Tiger puffer fish attach their eggs to rocks near the bottom of the sea, often at the mouths of bays. Then the larvae (幼鱼) move to the entries of rivers and lakes once they have grown a little. Then, having put on a lot of weight, they head out to sea. There’s no innocent childhood for the puffer fish, as Shin Oikawa of Kyushu University in Japan and his colleagues found out when they put the larvae of tiger puffer fish in the lab and monitored them for two months. They found that the larvae went through three steps in which their metabolic(新陈代谢) rates increased dramatically when they reached body weights of 0.002g, 0.01g, and 0.1g. When a larva went through one of these steps, its behaviour also changed. For instance, once a larva had passed the first level it would have grown its first tooth and could start attacking larvae that had not yet reached that stage. Similarly, any larva that had reached the 0.01g or 0.1g levels would start attacking lighter larvae.

　　The researchers noted that the baby fish had a “relatively small mouth”, so rather than swallowing their brothers and sisters whole, they would bite pieces out of them. Despite this limitation, the 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 chew on their fellows had an advantage. The extra food accelerated their growth and development. Tiger puffer fish are likely to be faster and swifter, so they can deal better with enemies.

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