  We consider the thermal Casimir effect in ideal Bose gases, where the
dispersion relation involves both terms quadratic and quartic in momentum. We
demonstrate that if macroscopic objects are immersed in such a fluid in spatial
dimensionality $d\in\{3,7, 11, \dots\}$ and at the critical temperature $T_c$,
the Casimir force acting between them is characterized by a sign which depends
on the separation $D$ between the bodies and changes from attractive at large
distances to repulsive at smaller separations. In consequence, an effective
potential which binds the two objects at a finite separation arises. We
demonstrate that for odd integer dimensionality $d\in \{3, 5, 7, \dots\}$, the
Casimir energy is a polynomial of degree $(d-1)$ in $D^{-2}$. We point out a
very special role of dimensionality $d=3$, where we derive a strikingly simple
form of the Casimir energy as a function of $D$ at Bose-Einstein condensation.
We discuss crossover between monotonous and oscillatory decay of the Casimir
interaction above the condensation temperature.
