Hello,

Thank you for asking your query at DoctorSpring.

Your symptom pattern is suggestive of an allergic reaction to the fish. The fact that you had response to anti histamines confirms it. You can take an OTC anti ulcer medication like Prilosec (Omeprazole) once daily before food for 4-5 days for the gas and possible gastritis. Continue the anti allergy medication for 1 more day

For now on do take caution while consuming fish. Prefer known species of food. Repeated exposure may lead on to sever allergic reaction (anaphylaxis). There are sophisticated testing methods available for food allergy. But in your case this is not required. Do mention this to your Family Physician / GP.

Hope this helps
Please feel free to ask followup questions
Thank you