Is a greenhouse aquarium suitable for shrimp?

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One reader would like to know if he can breed some Cherry shrimp in his unheated greenhouse aquarium. Neale Monks advises...

Q) I have an 80 l tank with a sponge filter and a heater and I was thinking of using it to breed some Cherry shrimp. Can I set it up in my unheated greenhouse?

CRAIG MASON, VIA EMAIL

A) NEALE MONKS SAYS: This is a great question, and to be honest, I’d expect robust, subtropical to warm temperate, shrimp to do just fine in a warm greenhouse. In fact, I’d be more concerned about overheating than cold, since Cherry shrimp can actually handle fairly cool conditions quite well. That said, setting the heater to 18-20°C as a back-up against cold nights would be a very wise move. At the same time, I’d want to make sure the tank didn’t overheat if exposed to direct sunlight. While I’m sure peaks of 28-30°C for a few hours on a summer day won’t do any harm, continual exposure to such high temperatures isn’t going to end well. My own experience with Cherry shrimp on an unheated windowsill tank was that they positively thrived in tanks where temperature went up and down through the course of 24 hours. Indeed, they bred like crazy on the back of all the algae and infusoria that accumulated on the floating plants and filter sponges. But as with any aquatic organism, high temperatures expose them to low oxygen levels, and such conditions can quickly stress and kill animals not adapted to them.

The sponge filter is a great call. These cultivate the infusoria that hatchling shrimps need to get a really good start in life. They also trap tiny particles of decaying organic matter as well as algae, and these help round out the diet of your shrimps. Sponge filters don’t create much turbulence or suction, which is another advantage, while the flow of air bubbles helps to ensure oxygen levels stay high. All in all, it’s a good way forward.

So far as overheating goes, strategic use of plants to shade the tank will probably be the first step. A thick covering of floating plants will likely help too. Cherry shrimp will jump, so while an uncovered tank is an option — and how my windowsill tank worked, with emergent Hygrophila covered in flowers adding to its charm — the downside was the regular appearance of dried shrimp skeletons on the windowsill or carpet. You could use a hood of course, but without adequate ventilation these are likely to trap in a lot of heat, so some care will be needed in the summer months. If you have a look at how marine aquarists deal with overheating hoods using small fans, that might give you some ideas of how to fix this problem, should it arise. Otherwise, allowing natural evaporation to remove heat, while topping up regularly with (ideally) demineralised water, should keep the tank at a sensible range of temperatures, even during the summer months.