博士 / 國立臺灣海洋大學 / 海洋生物研究所 / 104 / Copepods, as the main component of the meso-zooplankton, play an important role in pelagic systems in linking the lower trophic levels to the highest ones. In natural environments, carnivorous fish larvae prefer to capture and consume live feed, and copepods represent one of their most common food items. To provide a superior live feed for fish larvae in aquaculture, species of copepods are used aiming to increase the survival and the quality of the fish. In fact, copepods are interesting candidates to replace rotifers and Artemia due to their adequate size and higher nutrient content. In the aquaculture industry, native copepod species are preferred due to their adaptation to the local climate and environmental conditions, but their availability in terms of biomass is still an issue to solve. To establish necessary fundamental knowledge, the intent of the study was to describe the pelagic food web dynamics in two semi-intensive copepod farms. In Denmark live copepods are cultivated to feed turbot larvae, while in Taiwan they are cultured for grouper larvae feeding. The ecology, biology, and physiology of the major copepods species as well as farming techniques were studied over the course of 3 years.
In Denmark copepod abundances in production tanks were defined to be insufficient to sustain high survival rates of turbot larvae. A manipulation study with the addition of nutrients was accomplished to boost phytoplankton biomass and cascade into better fitness of copepods which, increasing in density, will fulfill the needs of the fish larvae. The study was successful, and higher density of copepods was reached, however the high level of nutrients governed the phytoplankton community that changed from diatom dominated to dinoflagellates. High pH and the presence of nuisance dinoflagellates reduced the survival of fish larvae in nutrient amended treatment and caused a shift in copepod species, with Acartia spp. taking over Centropages hamatus. Furthermore, resting copepod eggs of mainly Acartia spp. were found in great amount in the sediment of the tanks after the removal of seawater at the end of the production cycle. Those eggs could be collected, stored and hatched at the exact time when the turbot larvae start feeding. The use of nutrient-enriched copepods and the collection of resting eggs would potentially solve the need of adequate prey field when turbot start first feeding. Moreover, copepod production tanks would be separated from fish tanks to avoid water quality issues causing unwanted mortality.
With regard to Taiwan, this study presents the first description and recording of copepod cultures and their productivity. The copepod community in Taiwan was characterized by low species diversity and revealed no differences in species composition, with Pseudodiaptomus annandalei as the main species. The first campaign revealed that P. annandalei is an optimal candidate for live feed considering its strong resistance to different culturing conditions, fast growth and high FA content. During a yearlong study, the productivity of copepods and abundances remained quite stable, even though environmental changes were observed. However, copepod growth was lower compared to the first campaign and differed in FA composition, indicating that growth was dependent on the food available in the water column, considering both the type of phytoplankton and fish meal used as fertilizers. It was perceived that farmers exclusively collected adult copepods and copepodites as live feed for grouper, whereas nauplii, found in great measure, were not considered. To increase the income of the farmers, taking into consideration the sustainable actual harvest pressure, we estimated that the copepods and copepodites harvest could be doubled; moreover, nauplii could also be collected and be sold to feed fish larvae other than grouper at first feed.
This comparative study leads to a better understanding of copepod farming for use as feed for fish larvae as well as it helps to draw recommendations on how to improve the copepod aquaculture industry in both Denmark and Taiwan.
| Identifer | oai:union.ndltd.org:TW/104NTOU5270003 |
| Date | January 2015 |
| Creators | Elisa Blanda, 艾莉莎 |
| Contributors | Hwang, Jiang-Shiou, Benni Winding Hansen, 黃將修, Benni Winding Hansen |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 304 |
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