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Originally published May 22, 2013

Today, May 22, is International Biodiversity Day. Of the more than 1,500 species that you can see at Shedd, about 900 are fishes, almost equally divided between freshwater and marine species.

You'll find 120 species of South American catfishes in Amazon Rising. The large characin family is also well-represented in Amazon, with 66 species, including lots of tetras and a couple of piranhas. One more characin, the blind Mexican cave tetra, lives in the Islands and Lakes gallery.

Several multicolored Cichlid fish swim near a rocky bottom.
An orange and white Midas Cichlid is recognizable by the large hump on its head.

A midas cichlid, found in the Islands and Lakes Gallery at Shedd.

An electric blue cichlid swims near a pebbled habitat floor.

An electric blue cichlid, found in the Islands and Lakes Gallery at Shedd.

But according to collection manager Kathy Lee, “The cichlids appear to be more diversified in behavior and have many interesting feeding strategies.” They also have possibly the most creative common names in all of fishdom. Among the 59 species at Shedd, you’ll find the eartheater, Bolivian ram, blue julie, star sapphire, flavescent peacock and Malawi eye-biter.

Before we go into their differences, let’s look at what makes a cichlid a cichlid.

If you peer way inside the mouths of a hobbyist’s freshwater angelfish, a farm-raised tilapia and one of those African lake eye-biters, you’ll see what biologists call pharyngeal dentition—teeth in the throat. While a cichlid uses the often specialized teeth in its jaws to pick up, rasp, scrape, nibble, or grab and grip food, it chews or crunches the meal in its throat. Pharyngeal dentition is the single feature that this vast, varied family has in common—and it’s what allowed for the exuberant proliferation of species in the first place, through adaptation to niche feeding opportunities in every imaginable microhabitat of lake and river ecosystems. Essentially, for anything in the water that could be considered food, there’s a cichlid species that eats it.

A lot of cichlids are mainly herbivores, grazing on algae and plants. Others are dentrivores—scavengers—that eat all sorts of organic matter, helping to keep their habitats clean at the same time. Then there are predators, some of which are generalists, going after small fishes, insects, larvae and other food on the move. Pretty normal, so far.

A Flavescent Peacock Cichlid swims in its habitat in the Islands and Lakes gallery.

A flavescent peacock cichlid, found in the Islands and Lakes Gallery at Shedd.

A cockatoo dwarf cichlid, only about the length of an adult's thumb, with its brilliant yellow body and orange-dotted dorsal and tail fins is quite striking despite its small size.

A cockatoo dwarf cichlid broods over its young.

But the real beauty of the cichlids—in addition to their often bold patterns and brilliant colors—is the degree of specialization some species have pursued to get a meal. A number of cichlids practice fin-nipping, eating the protein-rich scales of other fishes. Fish eggs and larvae are fair game to many aquatic predators, but several cichlids ram the heads of mouth-brooding species, causing the parent to spit out the developing young. The elegant venustus cichlid in the Islands and Lakes gallery has turned ambush hunting into theater, playing dead on the lake floor to lure small scavenging fish within nabbing distance.

As for the Malawi eye-biter, from several accounts, that common moniker is accurate. The eye-biter is a lightning-fast ambush hunter that uses its extremely narrow body to angle in on prey with minimal visual presence. It targets smaller cichlids, often slashing the prey to more easily overpower it. And while this aggressive cichlid may not specialize in feeding on eyeballs, it may also blind its prey to disable it during the hunt, or resort to the unusual feeding behavior when food is scarce, based on examination of gut contents.

You can learn more about the incredible diversity of cichlids, their feeding habits and favored habitats, in Amazon Rising, the Rivers gallery and at what can only be called “The Amazing Wall of Cichlids” in the Islands and Lakes gallery. And see a few of them on our Facebook album.