My pitbull is on Phenobarbitol and Fish Oil, liver enzymes are high?

If his liver function is that compromised he probably isn't feeling well. Fish oil isn't going to cause behavioral changes, but pain from the liver issues could. The gas and diarrhea could be from the fish oil. Any sudden change in diet, including the addition of supplements like fish oil, can cause gastric upset.

I'm a little surprised that your vet would recommend fish oil for liver function. It can help, but there are other more effective supplements for liver function. Ask your vet about sylimarin (milk thistle) which is readily available under the brand name denosyl or denarmarin. When my cat's liver tanked after an anesthetic procedure my vet put him on denosyl for one month and it brought his liver values back from three times the normal range to back within normal limits. After that we were able to discontinue the denosyl, although some pets do need to be on it long term.

Probably a combination of both.

The way to tell is stop the fish oil. If he pops back to normal, there's your answer. You might need to find another alternative to straight fish oil.

Are you giving pill form or liquid? Can you cut back the amount and work the dog up to the full dosage slowly?

And do call the vet and let them know what's happening.

Well, i had a pitbull did you just get him? If so was it from a bad owner that didnt feed him? If so that was the case with my pitbull, we put him on gas-x and it seemed to help alot, about the attacking, pitbull's blood is in attacking to protect the owner. About the stool and gas, the change in food from nothing to a normal diet is a big change for a dog and the stomach reacts differently.

Hope it helps

fish oil tablets are not the cause of the aggressive behavior, however they could be a reason behind runny stool, although with that much of a sudden mood change I would bring him in to the vet expressing your concern. There may be a something else that your dog is reacting too.