Cories - suspended animation?

tanker

I went to the aquarium shop again today just to look around and dream about what I'm going to eventually have in my tanks. Today, the cories were just sitting there, like they were in suspended animation. They weren't rummaging around, just sitting there, perfectly still. Is this normal cory behaviour or a sign that all is not well with the cories at that shop?

Byron

I would be careful about purchasing corys in that tank.

First, obviously corys can't be foraging around the substrate 24 hours a day, they need rest too; and they are generally quite active at night. In my experience over 20 years with dozens of species of these interesting fish, some are out and about far more than others that I rarely see except at feeding times.

However, in a store tank, I would suspect this could be a sign of stress. Several factors come into play though. The length of time since they first arrived in the store, the water conditions in the tank, the number of corys and species are all relevant.

Corys do not travel well; they are highly susceptible to ammonia poisoning and when shipped too many in a bag they frequently arrive very stressed and at the point of death. I know of several store owners who regularly lose more corys than any other freshwater fish solely because of this. Often if they are not dead upon arrival, they succumb within a few days. Even moving a cory from one tank to another in my fish room can cause a temporary but significant change in behaviour, and my water parameters are near identical between my Amazonian tanks.

Most cory problems start with increased respiration--respirating faster than normal, especially if they are just sitting there--corys naturally respirate faster when swimming around and feeding. Second sign is lethargy, sitting motionless for long periods, plus increased respiration, is almost always a sing of trouble. In tanks with plants, they often do this closer to the surface, another sign of increasing problems. And sometimes they faint--just flop over on their side, still respirating--although this behaviour has been observed by me and others in perfectly healthy normal corys though very infrequently.

I can stand and observe a store tank of corys for several minutes and decide whether or not to risk buying them. I frankly don't really know what it is that I am seeing, but it is something. The few times I have taken the risk when I felt all was not well, the corys have died. I'm sorry if I can't really explain it.

Byron.

tanker

Thanks Byron. It was really quite strange. I've been in there quite often and they've always looked active on previous occasions. I asked the guy about it and (from memory) he said the airflow wasn't high in the tank and it makes them lethargic. He wiggled the air tube and they all seemed to "wake up" and started doing their "waggly" dances. It sounded odd. Why wouldn't the airflow be good?

Yesterday was very strange. I "did the rounds" of the shops around here (I'm very lucky, I have several in my area) and saw dead fish in every shop. Can the weather affect fish? We've recently had a change in the weather, it's become chilly and we've had some rain. Are fish affected by changes in barometric pressure, perhaps? Every other time, the fish in all of the tanks in all of the shops have looked healthy, but yesterday it was different.

Byron

If the temperature dropped and the tanks are not heated in some way, that could cause problems. Most tropical fish cannot tolerate sudden and/or significant drops in temperature.

Yes fish detect barometric pressure. Many tropical forest fish can be induced to spawn by doing a massive water change on a low-pressure day. It simulates tropical rains that trigger spawning at the start of the rainy/flood season. My characins very regularly go into frenzied display/pre-spawning behaviours on overcast days, even without a water change. But low pressure/stormy weather would not kill the fish, just the opposite if anything.

Another thought is something in the water. Water treatment services have been known to add stuff to the water for specific reasons, hopefully giving the public advance notice.

Could just be coincidence too. B.

tanker

I went to another shop yesterday, and all of their cories were sitting still as well. I wonder if the weather could be responsible. It was kind of oppressive, sort of humid with the rain.

Yes, it could well be. It's interesting to learn something new about fish responding to the weather though.