Dr Diego Vaz, our Senior Curator of Fish, looks after preserved fish specimens that come from the shallowest streams to the depths of the ocean.
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Fish behind the scenes
James Ashworth
Behind the scenes at the Natural History Museum, a team of dedicated curators looks after more than 80 million specimens and objects spanning the history of life on Earth.
In the latest in our new series, curator Dr Diego Vaz dives into the fish collection we care for.
Arms deep in a vat of preservatives, Dr Diego Vaz is having the time of his life.
While being up to your elbows in murky orange liquid might not be everyone’s idea of a good time, our Senior Curator of Fish smiles as he searches through one of the large metal containers in the centre of our Tank Room.
From the depths of the tank emerges a small sunfish, followed quickly by a long, eel-like frilled shark. Then, reaching right down into the liquid, Diego pulls out a Greenland shark – one of the longest-lived animals on Earth.
“There’s a lot more physical activity in this job than you might expect,” says Diego as he heaves out another large fish. “You’re moving specimens, heading up and down to the labs, dashing over to meet visitors – sometimes, I can exceed my daily step count without even leaving the building!”
“It might be a workout, but I love it. There’s no other job quite like this anywhere in the world.”
What does an ichthyologist do? Ichthyology is the study of fish, so ichthyologists are scientists who study fish, just like Diego.
This frilled shark is too big to be kept in one of our Tank Room’s glass jars, so instead it’s kept in a metal container alongside other large specimens.
Finding out about fish
Diego’s route to being a curator began with an insatiable desire to find out more about the natural world.
“I love questions,” Diego admits. “Sometimes they just come to me when I’m sitting at my desk, relaxing at home or heading out, and I just can’t help but investigate them.”
This curiosity led to him studying to be a taxonomist – a scientist that names and classifies species. Growing up in Brazil, with its extraordinary levels of biodiversity, meant that he had plenty of different animals that he could focus on.
Diego started by working with angel sharks – a group of seabed-dwelling ocean fish that are found across the world. As his career progressed, he developed an interest for all kinds of fishes, with a particular focus on comparing their skeletons. This involved visiting many museums to study the fish specimens they looked after – gradually drawing him towards being a curator.
“When you work with specimens, you naturally get involved in their curation,” says Diego. “It’s a privilege to work with them, so it’s our duty to leave these specimens better than they were when we found them – whether that’s improving their labelling or finding out new information about them.”
To understand more about fish, museum specimens such as this longnose butterflyfish are vital to scientists.
Museum fish specimens are stored in 70% alcohol. It’s this that’s helped to preserve this striated frogfish for decades.
How are fish preserved in museums?
As a senior curator, one of Diego’s biggest responsibilities is to enhance the fish collection he looks after. There are around eight million specimens in this collection, providing an unparalleled source of information about fish.
Such a collection is far more than just a library of specimens. It’s a window into the past, with each specimen coming with records of where and when it was collected. This information is fundamental for scientists, who can use it to investigate the health of fish populations, find new species, discover the impacts of climate change on the ocean and much more.
Adding to this collection provides more data to help with these investigations, but a lot of work needs to be done before a new specimen can be added to the stores. For starters, all the paperwork needs to be in order.
“All of our specimens have to be collected legally and ethically, and we need to have the paperwork that shows that,” explains Diego. “It’s not the 1800s anymore!”
Preservation has also moved on a lot from the 1800s. While historical fish might be stuffed or kept as skeletons, they’re now normally preserved whole.
To start with, scientists normally take a tissue sample from the fish and preserve it in liquid nitrogen at around -200°C. This is because the preservation process can damage DNA, so the frozen sample allows genetic analysis of the specimen to be carried out in the future.
Preserving fish isn’t easy, with multiple stages of preparation needed before a fish can be permanently placed in our care.
© Mark Humphries
The next step is to inject the fish with preservatives such as formalin. This forms strong chemical bonds that hold the animal’s body together and help to stop it from degrading. The specimen is then placed in a glass jar full of a strong ethanol solution to kill microbes and protect it from further decay.
Even something seemingly as simple as placing the fish in a jar is a delicate job, as different species need to be stored in different ways. Sharks, for example, have a very fragile snout that has a lot of research value, so they tend to be kept tail first. Bony fish, meanwhile, are better kept face down, as their fin rays are very fragile.
The last step is to place a label in the jar with the specimen that has its ID number, as well as details about what it is and where it came from. A lid is then placed onto the jar and sealed with Vaseline, which solidifies and acts like a glue in the cool conditions of the collections store.
Our fish specimens are regularly checked by Diego and the other fish curators to protect the collection.
The rainbow collection
Keeping track of all the specimens in this ever-growing collection takes up a lot of Diego’s time. It’s an enormous job, with the collection’s shelves stretching into the distance and laden with jars full of colourful alcohol ranging from pale yellows to brilliant oranges and vibrant reds to deep browns.
“The colour of the alcohol is the result of fluids leaking out into the preservative from inside the fish,” explains Diego. “The colour varies between different jars, but that’s not good or bad. It’s just the result of differences between the species and how they’ve been preserved.”
“The main thing is to make sure each jar contains around 70% ethanol, which helps to ensure the specimens are neither too soft or too brittle, and that the fluid covers the specimens inside.”
If a jar needs topping up, then Diego and the other members of the fish curation team use a special wine opener-like tool to lift the lid. They can also use this opportunity to update the specimen’s label and its collection listing to reflect any new discoveries.
“Science is always updating itself, and that’s especially true for taxonomy,” remarks Diego. “The names of species can change as we better understand their relationships with other animals and reassign them to different groups.”
“To help navigate these changes, fish curators can use Eschmeyer’s Catalogue of Fishes. It’s a really incredible endeavour that allows you to see all the names a fish has had, and I don’t think there’s anything quite like it for any other group of animals.”
It’s also an opportunity to make sure that the specimens are exactly where they’re meant to be. Keeping the location up to date in the Museum’s catalogue is vital to finding a specimen among the millions of fish housed in the spirit collection.
“It’s very important to keep the location data up to date, as there’s no easy way of finding a specimen otherwise,” Diego says. “I’ve spent hours looking for a specimen only to find that it’s on the next shelf over!”
“To try and prevent this, we conduct regular audits to make sure everything’s in the right place.”
Coelacanths were originally named from fossils that were hundreds of millions of years old, but later discoveries revealed they weren’t actually extinct!
Diego has recently been studying gobies, including the species Eviota afelei from the Pacific island of Guam, to find out more about them.
© Diego Vaz
Favourite fishes
One specimen that Diego always enjoys checking in on is the coelacanth. This legendary fish was once believed to have gone extinct in the era of the dinosaurs, but, astonishingly, living populations were discovered off the coast of Africa in the 1930s.
“The coelacanth is one of the most important specimens of the twentieth century,” adds Diego. “Not only does it have an incredible story, but it’s a reminder of how important museum curators are. Without Marjorie Courtenay-Latimer, this fish wouldn’t have been discovered.”
“It’s probably my favourite specimen that I look after.”
Other fishes that are close to Diego’s heart are the Eviota gobies he’s currently studying. This group of small fishes lives across the Indian and Pacific Oceans, but there’s a lot about them that isn’t well understood.
Diego’s trying to change that by using the goby specimens in the collection. He’s particularly interested in looking at the anatomy of these fishes to define species and the relationships between them.
Different stains can highlight different parts of a small fish’s body, with Alcian Blue binding to cartilage and Alizarin Red colouring bone.
© Diego Vaz
A closer look
To study these gobies, Diego needs to look at features that might only be visible under a microscope. To highlight these characteristics, one option for small fish is a process known as diaphonisation, also known as clearing and staining.
This involves dying certain parts of the animal’s body with brightly coloured chemicals to make them more visible. As it’s a permanent change, it’s not carried out on type specimens or other important specimens. The details diaphonisation reveals, however, can be important to clarify a species’ characteristics alongside the type specimen.
Fish come in all shapes and sizes – when it comes to small fish, Diego uses stains to help the key features to stand out.
To start the process, Diego has to dehydrate the fish in alcohol before carrying out the first stain using Alcian Blue dye. It’s a careful process that takes a lot of practice to get right.
“Alcian Blue dye binds to proteins in the animal’s cartilage and highlights it,” Diego says. “However, these proteins are also some of the first to decay after an animal’s death. If it isn’t preserved quickly, there won’t be anything left to stain.”
“The process also involves acetic acid, and the timing has to be precisely judged. Otherwise, the mixture will just eat away at the specimen and there’ll be nothing left.”
After the fish has been left for long enough, the acid is neutralised and the specimen gradually rehydrated. Diego can then add an enzyme known as trypsin, which eats away at the animal’s muscles so that it becomes completely transparent and reveals the stained tissues inside. Further dyes can then be added to highlight other parts of the animal’s body, such as the bones.
“It’s a bit like cooking,” says Diego. “The more you do it, the better you get at judging when something is ready, and how you can mix up the recipe to try something a bit different.”
Once the process is finished, the specimen will be stained in a variety of distinctive colours and ready for its close-up under the microscope.
One important specimen that we look after is this Greenland shark, which washed up on a beach in Northumberland, UK, in 2014.
Fish forever
As the fish collection continues to grow, there’s always something for Diego to be getting on with. Whether it’s topping up the tank of a deep-sea fish or relocating a small sardine in the stores, being a fish curator is a never-ending job.
“No one day in my job is the same as the next,” Diego says. “I might be helping out with a visitor one moment and then packaging up a specimen for an international loan the next.”
“In between, I’m squeezing in my own research when I can. I’m still studying gobies, but I’m also working with the fossil fish collection to re-describe angel sharks from the Jurassic.”
“It’s a lot to do, but I think there’s the potential to discover some new species that have never been identified before. That’s a really exciting possibility.”
Looking after eight million specimens isn’t a job for the faint-hearted, but Diego’s curiosity continues to drive him forward. His work is helping the mysteries of the deep blue sea to become a little bit clearer.
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