Thesis (Ph.D.)--Chulalongkorn University, 2007

This study consisted of three experiments, i.e. (1) Effect of L-carnitine on microalga Tetraselmis suecia, rotifer Brachionus plicatilis and larval seabass Lates calcarifer (2) The use of L-carnitine to enhance growth of rotifer B. plicatilis in recirculation culture system and (3) The development of closed-recirculating, continuous culture system for microalga T. suecica and rotifer B. plicatilis. The results revealed that T. suecica enriched with 0.1, 1 and 10 mg l[superscript -1] L-carnitine exhibited significantly higher specific growth rate than the control. The best specific growth rate was found at 10 mg l[superscript -1] L-carnitine. L-carnitine content in T. suecica ranged from 258-1,813 [micro]g g[superscript -1] dw and the highest was at 10 mg l[superscript -1] L-carnitine. The results of the study on the effect of L-carnitine on rotifer showed that growth of rotifer fed on T. suecica, that enriched with 1 mg l[superscript -1] L-carnitine was greater than other treatments, while the highest L-carnitine content has been found in rotifer that fed on T. suecica enriched with 10 mg l[superscript -1] L-carnitine. The experiment on rotifers fed an emulsion diet showed that the highest L-carnitine content has been found in rotifers enriched with 10 mg l[superscript -1] L-carnitine emulsion for 4 h. The study on the effect of L-carnitine on growth, survival and L-carnitine content of seabass larvae showed that the larvae fed on rotifers (that consumed T. suecica enriched with 10 mg l[superscript -1] L-carnitine) and rotifers fed on both with and without emulsion diet with 10 mg l[superscript -1] L-carnitine for 4 h were significantly larger in total length than other treatments. While the larvae fed on rotifers that consumed T. suecica without L-carnitine enrichment and no emulsion (control) were smallest. No significant difference has been found in the weights of rotifers of all treatments. The survival rates of fish larvae in all treatments were higher than the control treatment. The treatment of larvae fed on rotifers that consumed T. suecica enriched with 10 mg l[superscript -1] L-carnitine and rotifers fed on emulsion without L-carnitine showed the highest survival rate (39%). L-carnitine content in fish larvae were not detected in the control treatment and the treatment of larvae fed on rotifers that consumed T. suecica without L-carnitine enrichment, and rotifers fed on emulsion without L-carnitine. The results suggested that the treatment of rotifers fed on emulsion enriched with 10 mg l[superscript -1] L-carnitine for 4 h could be used for feeding of seabass larval. In the second experiment, the use L-carnitine in rotifer recirculation culture system at the initial cell density of 500 ind.ml[superscript -1] and exposed to 1 mg l[superscript -1] L-carnitine for 48 h. was conducted. The result showed that population density of rotifers exposed with L-carnitine was higher than control treatment from day 3 to day 9 of the culture period. There was no difference in water quality between two treatments, except for ammonium concentration. The final experiment was to develop and operate a closed-recirculating, continuous culture system to produce microalgae and rotifers for larval fish culture. This new, automated system had three sub-components, including an alga culture component, a rotifer culture and storage with harvest component and a water treatment and re-use component. Our trials with the closed-recirculating, continuous culture system demonstrated that this culture system is capable of sustained and acceptable levels of microalgae and rotifer production for at least 28 days. During a continuous culture trial, microalga T. suecica production averaged 1.63x10[superscript 10] cells day[superscript -1] while rotifer B. plicatilis production averaged 4.6x10[superscript 6] ind.day[superscript -1]. This 28 day culture trial demonstrated the benefits and advantages of this culture system compared with more commonly used batch or semi-continuous culture system for microalgae and rotifers.