It is now time to report on a recently renovated aquarium located near the exit of the Tropical Rain Forest exhibit, next to the habitat of the red piranha (Pygocentrus nattereri). The aquarium is home to a lively shoal of more than a dozen banded archerfish (Toxotes jaculatrix). Swimming among decorations that mimic a flooded mangrove forest, the largest of these fish already measure over 10 centimeters in length.
These remarkable fish have evolved an ingenious method for catching non-aquatic prey— with startling accuracy, they spit water to dislodge insects perched on overhanging vegetation. Staff members of the Tropical Freshwater Species Department have trained them to use their remarkable ability within the environment of the exhibit. As Artem Baranov, Head of the Department, explains, a piece of driftwood suspended above the water holds tasty treats to encourage the fish to show off their hunting behavior.
Beyond their singular method of feeding, the archerfish are distinguished by their two different types of color vision. The cones in the bottom half of their eyes, which look upwards, are adapted to perceive the colors dominant above the water, while the cones in the top half, which look downwards, are tuned to detect the colors dominating the underwater environment. This special characteristic allows archerfish to easily spot prey both on land and underwater. Their capabilities also include excellent memory: the “spitting sharpshooters” have been shown to recognize and remember individual human faces. Some scientists even believe that they possess numerical competence, at least being able to discriminate between quantities of spots on an object.
Their cohabitants, spotted green pufferfish (Dichtomyctere nigroviridis), are equally fascinating. Similarly to their relatives, the infamous fugu, they carry tetrodotoxin, a potent neurotoxin hazardous to humans, in some of their organs and tissues. However, this chemical defense is not their sole adaptation. They use the characteristic trick of the family Tetraodontidae, inflating their bodies into a spiny sphere when threatened. The staple of their diet, both in the wild and in captivity, are gastropods, for instance snails. These hard-shelled mollusks serve not only as nutrition, but also help to wear down the continuously growing teeth of puffers. The brightly colored fish with black spots have slightly clumsy appearance, but they are surprisingly maneuverable and can make quick turns in any direction. When the pufferfish gracefully glides fluttering its pectoral fins, it resembles the sphinx moth hovering over a flower. Like the banded archerfish, the spotted green pufferfish are highly intelligent, curious, and can distinguish between individual humans.
Both fish species prefer brackish water as they inhabit coastal environments in the wild: river estuaries, lagoons or mangrove forests. Visitors are invited to observe these remarkable creatures in the Tropical Rain Forest exhibit, open daily except Monday.
