Essential Fatty Acid Assimilation and Synthesis in Larvae of the Bivalve Crassostrea gigas

Abstract

Essential fatty acids (EFA) are important for bivalve larval survival and growth. The purpose of this study was to quantitatively assess for the first time through a mass-balance approach dietary EFA incorporation and synthesis within Crassostrea gigas larvae. A first experiment was carried out using two microalgae, Tisochrysis lutea (T) and Chaetoceros neogracile (Cg), as mono- and bi-specific diets. A second experiment using a similar design was performed to confirm and extend the results obtained in the first. Flow-through larval rearing was used for accurate control of food supply and measurement of ingestion. Non-methylene-interrupted fatty acids were synthetized from precursors supplied in the diet: 16:1n-7 and 18:1n-9, mediated by Δ5 desaturase. Moreover, this Δ5 desaturase presumably allowed larvae to convert 20:3n-6 and 20:4n-3 to 20:4n-6 and 20:5n-3, respectively, when the product EFA were poorly or not supplied in the diet, as when larvae were fed T exclusively. Under our experimental conditions, none of the diets induced 22:6n-3 synthesis; however, 22:6n-3 incorporation into larval tissues occurred selectively under non-limiting dietary supply to maintain optimal levels in the larvae. This combination of flow-through larval rearing and biochemical analysis of FA levels could be applied to additional dietary experiments to precisely define optimal levels of EFA supply.

Larval development and fatty acid composition of Ostrea edulis (L.) fed four different single diets from conditioning to pre-settlement

“…These lipids play important structural roles in regulating cell‐membrane fluidity and other cellular functions (Hall, Parrish, & Thompson, ; Hazel, Williams, Livermore, & Mozingo, ). In general, bivalves have limited or no ability to synthesize PUFAs or to elongate shorter‐chained compounds (da Costa et al., ) but require these for growth and development (Chu & Greaves, ; Delaunay, Marty, Moal, & Samain, ; Marty et al., ; Waldock & Holland, ; Whyte, Bourne, & Hodgson, ). Although the effects of nutrition on larval growth and survival have been studied extensively in a wide range of molluscs (see review of Marshall, Mc Kinley, & Pearce, ), the effects of food on broodstock and subsequent larval development performances have received less attention.…”

“…Moreover, several studies (Helm, Holland, Utting, & East, 1991;Jonsson, Berntsson, Andr e, & W€ angberg, 1999) have suggested that some PUFAs are essential for survival and development of O. edulis larvae as demonstrated for C. gigas larvae (da Costa, Robert, Qu er e, Wikfors, & Soudant, 2015).…”

Fatty Acid Profile of Pacific Oyster, Crassostrea gigas, Fed Different Ratios of Dietary Seaweed and Microalgae during Broodstock Conditioning

“…Although it has been widely accepted that the capacity of bivalves to synthesize EFA is not sufficient or absent to meet nutritional requirements (da Costa et al, ), Waldock and Holland () suggested that C. gigas juveniles have the ability to elongate and desaturate the FA 18:3n‐3 to 20:5n‐3 and 22:6n‐3, but at insufficient rates to sustain optimal growth (Waldock and Holland, ). Nonetheless, more recently, a metabolic sequence was suggested in which an elongation of 18:4n‐3 to 20:4n‐3 occurred, followed by a desaturation at the Δ5 position to 20:5n‐3 (da Costa et al, ). The same authors also proposed an alternative sequence in which 18:3n‐3 is elongated to 20:3n‐3 and then desaturated to 20:4n‐3 by Δ8.…”

“…In the present study, both 18:3n‐3 and 18:4n‐3 dietary contents were higher with a dietary 100% microalgae level. This may suggest that the higher richness of the microalgae diet in these FA enabled the oysters to spare their initial reserves, which, in turn, may indicate a metabolic consumption of 18:3n‐3 and 18:4n‐3 in the synthesis of FA with a lengthier chain (da Costa et al, ; Waldock and Holland, ).…”

“…This way and according to Rato et al (), when oysters are conditioned with a suitable diet, sufficient to meet nutritional requirements, such as 25% SW + 75% Alg and 100% Alg, the reserves of EPA and DHA are channeled to gametogenesis, leading to a higher percentage of viable (free‐living) veliger larvae. In the case of 100% SW oysters, it seems that they mimic the behavior of C. gigas starved larvae, which selectively retained DHA during starvation, because they play other structural roles (da Costa et al, ).…”