The Grimsby-based firm, which rivals frozen-food manufacturers such as Birdseye, has held talks with agencies for a new brief.
The agency review is being co-ordinated by the AAR Group.
Young's produced around 240 million products last year, 80 million under its own brand. Last year it launched a range of ready meals under the 'Make Fish the Dish of the Day' slogan.
Brahm, which will continue to work with Young's on its food-service side, said the parting was amicable.