Is oyster broodstock feeding always necessary? A study using oocyte quality predictors and validators in
The effect of providing algal food to female Crassostrea gigas broodstock sampled at a favourable time of year was investigated using pre-defined indices of oocyte quality and subsequent larval and post-larval performances. Broodstock were collected in the Aber Benoît estuary (Brittany, France) at the end of April 2002 and were divided into two groups, a starved control (S, 1 µm – filtered seawater) and a fed group (F, ad libidum algal mixture of Isochrysis galbana clone T-Iso and Chaetoceros calcitrans), maintained under these conditions for six weeks prior to fertilizations. For each conditioning type, two batches of larvae and post-larvae were reared from two identified females. Quality criteria were defined in terms of predictors (oocyte lipid contents, mature oocyte diameters, ovarian maturity and presence/absence of atresia) and validators (larval growth, algal consumption and time to settlement, and post-larval growth). Each female was considered as a treatment, and parametric and non-parametric ANOVAs were performed, where appropriate, on predictors and validators between each treatment. In both conditions, a surplus of oocytes was produced, in relation to expected market conditions. No effect of the conditioning treatment was detected either on oocyte quality predictors or on subsequent validators. It is likely that winter reserve accumulation is more important than trophic conditioning for successful gametogenesis in the productive Aber Benoît environment. Given the considerable cost of abundant feeding during the conditioning of broodstock collected at the end of winter and destined for gamete stripping (the prevalent practice in France), we suggest that feeding be minimal or suppressed altogether when the condition index is favourable.
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