Search

The n-3 long chain polyunsaturated fatty acids (LC-PUFAs) are well studied bioactive molecules with important health benefits. These have gained tremendous importance and the global demand of these-PUFAs have risen during last decade. As humans other animals do not carry the require genes necessary for the formation of n-3 fatty acids these must be obtained from other natural sources. The current natural source of n-3 PUFAs is fatty fishes which accumulate these fatty acids in their oil due to its alga rich diet. In recent past excessive harvesting of sea fishes for its health benefits have rendered fisheries to be unsustainable making it important to explore alternate sustainable n-3 PUFA sources. Eukaryotic algae are a very diverse group of organisms capable of producing various bioactive compounds. Lipid analyses of various algae have shown the presence of n-3PUFAs especially EPA and DHA. Various genera of algae such as Nannochloropsis, Schizochytrium, Isochrysis and Phaeodactylum have received due attention for their ability to produce n-3 LC-PUFAs. Isolation and characterization of various desaturases, elongases and other genes involved in n-3 PUFA biosynthesis has been a major target to understand lipid biosynthesis in algae. Marine microalgae are rapidly gaining identity as the alternate natural source for industrial production of EPA and DHA.

Collection and culture of live foods to be used in studies of feeds for rearing finfish and shellfish larvae in Taiwan began in 1982. Today, 31 species (49 strains) of microalgae, three species (nine strains) of rotifers, one cladoceran and one copepod are hold as start culture. Microalgae are collected from local waters and obtained from foreign collection centers. The most common genera are Chlorella,Nannochloropsis, Tetraselmis, Chaetoceros,Skeletonema,Isochrysis, and Pavlova Some interesting genera such as Ellipsoidion, Nannochloris, Synechococcus, and Alexandrium are also included. Three types of rotifers, i.e. L, S, and SS-type, which are classified as Brachionus plicatilis,B. rotundiformis,and Brachionus sp. are found in Taiwan waters. Among the rotifers, six strains have been isolated and cultured. Another L-type strain and two SS-type strains were obtained from foreign sources. The cladoceran Diaphanosoma aspinosum and copepod Apocyclops royi are the most common species used in aquaculture. Studies of live foods including their morphology, culture techniques, fatty acid composition and nutritional value as feeds have been undertaken.

The overall status of seedling production in Korea is discussed. In shellfish culture, such as oyster and ark shell, seedlings are obtained by natural seedling collection. Shellfish seedling production has been decreasing rapidly due to coastal pollution and continuous dense culture over the years. This has lead to the development of artificial production of shellfish seedlings. However, the mass production of seedlings in the hatchery is not yet fully developed in Korea. Isochrysis, Pavlova, Chaetoceros and Thalassiosira are the main live food organisms for the artificial seedling production. These species can be cultured indoors, but the technology for their outdoor culture is not established.

Fertilized oyster eggs, S-rotifer (Brachionus rotundiformis) and SS-rotifer (Brachionus sp.), were tested either solely or in combination for their suitability as feed for early stage grouper (Epinephelus coioides) larvae. Sizes of S-rotifers ranged between 143–224 µm lorica length with mean 182±21µm, and SS-rotifers between 122–176pm lorica length with mean 154±13µm. The results indicated that both fertilized oyster eggs and SS-rotifers were suitable as feed at F1 (first feeding day). However, poor growth was recorded when providing oyster eggs solely for the periods F1–F3. Although growth of larvae at F6 had no difference between the sole SS-rotifers and the oyster eggs additionally provided for Fl–F3, better survival of larvae at F15 was obtained when providing combinations of SS-rotifers with oyster eggs for F1–F3. Besides, better growth and survival of larvae at F15 was found when providing S-rotifers enriched with Kirin yeast for F7–F15. The highest survival and fastest growth of larvae at F15 was found when providing oyster eggs for Fl–F3, SS-rotifers for F1–F6, S-rotifers for F7–F15, both rotifers enriched with Kirin yeast, and Isochrysis for Fl–F15. Total fatty acid (TFA), EPA, DHA content, and DHA/EPA (DIE) ratio of larvae changed with their sizes and corresponded to that of their feeds. The F15 larvae having a higher TFA grew faster, having higher DHA or EPA survived better.

A detailed study of the life history of the rotifer Brachionus plicatilis was done at 20 °C, 20 ppt salinity, and 90 mg C 1−1 food concentration. Rotifers were grown individually in culture plate wells (150 µl culture volume) and fed Isochrysis galbana Tahiti, Tetraselmis sp., Nannochloris atomus, or a l : 1 mixture (weight) of two of the algae. Observations were made every 2–8 hr and rotifers were sized and transferred to new food daily. A total of 19 different parameters were compared. Rotifers fed Isochrysis averaged 21 offspring per female, a 6.7 day reproductive period, a lifespan of 10.5 days and a mean length of 234 µm. After Isochrysis, the foods giving the highest growth, survival, and reproduction in decreasing order were Isochrysis + Nannochloris, Nannochloris, Isochrysis + Tetraselmis, Tetraselmis + Nannochloris, and Tetraselmis. Although the small volume culture system used in this study seems appropriate for studying life history of B. plicatilis, the results cannot always be directly applied to larger cultures.