hi hui hui,
my dear son attends infant care and they use salmon fish inside their porridge. i started by dear son on their porridge (using brown rice) when he was 7mths and he got diarrhea. i dont't think they didn't prepare cleanly coz the other kids were ok. so it could be either he not ready to digest the brown rice or the salmon fish is too oily.
i went to this website called www.wholesomebabyfood.com and they only recommend introducing fish at 10mths. thought i've asked some friends and they said better to start on "ngor heer" (aka threadfin) than salmon.
hope this helps.