We consider the role of weak interatomic interactions on the fluctuations o
f the number of condensed atoms within canonical and microcanonical ensembl
es. Unlike the corresponding case of the ideal gas this is not a clean, wel
l-defined problem of mathematical physics. Two related reasons are the foll
owing: there is no unique way of defining the condensate fraction of the in
teracting system and no exact energy levels of the interacting system are k
nown. [S0031-9007(99)09269-8].