experiment is intended to examine a difference between the use of a cage with rotation SS collector (System A) and without cage with the collector (System C) in 48hr fixed quantity feeding (210g/3 times a day). Last, the third experiment aims to test a difference between System A and the use of an air lift particle collector (System D) in water quality in order to measure the residues removal effect of the two collectors (System A and System D).
The results of the first experiment indicate that the amount of ammonia nitrogen (N), nitrite-N and nitrate-N in System A is lower than that in System B, so is the amount of solid substance (SS). The first experiment yields support for the use of a cage rotation particle collector in improving water quality. Along the same line, the results of the second experiment point out that water, due to the nonuse of a net cage that the movement of grouper causes the bottom residues to break, is therefore polluted. In consequence, the amount of ammonia nitrogen (N) and nitrite-N in System C is higher than that in System A, so is SS. Also, the residues collection in System B is lower than that in System A. Lastly, the results of the third experiment show that the amount of ammonia nitrogen (N) in System D is higher than that in System A but the amount of nitrate-N in between System D and System A shows no significant difference. In addition, the amount of SS and residues collection in System A is higher than that in System D.
Throughout the experiments conducted above, the installment of the cage rotation SS collector is proved to improve water quality to the effect that feces and food residues at the bottom of nursing tanks can be removed. This apparatus is mainly designed for grouper fingerlings reared in the net cage. If the fingerlings are reared without the cage, the removal effect of this apparatus is not significant.
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