It does not matter whether you give raw or tinned or if the fish is in brine, as of course you can just drain the brine.
I use sardines in tomato sauce if I use tinned as that is what my dogs like.
if your dog is having issues at this age it is unusual.
Yumove have a new supplemnt out designed for young dogs I would look at this.
Yumove Young & Active - Lintbells
Other things I would consider are as follows:
Bromelain - naturally occurring enzyme sourced from the pineapple plant. It is predominantly found in the stem. Standardized extract is available alone or in combination with other products. It contains numerous anti-inflammatory chemicals and reduces the inflammatory response by alleviating pressure within the joint and allowing a greater ROM (range of movement).
Cetyl-Myristoleate - extracted from the Kombo nut, found in the commercial product Cetyl - M
Chondroitin - chondroitin sulphate is an important component of cartilage and the marine form is considered more bio available and powerful than the bovine form
Cod Liver Oil - contains around three times less Omega 3 EFA (essential fatty acids) than that of FBO. Also, as CLO contains a significant amount of Vitamins A and D pregnant bitches should not be given this supplement; if a dog is being fed a commercial diet, you should check that recommended doses are not being exceeded as of course these contain Vitamins A and D. Raw fed dogs will normally have sufficient of these vitamins via liver and bones.
Devils Claw - is a traditional herbal product, known as wood spider, a plant native to South Africa and traditionally taken as tea. The main anti-inflammatory agent is harpagoside which helps prevent the conversion of arachidonic acid into pro inflammatory messengers
Fish Body Oil - is extracted from the flesh of oily fish such as salmon, herrings, sardines, pilchards and mackerel. They are a rich source of EPA and DHA (always ensure that the quantities of both are identified on the labels of FBO).
Flaxseed Oil - (Linseed Oil) is ALA (alpha-linolenic acid) which the dog has to convert to EPA and DHA, thus it is not such an efficient or effective source of Omega 3 as FBO from either the point of bio-availability or cost.
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Ginger Extract - another traditional product which contains anti inflammatory properties
Glucosamine - is an amino sugar which is one of the main building blocks of cartilage; the HCl form is purer than the 2KCl form
Green Lipped Mussel - contains glycosaminoglycans
Hyaluronic Acid - aids joint lubrication and shock absorption
MSM - provides a source of sulphur molecules required for the formation of connective tissue
Rosehip extract - contain antioxidants such as Vitamin C both of which may have an anti inflammatory action.
Turmeric - contains curcumin, better to take a supplement which contains standardised extract than just the off the shelf powdered spice.
Vitamin C - essential in the formation of collagen
Vitamin E - if you give FBO then you should also supplement with this vitamin as the former depletes the body of the latter.