I've bought some of the \link{http://www.zooplus.co.uk/shop/cats/canned_cat_food_pouches/schesir/schesir_savings_packs/289367\Schesir pouches} & it's their absolute favourite thing, they can't get it down fast enough, but it's nearly £8 a kilo 
They have Royal Canin biscuits + Bozita or Animonda Carny wet food regularly, the tuna is just a treat & not every day. Would tinned tuna chunks in sunflower oil be just as good???