| Summary: | 碩士 === 國立中山大學 === 海洋資源學系 === 87 === The purpose of this study is to compare the dissolution of the eel floating feed with pasted feed in the water, and the impact of the aforesaid two feeds on the growth of the germs in the water and the change of the water quality when the remaining feeds are not recollected. Three devices of still, cyclic flow, and cyclic water flow with exposed air container are designed for comparing the influence of the water flow and soluble oxygen on the feeds. The difference between various brands, the impact of various temperatures on the pasted feed, and the influence of surface area on the pasted feed are also examined.
In the light of the dissolution condition of the floating and pasted feed in the water, the recollection rate may be above 80% if the feeds are collected before 9 and 4 hours, respectively. After that, the dissolution will speed up. After 14.5 and 6 hours, the recollection rate will be less than 5%, and the feed sediments will occur in the water.
Provided that the remaining feed is not recollected, the average PO4-P of the floating feed generated under the three devices will be 1.8 times the average of that of the pasted feed, while the average of Ammonia-N in the device of still and cyclic flow is 2.5 times the Ammonia-N of the pasted feed's. The initial ascending rate of the turbidity is also higher in floating feed than that in pasted feed (namely, the dissolved rate of the feed), yet no difference is shown as they reached the highest turbidity. Under the same device, there is neither significant difference between the oxygen-soluble saturation's descending rate of the floating and pasted feed, nor on the following: the growth rate of the active germ and inactive germ; and the average of NO2-N, NO3-N and PO4-P. In addition, under different devices, the descending oxygen-soluble rates of the floating and pasted feed in the still and cyclic water-flow devices are higher than those of the cyclic water which is connected to exposed air container, and thus lead to great distinction. The germs grow rapidly with water flow (cyclic water flow and exposed air container connected cyclic water), in which the total of the germs is 10 times the number of the other two devices when the degree of the oxygen-soluble saturation is maintained above 60% (exposed air container connected cyclic water). In regards to the ascending rate of the water turbidity caused by the feed, the said rate of the floating feed in the exposed air container connected cyclic water is higher than the cyclic water flow and still devices, while that of the pasted feed in the exposed air container connected cyclic water and cyclic water is a great deal higher than it is in the still one.
Among different brands, the highest average PO4-P of the floating feed is 1.8 time the lowest, and is 2.8 time in the pasted feed. And the clearest distinction between floating and pasted feed is 2.7 time in the same brand. If the turbidity of this kind of floating feed is higher, then the pasted feed of the same brand is higher. But the average PO4-P of this brand is lower. These are due to different phosphate composition among different brands, and the different production process between the floating and pasted feed in the same brand. In the water with pasted feed, the germs grow quicker in 300C than 200C, in which the number of germs in the former is ten times the amount of the latter; the ascending rate of the water turbidity is 5.7 times the rate in 200C; 4.7 times the PO4-P, and 1.7 times the average of Ammonia-N, while no sign of great variance in NO2-N and NO3-N. The enlargement of the pasted feed's surface area will have significant impact on the turbidity, number of germs, and oxygen-soluble saturation, and the points of NO2-N, NO3-N and PO4-P are also higher. When the surface area is enlarged to 1.8 and 2.5 times, the ascending rate of turbidity will be doubled, with no significant difference when the rest of the factors are above 1.8 times. However, the small surface area of the pasted feed may accumulate the Ammonia-N.
The surface area of the floating feed is 8 times that of the pasted feed of equivalent weight. When the surface area of the pasted feed is enlarged to 2.5 times, the turbidity, PO4-P, and the descending oxygen-soluble condition of the floating and pasted feed are quite similar. Hence, the surface area is also a factor that leads to the different water quality between the floating and pasted feed. According to this research, when the remaining baits are not recollected, the pasted feed has less impact on the water quality than the floating feed. Namely, although the pasted feed will dissolve quicker in the water, its dissolved amount is not more than the floating feed's, and thus results in a view which is different from the normal opinion that the floating feed may keep the water quality better.
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