Effect of nutrition on Crassostrea gigas larval development and the evolution of physiological indices Part B: Effects of temporary food deprivation

In the natural environment bivalve larvae are exposed to variable conditions and can therefore face periods of food shortage. To understand the resistance of early life stages of Pacific oyster (Crassostrea gigas), larvae were experimentally starved for 4 days at different periods of their development, and the resulting variations in their lipid reserves then analysed using image analysis and biochemical techniques. Faced with a temporary lack of food, the larvae halted their growth in size and weight and started to live off their lipid reserves; this effect was highly marked when the period of food deprivation was at the beginning of larval rearing, but was less marked when food deprivation was after day 14. The larvae conserved their developmental capacity despite these starvation treatments: when feeding was resumed, the larvae started to grow once more, rebuilt their reserves and showed a survival rate between 45 and 91% to the end of the experiment. Apart from the treatment where larvae were starved between days 6 and 10, high percentages became competent (56-85%) leading to a metamorphosis rate of 58-93%. Coloration of neutral lipids with Nile Red, followed by their quantification using image analysis to calculate lipid surface relative to total larval surface (OLI: overall lipid index) was particularly suited to studying the evolution of reserves through larval development. Results collected in this way supported those obtained in parallel using biochemical tests: triacylglycerols/sterols ratio (TAG/ST). The image analysis method offers the advantage of requiring less biological material to obtain a result; the correlation coefficient between OLI and TAG/ST ratio was 0.75. (C) 2010 Elsevier B.V. All rights reserved.