i know that house it's like fort knox, massive tall concrete fence around it, steel gates, cameras everywhere etc. i'll put money on it that it's an inside job. if they were just common thieves then i'd be surprised if they can sell on that many fish let alone store them until they are sold. they were probably stealing to fill an order. someone on here will probably hear something about it....  
it's possible the pond was heated. it's even possible it was salt. with 200mill, anything is possible! 
also, 10 points for alliteration.