Shows like Blue Planet depict the wonderful variation of life in the ocean, but when it comes to conservation efforts, it's the unattractive fish that need our support the most, a study carried out by an international team of researchers has found. Species with drab colouring and elongated bodies were found to be least aesthetically-pleasing, but they were also the most at threat of extinction and more at risk of exploitation by fisheries.

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These 'ugly' fish have unique traits that make them important, ecologically speaking, and their loss would have a huge impact on the biodiversity of Earth's reefs, say the authors of the new study.

To rank species of reef fish in order of beauty, ecologists first asked members of the public to decide which was the most beautiful fish for each of 30 different pairs of images. From there, the team developed an algorithm that could identify the attributes of an attractive fish, and went on to rank more than 4,000 pictures of fish.

A bocaccio rockfish, which has a grey-purple toned body with orange fins
The rare bocaccio rockfish ( Sebastes paucispinis) was deemed unattractive and plain, but it's an endangered, ecologically-important reef fish © Getty Images

Read more about life on the reef:

"Bright, colourful fish species with rounder bodies tended to be rated as the most beautiful," said co-author Prof Nicolas Mouquet, of the University of Montpellier, France. "I find the word 'ugly' too strong, but that's obviously more catchy than 'less attractive', which we use in our study. This is why the examples [of unattractive fish] do not correspond to what readers have in mind – if you Google 'ugly fish' you’ll find very different images to those here."

Among the unattractive reef fish determined by the new study were the bluefish (Pomatomus saltatrix), the bocaccio rockfish (Sebastes paucispinis) and the white steenbras (Lithognathus lithognathus).

"These three fishes are among the less beautiful species in our dataset, and they are threatened and of some commercial interest – which often means that they are over-exploited," said Mouquet.

To determine the ecological importance of different species, Mouquet and the team compared the fishes' traits to determine how unique they were. Things like body size, habitat, food and preferred temperature were all considered, and it was found that the more unique species actually turned out to be the more plain ones.

A shoal of fish that are grey in colour.
The bluefish ( Pomatomus saltatrix) was rated one of the more unattractive reef species © Getty Images

Our opinion of animals' attractiveness relates to our overall interest in a species, which the authors of the new paper say could influence where we put our conservation efforts and donations. The aesthetic bias also affects scientific research, as people are drawn to study brightly coloured reef fish – a previous study showed publications are overwhelmingly biased towards yellow fishes.

It's hoped that by making people aware of the impacts of beauty biases, more research, support and conservation can go into these ecologically important species. And, the deep learning algorithm developed by Mouquet and the team could go on to help us understand the impact of our aesthetic judgements on threatened birds, mammals, reptiles and others.

Read more about marine life:

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Authors

Amy ArthurEditorial Assistant, BBC Science Focus

Amy is the Editorial Assistant at BBC Science Focus. Her BA degree specialised in science publishing and she has been working as a journalist since graduating in 2018. In 2020, Amy was named Editorial Assistant of the Year by the British Society of Magazine Editors. She looks after all things books, culture and media. Her interests range from natural history and wildlife, to women in STEM and accessibility tech.

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