The Giant Fish That Makes Milk

as the biggest river in the world the amazon is renowned for its unique wildlife there's the infamously carnivorous piranha the elusive pink dolphin and blind electric eels but perhaps stranger than almost any other fish is the arapaima the largest freshwater fish in the world they generally grow to be 3 meters long and weigh up to 200 kilograms for comparison that's how big bottle-nosed dolphins usually get and the size of the arapaima is hardly the most unusual thing about them the closer you look the weirder they get from bony tongues to ceramic scales they've proven themselves to be among the fittest of survivors and if you were to observe them shortly after their eggs hatch and their offspring start swimming you would see something that appears to break the rules of biology adult arapaima feeding their young with their own milk but scientists have struggled to understand the strange adaptations and behavior of the arapaima because the fish have become increasingly endangered due to overfishing luckily protecting the arapaima might also lead to greater protections for the amazon rainforest as well making them not only a worthy subject of research but potentially the linchpin for the conservation of the entire ecosystem the earliest ancestors of the arapaima were the first members of the osteoglossomorpha super order who appeared about 187 million years ago in the early jurassic the name of this group literally means bony tongues indicating that unique adaptation at this point the fish weren't amazon dwellers since the river didn't start forming until 11 million years ago around 23 million years ago the arapaima assumed the form that it has today making it among the oldest living freshwater fish on the planet and by this point it had a number of adaptations that made it perfectly suited for the low oxygen freshwater river unlike most fish arapaima get 90 percent of their oxygen needs from the air instead of the water they have a modified swim bladder which functions almost like lungs allowing them to suck oxygen from above the water they can even survive out of the water for up to 24 hours to understand just how remarkable this organ is in arapaima it's worth diving a little deeper into swim bladders more generally for most fish the swim bladder is filled with air to help them maintain buoyancy at different depths some fish have swim bladders which are connected to their gastrointestinal system in this kind of fish like goldfish and carp they gulp air to inflate the swim bladder then burp air to deflate it in other types of fish swim bladders aren't connected to the digestive tract they empty and fill their swim bladders by diffusing gas from their blood for these fish the swim bladders have nothing to do with breathing they're more like flotation devices these fish have gills that filter oxygen from the water and then pass it into the bloodstream arapaima on the other hand have a very large swim bladder that essentially runs the length of their bellies the organ is characterized by small wrinkles which increases the surface area to allow for better absorption of oxygen and when scientists studied the tissue that lines the arapaima swim bladder they found it was very similar to the tissue seen in the gills of fish that don't breathe air this swim bladder isn't a true lung like you'd see in a mammal but it serves a very similar purpose despite having gills arapaima drowned within 10 to 15 minutes if they stay completely underwater this might seem like a weird adaptation for a fish considering they live in the water but it's actually a good survival strategy if you live in branches of a river like the amazon that regularly floods its banks when the river infiltrates the forest during the annual wet season the water is filled with decaying vegetation this creates highly anaerobic conditions in other words a very low oxygen content this would be a big problem for most fish but it doesn't bother the arapaima in fact being able to breathe air in low oxygen environments actually gives them a competitive advantage in hunting while other fish are moving more slowly to deal with less oxygen in the water the arapaima can still shoot forward at full speed to capture prey arapaima are a formidable predator in the waters of the amazon they trap prey by opening their mouths in a way that creates suction sucking fish crabs and even birds and small mammals into their jaws from there the prey is crushed between their bony tongues sharp upper palate and teeth not the best way to go in the amazon few animals sit higher on the food chain the only predators of these giant creatures are jaguars amazonian alligators and as you would guess human beings and even though arapaima regularly swim in piranha-infested waters they have an amazing adaptation that protects them from being attacked by schools of these dangerous fish incredibly tough scales arapaima skin makes up 10 of their body weight and is surprisingly useful for human products called leather the incredibly durable material is used for clothing purses and boots and their scales are truly a marvel of natural engineering made up of two layers the scales are both flexible and tough meaning the fish can move without any trouble but are also very well protected from puncture wounds the top layer of the scales are actually mineralized making it almost like a flexible ceramic it's similar to our bones but all of the hard material is collected at the surface and the lower level is collagen fibrils which grow in the pattern of a spiral staircase this structure means that even if the hard outer layer is punctured the collagen will break at different angles and preserve the overall integrity it might be deformed but it won't shatter like a window scientists are studying the arapaima scales to see if they can use it to improve bulletproof armor which works similarly by combining soft padding with a hard plastic but the problem is that this type of armor requires a third material a sealant to bind the two layers together in arapima the binding happens on a molecular level the two layers of the scale simply grow together which has proven difficult to replicate in the lab and on top of all of these impressive adaptations there's one that's so strange it has perplexed both locals and scientists for years something that seems like it shouldn't come from a fish at all when you think of the animals that care for their young you probably think of animals like us the primates elephants dogs or cats in fact all mammals care for their young because all mammals by definition provide milk for their babies sometimes for months and months most fish in the world by contrast simply lay their eggs somewhere safe and then bounce but for generations indigenous people of the amazon have observed something baffling arapaima producing what looks like milk and their babies swimming through it the creamy white fluid comes out of cavities in the skull of both male and female arapaima during the reproductive period for a long time people thought this was some kind of nursing strategy but in 2017 researchers analyzed the chemical compounds of the milk and were surprised by what they found instead of being full of protein like milk would be the cephalic fluid was a mixture of hormones and chemicals that are related to immunological processes in other words the milk wasn't nourishing the young but it was clearly doing something because there was an increase in its production for both males and females when they were having offspring and the young fish seemed to be absorbing it one of the hormones they found is called prolactin this was perplexing prolactin is the hormone that mainly stimulates breast growth and production of milk in mammals but the arapaima milk isn't really milk like ours is here prolactin must be serving a different purpose in mammals and birds prolactin is also known to enter the brain to affect neuronal function inducing parental behavior in one study rodents were found to retrieve and groom their pups more often with more prolactin in their system in birds prolactin increases parental behavior like nesting incubation and feeding researchers think that in fish prolactin could be increasing parental behavior just as it does in the other vertebrates and the arapaima are indeed caring parents not only do the parents build a nest to hold the eggs and then guard it from predators the males also help the little fish for up to three months after they hatch the male's head turn a darker color perhaps to offer camouflage to their young and they sometimes bring the fry into their mouths to move them to another location if predators get too close scientists also think the arapaima milk could work as a chemoattractant keeping the offspring close to the head of the male keeping them safer and causing them to follow as he searches for plankton-rich water that they can feed in overall arapaima babies who are exposed to the arapaima milk grow bigger and are more likely to survive compared to ones who are raised without the milk but unfortunately there's still a lot researchers are struggling to understand about the behavior and life cycle of this giant fish and that's partially because in some parts of the amazon arapaima came very close to extinction for millions of years arapaima used their many adaptations to rule the amazon river but with the arrival of more and more humans we eventually became their main hunters and even though the giant fish are well adapted to withstand predation from almost any other creature their need to rise to the surface for air makes them very appealing targets for humans with sharp sticks for centuries local indigenous people relied on arapaima for sustenance without causing any strong negative impact to the populations but the combination of outsiders coming in to catch the fish and locals catching an increasing number of arapaima to sell commercially the populations around brazil and guyana plummeted but there's strong evidence that protecting the fish and creating restrictions for when the fish can be harvested can be very effective in helping the arapaima populations rebound in communities in brazil protective measures like catch limits and a total fishing ban at certain times of the year allowed the populations to grow over 400 in eight years lakes that had only 20 arapaima left ended up with more than two thousand but of course arapaima live across a wide geographical range and conditions are different from one place to another in some places mining and deforestation are a big threat in others the commercial over-harvesting of the arapaima is the main problem different communities respond with different solutions based on their needs take riwa village in guyana for example the arapaima were traditionally an important source of nutrition for the local indigenous people but overfishing led to a huge decrease in their population with help from scientists who established surveys to monitor the range and population size of the arapaima the village was able to create regulations to protect the fish in their area they also built an eco lodge and started a fishing business that offered catch and release programs to anglers visiting the region for tourism not only does this program prevent arapaima from being killed it also provides income for the villagers who previously relied on over harvesting the fish for their income and the scientists who work in guyana have suggested taking arapaima conservation one step further because arapaima used the floodplains as part of their habitat there's a strong need to protect the forests as well as the river when it comes to policy makers deciding what parts of the forest to protect ensuring the survival of arapaima requires extending protections beyond the dry season banks of the amazon and this kind of protection could help a number of other species who make their homes in the forests as well as the river there's still a lot we don't know about the arapaima but with any luck helping protect the means they'll continue to reign as the giants of the amazon and give us plenty of chances to learn more about them the arapaima and all of its strangeness is a product of its wild and unpredictable habitat the extreme seasonal flooding of the amazon has shaped its evolution for millions of years it's a phenomenon that turns the forest floor into the riverbed huge stretches of land underwater for six months of the year these floods create thousands of river islands in an archipelago that stretches for thousands of kilometers the largest collection of river islands in the world the arapaima is not the only creature who has been forged from these watery circumstances these river islands are home to some of the most unusual creatures everything living there during the floods is forced to adapt or die in the documentary amazon river islands the floating forest on curiosity stream you can learn about the fish that feed from the treetops floating islands of ants and the trees and plants that have learned to survive for months underwater it's an episode in a series called wildest islands all of which gives you a glimpse into some of the most interesting micro habitats around the world curiosity stream is a streaming platform with thousands of high quality documentaries like this one and now curiositystream has partnered with us to offer an incredible deal by signing up to curiositystream you now also get a subscription to nebula nebula is a streaming platform made by me and several other educational youtube content creators it's a place where we can upload our videos ad free and a place where we can experiment with new original content one of these new projects for us is our podcast called modulus it's available ad-free on nebula and is where we explore the human stories behind the science we cover here on youtube in the latest episode brian from real 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Channel: Real Science

Views: 845,161

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Id: MxjIk_vXGlw

Length: 15min 52sec (952 seconds)

Published: Sat Mar 06 2021

Reddit Comments

[u/PureSalty101]

Unless the arapaima player specs into parental instincts, I dont see this being too useful