| Summary: | 碩士 === 國立臺灣海洋大學 === 水產養殖學系 === 93 === In developing countries not having aquaculture industry, it is very necessary to develop relevant fish diets based on locally available and low cost foodstuffs. Five experiments were conducted indoor to determine best ways to produce duckweed, and its use with rice bran and blood meal to efficiently feed juvenile tilapia at farm level.
Experiment 1- Productivity of Lemna perpusilla and Spirodela polyrrhiza was comparatively tested in various environments. Duckweed productivity in spring was higher than that in winter. L. perpusilla had higher productivity than S. polyrrhiza. Sediment was a steady nutrient provider and consequently favored duckweed productivity. One-time fertilization did not have effects on nitrogen nutrient in water nor duckweed productivity. Besides productive species, optimal growing season, contribution of nutrients from sediment, and routine harvesting should be also taken into account in duckweed culture.
Experiment 2- We studied feeding preference of 3 sizes of juvenile tilapia for L. perpusilla and S. polyrrhiza. Fish preferred L. perpusilla. Duckweed fronds width appeared as a factor affecting such preference.
Experiment 3- We assessed the effect of fish stocking density on ingestion of duckweed at 2 temperatures. At 24oC, ingestion rate increased with stocking density but not in the case at 27oC. Specific and various behaviors that affected feeding of fish were observed at 1 and 2 fish/bucket.
Experiment 4- The efficiency of fresh L. perpusilla, pure L. perpusilla pellet and L. perpusilla mixed with rice bran pellet was determined. Pelletization of L. perpusilla reduced dietary performance as compared to fresh material, while 25% rice bran incorporation increased pellet dietary performance. Methionine supplement through rice bran inclusion could explain such improvement.
Experiment 5- The optimal percent of blood meal in rice bran pellet in terms of palatability, and food utilization, between 5, 12, 20, 27, 33, 40% was determined. Blood meal inclusion negatively affected feed intake rate; 7.9% blood meal level was found as maximum giving highest feed intake rate. Among the diet types tested, one with 12% blood meal gave the best fish growth and food utilization.
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