If you are trying to fish and you are not having any success, you can say "I'm not catching anything" or "I'm not getting any bites." You could also say "The fish aren't biting" or "I'm not having any luck." If you want to be more specific, you can say "I'm not catching any (type of fish) today." For example, "I'm not catching any bass today" or "I'm not catching any trout today."