To cite fitdistrplus in publications use:

M. L. Delignette-Muller, R. Pouillot, J.-B. Denis and C. Dutang (2013), fitdistrplus: help to fit of a parametric distribution to non-censored or censored data

Corresponding BibTeX entry:

  @Manual{,
    title = {fitdistrplus: help to fit of a parametric distribution to
      non-censored or censored data },
    author = {Marie Laure Delignette-Muller and Regis Pouillot and
      Jean-Baptiste Denis and Christophe Dutang},
    year = {2013},
    note = {R package version 1.0-1},
  }