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Cold-Blooded Animals

Howe and I were chatting over lunch about pets, and it occurred to me that I’ve never met anyone who has had baby Koi hatched at home. The respective theories we put forward would soon reveal our academic inclinations: I gave a more social “big fish eat small fish” explanation, while Howe explained the phenomenon on a more scientific basis.

I explained that since there aren’t many hideouts such as rock crevices in an artificial aquatic environment for mother Koi to lay their eggs safely or for the small fry to hide, other adult Koi may gobble the exposed eggs or small fry up – just like what most fish do.

This is the tragic scenario frequently played out in my fish tank back home. Newly born guppies face almost certain death if we don’t provide some water plants for them to hide from the adult guppies. Often we would be overjoyed in the morning to discover twenty baby guppies have been born the night before, only to find most of them vanished by the afternoon. It happened so quickly that we sometimes wonder if we had miscounted the number of baby guppies earlier.

But Howe, who specialises in genetics and keeps many Koi at home, believed those colourful Koi we keep are unable to spawn naturally after being cross-bred so many times — perhaps even with other species of fish — to obtain the desired colours.

Later I did some research on the internet and it turned out my theory was correct. The popular belief is that Koi aren’t carnivorous, since owners usually feed their Koi with processed fish food and not other small fishes, unlike Arowana. However, Koi do eat their own eggs and small fry. Koi also get along well with goldfish or other tropical fish — as long as the other fish aren’t small enough to eat.

I guess fish are cold-blooded for a reason.

09 January 2005 · Science

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