Techniques for delivery of arachidonic acid to pacific oyster, Crassostrea gigas, spat

Abstract

The present study tested two techniques for dietary supplementation of Crassostrea gigas spat with PUFA, such as arachidonic acid (AA). The first technique consisted of a preliminary enrichment and growth of an algal concentrate (T-ISO, Isochrysis sp.) with AA dissolved in an ethanol solution, the whole culture then being fed to the spat. This enrichment increased the AA weight percentage in T-ISO neutral and polar lipids from 0.6 to 22.4% and from 0.4 to 6.8%, respectively. The second delivery technique was direct addition separately of free AA dissolved in ethanol solution and algal concentrate (T-ISO + AA) to the spat-rearing tank. To test the efficiency of these delivery techniques, oyster spat were supplemented with AA-enriched T-ISO, T-ISO + AA, and T-ISO alone. The possible biological impacts of these dietary treatments were assessed by measuring growth, condition index, and TAG content of oyster spat. Dry weight and condition index of spat fed AA-enriched T-ISO decreased by 24 and 49%, respectively, after 26 d of feeding; basically, TAG content declined 88% after 34 d of conditioning. When AA was added directly to seawater, spat growth and condition index were comparable with those of oysters fed T-ISO alone. AA incorporation in oyster tissues was assessed by analysis of the FA compositions in both neutral and polar lipid fractions. After 34 d, AA content in neutral lipids reached 7 and 11.7% in the spat fed, respectively, AA-enriched T-ISO and T-ISO + AA, as compared with 1.1% in spat fed only T-ISO. AA incorporation was greater in polar lipids than in neutral lipids, reaching 7.8 and 12.5% in spat fed AA-enriched T-ISO and T-ISO + AA, respectively. A direct addition of PUFA along with the food supply represents an effective and promising means to supplement PUFA to oyster spat.

Effects of nutrition on larval growth and survival in bivalves

“…2006a). In addition, the fatty acid content of algae can be directly manipulated by adding fatty acid supplements to algal culture water (von Elert 2002; Seguineau et al. 2005).…”

“…2005). Despite the ease with which this process is accomplished, the results of Seguineau et al. (2005) suggested that there might be biological changes to enriched algae that make it less suitable as food.…”

“…Methods for the modification of protein, TAG and EFAs in live algae have been established (Utting 1986; Thompson et al. 1990, 1992; von Elert 2002; Seguineau et al. 2005), but little research on how these modified feeds affect larval performance has been conducted.…”

“…Culturing algae under varying conditions can modify their biochemical composition (Utting 1985;Thompson et al 1990Ponis et al 2006a). In addition, the fatty acid content of algae can be directly manipulated by adding fatty acid supplements to algal culture water (von Elert 2002;Seguineau et al 2005). Manipulation of algae may be a relatively simple way to alter feed compositions without culturing several species, allowing the culturist to focus on algal species that are known to have high ingestion and digestion rates.…”

“…Studies have shown that EPA, DHA and AA levels in Scenedesmus obliquus MEYEN can be increased from non-detectable amounts to 10-20% of the measured fatty acids by directly adding fatty acids to the culture (von Elert 2002). It can take less than 4 h for algae to become enriched with specific fatty acids as demonstrated with Stephanodiscus hantzschii GRUNOW enriched with a-linolenic acid (von Elert 2002) and T-iso enriched with AA (Seguineau et al 2005). Despite the ease with which this process is accomplished, the results of Seguineau et al (2005) suggested that there might be biological changes to enriched algae that make it less suitable as food.…”