I have a female call duck, 7 months old, who hasn't started laying yet. She has one other companion who is completely fine. She's showing signs of: - lethargy - loss of appetite - laboured breathing - a tiny bit of diarrhoea (but that may just be the rain watering it down) - she just looks worn down She's still walking around, preening and swimming occasionally but very slowly. The only thing I could find that matches her symptoms is Avian cholera but surely the other duck would have it too? Should I clean out her pond as a precaution?