How to declare class that extends Drupal d2d Migrate class
Change your code like and try

 $migrations['CadeFields'] = array(
  'class_name' =&gt; 'CadeMigrateFields',
  'description' =&gt; t('Give your description abt this migration'),
  'source_type' =&gt; 'GIVE THE DRUPAL 6 NODE TYPE YOU ARE MIGRATING',
  'destination_type' =&gt; 'GIVE THE DRUPAL 7 NODE TYPE',
 );