why cant i eat fish? anytime i eat tilapia,catfish or pollock i get violently ill.?

[Twist]

now that ive been sick from it even the smell or thought of it makes me feel sick...whats the problem? i dont think it tastes terrible or anything it just makes me throw up, sometimes the first bite i swallow.

i can eat tuna ,herring, shrimp and shellfish though.....