Sadness at Houghton Hall

Much distress in Houghton Hall as our tropical fishes are dying off. In the space of three days we’ve lost nearly all the larger fish and are left with a few baby guppies and about half a dozen neon tetras.
What’s the cause? A new bulb encouraged massive growth of plants. We recently introduced five Assassin Snails to control our snail infestation. A grey tetra ballooned to twice its size with what must have been a tumour. All are suspects.
Worst of all was the death of Colin the Catfish. He (she? it?) was one of the first fish we bought, over 10 years ago. A tiny black sliver when we introduced him, he grew into a 6-inch monster. With olive green with yellow spots, tiny pinprick eyes and evil spiny fins, he was scary enough without the added thrill of his regular sudden, furtive emergence from behind his castle to leap onto the glass of the tank and suck the algae with a movement reminiscent of the Alien facehugger. He frightened many visitors that way.
The various flouncy, pretty, showy fish that populated the tank over the years seemed like some kind of middle-class fancy dress party. All ignored Colin, a much more primitive-looking bottom-dwelling beast, a triumphant evolutionary dead-end with a Fuck Off attitude to any poncy-tailed imposter visiting the bottom of the tank to retrieve a fallen flake. He was evil-tempered and a master of the insolent disappearing trick: he’d crawl on his fins and then with a flick of the tail, disappear in a cloud of plant matter to attack intruders.
As hardy as a cockroach after Armageddon, he’d survived every epidemic that struck this tiny community over the last decade. Until yesterday.
There he was, slightly paler, stiff as a board and resting insolently on top of the box filter from where he would occasionally launch assaults on other occupants.
He’s now in a Ferrari aftershave box provided by our teenage son, awaiting burial when the kids return from school.