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Scaring fish straight!

By Leonard Ho - Posted Apr 01, 2013 09:00 AM
The 35,000 sardines in the Kuroshio Current Exhibit at Nagoyako Aquarium (Japan) were once well behaved. They grouped themselves in a coordinated school, creating a "pilchard tornado" - a massive whirling ball of fish that delighted aquarium-goers. But as time went on, the sardines began to break formation. Aquarium officials had to do something to get their fish back in line.
Scaring fish straight!

Chromis behaving naturally in the wild. Photo by Jeremiah Blatz

The aquarium's solution was to introduce 15 Pacific bluefin tuna to the huge 5 meters (16ft.) tall by 14 meters (46ft.) wide tank.  Without predators, the sardines simply got too comfortable with their habitat and became lax with their schooling defenses.  Aquarium officials hope the additional predators will scare the sardines back into formation.  If not, officials may consider adding sailfish to the exhibit as well.

If you've wondered why your anthias aren't schooling or why your chromis aren't huddled in the branches of Acropora, it's likely because they've grown too safe with their environment.  While predators obviously stress prey, the lack of threat for these dither fish causes them not only to drop their defensive mechanisms but may also encourage them to misbehave (e.g. become aggressive) against their own kind.  And studies have shown that fish kept in un-stimulating aquariums grow increasingly more stupid.

Clearly, no fishkeeper is going to introduce predators into their aquariums to threaten ... and eat their expensive fish (It's like shooting fish in a barrel for the predators).  But maybe a little artificial threat might not be bad  for aquariums with small social fish - especially if they are "misbehaving."  Aquarists may want to try showing images or videos of predators in front of their aquariums to visually scare (for lack of better word) their fish.  Fish are also very responsive to smells (Read about the Olfaction in Aquarium Fishes).  Perhaps the scent of predators such as groupers housed in attached refugiums can induce small fish to exhibit their natural defensive behaviors.  If a manufacturer can bottle the scent of "fear," I'm sure there is a good market for this type of additive.

FYI: When sardines do their thing, this is what the pilchard tornado should look like.

[Via Rocketnews24 via The Asahi Shimubun Digital (Japanese)]

Author: Leonard Ho
Location: Southern California

I'm a passionate aquarist of over 30 years, a coral reef lover, and the blog editor for Advanced Aquarist. While aquarium gadgets interest me, it's really livestock (especially fish), artistry of aquariums, and "method behind the madness" processes that captivate my attention.

Website: http://www.advancedaquarist.com.

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