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When Aquarium Sardines Start Acting Lazy? You Call In The Tuna Squad! Japan, April 1, 13

The Nagoyako Aquarium in Nagoya, Aichi Prefecture, is experiencing an unusual problem — lazy sardines. That’s right, according to a recent story on Japanese newspaper Asahi’s digital site, the sardines at Nagoyako Aquarium are not behaving as they should, supposedly because “they have it too easy” in the protected environment of their tank. And in order not to disappoint visitors, it looks like the aquarium will have to call in the “tuna squad” to whip the sardines’ act into shape. But what could be causing these errant fish to misbehave?

The sardines in question — maiwashi or Japanese pilchards to be more exact — are kept in the “Kuroshio Tank” of the aquarium in an environment based roughly on the conditions that exist in the Kuroshio Current off the coast of Japan. The tank, 5 meters (16ft.) tall and 14 meters (46ft.) wide, contains fish of varying sizes that coexist in nature in the Kuroshio environment.


The tank’s main attraction is the “pilchard tornado” created by the sardines as they group together to feed in a large whirl-shaped formation. A splendid sight to behold, this behavior is a defense mechanism on the part of the sardines to protect themselves from larger fish, as rocks and other structures that can provide shelter are typically not found in the offshore waters of the Kuroshio Current. The sardines at the Nagoyako Aquarium too exhibited this characteristic behavior, delighting visitors, and all seemed well in the world of the Kuroshio Tank — until recently, when lone sardines started swimming in a different corner of the tank away from the group.

Now, it appears some sardines in the tank have been going rogue and disrupting the tornado teamwork, much to the dismay of the aquarium staff, and the caretakers actually think it may be because the sardines are confident that they won’t be eaten and getting lax with their defenses.

Although the tank is designed within reason to show conditions close to what exists in the natural environment, it obviously wouldn’t do for the larger fish to eat up the sardine population in the tank, so it has been part of the aquarium’s feeding program to keep the larger fish well-fed and full enough not to prey on the sardines. Unfortunately, this may have led to the sardines becoming “over-confident” of their protected status. According to the staff, some of the sardines are even fearless enough to compete for feed with bonito that are three times their size and actually their predators in the wild.

To restore a sense of order among the unruly sardines, the aquarium has decided to add 15 Pacific bluefin tuna into the tank. There are already tuna in the tank, but only two at present, and the aquarium is hoping a larger number will have the effect of “scaring” the sardines back into their usual behavior.

This isn’t the first time attempts have been made to shake up the slacking sardines. A scalloped hammerhead shark that was brought in from Kagoshima Prefecture in southern Japan unfortunately was unable to adapt to the tank’s water temperature and died. Some Japanese Spanish mackerel were also introduced into the tank, only to die from being bitten by sharks. The only type of fish that has been moderately successful in keeping the sardines on their toes (or should I say fins in this case) has been the ocean sunfish. At present, the sardines seem to recognize and avoid the five large sunfish in the tank.