ASK A SCIENTIST2019-03-21T11:00:41+00:00

ASK A SCIENTIST

Here are the questions we have received so far. If after reading them you are still wondering about something, scroll down to the bottom of the page and send us your question by filling out the form. We will answer you and also post your question here.

 

THE QUESTIONS WE HAVE RECEIVED SO FAR

Which is the tuna’s natural predator?

A group of students from the Lycée Français in Mallorca asked us:
Which is the tuna’s natural predator?

Patricia from Planet Tuna answered: When we think of tuna, we usually think of big fish at the top of the food chain. But we have to remember that they hatch from a 1-millimeter egg. So their predators change a lot throughout their life cycle. When they’re only a few days old, during the egg and larva stages, their predators are usually other fish larvae, or even young of their own species, and invertebrates such as jellyfish. As they grow, they can swim faster and get away from smaller predators. At that point, their predators are other fish, but when they reach adulthood, only large predators are able to feed on tuna: other, larger tuna and similar species, large sharks, and killer whales. And, of course, humans.

Do tuna sleep? And if so, how?

A group of students from the Lycée Français in Mallorca asked us:
Do tuna sleep? And if so, how?

Patricia and Hannah from Planet Tuna answered: First of all we would have to define what we consider sleeping. As humans, we associate sleeping with closing our eyelids, not moving our bodies, and, in many cases, lying down. When it’s dark out, our pineal gland releases melatonin and our body recognizes that it’s time to “shut down the neurons.” If we were to measure the brain’s electrical activity with an EEG when we’re asleep, we would identify a different pattern from the one we would see if we were awake.
Tuna don’t have eyelids, so their eyes are always open. That, in and of itself, doesn’t necessarily mean they’re not asleep: we can’t close our ears, for example, and that doesn’t stop us from sleeping. Tuna can’t ever stop swimming, because they need the oxygen they get from filtering water while they move. If you look into a tank with tuna larvae or juveniles at night, you see they move more slowly, but although we’ve tried, we haven’t yet managed to measure their swimming speed in the dark, nor have we been able to record them without any light. And it appears that the brain activity we associate with sleep in mammals is different from that of fish. There are indications that tuna release melatonin, but we’re not yet sure about the relationship between their daily rhythm and that secretion. So for now all we can say is that, although there’s no scientific evidence of their sleeping, they probably enter some similar state in which they rest and save energy.

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