Microalgae are an exceptional source of polyunsaturated fatty acids, vitamins, proteins, carbohydrates and amino acids that can improve fish growth. Their biomass nutritional value is determined by these nutrients and therefore, parameters affecting growth and biomass composition (pH, growth media, temperature and photoperiod) are often adjusted.
Tetraselmis striata was cultivated in drilling waters (salinity 29 ‰) obtained from the commercial fish farm Plagton S.A.. Previous studies showed that the microalga displayed optimum growth using 0.2 gr L-1 of the commercial fertilizer Nutri-Leef (30%-TN, 10%-P, 10%-K) together with an inorganic carbon source (0.18 gr L-1, NaHCO3) at a pH value of 8. Under these optimized conditions, the effects of photoperiod and temperature on growth and biomass composition were evaluated. Initially, the photoperiod effect was studied at a temperature of 25 ±1oC. Tetraselmis was cultivated in constant light (24:0, L(Light):D(Dark)) and then 20:4, 18:6, 12:12 L:D exposure. The results revealed that biomass was significantly affected by light absence. The highest productivity of 93.7 mg L-1 d-1 was noted at 24:0 L:D but gradually reduced as the dark periods lengthened. Protein contents ranged between 50.3 to 49.9%, while only at 12:12 L:D were lower at the value of 42.9 %. Lipid contents were 23.5 to 29.7%, while carbohydrate contents were ranged from 14.6-19.7%. Pigments also exhibited higher accumulation rates under 24 h light photoperiod (5.1%) and thus continuous illumination was selected as the optimum growth condition. The growth temperatures of 19±1oC and 28 ±1oC were then studied. Recorded biomass productivity values were 69.3 and 55.0 mg L-1 d-1 respectively, while protein (43.6-40%) and pigment (3.4-2.7%) contents reduced slightly under these conditions. Thus, optimum growth and biomass composition for Tetraselmis is achieved at constant light and at 25oC. High quality biomass important for fish growth can be produced under these conditions.