DIURNAL CHANGES IN GROSS CHEMICAL-COMPOSITION AND FATTY-ACID PROFILESOF ISOCHRYSIS-GALBANA TK1 IN OUTDOOR CLOSED TUBULAR PHOTOBIOREACTORS

Isochrysis galbana TK1, a widely used phytoplankton feed in marine fis h larviculture due to its high level of essential fatty acids, was gro wn in a closed tubular photobioreactor. The diurnal changes of total l ipid, carbohydrate, protein, fatty acid profile, and cell surface area were measured. When expressed as a percentage of biomass dry weight, carbohydrate showed a change parallel to light intensity and temperatu re. In contrast, the variation of protein was the reverse of the chang e in carbohydrate. When expressed as a ratio to protein, both carbohyd rate and lipid showed a change parallel to light intensity and tempera ture. The fatty acid profile changed as follows: C18:0 and C18:1 accum ulated during the day while PUFAs, including C18:2, C18:3, C18:4, C20: 5 and C22:6, and the saturated fatty acid, C16:0 increased in the dark . The results show that the nutritional value of I. galbana biomass, u sed in fish laviculture, could vary with time of harvest of the algal culture.