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Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world.

Species:

Habitat: Deep in the seas around Japan, and the north-west Pacific; fish tanks in sushi restaurants, looking nervous

If you were looking for an animal to take the title of “most kick-ass fish in the sea”, then the tiger puffer would have to be a strong contender.

Not only is it lethally poisonous – though that doesn’t stop people trying to eat it – and able to scare off predators by inflating itself to become much larger than normal, when it is young it munches on its own brothers and sisters.

Tiger puffers attach their eggs to rocks near the bottom of the sea, often . The larvae hatch, then move to estuaries or mudflats once they have grown a little. Having put on , they head out to sea.

It’s no innocent childhood for the pufferfish, though, as of Kyushu University in Fukuoka, Japan, and colleagues found when they hatched tiger puffer larvae in the lab and monitored them for two months.

Play nicely

They found that the larvae went through three step changes in which their metabolic rates increased dramatically, when they reached body weights of 0.002 grams, 0.01g and 0.1g. When a larva went through one of these changes, its behaviour also changed. For instance, once a larva had passed the first benchmark it would have grown its first teeth and could start attacking larvae that had not yet reached that stage. Similarly, any larva that had reached the 0.01g or 0.1g benchmarks would start attacking larvae that hadn’t.

The researchers noted that the baby fish had a “relatively small gape size”, so rather than swallowing their brothers and sisters whole, they would bite chunks out of them. Despite this limitation, the cannibalistic fish caused plenty of deaths – up to 12 per cent of the deaths that happened in the lab each day.

Those fish that grew fast enough to be able to gorge on their fellows had an advantage. The extra food accelerated their growth and development still further. Cannibal fish are likely to be faster and more agile, and so deal better with predators.

Come and have a go

If pufferfish have a tough upbringing, it’s nothing compared with the intimidating tricks of the adults.

As the name suggests, can inflate themselves to make themselves seem much larger than they really are, thus scaring off predators or enemies. They do this by , which are extremely elastic, with water. The inflation mechanism seems to have .

If that’s not enough of a deterrent, the tiger puffer – like most of the other Takifugu species – carries a deadly cargo of , mostly in its ovaries and liver.

Last supper

Eat one and the poison will paralyse your muscles, including the diaphragm muscles responsible for breathing – so death is usually by asphyxiation. Famously, the fish is a delicacy in Japan, where highly qualified chefs produce dishes that contain safe levels of the poison.

The puffer does not go to the trouble of producing tetrodotoxin itself. Instead, it hosts bacteria that synthesise the stuff. It obtains these bacteria from its diet, so the youngest adult fish are not poisonous.

The tiger puffer is also one of the growing band of species that has . It proved to be much “cleaner” than the human one, lacking most of the junk DNA that clutters our chromosomes: this fish is so kick-ass that it has ruthlessly cleared out its own genome.

Journal reference: , ()

Read previous Zoologger columns: The most bizarre life story on Earth?, Keep freeloaders happy with rotting corpses, Robin Hood meets his underwater match, The mud creature that lives without oxygen, Magneto-bat steers by a built-in compass, The world’s most promiscuous… snail, Pregnant males are pro-choice for abortion, Mummy, can I have some more carrion soup?, The largest arthropod to prowl the land.