May 6 (Reuters) - Canada's Brookfield Asset Management will invest about $1.5 billion in private credit manager Castlelake, the companies said in a joint statement on Monday.

As part of the deal, Brookfield will also acquire a 51% stake in Castlelake's fee-related earnings (FRE). The private credit manager will continue to operate its business independently, retaining its current governance and leadership structure.

The deal comes as private capital groups have been struggling to raise funds, and investors in private equity funds are choosing to concentrate their investments with fewer, larger managers.

FRE is a performance measure used to assess an asset manager's ability to generate profits from revenues that are measured and received on a recurring basis. It includes management and advisory fees.

Castlelake is an alternative asset manager specializing in asset-based private credit, including aviation and speciality finance.

(Reporting by Jaiveer Singh Shekhawat in Bengaluru; Editing by Shilpi Majumdar and Ravi Prakash Kumar)