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Go Green with the Emerald Crab

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I’ve always found crabs fascinating. With their tough exoskeleton and menacing claws, they also offer a big personality to any aquarium, salt or fresh. Most people think red when it comes to crabs, but surprisingly, crabs come in a broad range of colors, just like fish.

Colors for livestock in aquariums mean beautiful hues of red, blue, and yellow. A color not often seen or appreciated as much in aquariums is green. I’m going to change all that – let me tell you a bit about a green crab that will bring some action into your reef, help you keep in clean, and look cool at the same time.

Related: Keeping Fiddler Crabs in Your Brackish Tank

The emerald crab is a small crab species, growing to about two inches. While they are a semi-aggressive species, depending on what other livestock are kept in the tank, they can be safe to keep along with other fish. They are opportunistic feeders, so they will scavenge for anything left behind on the substrate of the tank, grab food from the water column, and yes, can even snag a small fish. The perk is that they keep the reef floor in pristine condition so that you don’t have to work as hard – just sit back and enjoy the show.

Emerald crabs can be territorial, and if you keep several of them in one tank, they need to have space to claim their own ground or they will fight. The tiny crabs have been known to stress corals, so be mindful of the amount of space that you give these little fighters, so that they can co-exist with everything else in the tank.

Related: Freshwater Clams: An Underutilized Invertebrate

The emerald crab is most active in the night time. During the day, or when the tank lights are on, they will hide among the live rock. When the tank lights go out, they will emerge from their hideouts to scavenge for food.

Because the emerald crab is an opportunistic feeder, they need algae to supplement their diet. A mature set up is best for them, in order for scavenging. Because of their small size, they can be kept in an aquarium as small as 20 gallons, which makes them appealing for those who prefer smaller saltwater set ups.

Along with algae, the emerald crab will also eat meaty foods scavenged from what the fish do not consume. If there is a severe lack of algae in the aquarium, which makes up the majority of their diet, it can be supplemented with freeze dried or fresh greens.

The emerald crab can bring a lot of joy to your aquarium, and be a vital member of your reef’s cleanup crew. They do well in a wide range of water conditions, tank sizes, and stocking. Crabs are interesting to watch at night, so adding a red light to your aquarium can allow you to monitor the night life and enjoy your crap to the fullest.


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