Colonies of the compound tunicate Botryllus schlosseri show the capacity for colony specificity resulting either in vascular fusion or in rejection between genetically distinct colonies. Cosettlement of kin colonies increases the probability of fusion between allogeneic colonies. However, laboratory studies revealed that fusion terminates in the resorption of one partner, and that fusion raises the threat of somatic/germ cell parasitism. Here we tested in a laboratory study, done with 88 oozooids from 4 gravid colonies, the suggestion that colony fusion between relatives may be beneficial to one or both members of a chimera by increasing the size, the fecundity and/or survivorship.