I tried those salmon flavoured gel too many mths ago, ET shake them off. The whole tube is wasted cos he simply refused it. You may wanna try giving fish oil once a week or even psyllium husk if you have. I happened to have both, cos hubby and myself had been taking that for years. Especially when you use 1 whole fish oil capsule, you will see kitty passing hair out in their poop. But I can only add fish oil in salmon of which I give only once a week. It works so well for ET. Other times, I give psyllium husk, just a little, but looks like it may be too little, cos I don't see hair in his poop daily and then after a while ET cannot keep food down. When I increase dosage of psyllium husk, he will certainly pass out large amount of hair the following day. There may be some forumers here who don't think its safe to add fibre to kitty's diet. But google on psyllium husk, its water soluble fibre, it works to lubricate the intestine.
Anyway, I have read that olive oil or flaxseed oil works too if kitty doesn't like the smell or taste of fish oil.