RIO DE JANEIRO--(BUSINESS WIRE)--Fitch Ratings has affirmed MRV Engenharia e Participacoes S.A.'s (MRV) long-term national scale rating at 'AA-(bra)'. The Rating Outlook is Stable. A full list of rating actions follows at the end of this release. KEY RATING DRIVERS MRV's ratings remain supported by the company's satisfactory capacity to preserve its conservative credit metrics in a more instable business environment, preserving sales speed above industry average and still low inventory of concl