Our results in communal rearing(data set I, experiment 1/92, communal rearing) may indicate that some competition between hybrid S.aurata×P.major and parental species could affect growth.Alternatively, a separate culture of the different species strains or fish varieties is the ultimate objective in industrial rearing. Therefore separate rearing conditions may be considered as a more appropriate toot for evaluating the culture performance of different species their hybrids or chromosomally manipulated forms.