I have two shelties and feed them sardines in oil twice a week. It is good to hear that the cheapies work just as well as the John West varieties. I had been feeding mine John West as they have more Omega 3, DHA etc. I am a serial label analyser. I bought Brunswick today as it has 89% sardines where the other brands have around the 70%. I found that the varieties with more oil have more Omega 3s etc. Tuna isn't as oily a fish as sardines and therefore doesn't have as much of a benefit as sardines. Sardines from my label studies have shown to have the most Omega 3s in them.
Regards
BarBell