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Dragon fish could hold key information on crucial moment in evolution

A species of fish native to Africa could shed light on the evolutionary process that led fish to move on to dry land. The Dragon fish, Polypterus senegalus is not a normal fish – it has two lungs, and can survive outside of water. In a new eight-month experiment researchers have shown that if a Dragon fish is raised outside of water, the fish changes notably. The fish raised out of water showed differences in their bones and muscles involved in movement not shown in those raised in water.

Fish moved on to dry land and evolved into quadruped vertebrates around 400 million years ago, and it is thought that the Dragon fish is a living demonstration of a phenomenon known as developmental plasticity. This theory states that a creature’s physiology can be changed by environmental factors, and that overtime, these changes are incorporated in to the animal’s genome.

Hans Larsson, of McGill University’s Redpath Museum says that the aim of the experiment was to see the physical changes on Dragon fish that are raised out of the water.
“We wanted to push them in this new environment to see if we could reveal this cryptic variation, and if it works, what does it look like?”

The experiment showed that, as hoped, the Dragon fish raised outside of an aquatic environment were extremely similar to the fish that first emerged from the ocean. The fish were kept in a tank with just 1mm of water on the surface, and kept the fish damp using vegetable misters.

After eight months, the fish raised outside of water were compared to those raised in a normal environment for the species. The fish raised outside of water were found to have undergone many changes, including being more skilful at walking, yet were no less skilled at swimming, positioned their pectoral fins closer to the center of their body and slipped less, and demonstrated an elongation of their ‘chest’ area, and began to separate this part of the body from their skull.

In the future, researchers hope to conduct further experiments on the species, including measuring the force of the fishes’ ‘steps’, as well as further comparisons of the fish to the fossil record. Their paper is published in the journal Nature.

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