FYFD

Tag: fish

  • Measuring Mucus by Dragging Dead Fish

    Measuring Mucus by Dragging Dead Fish

    A fish‘s mucus layer is critical; it protects from pathogens, reduces drag in the water, and, in some cases, protects against predators. But little is known about how mucus could affect terrestrial locomotion in species like the northern snakehead, which can breathe out of the water and move across land. So researchers explored the snakehead’s mucus layer by measuring the force required to drag them (and two other non-terrestrial species) across different surfaces.

    The team tested the same, freshly euthanized fish twice: once with its mucus layer intact and again once the mucus was washed off. Unsurprisingly, the fish’s friction was much lower with its mucus. But they also found that the snakehead was slipperier than either the scaled carp or the scale-free catfish. The biologists suggest that the snakehead could have evolved a slipperier mucus to help it move more easily on land, thereby extending the distance it can cover.

    As a fluid dynamicist, I think fish mucus sounds like a great new playground for the rheologists among us. (Image and research credit: F. Lopez-Chilel and N. Bressman; via PopSci)

    Fediverse Reactions
  • Featured Video Play Icon

    Fish Ladders Keep Species Swimming

    Dams often use fish ladders to help migratory species make their way upstream without interruption. In this video, Grady from Practical Engineering discusses some of the considerations that go into this special infrastructure and what kinds of designs work for different species. The first challenge for any dam is attracting fish to the ladder, which is often done by regulating the water flow at the entrance to create the velocity and turbulence that fish look for when going upstream.

    Once fish are in the ladder, they travel up a series of jumps that break the dam’s elevation into manageable steps. Different dams use various baffle designs to create jumps suited to their local species and the way they like to swim. Calmer spots in each section give fish a spot to rest before they carry on. In well-designed systems, the vast majority (97%!) of fish that enter a ladder make it through to the other side. (Video and image credit: Practical Engineering)

    Fediverse Reactions
  • Featured Video Play Icon

    Helping Fish Bypass Hydro Power Dams

    Many dams in the U.S. were built at a time when their ecological impact was not a major concern. But, thanks to ongoing efforts to study affected species and upgrade infrastructure, many dams now balance human energy needs with the needs of non-humans, like migratory fish populations. In this video, Grady from Practical Engineering takes us behind-the-scenes at McNary Dam in the Pacific Northwest, where special plans and equipment help adult fish swim upstream and juvenile fish pass downstream with as little impact as possible. It’s impressive just how widespread and thorough their infrastructure for letting fish and lampreys through is! There are even facilities to help naturalists track and study the populations passing through. (Video and image credit: Practical Engineering)

  • Featured Video Play Icon

    Inside a Zebrafish Heart

    This glimpse inside a 5-day-old zebrafish’s heart shows why they’re often used as a model organism in cardiac studies. The fish’s heart rate is similar to humans and its two-chamber heart — one atrium and one ventricle, both seen here — serves as a simplified version of ours. Check out the slowed-down section of the video to clearly see blood filling and expanding one chamber before it’s pumped onward. Perhaps the most unusual feature of the zebrafish’s heart is its ability to regenerate; after amputation of up to 20% of its ventricle, the fish can fully regenerate its heart. That’s a pretty incredible recovery, especially when you consider that the heart has to keep pumping the entire time! (Video credit: M. Weber/2023 Nikon Small World in Motion Competition)

  • Featured Video Play Icon

    Blood Flow in a Fin

    This award-winning video shows blood flowing through the tail fin of a small fish. Cells flow outward in a central vessel, then split to either side for the return journey. In this microscopic video, the speed of individual cells seems quite fast, even though the vessels themselves are only wide enough for the blood cells to move in single file. Flow at the microscale can be counterintuitive like that. (Video and image credit: F. Weston for the 2023 Nikon Small World in Motion Competition; via Colossal)

  • Fish Fins Work Together

    Fish Fins Work Together

    Researchers studying how fish swim have long focused on their tail fins and the flows created there. But a fish’s other fins have important effects, too, as seen in this recent study. Researchers built a CFD simulation based on observations of a swimming rainbow trout, focusing on the flow from its back and tail fins. They found that the vortex created by the back fin stabilizes and strengthens the one generated by the tail. It also played a role in reducing drag on the fish by maintaining the pressure difference across the body. When they tried changing the size and geometry of the fins, the fish’s efficiency suffered, indicating that evolution has already optimized the trout’s fins for swimming efficiency. (Image credits: top – J. Sailer, simulation – J. Guo et al.; research credit: J. Guo et al.; via APS Physics)

    Visualization of flow around a digitized rainbow trout.
    Visualization of flow around a digitized rainbow trout.
  • Hunting By Whisker

    Hunting By Whisker

    Seals and sea lions often hunt fish in waters too dark or turbid to rely on eyesight. Instead, they follow their whiskers, using the turbulence generated by a fish’s wake. The vortices shed by the fish cause the seal’s whiskers to vibrate, giving them sensory information. To better understand what a seal can derive from this, a recent experiment looked at what a thin whisker can pick up from an upstream cylinder.

    As expected, the strength of the whisker’s vibration fell off the farther away the cylinder was. But the researchers found that, if they moved the cylinder quickly — like a fish trying to dart away — the vibration of the whisker was stronger. They also found that the whisker was sensitive to misalignment. If the cylinder was placed ahead and to the side of the whisker, the whisker would still vibrate but would do so around a different equilibrium position. That result implies that a seal can get information both about the fish’s speed and direction, simply from the twitch of its whiskers. (Image credit: seal – K. Luke, illustration – P. Gong et al.; research credit: P. Gong et al.; via APS Physics)

    Illustration of a seal following a fish versus the experiment, a whisker following a cylinder's wake.
    Illustration of a seal following a fish versus the experiment, a whisker following a cylinder’s wake.
  • Swimming Intermittently

    Swimming Intermittently

    Many fish do not swim continuously; instead, they use an intermittent motion, swimming in a sudden burst and then coasting. This intermittent swimming is tough to simulate, due to its unsteady nature, but a new study does so using some clever computational techniques.

    Animation showing a fish swimming in a burst-and-coast pattern.
    Animation showing a fish swimming in a burst-and-coast pattern.

    Researchers suspected that the energy intensity of a fish’s burst could be balanced by the low-drag, low-effort phase of coasting. And, indeed, that’s consistent with the team’s results. But they found that the swimming method does require careful optimization; with the wrong cadence, the burst-and-coast technique can be incredibly energy intensive. In nature, of course, fish have had millions of years to optimize their technique, but the results serve as a warning to those building fish-based robots. Those biorobots will need careful optimization to benefit from this swimming style. (Image credit: tetra – Adobe Stock Images, simulation – G. Li et al.; research credit: G. Li et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Featured Video Play Icon

    Simulating Schools

    In nature, fish school for many reasons: protection from predators, increased sensing, and hydrodynamic advantages. To capture this complex behavior, researchers are building their own digital fish, governed by known rules. Here, scientists give each fish social rules — based on vision range and preferred distance from a neighbor — and hydrodynamic rules — based on a fish’s wake. With the rules in place, they can then observe the schooling behaviors of their digital fish. Like their real counterparts, these schools show different flocking based on apparent “moods”. (Image and video credit: J. Zhou et al.)

  • Under the Sea

    Under the Sea

    Deep below the ocean surface, light is in short supply. But dive photographer Steven Kovacs specializes in capturing the ethereal creatures that live in this darkness. Many of his subjects are larval fish, whose forms defy our hydrodynamic expectations. Why would young (presumably less energetic) fish have so many long, drag-inducing appendages? Clearly there’s more to life under the sea than streamlining alone!

    Perhaps our instincts are wrong and these shapes are not as detrimental as they look at first glance. Flexibility can make a drastic difference in hydrodynamics, after all. And some of these species are preparing themselves for a life not spent entirely underwater, anyway. (Image credit: S. Kovacs; via Colossal)