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ABSTRACT. The estuarine diatom Thalassiosira weissflogii (Fryxell & Hasle, 1977) has been widely used as live feed in aquaculture. The growth rate and biochemical composition of microalgae are highly influenced by environmental factors such as, light, salinity and nutrient availability. Salinity is difficult to control in some shrimp laboratories specialized in larvae production, because these laboratories depend upon the levels measured in estuaries or coastal lagoons, which are the water sources for larvae culture. The present study evaluated the effect of different salinities (25, 30, 35, 40, 45 and 50 psu), on the growth and chemical composition of T. weisflogii at three culture phases, under laboratory conditions. The highest growth rate and maximum cell density were found at 25 psu. Decrease in size and striking changes in morphology of the cells were observed at the higher salinities and drastic changes occurred at 50 psu. Protein and carbohydrate content were higher at low salinities (25 and 30 psu) during the stationary phase. The lipid production was higher at low salinities, but diminished as the phase changes occurred; in contrast, the lipid content was unaffected by the growth phase at higher salinities (≥35 psu). The higher growth rate and better biochemical composition were obtained at 25 and 30 psu. Keywords: estuarine diatom, microalgae culture, proximate composition. Efecto de la salinidad en el crecimiento y composición química de la diatomeaThalassiosira weissflogii en tres fases de cultivo RESUMEN. La diatomea estuarina Thalassiosira weissflogii (Fryxell & Hasle, 1977) ha sido utilizada como alimento vivo en acuacultura. La composición bioquímica del alimento vivo afecta la nutrición de los organismos durante su cultivo. La tasa de crecimiento y composición bioquímica de las microalgas están altamente influenciadas por factores ambientales como luz, salinidad y disponibilidad de nutrientes. En algunos laboratorios productores de larvas de camarón, es difícil controlar la salinidad, debido a que éstos dependen de los niveles presentes en estuarios o lagunas costeras, los cuales son la fuente de agua para el cultivo larvario. El presente estudio evaluó el efecto de diferentes salinidades (25, 30, 35, 40, 45 y 50 psu), sobre el crecimiento y la composición proximal de T. weissflogii en tres fases de cultivo, bajo condiciones de laboratorio. Las mayores tasas de crecimiento y la máxima densidad celular se obtuvieron a 25 psu. Se observó una reducción en tamaño y cambios en la morfología de las células a altas salinidades y los cambios drásticos ocurrieron a 50 psu. El contenido de proteínas y de carbohidratos fue más elevado a salinidades bajas (25 y 30 psu), durante la fase estacionaria de crecimiento. La producción de lípidos fue elevada a bajas salinidades y disminuyó a medida que cambiaba de fase; no se observó un efecto de las fases del cultivo sobre el contenido de lípidos en altas salinidades (≥35 psu). La mayor tasa de crecimiento y la mejor composición bioquímica se obtuvieron 25 y 30...

The objective of this study was to evaluate the particulate matter uptake, survival, condition index (CI), and proximate composition of Crassostrea gigas, cocultured in seawater with tilapia. We used three densities of oysters (two, four, and eight) and one control (no oysters) per 150 g of tilapia biomass. Water quality parameters were measured daily, whereas NH 4 -N, NO 2 -N, NO 3 -N, PO 4 , total Kjeldahl nitrogen (TKN), chlorophyll a (Chl a), total suspended solids (TSS) proximate composition and CI of C. gigas were determined at the beginning and at the end of the study. No significant differences in nutrient content were observed between treatments. Significant differences were observed in TKN, Chl a, and TSS between the control and the oyster tanks. Maximum removal percentages were 43.16 for TKN (two oyster treatment), 80.23 for Chl a, and 73.55 for TSS (both in eight oyster treatment). Survival of C. gigas was 100% in all treatments. Significantly higher growth was only observed in two oyster treatment. Protein and carbohydrate content in the oyster tissues diminished in all treatments, whereas lipid increased in treatments with two and four oysters. These results indicate that TSS produced from tilapia can be used as a source of food for C. gigas.