1.6 to 1.9 Categories issues

I have upgraded from 1.6 to 1.9 and have been adding the custom changes to the new version.
However, it appears that the object model has changed and the folowing call is now different-

original call
CategoryManager.GetAllCategories(this.CategoryId);
replacement
this.CategoryService.GetAllCategories();

Can you tell me how I can replicate the CategoryManager.GetAllCategories(this.CategoryId); to filter categories by CategoryID?

kind regards