Cats can eat fish as part of a balanced diet.
Feeding fish as the only source of food can lead to crystallization within the urinary tract system, so it is advisable to give cats a variety of meat products.
Feline Lower Urinary Tract Disease (FLUTD)
- Cat foods that contain large amounts of animal- and fish-based proteins produce a more acidic urine. Eukanuba.com
Cats can easily snack on tinned fish, like tuna and have pet food products containing fish.
- Fish, such as tinned sardines in springwater; tinned tuna and tinned salmon (care with any fish bones) can also be offered as a treat occasionally. Please avoid feeding fish constantly
RSPCA Australia
As for sulfide based preservatives, that can be found in a range of products, these should be avoided altogether.
- Raw food offered to cats should always be fresh
- Choose human-grade raw meat and raw meaty bones because some pet meat/pet mince/pet rolls/pet meat and bone products can contain preservatives which can be detrimental to the cat's health (e.g. sulphite preservative induced thiamine deficiency which can be fatal) . However avoid sausages, sausage meat and cooked manufactured meats as they can contain sulphites.
RSPCA Australia