So I think this all started from a lecture that mentioned Zebrafish, which meant I looked up some facts...and then I got obsessed.
Originally published to WILD Magazine.
Zebra Fish: Why am I so obsessed with them, and why should you care?
Ani Talwar discusses the role Zebrafish play in helping medical advancement and understanding.
Zebrafish… a small fish living in freshwater with a lifespan of roughly two years and a relatively random animal for an article. If you’ve come across any of my previous articles you’ll probably see I’m not against finding a random animal and then learning what makes it so cool to the nature it lives in, but Zebrafish are not random, and they are not only useful to their habitat, but in understanding a lot about what affects us as humans too.
In the last 10 years, the use of zebrafish has increased massively in the medical world, making it the second most used animal in medical based research. In fact, it was found (by the Wellcome Trust Sanger Institute) their genetic sequence has an 84% match to human disease genes. This means that 84% of human diseases have a corresponding gene in zebrafish. Therefore, by studying the influence and effect of diseases in these fish, we can improve our understanding as to what might happen to humans.
As an animal in its natural state, the study of zebrafish growth can teach us a lot:
When growing, the zebrafish egg is developed outside of the mother’s womb, so it can be studied as it develops. The Zebrafish embryo is nearly see–through, meaning the development of structures within it can be more easily observed, to the extent that every blood vessel in a living embryo can be seen.
The growth of the embryo is so fast that the human equivalent of 1 month’s worth of embryo growth occurs in just a day in zebrafish! The way you can observe a zebrafish embryo like this means that you do not need as many invasive techniques can be used to observe changes, and the results you get are more reproducible.
Furthermore, the reproductive rate of zebrafish means that there is a consistent supply. They produce 200/300 offspring per pairing, compared to the 15 pups in 21 days a mouse could produce.
The value of the zebrafish extends further than just the embryo and reproduction as well. When it comes to a broken heart, most references are likely to be metaphorical, but not for the zebrafish. Adult zebrafish can restore their own hearts after being hurt, which could be useful in studying the response of heart attacks in people.
Is it ok to study them?
As useful as all these studies are, the term animal cruelty when it comes to animal testing is not an unheard one, and I’ve thought about this too. Animal regulations highlight that the animal you chose to test on must be capable of giving you the knowledge you desire but be the least capable of feeling that a study animal could be. When it comes to testing on mice, rats or fish, the latter is the least sentient, and therefore the better of the three to be testing. The EU Directive 2010/63/EU says that an animal experiment must be carried out on the most undeveloped available system, so the ability to study zebrafish as embryo’s could mean a reduction in studies that use adult fish and mammals.
In scientific studies of zebrafish, chemicals you study can be applied directly to the water, so far less chemical or test compound is actually needed, compared to tests that would be done on a mammal. Whilst mammal studies are used because they mimic human risk, early stage development tests of this nature are more costly, take longer, and require a lot of testing compound to be carried out but using a cell based test instead then reduces your ability to be sure your result mimics a human.
Am I all bark and no bite…or rather all fins and no swim?
I’ve mentioned a lot of theory here, but there is evidence of it being put into practice as well. A study in 2007 (which you can read here) into ‘developmental biology of hematopoiesis, using the zebrafish,’ which means looking at the way your bone marrow makes your blood cells and platelets, using zebrafish as a model. The study used known chemicals, and tested their effects on Zebrafish to find 35 chemicals that suggest more stem cells will be produced.
Furthermore, another test was done on melanoma disease once a pattern was identified whereby patients suffered a relapse 6 months after recovery. The study found a specific inhibitor of one of the genes that contributes to melanoma formation and when the paper was written in 2018, the knowledge had been used to treat 3 patients already, with the aim to extend the recovery time without a relapse from 7-10.5 months.
So, Zebrafish might seem like a random article inspiration, and indeed they were a random animal for me the first time I heard about them, but hopefully you can see why they’re so much more than just a random animal. If you’re interested in where I found this whacky bit of inspiration that led to a whole study, check out the series Unnatural Selection!
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