Oh, I am very sorry for you, – that must be so hard.
I will hurry to tell you, that in fact … last time I went to my local very good fish shop (has one person there with really good knowledge regarding parosphromenus) – he actually told me, they had had two shipments lately of wildcaught fish – they arrived well and fine, they put them in a tank to settle … next morning all dead. They have had wildcaught paros many times and never had this happen before. They were quite puzzled.
I dont know excatly which species this was, but since opallios is around here too it could have been them.