E3 will initially be tasked with updating the look and feel of the sites to bring them in line with new brand identity and to change the perception of Fish4 as a "search focused site" to one which provides help and advice to users.
E3 will also be tasked with improving the overall commercial performance of the sites by reviewing ad inventory including the addition of contextual advertising and improving conversion for e-commerce processes through usability testing.
Lisa Walker, Fish4 marketing director, said: "We appointed E3 because they demonstrated their ability to really get under the skin of our brand. E3 had real and tangible audience insight and suggested lots of innovative ways to support our users and maximise our commercial relationships with customers."
Stuart Avery, managing director of E3, said: "Most job sites assume a search box is the best way to find jobs online. However user behaviour shows browsing is just as important online as it is when flicking through the recruitment pages of a paper.
"Many users don't actually know what they're looking for and in some cases they'll literally type the word "anything" and hit search!"
Fish4 was developed in 1999 and is run by Newsquest Media Group, Trinity Mirror and Guardian Media Group Regional Newspapers.