Climate change in our fish tank

You wouldn’t think you could have a climate change caused ecological disaster in our fish tank. But last week’s heat wave was so extreme it overheated the water, killing a few of the fish as well as unseen zillions of microscopic algae. Days later they clogged the filter in a rank slimy dark mass and very quickly turned the water anoxic and disgustingly rank. Lost a couple fish. I think the last of our herd of danios was rendered extinct. I was looking for the clown loach in the cloudy water. It’s five inches long, tiger striped and a furiously active beast, but there was neither hide nor hair. Nor scale. Suddenly like a vision out of Moby Dick it appeared, it’s creamy white underside a flash of light in the gloom, desperately trying to reach the surface and oxygen. It hung vertically in the water, gasping, slowly suffocating. I reached in and grabbed at it but it slipped out of my fingers and disappeared into the plants. I began thinking about where to get his replacement (they’re champion snail eaters .) Then it was there again, hanging vertically, surreal, dying. I took a bucket, put a couple inches of water in it, and grabbed the loach again, it was too weak to wriggle free. I dropped it in the bucket. It rested on the bottom with its mouth at the surface, barely breathing. Nothing more I could do. An hour later I heard some furious thrashing about in the bucket. A temper tantrum was a good sign. I added more water. Within two hours it was back to its surly self. When I’m done with the aquarium clean up—you don’t even wanna know what comes up when you siphon the floor of a fish tank—and replace a third of the water, I’ll put him back in. The filter has already cleaned and oxygenated the water to such a degree that the platys and wandering about picking up food on the bottom—they spent the last couple days at the very top. I had a fan blowing across the surface all night as well, and though I’m not sure how it definitely helps to oxygenate (and cool) the water, like a cooling ocean breeze. The fish certainly dug it, all of them scurrying about where the air flow is strongest. Fish, who the fuck knows. Anyway, another crisis averted. Not quite as creepy as when the zebra danios became pescicidal maniacs, but definitely more icky.

I suppose you want a picture. Better yet a video. Here, a perfectly healthy clown loach. Animal Planet, call me.

Demographics

You’ll be pleased to find out that I just purchased twenty ghost shrimp on EBay. I thought the loach had eaten the previous herd of ten, but I was delighted to discover there were survivors. So now I’m getting a bunch more, figuring the loach will take his share but the rest will be around to partake in the great fish dying due anytime now, as the vast herd of platys reaches their life expectancy and bloops their last bloop. Some fish corpses float, some sink. The floaters I scoop up with the net and toss into the planter out front. No point in wasting good fertilizer. The sinkers are a pain in the ass. So the shrimp get those. They can reduce a fish carcass to nothing in a matter of days. I’d rather not think about it. And the platys own culinary kinks guarantee the population will not recover, because a platy’s favorite dish is fresh born platy. None of the babies survive the feasts, and as there is no longer a dense jungle of floating vegetation for the fry to hide in—they ate that too, for roughage I guess—the babies are easy pickings. You can see the adults gathering together and leisurely devouring platy DNA. It’s fucked up. But it did neatly stop the aquarium’s population explosion, and there was one baby, as in a single fish, that has made it to adulthood in the past year. They’re efficient, you gotta give them that. So efficient they’re eating themselves into extinction in our tank. Platys live three to four years, typically, but invariably fish in our tank live to the outer edge of their life expectancy, so I won’t be surprised to see many of them last for five. But eventually the lot of them, nearly all of which born in a single year, will go to fish heaven, leaving all sorts of niches for us to fill with species that don’t fuck so goddamn much. It’s like having an aquarium full of drummers.

I’m not sure when exactly the zebra danios turned into killers.

Our zebra danios have gotten scary. Where once they’d dash about madly at the top of the tank waiting for the flakes of food, now they wake slowly from sleep, huddled together, then in a three fish column begin moving slowly (not their usual frantic dash) into the plants, moving around them, seeking meat. The flakes of fish food float down all around them but they pay no attention. They keep prowling, methodically, maybe an inch or two from the bottom of the tank. I’ve come to suspect that this was how they killed the other fish, by catching them before they were completely awake there amid the plants. I can only imagine that all three would rush in, striking, chomping, killing. In the wild they eat insects and crustaceans and worms, so they are hunters, yet in the thirty some years we’ve been stocking our aquariums with them I have never witnessed them do anything more than grab flakes of fish food drifting by. I have certainly never seen this sort of apparently coordinated behavior. It seems that almost every vertebrate has within it the predatory behavior. We are all hunters. Hell, it was predation that drove evolution itself, the whole Cambrian Explosion with all its crazy speciation was the result of the ever evolving contest between predator and prey. And here, somehow, in our little aquarium, something turned these little inch and half long fish from eaters of fish food to eaters of fish, eaters of even their own kind (as there were five of them just two weeks ago). All was peaceful until the clown loach died. That loach, though never deliberately bothering any of the other fish, was at seven inches long to them like a whale shark is to us. It ruled the floor, digging up snails. The danios stayed up several inches in the tank, away from its sudden movements. But then the loach, one day two or three weeks ago, was dead. Old age. I noticed the next morning that the danios were down zipping around at the bottom of the tank. The neon tetras calmly minded their own business, the two glass catfish scooted about. Everyone, danios included, got very excited at feeding time, like they always did. Everyone swam around excitedly, grabbing bits of tetra min flakes floating by.

I’m not sure when exactly the danios turned into killers. Within two weeks I realized that all the fish were gone but these three zebra danios. Alone in the tank, they chased each other madly about, zipping one way, then another. I was mystified. Where had all the other fish gone? I did some research, and found desperate pleas on aquarium websites. “Help, my zebra danios are eating each other!!!!” or “My zebra danios are killing my other fish!!!” I read in shock just how murderous the little beasts can be. No one seemed to know why, but there was usually a dominant fish that sets it off. A handy bit of evolution, that, where some members of the species will suddenly go rogue, turn alpha, and eat everything piscene in sight. Obviously there is a genetic advantage in there somehow. Perhaps a surge in zebra danio testosterone. But I have no idea. Looking at the tank again, one of the danios is swimming like a lunatic now, frenzied. The other two have ducked behind the leaves. Perhaps there is murder afoot.

zebra-danio2

It doesn’t look like a killer.