golden orfe dying

Question
QUESTION: In the last two months 4 of our orfe have died they were all over 7 years old,appeared in good condition and were about 12-15 inches in length. There are 50 plus other fish in the pond of various kinds. Maximum depth of pond is 1 metre and contains about 4500 gallons.
ANSWER: Hi Maureen,
Thanx for your question.  What is your location, climactic conditions, etc.  There's no way I can possibly answer this question without much more detailed information.  Weather history, etc.  I hope this helps.
Tom

---------- FOLLOW-UP ----------

QUESTION:   Further to your reply on mature golden orfe dying-
    We are situated in south Wales, this winter the pond has had ice covering 2/3rds of it's surface on about 4 occaisions this is less than in previous years. a pump moves 2500 gallons per hour through a filter and the into a waterfall. No other fish have died and the one remaining golden orfe appears healthy.
      Many thanks for your help
         Regards
         Maureen  

Answer
Hi Maureen,
Thanx for the followup.  In my research, I learned that Orfes are very, very sensitive to any changes in water conditions.  They prefer to be in schools of at least 3 or more fish (as you have).  They may have just simply gotten stressed this season.  If the others appear healthy it may just be an unfortunate turn of events.  I had some orfes for a few years and one year they just disappeared.  Many people don't like them because they can be hard to keep alive.  They need lots of oxygen.  It sounds like the ice may have inhibited the transfer of oxygen into the pond and chemicals like methane and ammonia out of the pond.  I'll bet that was the death knell for the ones you lost and the other guys were just lucky survivor.  I hope this helps.
Tom