He is the first member of the Animal Justice Party to be elected to an Australian parliament, but now Mark Pearson's credibility is being attacked by angry vegans after he was spotted eating seafood at a Japanese restaurant.

Mr Pearson, a veteran animal rights activist, concedes that he ate fish at the Sydney restaurant but described claims on a vegan community Facebook site he is a regular consumer of seafood there as "absolute rubbish".

"There was some fish on one of the dishes and I had a bit of it," he told Fairfax Media.

"I strayed for that moment; for that morsel. It's all over. I think the people in the party have forgiven me and now we have to get on and do the work for animals."