It's a fish-eat-fish world, so many fish have evolved unusual body shapes to deter other fish from swallowing them, new research finds. The study, published in the journal Proceedings of the Royal Society B, points out that biting off more than one can chew is not an option for most aquatic predators. As a result, thousands of prey species have evolved bodies that are ultra wide, round, narrow, spiked or are otherwise designed not to be the perfect morsel. "Almost every fish that eats other fishes captures their prey with their mouths, and so the prey must fit into their mouth; this is also true for some fish-eating birds, such grebes and herons," lead author Samantha Price of the University of California at Davis' Department of Evolution and Ecology told Discovery News. "Not all predators are gape-limited, but over the history of fishes, it is likely that many of the predators would have been limited by the size of their mouth." This sea devil can be both predator and prey, as its human-like mouth, yet flat body shape, suggest. There are multiple reasons for "misshapen" bodies among fish, but avoiding fitting into a hunter's mouth turns out to be a critical one.Photos: These Fish Were Made For Walking
Imagine trying to fit this into your mouth. The flying gurnard makes maximum use of body area without investing much energy in fleshy substance. The new study, which looked at over 25,000 living fish species, found that evolution of fish such as this was shaped by gape-limited predators, meaning marine hunters that can only open their mouths so far.Photos: Sneezing Monkey, Walking Fish Among New Species
In addition to body shape, many fish have evolved bumpy skin, fin spines and other features that deter a predator from simply sucking the fish into their mouth like a smooth piece of sushi. The researchers determined that fish with spines that extend vertically evolve toward "deeper" bodies. Deep in this case means having a more vertical yet narrow, rounded body, sort of like a pancake on its side. The slantbrow batfish is just the opposite. It is considered to be a wider-bodied fish, like a flat, albeit misshapen, pancake floating in the water. These wider-bodied fish often evolve spines that extend horizontally. Price said that the spines and body depth "work together to defend against predators." She continued that if the prey fish "becomes bigger, the predator will not be able to eat it, but increasing the overall size is energetically costly, so it is better just to increase a single dimension: either width or depth."Half of All Marine Life Lost in Just 40 Years
On the predator side are fish like this giant grouper. Sharks often grab our attention because of their appearance and apex predator status, but groupers like this have been known to eat sharks from time to time using their huge mouths and relentless hunting tactics.Photos: Mix Of Species Gain Haven In New Marine Reserve
Wendy Rathey, Wikimedia Commons
The leafy sea dragon belongs to the marine fish family that also includes seahorses and pipefish. Its small fins not only increase its body surface area, but they are also difficult to view as they subtly undulate while the seadragon moves slowly through the water. Here, camouflage is another benefit of body shape. When in motion, this seadragon looks remarkably like a piece of floating seaweed.Camouflage Tech Copies Cuttlefish's Disappearing Act
Nick Hobgood, Wikimedia Commons
Garden eels, needlefish and spaghetti eels use another tactic to avoid being eaten. Like actual spaghetti, they are extremely thin and tend to slip out of a predator's mouth.Eels Migrate a Staggering 1,500 Miles
Benson Kua, Flickr
"Fishes display an incredible diversity of body sizes, including lineages that are almost as wide or as deep as they are long," Price said. "Our findings suggest that predation has helped shape this diversity, although many other factors, such as habitat or diet, are also likely to be important drivers of fish body form evolution."Fish Listen to Music, Prefer Bach
Jens Petersen, Wikimedia Commons
This red lionfish looks to be posing for the camera, displaying its showy colors and fins. Predators would do well to notice and move away, as lionfish are venomous. Spines on such fish therefore are doubly dangerous. "The spines can damage the predator and species that have venom associated with the spines will cause even more problems," Price explained. "There are some rather grisly photos online of some injuries to fishermen and swimmers who have been on the wrong end of fish spines!"Big Lionfish Found at Disturbing Depths
Moonfish are classic examples of fish that have evolved extremely deep body sizes that the researchers say deter gape-limited predators. The moonfish body is also sharp-edged and covered on the top and bottom with small spines that make handling them challenging. Brian Sidlauskas is an associate professor and curator of fishes at Oregon State University's Department of Fisheries and Wildlife. He told Discovery News that the new study provides "an elegant demonstration" of at least one "critical piece" of fish body form evolution.First Warm-Blooded Fish Identified
Bruce Moravchik, NOAA
When deflated, puffer fish look like helpless, tiny prey. Once inflated, though, they become deadly mouthfuls for many would-be diners. Prosanta Chakrabarty of Louisiana State University agrees that spines not only work against predators via their sharpness and possible venom, but also because they help certain fish to become wider or deeper bodied. "That might sound intuitive, but it really isn't," he informed Discovery News. "Your bodies are constrained in how deep or wide they can get because these animals still need to try to avoid predators, get their own prey, move around the water column, and find mates." He continued, "The spines, which are not similarly constrained, allow these fishes to reach these depths and widths despite the constraints on the body. That is a microevolutionary solution to a macroevolutionary constraint."Puffed-Up Blowfish Aren't Holding Their Breath
The popular drug fluoxetine, commonly sold under the name Prozac, has been detected in aquatic ecosystems worldwide, and now new research finds that Siamese fighting fish exposed to the drug become timid and weak, hurting their chances for survival.
The study, published in the Journal of Experimental Biology, shows how this and other drugs polluting the environment can impact wildlife.
“There has been growing concern over the past two decades regarding the prevalence of pharmaceuticals and personal care products in waterways worldwide,” lead author Teresa Dzieweczynski of the University of New England and her colleagues Brennah Campbell and Jessica Kane wrote.
The researchers say that many products, including fluoxetine, “are still in their active form when they enter sewage treatment systems, where they have limited removal because of their water solubility and resistance to biodegradation.”
The problem can therefore happen quite innocently, such as when a person on Prozac or certain other drugs goes to the bathroom and flushes. We trust that sewage treatment systems clean up our waste, but as the scientists point out, that cannot always happen due to the chemical nature of many drugs.
Since fluoxetine is common in some rivers where Siamese fighting fish live, Dzieweczynski and her team investigated how the drug can affect these fish, which are known for both their beauty and boldness.
The researchers compared the behavior of fish exposed to various amounts of fluoxetine to those that had no exposure to the drug.
The scientists wrote that “males exposed to fluoxetine were less bold and less consistent in their behavioral responses, and the correlations between boldness over time and across assays were weaker than those for unexposed males.”
This might at first sound like a good thing. After all, Prozac for humans has been hailed as a wonder drug since the mid 1980s. It is used to treat human psychiatric disorders such as depression and post-traumatic stress disorder. How the drug works has never been fully determined, but it is believed to increase levels of the neurotransmitter serotonin in the synapse between nerves by reducing reabsorption into nerve cells to relieve symptoms.
For Siamese fighting fish, however, the drug-induced timidity could hurt the fish’s chances for survival.
“If exposure affects boldness, fitness may be decreased as individuals that fail to forage, avoid predators or attract mates will obviously have decreased fitness,” the researchers explained.
They continued, “Perhaps most importantly and alarmingly, the effects of exposure lasted even after fluoxetine was removed.”
The scientists call for additional studies on the chronic effects of the drug, not only to determine how best to protect wildlife from exposure to it, but also to determine more about how it impacts, in the long term, the people who are taking it.