Fish Fertilize Trees
By Maya C. Lemaire
The Misunderstood Fish
We humans tend to believe that any organism that does not think like us is unintelligent, when in fact, quite the contrary is true. A freshwater salmon has a staggering IQ of 130, while the average human IQ is just 100. Apart from IQs and numbers, fish have remarkable abilities to survive underwater. However, fishes are one of the most commonly cultivated(farmed) and killed creatures in the world, with over a trillion fish caught and killed globally every year, excluding those in fish farms. These fish are often slaughtered inhumanely, mainly with the false belief that all fish are dumb, insentient beings.
What a fish perceives
Apart from the obvious lack of eyelids, a fishes’ eyes resemble our own. Their eyeballs include three pairs of muscles that allow the eye to swivel around on all axes, fibers that hold the lens in place, and retractor muscles that change the distance of the lens from the retina. As the evolutionary forebears of land-dwelling animals, fishes have originated this system of seeing.
However, unlike us, seahorses, blennies, gobies, and flounders have further upgraded their eye musculature so that each eye can rotate independently, like chameleons. This means that they can process two visual fields at a time. Because it is so radically different from humans, scientists have set up experiments to better understand these mental experiences.
Larger and faster predatory fishes rely on keen vision to catch prey. However, hunting underwater presents a new set of visual challenges. The deeper they go, there is less light available to see. Another problem is that the rapid drop in water temperature numbs the brain and slows muscle function. To compensate, some fishes have evolved an ingenious way to bear the greater depths of the ocean. Swordfishes can harness the heat generated by muscles; they can heat up their eyes twenty to thirty degrees Fahrenheit above water temperature. Studies suggest that this eye warming strategy improves the fish’s ability to track swift movements in prey up to ten times.
A swordfish up close - (“Creature Feature: Swordfish - Twilight Zone”)
As they did with color vision, fish probably were the first to develop a sense of hearing. Despite the common assumption that all fishes are silent, they actually have more ways of producing sounds than any other group of vertebrate animals. Unlike the method all other vertebrates use, which is the vibration of air against membranes, fishes rapidly contract a pair of vocal muscles to vibrate their own swim bladder. They can also grate their teeth into their jaws, rub bones or gill covers together, or even expel bubbles from their anuses!
In many ways, fish hearing surpasses our own. Most fishes hear in the range of 50 hertz (Hz) to 3,000 Hz, which is within our range of 20 Hz to 20,000 Hz. But studies now document fish sensitivity to the ultrasounds, in the upper range of bat hearing: up to 180,0000 Hz in some species. Which is way above the human limit. At the other end of the hearing spectrum, some fishes such as cods can hear infrasounds as low as 1 Hz.
Fishes have a good sense of smell. They use it for many things - for finding food, finding mates, identifying danger, and homing. Especially in aquatic environments where murky conditions make vision unreliable, smells can prove pretty useful. Unlike other vertebrates, a fish’s nostril does not have the double duty of smelling and breathing; it is used exclusively for smell. A sockeye salmon can sense shrimp extract at concentrations equal to five teaspoons in an Olympic-sized swimming pool. Other salmon species can detect the smell of a seal diluted to two-thirds of a drop in the same pool. But the champion sniffer, the American eel, can detect less than one-millionth of a drop of home water in the Olympic pool. Like salmons, eels make long migrations back to specific spawning sites, and they get there following a subtle gradient of scent.
Scent is also used when alarming others when there is a (potential) presence of danger. Karl von Frisch, an Austrian biologist, discovered a phenomenon in fishes when he accidentally injured one of his captive minnows. Immediately, other fish in the tank began showing classic predator-evading behavior—darting back and forth and freezing in place. Later experiments showed that injured minnows (among other fish species), release a pheromone that triggered a social response in members of the same species. Von Frisch coined the term schreckstoff (translating literally to “scary stuff”) for these pheromones.
It is widely assumed that fishes’ release of chemicals for communication is passive and not done consciously, because of their lack of external scent glands or scent-making behavior. A shabby presumption, says Jonathan Balcombe. Male sheepshead swordtails use at least two tactics to make females have a higher chance of detecting their pheromones: a) they urinate more when around females, and b) when courting, males place themselves upstream of females.
American eel, - (Wikipedia)
Sheepshead swordtails, male and female - (Pinterest)
For fish, taste is mainly used for food recognition. Like us, they have tongues and a
system in which taste signals can be sent to the brain. Also like us, most of a fish’s
taste buds are located in the mouth and throat. But because they are quite literally
immersed in the medium they smell and taste in, many have taste buds on other
parts of the body, often the lips and snout. Fish also have more taste buds than any
other animal. A channel catfish, only about 20 cm long, has 680,000 taste buds on its entire body, including the fins. Humans only have about 10,000.
In addition, fish also have food preferences that may even be distinctive to individuals, leading to the idea that fish also have personalities. Studies find that picky eaters are not rare. Stéphan Keebs, author of Fish Behaviour in the Aquarium and in the Wild, describes a fish’s reaction to the taste of toad tadpoles—a toxic and unpleasant item in its environment:
“It must be said that a very hungry bass, it's back to the wall, will stoop to eat toad tadpoles. But if the reaction of fishes that mistakenly take tadpoles in their mouth is anything to go by—they violently shake their head and you can almost see the grimace on their face—having tadpoles on the menu is no great culinary experience for a fish.”
In some ways, fishes and humans can be startlingly similar.
What a fish feels
Do fish feel pain? While it may seem obvious to some of us that they do so based on their appearance, their behavior, and their membership in the group of vertebrate animals, many people believe otherwise. However, several studies show that fish are sentient beings.
To be able to feel pain is not a trifling matter. It requires conscious experience. Organisms can recoil from a negative stimulus without feeling any pain. It could be a reflexive response in which nerves and muscles move without any mental engagement. Therefore, it is important to know how aware fishes are of their surroundings.
In one experiment, trout were injected with either bee venom, vinegar, neutral saline solution, or handled but not injected. The last two were control groups, to cancel out distress caused by the injection itself or being handled. The scientists measured the gill beat rates—how quickly gill covers opened and closed—a proven method to show distress in fish. All trout appeared distressed, but in the two control groups (saline solution and handled) the gill beat rose from 50bpm, which is the resting rate, to about 70bpm. The bee venom and vinegar groups rose to about 90bpm.
Prior to the injections, the trout had been trained to swim to a ring when a light went on. After the injections, however, none of the trouts approached the ring, even when they had not been fed for a day. After one hour, the fish’s gill beats in the control groups returned to normal, while the fish from bee venom and vinegar groups didn’t return to normal until 5.5 hours later. The fish in the control groups began approaching the ring after 1 hour and 20 minutes after the injection, while the fish from the other groups took three times as long before they started showing interest. In addition, the trouts’ negative reactions were significantly reduced with the introduction of the drug morphine.
These experiments, among others, strongly suggest that fishes are actively feeling pain and not merely responding reflexively.
On a lighter note. If fish can feel pain, can they also feel joy? If you have ever been out boating, fishing, or bird-watching at lakes and rivers, you have most likely seen fish jumping out of the water. But why might they do this?
Of course, fish exit the water in a desperate attempt to escape predators. Dolphins manipulate this behavior, deliberately cornering their prey and catching the panicked fishes in midair. But just as how we may sprint for fun or from fear, different emotions might motivate fishes to jump. Mobula rays don’t hurl their large bodies (seventeen-foot wingspan and over a ton in weight) skyward up to ten feet before splashing down with a loud slap in fear. This behavior is seen in ten recognized species of Mobula rays and has earned them the nickname “flying mobulas”. As males often initiate this behavior, some speculate that there might be a courtship role. Other scientists think it might be a parasite removal strategy. Whatever its function, the mobulas seem to be enjoying themselves.
Another fish known for their jumpy behavior is the mullet. They soar through the air in one or two successive jumps, but some have seen mullets jump in seven consecutive leaps. Because they usually land on their sides, some theories suggest they do this to displace skin parasites. Others say they do it to inhale oxygen, which is supported by the fact that mullets leap more when the oxygen level is lower in water; however this is canceled out because jumping costs more energy than what is taken in by gulping air.
Might they be leaping for fun? Gordon M. Burghardt published accounts of dozens of fish species leaping over floating obstacles—sticks, turtles, even dead fish!—for no clear reason other than entertainment. So far, nobody has subjected this possibility to a scientific experiment, but it would be an intriguing topic to experiment for.
“Flying mobulas” - (Natural History Museum)
Who a fish knows
As many little prey fish there are, there are many types of predatory fishes. Few fish hunt
alone. Cooperative hunting is known to occur in several fish species. For example, shoals
of barracuda will swim in a tight spiral, herding prey into shallow waters for easier hunting.
Similarly, the parabolic shape of a shoal of hunting tunas indicates that tunas also hunt
Lions are renowned for their cooperative hunting prowess. As are orcas. Is it possible that fishes also signal their intention to hunt?
The lion’s marine namesake, lionfish, are named for their ‘mane’ of long, ribbonlike, poisonous pectoral fins, but in hindsight they could as well have been named for their cooperative hunting style. A 2014 study of two species of lionfish describes a distinctive flared-fin display used to signal to one another the desire to hunt together. The approaching fish swims to the other with its head down and pectoral fins flared, then rapidly undulates its fin for a few seconds, followed by the slow waving of alternate pectoral fins. The receiving fish almost always responds with fin waving, then the pair move off to hunt. Cooperators had higher success rates than lionfishes hunting alone.
In 2013, a research team came upon some cooperative hunting by Red Sea groupers, only this time the signal resembled something we do to communicate the location of a hidden object: pointing. Unlike other gestures these fish make, the “headstand” signal actually points to a fish or some other edible creature out of sight or reach. Therefore, it is a referential gesture, which, outside of humans, had only previously been attributed to the great apes or ravens—two groups known to be Einsteins of the animal world.
Biologists Simone Pika and Thomas Bugnyar proposed five criteria for referential gestures, which the headstand signal meets:
It is directed toward an object - prey hiding in a reef;
Purely communicative and mechanically ineffective - i.e. the act does not directly catch prey;
It is directed toward a potential recipient - e.g. an octopus, a wrasse etc.;
It elicits a voluntary response - e.g. the grouper comes over to look for the prey; and
It demonstrates intentionality.
Democracy and peacekeeping
Hunting collaborations involve two fish minds working to translate and transfer desires into favorable outcomes. Another way that desires may lead to social outcomes is through collective decision making.
“One common property we see in animal groups from schooling fish to flocking birds to primate groups is that they effectively vote to decide where to go and what to do,” says Iain Couzin, an evolutionary biologist at Princeton University. “When one fish heads toward a potential source of food, the other fish vote with their fins on whether to follow.” This highly democratic process helps animals make decisions as a group that are better than those of any single member. The speed and accuracy of decisions increase with the size of the group, because they efficiently combine the diverse information possessed by group members.
Fish don’t just follow random individuals either. Fish are more likely to follow a few informed experts or leaders. They may also be informed of who to follow by the appearance of individual fishes. A healthier, more robust fish would be considered a better decision maker than a frailer fish.
Fishes also have to contend with conflicts among their own kind, but because injury and death are bad outcomes, especially if you have to survive and reproduce, physical fighting between rivals is rare. Like other animals, fish use ritualized displays of strength to avoid a more serious conflict that would risk injury to either opponent.
Some tactics to impress upon others that fighting them is not a good idea are: opening gill covers, spreading their fins to look big as possible, booming sounds, head shakes, body twists, or performing color changes.
Fishes also appease. An effective way they do this is by exposing vulnerable body parts, similar to how wolves expose their throats. In female to female disputes, a male golden mbuna will break up the fight without favoring either combatant. If one female is unfamiliar, the male will favor her, which increases the chance that she will settle into the group.
A shoal of fish - (Wikipedia Contributors, “Shoaling and Schooling”)
Caregiving has evolved at least twenty-two different times in fishes. About one in four of all fish species—some 8,000 species—devote at least some form of caregiving to their offspring. This ranges from protecting eggs to looking after the offspring’s most vulnerable weeks of life.
Some fishes carry their own eggs, to improve their survival. This may be holding them in the mouth, or carrying them in a pouch. The catfish from Guiana, however, actually wears its eggs. The parent rolls in the egg mass so they stick to the skin, where they are then overgrown by a new layer of skin until the embryos are developed enough to emerge.
Banded arcaras lay their eggs on a carefully chosen loose leaf. The parents ‘test out’ leaves by pulling, lifting, or turning to find the optimum nest. After spawning, the parents then guard the eggs. If disturbed, the parent acaras seize one end of the leaf carrying the eggs and drag it to safer locations.
Alternatively, parents may hide their eggs by constructing shelters or other elaborate structures. Whitetail major damselfish like to clean their nesting site first. To do this, they pick up sand in their mouths and spit it with force on the chosen rock face. Then they fan the area with their fins. Finally, they remove any remaining sand grains by plucking them off with their mouths.
Unusually, it is the males of seahorses that give birth to young
Image - (Wikipedia Contributors, “Seahorse”)
Despite our prejudices, evidence strongly suggests that fishes are sentient beings and are much smarter than we think. If we understand that we are not unlike and that they deserve our consideration, maybe we will learn to respect our underwater cousins.
Written by Jiyoo Kim
Edited By: Samuel Lim & Jynna Wongswan
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