I was right. Latest and final casualty:
The boys in the office suspected that the other fishes must've died of stress when we changed the water and washed the pebbles last week. So since I didn't go to work last Monday, they took the task of fishing out the dead bodies and changing the water again. Apparently, it didn't help that this last one spent two days swimming in mineral water. She must've died of loneliness. Lonely sucks.
Lonely is different from alone because you can be alone but not lonely, and you can be surrounded by a thousand people and still feel lonely.