博士 / 國立臺灣海洋大學 / 海洋生物研究所 / 107 / Since the early 90´s, the world’s fisheries have stagnated and today, around half of all fish comes from aquaculture. The aquaculture industry is the fastest growing food sector, but the industry has difficulties with domesticating many fish species. One of the main limitations is the initial diet for the fish larvae. Fish larvae are visual predators, and for many species, live feed is a necessity. Copepods have been found to be an ideal live feed, because of a high nutritional quality compared to the predominantly used live feeds; rotifers and Artemia. Further, fish larvae shows a preference for copepods compared to when offered rotifers and Artemia. Difficulties in production of copepods have, so far, limited their usage in larval fish production. The growth of fish larvae is dependent on the energy content of its prey. The energy content of a copepod increase with its size, and a fish larva should therefore be offered the maximum size that it can effectively capture. This thesis investigated in four studies the relevance of copepod size for fish larvae culture. How effectively a fish larva could capture various sizes of copepods, and which copepod sizes that was optimal for a fish larva through its ontogenetic development. Further, it was investigated how to produce set sizes of copepods and how to implement it in a larval fish production. This has been assessed by behavioural, physiological and ecological studies of copepods and fish larvae in Denmark and Taiwan.
A copepod life cycle consists of a number of development stages, where the morphology and motility change significantly, which might affect the ability of a fish to detect the copepod. Adult copepods and the initial live stage of copepods, nauplii, were offered to juvenile false particular clown fish. The clownfish reaction distance to nauplii was significantly shorter than to adult copepods. This was compensated by the clownfish by reacting to the nauplii in a large arc, which resulted in an equivalent attack rate. When the prey is perceived and the fish advance towards the prey, it needs to remain stealthy in its approach to avoid detection by the prey. The capture efficiency and approach kinematics for the initial life stages of turbot larva were investigated when offered various sizes of copepods. The ability of the turbot larvae to capture small nauplii did not change significantly through their development, but the ability to capture large nauplii increased with the development of the fish larvae. The capture success of the larvae was found to be dependent on their approach, where the speed was the controlling factor. The fish larvae used the same approach speed for all sizes of copepods, but changed the approach speed depended on the age of the larva. This indicates that fish larvae employ a specific approach kinematic dependent on their age, and the prey size should therefore correlate with its approach capabilities. An efficient use of an appropriate copepod size requires a high production of copepods of those specific sizes. The typical production form for copepods in Taiwan is extensive large open ponds, where the common copepod species is the egg-carrying copepod Pseudodiaptomus annandalei. The harvest of copepods from these ponds is often limited by a low density of copepods. To test if they are density limited, adult P. annandalei were stocked in the laboratory at increasing densities. The number of ovigerous copepods was used as a proxy for nauplii production. The rate of ovigerous copepods decreased when the stocking density reached the densities typically observed in Taiwanese copepod ponds. The current harvest techniques in Taiwanese ponds only permit the harvest of adult copepods. A user friendly protocol was developed on how to produce distinct size fractions of nauplii from adult copepods without separating each size fraction of nauplii mechanically. Four narrow size fractions of nauplii were produced with significantly different size, fatty acid content and escape performances. Each size group was starved for 48 hours to test if each size group would maintain its distinct size by starvation. Minor growth was observed under the starvation, and they maintained their distinct size groups. However, the fatty acid content and escape performance was highly reduced.
To solve the bottleneck of producing fish larvae for on-growth, the correct size of live prey through the ontogenetic development of the fish larva is essential for a further growth of the aquaculture industry. There is no doubt that copepods, as the initial live feed, are the answer to production of new fish species.
| Identifer | oai:union.ndltd.org:TW/107NTOU5270004 |
| Date | January 2018 |
| Creators | Jacob Kring Højgaard, 亞克柏 |
| Contributors | Hwang, Jing-Shiou, 黃將修 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 115 |
Page generated in 0.0022 seconds