Biological parameters of the cupped oyster Crassostrea gigas such as growth, reproductive effort (duration of the gametogenesis, date of spawning, and fecundity) differ widely among oysters in the same location. Furthermore, most of the traditional methods, like histological observations, could lead to large variability on the observations and the measurements ofthese traits, and large uncertainties on their changes over time. These can be drastically reduced by using Magnetic Resonance Imaging (MRI) which is a non invasive method allowing to measure the same individual during its development. Forty oysters were assessed using MRI for the volume of whole soft body, the intra valves space, the adductor muscle, and the gonad, which also include the digestive gland. Then, the same 40 oysters were observed by histological cross section for the same traits recorded by MRI. Comparison of the two methods showed highly significant linear relationship for the area of the gonad measured on the same transverse section of the oyster, as well as the area through histology and the volume of the gonad through MRI. The limits of the MRI method are discussed. This method will be used to assess the volume of the gonad of a segregating biparental family in order to evaluate the individual reproductive effort, the time of maturation and spawning, and try to detect parts of the genome correlated to those traits of aquaculture interest.