Thanks to special adaptations, this climbing perch can stay on land for longer periods of time.
The fish pictured here is a climbing fish (Anabas testudineus) – a perch species that can stay on dry land for up to a week to change its biotope. While normal fish would quickly suffocate without water, the freshwater native climbing fish is specially adapted to the temporary shore leave. On the one hand, it is helped by its labyrinth organ, a ribbed bony plate covered with a mucous membrane rich in veins that lies in a bulge in the gill cavity. It allows the fish to breathe air.
In addition, the climbing fish also has an adaptation at the cell level. Because almost all living beings need the ability to regulate the fluid balance in their cells in order to survive. The interior of biomembranes is normally water-repellent, making it difficult for water molecules to be transported. So that the fish can supply its cells with additional moisture or seal them off, depending on the environment, it has special tubes in its membranes, the so-called aquaporins. In contrast to purely passive diffusion, these channels formed by proteins can actively control the transport of liquid.
A team of researchers from Sweden and Singapore has studied the exact functioning of these water channels in climbing fish. They discovered an unusual fold on the outside of the aquaporins. The functional and structural examination of the fold suggests that it is a quick-closing valve. "Depending on the changing environmental conditions of the fish, the valve enables the channel to be opened and closed quickly and at short notice," explains Kristina Hedfalk, a biochemist at the University of Gothenburg.
This finding not only contributes to understanding the special adaptations of climbing fish, but also provides insights into the basic functions of water channels in cells. In fact, these regulatory processes also play an important role in humans. For example, corresponding drugs for the treatment of cerebral edema could be developed on this basis. In the case of such sudden water retention, a rapid reduction in pressure can prevent damage to the brain and thus save lives.