800 ornamental fish mysteriously disappear from an aquarium; the investigation results are truly surprising, part one

Staff at Shenzhen Ocean World discovered that of the 500 ornamental fish placed in the shark tank a week earlier, most had vanished without a trace. This phenomenon, never seen before, drew the park's attention: where had all these fish gone? And the results of the subsequent inventory were truly surprising.

Ornamental fish are placed in the shark tank to maintain the sharks' natural living state and enhance the viewing experience. The park had never encountered such an abnormal, sharp decline of ornamental fish in the shark tank. Sharks are relatively fierce fish; they prey on the weaker, smaller fish, so the ornamental fish would certainly dwindle gradually. Yet hundreds of ornamental fish disappearing in large numbers within a week was somewhat unexpected. These ornamental fish were hiding in the landscaping built specifically as shelter for them, simply invisible on the surface: newly introduced fish, unaccustomed to the new environment and feeling stressed, could conceivably squeeze two or three hundred of themselves into the landscaping.

To determine whether the ornamental fish were still in the shark tank, curator Zhou Yunxin immediately sent staff into the water to take a count, with particular focus on searching every piece of landscaping where ornamental fish could hide. They opened all the doors in the landscaping that could be opened; for the deeper caves, they used long poles to reach in and stir things up, driving out as many of the hiding ornamental fish as possible to make a rough count.

The inventory results left Zhou Yunxin disappointed: the ornamental fish really had vanished into thin air. After watching the shark tank's activity for several consecutive days without finding any clue, she once again placed 300 ornamental fish into the shark tank. Yet just two days later, the tank was empty again; these fish had all mysteriously disappeared, with no one knowing where they went: no live fish to be seen, no dead bodies to be found. Even if the fish had died, there should be corpses; and if they had rotted, some remaining fish bones should still be visible.

The large number of missing ornamental fish had already caused nearly 100,000 yuan in losses for Ocean World, and Zhou Yunxin and the staff began investigating and analyzing the cause. Everyone's first reaction was that the sharks had eaten them, but this idea was quickly rejected: among the various landscape structures in the pool, some were hollow and some were relatively tall; those hollow places provided these small fish with excellent shelter: when sharks attack or prey on them, they can hide in their own little homes, which the generally larger sharks cannot enter.

Ordinarily, the small fish swam right up to the sharks' mouths without any danger, each going about its own business. Logically, the longer they were kept, the less wild the sharks would become, and since staff regularly and actively fed them, the sharks generally would not bother expending effort to hunt. Could it be that the sharks had gradually grown and their appetites had increased? Zhou Yunxin decided to increase the amount of food provided, to eliminate the possibility of sharks preying on the small fish out of hunger.

At first it had some effect, but it did not last long; the fish in the tank still declined sharply in a short period.

Just as the ornamental fish continued to disappear in large numbers and Zhou Yunxin was at a loss over what to do, staff discovered that some sharks had fallen ill. Zhou Yunxin suddenly had a flash of insight: if these ornamental fish had gotten stuck in the landscaping and died, their decomposition would cause the water quality to worsen progressively; that was possible. But the test results of the pool water showed that although the water quality was poor, it would not cause mass fish deaths, and at the same time there were no large numbers of corpses proving that the ornamental fish had died in the pool. With no other cause to be found, only the process of elimination remained.

On Zhou Yunxin's suggestion, Shenzhen Ocean World renovated its water treatment system: in addition to strengthening the circulation of the biochemical pool, a separate small circulation system was added to make the water clearer. But after the renovation, the effect was not obvious.

Aquarium mystery: the shark tank suffers heavy losses yet the cause is hard to determine; a bewildering investigation begins

To find the truth behind the disappearance of the ornamental fish, Zhou Yunxin arranged for staff to take turns on duty, implementing 24-hour monitoring with someone always present day and night, constantly watching the shark tank's activity and reporting immediately if anything happened. Yet even so, the disappearance of the ornamental fish could not be curbed: after a week of monitoring, the staff found no abnormal conditions, and the ornamental fish were still steadily decreasing. This put even greater pressure on Zhou Yunxin. Then, on the ninth night of monitoring, the duty staff were astonished to discover: in the very same tank where the ornamental fish had disappeared in large numbers, several sharks were tearing at a blacktip reef shark over 1 meter long, biting it until it was covered in blood and barely breathing.

Shocked, the staff immediately reported the situation to Zhou Yunxin. Zhou Yunxin's first reaction was: this tank has already fallen into chaos! Sharks have extraordinarily keen smell and an extremely strong ability to distinguish blood; once something in the water is bitten and bleeds, a shark can even detect from a concentration of one part per million of blood where the bleeding creature is located, and will immediately rush over to surround and bite it. At this moment, one shark in the tank had been bitten and was bleeding, so how could the other sharks not come to surround and bite it? With so many sharks scrambling in the tank, rushing and colliding as they lunged at that injured shark, how could it not fall into chaos?

Zhou Yunxin had the staff isolate the injured blacktip reef shark as much as possible to prevent the situation from escalating further. But when the staff retrieved it, only half of the bitten blacktip reef shark's body remained. Previously, when this kind of situation had not occurred, everyone felt that being with the sharks was relatively safe and not dangerous. After this incident, everyone felt a bit jittery, thinking that being with the sharks was not as safe as they had originally imagined.

Aquarium mystery: the shark tank suffers heavy losses yet the cause is hard to determine; a bewildering investigation begins

To know what happens next, please see the next installment; the exciting content always has to make its grand finale, thank you all for your support.