NITROGEN LIMITATION AND CHANGES IN SALINITY AFFECTS CHEMICAL-PROXIMATE-COMPOSITION OF Thalassiosira weissflogii

Abstract

Microalgae are a crucial factor in aquaculture activities, since they are used as live food in the larvae stage of shrimp, mollusks, and fish. Nevertheless, just a few microalga species are produce. In this study we evaluate the effect of salinity at 25, 35, 45 and 55 practical salinity unit (psu), in F/2 media as control group and two nitrogen (NaNO3) limited media, F/4 and F/8 on the diatom Thalassiosira weissflogii. To value the development of the diatom, kinetic growth curves, pH, biomass production and chemical-proximate composition were estimated. The highest growth rate and organic matter values were in media F/4 and 35 psu. Meanwhile, media F/8 at 55 psu presented the highest amount of ash and a very low growth rate. T. weissflogii is affected by high salinity concentration, however the limitation of nitrogen with 25 and 35 psu did not affect growth considerably. Concerning the chemical-proximate composition of T. weissflogii, media F/4 at 25 psu, presented the highest percentages of carbohydrates and proteins. In the same way, medium F2 at 25 psu, reported the highest amounts of carotenes. The results showed that high salinity was the variable that major affected the cell density, biomass production and chemical-proximate composition of T. weissflogii.