Abstract
Rotifers are an important live feed for first feeding larvae of many fish species. The use of concentrated algae cells in the mass culture of the rotifer Brachionus plicatilis (Brachionidae) has opened new horizons for research on this organism. Pastes of Rhodomonas salina (Pyrenomonadaceae) obtained either by centrifugation or flocculation with chitosan were preserved, with or without vitamin C, at -20 degrees C for four weeks and were evaluated biochemically (proteins, lipids, pigments and fatty acids contents) and subsequently, were used to feed the rotifer Brachionus plicatilis at a ratio of 25 mg/L/day. Four different microalgae pastes were prepared: (1) centrifuged and preserved with vitamin C (CV), (2) centrifuged and preserved without vitamin C (C), (3) flocculated and with vitamin C (FV) and (4) flocculated without vitamin C (F). All treatments showed similar contents of proteins and total lipids with respect to control culture (a fresh culture of R. salina), with mean values of 40.0 +/- 2.32% and 12.0 +/- 1.45%, respectively. The pheophytin a/chlorophyll a ratio, a general indicator of the chemical status of microalgal concentrates, was similar (0.09-0.11) between centrifuged pastes and control culture, but was found to be higher in flocculated pastes (1.28-1.48). The fatty acid profile varied with respect to the control culture, mainly in the proportion of the essential polyunsaturated fatty acids (PUFAs): eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Total PUFAs, EPA and DHA contents were statistically similar between centrifuged pastes and control culture (PUFAs: 47%, EPA: 4% and DHA: 4.7%), whereas values obtained for flocculated pastes were significantly lower. The rotifers grew equally well when fed with centrifuged pastes or control culture (maximum density: 320 rotifers/mL; instantaneous growth rate: 0.23 rotifers/day, fecundity: 1.49 eggs/female and productivity: 43 x 10(3) rotifers/L/day. No significant effect of vitamin C was found when used as a paste preservative. We concluded that centrifugation is an effective harvesting method, and that freezing to -20 degrees C for four weeks (no vitamin added), may help maintain the nutritional quality of R. salina paste, similar to fresh microalgae and can be offered to Brachionus plicatilis.
Highlights
La centrifugación es el método más usado para obtener concentrados microalgales; mientras que la floculación, un método ampliamente usado en la industria para remover sólidos en suspensión, también ha sido exitosamente aplicado a la cosecha de biomasa microalgal (Molina-Grima et al 2003)
Ensayos de alimentación del rotífero B. plicatilis con pastas algales: Los cultivos de B. plicatilis se realizaron, por cuadruplicado, en matraces de 500ml de capacidad con 250ml de agua de mar (37UPS) filtrada a través de una batería de filtros: 10; 5; 1; 0.1μm y esterilizada mediante tratamiento con luz UV
Essential fatty acid enrichment of cultured rotifers (Brachionus plicatilis, Müller) using frozen-concentrated microalgae
Summary
Cepa de microalga y del rotífero: La cepa CS174 de Rhodomonas salina (Wislouch) Hill & Wetherbee (1989) fue obtenida del Cepario CSIRO Algal Culture Collection, CSIRO Division of Marine Research, Hobart, Tasmania. Estos nuevos cultivos se realizaron por cuadruplicado con una densidad inicial de 1x105cel/mL, en medio f/2 (Guillard 1975) con una concentración de nitrato y fosfato de 3.5mM y 0.018mM, respectivamente, utilizando agua de mar (37UPS) filtrada y esterilizada en autoclave (15psi/120°C/15 min). Producción de pastas algales de Rhodomonas salina: Cuando los cultivos alcanzaron la fase de crecimiento exponencial tardía (6to día), se procedió a realizar la cosecha total, para lo cual se evaluaron dos métodos: (a).Centrifugación: consistió en centrifugar 6L de cultivo, de cada réplica, a 3 000rpm/5min, usando tubos cónicos de 15mL de capacidad. Ensayos de alimentación del rotífero B. plicatilis con pastas algales: Los cultivos de B. plicatilis se realizaron, por cuadruplicado, en matraces de 500ml de capacidad con 250ml de agua de mar (37UPS) filtrada a través de una batería de filtros: 10; 5; 1; 0.1μm y esterilizada mediante tratamiento con luz UV. Los valores promedio (media±desviación estándar) para estos parámetros fueron 40.0±2.3% de proteínas y 12.0±1.4% de lípidos
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