Ive heard that or read it somewhere a while ago. I would be interested to know though as I feed it to two of mine although only the stated amount. But it really has helped put meat on my to skinny bone's.
I don't know what the threshhold is for 'too much'. So I would suggest if you want to use cod liver oil, go on and use it - but use in a rotation of oils. Fish oil, salmon oil, krill oil, coconut oil, cod liver oil, etc. The plant oils such as flax oil, olive oils, or coconut oils aren't supposed to be beneficial to dogs, but I have seen arguments on both sides, especially towards coconut oil being a great supplement.
So do some research and rotate your oils for best results.
Lucy those look great. Just poke a hole in one and drain on food a couple times a week. Use to bowel tolerance, it's very hard to overdo omega 3's so don't worry about giving too much or having to have an exact dosage correct.