  Covariant tensor representations of gl(m|n) occur as irreducible components
of tensor powers of the natural (m+n)-dimensional representation. We construct
a basis of each covariant representation and give explicit formulas for the
action of the generators of gl(m|n) in this basis. The basis has the property
that the natural Lie subalgebras gl(m) and gl(n) act by the classical
Gelfand-Tsetlin formulas. The main role in the construction is played by the
fact that the subspace of gl(m)-highest vectors in any finite-dimensional
irreducible representation of gl(m|n) carries a structure of an irreducible
module over the Yangian Y(gl(n)). One consequence is a new proof of the
character formula for the covariant representations first found by Berele and
Regev and by Sergeev.
