| Benthic diatoms collected from hanging cages which were suspended beneath the surface of the coastal seawater near the seed production hatcheries were isolated by spreading plating method and their potential as food for aquaculture evaluated based on their biology characteristics, nutritional component, growth conditions and application to sea animals.The results show that there are eight benthic diatoms which are Rhaphoneis surirella, Navicula seminulum, Hantzschia amphioxys var. leptocephala, Amphora proteus var. oculata, Navicula corymbosa, Nitzschia sp., Navicula parva and Amphora coffeaeformis. All species were within the size range ingested by juvenile sea urchins and postlarval abalone, i.e. 6.7μm×3.3μm-35.9μm×9.6μm. Cellular growth rates ranged from 0.44 divisions·day-1(Rhaphoneis surirella) to 0.73 divisions-day-1(Navicula seminulum).The contents of protein, intracellular carbohydrate, extracellular carbohydrate, lipid and ash weight from eight benthic diatom species at four growth rates are 1.21%-9.73%,2.67%-20.76%,2.08mg/L-16.23mg/L,26.03%-50.71%and 18.18%-48.10%, respectively. Protein contents of N. seminulum, H. amphioxys var. leptocephala, Nitzschia sp. and A. coffeaeformis are higher than other diatoms. The contents of intracellular carbohydrate and extracellular carbohydrate from Nitzschia sp. and A. coffeaeformis are higher. Lipid content of A. proteus var. oculata is the highest in all diatoms. Ash weight of R. surirella is highest than the others. The fatty acid composition differs between diatoms at different growth phases. Among them, N. corymbosa is most abundant in fatty acid composition, and there are EPA and DHA in N. seminulum, H. amphioxys var. leptocephala, N. corymbosa, N. parva and A. coffeaeformis. Moreover, all diatoms are also rich in Mineral-element compositionNutritional component showed significant differences between diatoms at 3, 8, 15 and 25 days. Highest contents of protein and intracellular carbohydrate from diatoms are found at 8 and 15 days. Extracellular carbohydrate contents of diatoms increase always during the experiment. Highest lipid content is found at day 8. Diatoms have the highest amounts of ash at 3 and 25 days. Fatty acid is most abundant at day 15.The favourable and optimum temperature, light intensity, salinity and pH conditions for eight benthic diatom species are 15℃-30℃and 20℃-25℃, 500 lx-9500 lx and 1500 lx-55001x, 25-50 and 30-35, 7-9 and 8-8.5. Temperature and pH do less significantly affect all nutrient contents of diatoms. Protein contents of diatoms increase under lower temperature condition, while lower and higher temperature affect lipid contents of diatoms. Light intensity and salinity do less significantly affect protein and intracellular carbohydrate contents of diatoms, and significantly affect extracellular carbohydrate and lipid contents of diatoms. Nutritent contents are higher at lower and higher light intensity than at optimum one. Protein contents of diatoms cultured under lower salinity condition are higher, and intracellular carbohydrate, extracellular carbohydrate and lipid contents cultured under higher salinity condition are higher.A significantly higher number of larval abalone settled on N. seminulum, H. amphioxys var. leptocephala and compared to the control and others plates. Moreover, Nitzschia sp. and N. corymbosa strongly induce larval settlement of Strongylocentrotus intermedius and Haliotis discus hannai. Growth and survival of abalone are also greatest on R. surirella, and that of sea urchin on Amphora proteus var. oculata are higher than ones on other diatoms. Nitzschia sp. and N. corymbosa also accelerate growth and survival of S. intermedius and H. discus hannai. These results indicate the effectiveness of Nitzschia sp., R. surirella, A. proteus var. oculata and N. corymbosa as single species over mixed diatoms and natural diatoms in larval settlement and juvenile growth of S. intermedius and H. discus hannai. |
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