Fitch Ratings has downgraded its ratings for six collateralised debt obligation asset managers and $29.8bn (€20.1bn) of CDOs with exposure to US residential mortgages, as rating agencies continue to analyse the impact of the credit crunch.

Fitch reviewed its CDO asset manager ratings, leading to six managers' ratings being downgraded. The ratings of seven were unchanged and four were placed on a "negative rating watch" meaning that the agency expects a downgrade may be necessary, but is waiting for further disclosures. Another three managers remain under a negative rating watch.