David Cameron and Boris Johnson have clashed over the impact of the European Union on the British fishing industry.
In an interview with the BBC's Countryfile, Vote Leave figurehead Mr Johnson said Brexit would free the UK from "crazy" rules and give fishermen a boost.
But the Prime Minister told the programme that pressure from London to amend the Common Fisheries Policy had already removed many of the obstacles.
Mr Johnson, a Tory MP and former London mayor, said EU restrictions had inflicted a "tragedy" on traditional fleets - with the workforce at best a half of what it had been.
"Look at what's happened to our coastal towns, they are areas where in many cases you've seen too much poverty. Bringing back the fishing industry in those areas would be fantastic," he said.
"I'm not hostile to our friends and partners in the European Union, I just think we can do it just as well ourselves if we managed our waters.
"Some of the rules, chucking back perfectly good fish to manage the quotas, I mean come on that's got to be crazy, there's got to be a better way of doing it."
Mr Cameron hit back: "Since I've been PM actually the value of the British fishing industry and fish processing industry has gone up.
"With this greater regional control that we've managed to negotiate you're seeing fish stocks recover.
"Look at the most recent figures: we're actually allowing our fishermen now to land more plaice, more cod. Over the last five years, the UK-landed fish has actually increased by 20%.
"So I think when we talk about the common fisheries policy, it needed to change, a lot of it has changed.
"Is it perfect? No. Are we better off fighting from within? Yes. Is this market vital for our farmers and our fishermen? Absolutely yes."
Mr Cameron said the EU had a "mixed score card" on environmental protection - but defended measures such as protection for newts, which has thwarted housebuilding.
"Sometimes it feels a bit over prescriptive and can be frustrating but generally speaking, actually, we have to have rules on habitat," he said.
"If you look at species and biodiversity, things are getting better.
"Sometimes they will be frustrating for developers and house builders, but actually it's an important thing that we try to leave a country at the end of our time where species are thriving and not degrading."