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Asked by to Rebecca, Heather on 17 Jun 2014. This question was also asked by .
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Rebecca Gladstone answered on 17 Jun 2014:
Now I personally don’t know very much about deep sea fish but the first thing I notice from the information online is how little information there is, which says a lot about how hostile the environment is that they live in, making it more difficult for us to study!
You are absolutely right, the deep water arrow tooth eel lives in a very hostile environment and needs to be very specialised to live at below 1000 meters. At this depth there is no light so fish here including the eel will not rely on sight in the same way we do, sound and smell will be much more important.
It is also cold and food is in short supply. Fish at these depths have to conserve energy by not moving much and waiting for food to come to them, what ever it might be, they can’t afford to be fussy!
Finally the huge pressure of the water around them means that fishes like the eels are long and thin and have soft cartilage like our ears, instead of bones which would break under the pressure of the water. These fish are also made up of much more water than us so that they can be almost the same as their surroundings, all of this stops them being crushed by the water.
All of these features that help them survive will be written in the eels genome, we could compare the deep water arrow tooth eels genome to a genome of a closely related eel that doesn’t live at such depths and look at the differences between the genes that are involved in sight, hearing, their watery muscle and the way they use energy, things that we know are helping it survive. We could also then look for any other differences between the two genomes that we don’t know what they contribute to surviving at extreme depths and then go and look at those genes in more detail to discover something new.
I am sorry I don’t know and couldn’t find out any more about the eel specifically, we need more interested people like you to try and find ways to study them in their hostile environment and or study their genome so that we can link the differences and adaptations in the genome to what the eel looks like and behaves like!
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Heather Ritchie answered on 17 Jun 2014:
What a great question! And not unlike the questions myself and many other scientists are asking.
Arrow-tooth eels are exceptional animals and we caught one in our last cruise in November 2013. I was actually going to put a picture of it on my profile on here but instead I put up an image of the crustaceans I work with. (There are some lovely images including the arrow-tooth on this blog of our cruise. There is a picture of him with its scientific name Histiobranchus sp. http://hadeep.wordpress.com/ )
These deep-sea animals have many adaptations which allow them to survive in such an extreme environment. Some of these adaptations are physiological (how they look etc) and include having extremely sharp teeth which are ideal for hunting prey, and they also have an incredible sense of smell and we have taken videos which show they are able to locate a dead fish as the smell moves down a current. Other adaptations are behavioural (how they act etc) which can include their hunting strategies which are to rip flesh from dead animals or some fish will actually locate a dead animals but instead of eating it they will sit and wait until other fish or crustaceans appear and will eat them instead as they are fresher!
Several of my friends and colleagues are also looking at how deep-sea fish can use lipids (which are a type of fat) to survive in the extreme environment. Firstly the fats are a good source for storing energy but they are also light and help fish to float and to control their buoyancy.
The most exciting thing about deep-sea work at the moment is that we don’t actually have very much genomic data on any of these animals. As you can imagine it is very difficult to get samples. Scientists have been taking videos of arrow-tooth eels for years and last year is the first time people I work with have managed to capture one in a trap. What we would hope to do in the future is to look at the genomic data not just for arrow-tooths but many other fish and invertebrates and to examine the differences in their DNA to see if there are any differences between them. Once we know where the differences are we can use a variety of DNA databases to work out which genes the differences are happening in and then we will be able to say which genes are responsible for these adaptations in these incredible animals.
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