The sulfides are to prevent black spot......The chemicals are used on poor quality shrimp. Many humans are sensitive to Sulfides and i would not assume fish are immune. Always check labels on shrimp and frozen seafood. ingredients should be shrimp and perhaps salt. Anything else including tripolyphosphate ( for drip loss) or sulfides ruins the product. The chemicals are used when the shrimp are subjected to long periods of time between harvest and processing which can occur both at sea or from ponds. There is very little oversite on this process and many manufacturers use way too much chemicals. The best quality products are processed either as caught on the ships or at a processing plant at the site of harvest.