Doctors recommend 1500mg of glucosamine a day. In my opinion the best glucosamine supplement is called Flexicose Liquid Jointcare. You can purchase this from www.fairfresh.co.uk. The other thing which is extremely good for creaky knees is a product called Ortho-bone from AOR which is a bioavailable form of Calcium / Magnesium formula (MCHC) . It also contains strontium which helps absorption of calcium to bone by 10 times.
If you are vegetarian the best calcium supplement for Calcium absorption is called Calcium citrate malate.
As plumber and motorcyclist for 40 years and a sailor for 20 my knees are a bit shot. I take Omega 3 oil capsules and Glucosamine and Chondroitian morning and night See Health Span on the net.
I didn't realise you had a fish allergy. Most glucosamine is derived from shellfish, therefore i recommend you ask your doctor if this would give you an allergic reaction.