Score
Title
858
How To Search ELI5: A Quick Reminder About Rule 7
14644
ELI5: Why do cars travel in packs on the highway, even when there are no traffic stops to create groups?
11
ELI5: Why are our fingertips, ear holes and nostrils all approximately the same size?
7
ELI5: Why do body parts (fingers, eyes, etc) twitch randomly?
11
ELI5 Retarded Time
4
ELI5: Umbral Moonshine
4
ELI5: Why do jet skis shoot a stream of water straight up when they go forward?
7
ELI5: Why are some sounds, like nails on a chalkboard, so universally hated by humans?
4
ELI5: How does ethylene make fruits and vegetables ripen faster?
3
ELI5: Why are solar gardens good investments for wealthy people?
3
ELI5: Why does a copied URL dirrct me yo a different page?
2
ELI5: Why is it not blinding to look directly at the sun early in a sun rise or late into a sun set?
2
ELI5 why is the polar star always north?
12
ELI5: How many ants does it take to make a functioning ant colony?
17
ELI5: SD. SS. SA. Gestapo. Wehrmacht. Sipo. Kripo. What were they all and how do they relate to each other?
4
ELI5: If I use the same amount of coffee grounds but more water, does my caffeine content change?
2
ELI5: Why do animals appear to care so much for their young, but not so much when the 'children' get older?
3
ELI5; What is the difference between a break and a fracture?
6
ELI5: Air movement in a house
2
ELI5: Why does the wind typically pick up during the middle of the day and die down in the evenings?
1
ELI5: Why does NASCAR race on oval tracks, rather than the more complicated layouts of other motorsports?
4
ELI5: How can sperm cells "swim" through something as thick as seminal fluid? You wouldn't be able to swim through honey for example.
4
ELI5: Why can't there be an "universe's point of reference" in relativism?
2
ELI5: Why do our eyes lose focus after staring at something for a while?
5
ELI5: Why/how can most species of animals hold their breath underwater for far longer than humans can?
1
ELI5: Risk Parity strategies in investing - how they work and what are the advantages/disadvantages?
1
ELI5: How is a bank started?
2
ELI5:Why is eating healthy 80% of being healthy?
1
ELI5: How is it possible to perceive a game servers tick rate going from 30 to 60 when your ping is not that fast?
5
ELI5: Objectively, what are the limitations of carbon dating?
1
ELI5: Security as a Service
0
ELI5: How do space shuttles launch off the modified 747s?
1
ELI5: What the hell is Umbral Moonshine?
8
ELI5: Why are cones and pyramids exactly 1/3 of a cylinder or prism's volume?
1
ELI5: How much does food affect building strength?
6
ELI5: What causes exhausts to have that rasp-y sound people tend to associate with tuners? (civics, integras, etc)
2
ELI5: Why is it stated sharks will suffocate if they quit swimming, but I see examples like the white-tipped reef shark who spend the day laying on the bottom?
0
ELI5: Why are steroids more popular in baseball than football or basketball?
0
ELI5: Why does the body make women throw up or get nauseous when pregnant?
16
ELI5: When and why did 8 hours of sleep become the standard for a solid night’s rest?
2
ELI5:How some stars become pulsars?
16 taggartism Well, I typed out an explanation, but then did a quick search to see if I could phrase things better. I am an aspiring marine biologist, but this fisheries scientist put it pretty well a year ago. I suggest you read his explanation. @mynameismrguyperson --- "Fisheries scientist here. I am seeing a lot of incomplete or partially correct answers here. This might be more ELI15. Freshwater fishes tend to have much higher concentrations of ions (like sodium) in their blood compared with the concentrations in the water. Their bodies are designed to expel large volumes of very dilute urine frequently. This works to their advantage in a freshwater environment because they are surrounded by water with low salt concentrations. So, just pee a lot and hang onto what little salts you have. They also have specialized cells in their gills to allow them to directly take up sodium and chloride from the water to fine-tune the salt balance in their blood and cells. Saltwater fishes face the opposite problem. They need to maintain salt concentrations in their blood that are much lower than the surrounding environment. To do this, they actively drink water and form a highly-concentrated urine to expel the excess salts. They also actively expel salts at their gills. So the basic freshwater strategy is to pee like hell and absorb salt. The basic saltwater strategy is to drink and hold it so they can absorb as much of the water (while leaving behind the salts) as possible. Put either of these fishes in the opposite environment, and these critical systems fail to function. The "pee like hell" strategy will quickly deplete cells of water in a saltwater environment, while the "drink and hold it" strategy will completely water-log them. These salt concentrations are critical to many bodily functions. Just think about what happens to people when they get dehydrated or, in some cases, drink TOO MUCH water. They are at real risk of death. Same for these fish. What about things like salmon? Or sharks? Many salmon and their relatives live in both fresh and saltwater at different points in their lives. Pacific salmon (e.g., Chinook salmon) are born in freshwater. They have nice, normal freshwater adaptations. However, when they reach a certain age and are ready to leave their rivers, they go through dramatic physical transformations during which they develop the necessary adaptations to live in a marine environment. When they are old enough, and are ready to breed in freshwater as adults, they undergo yet another transformation. This, and the energy required to to migrate and produce eggs/sperm, exacts such a toll on the fish that they almost always die immediately after spawning. Moving between fresh and saltwater is not easy. What about sharks, like bullsharks? How do they move between fresh and saltwater? Sharks are very different from what people normally call "fish". They also have a completely different strategy for surviving in saltwater, which will inform us about how some survive in freshwater. Rather than deal with the threat of constant water loss by drinking saltwater and excreting the extra salt, a shark's blood is filled with urea (a nitrogen-based compound that makes your pee stink [EDIT: the stink is actually from the urea decomposing into ammonia; urea is odorless on its own]). In fact, they store so much of it that their blood ion concentrations are actually close to that of sea water. Sharks that can spend time in freshwater are able to expel excess urea (which is just a metabolic waste product, hence why it's in your pee) rather than retain it in their blood. This allows them to adjust the levels of dissolved ions in their blood so that they can flexibly move between salt and freshwaters. Now, this doesn't cover everything (there are 25,000+ fish species), but hopefully it gives a more complete overview... EDIT: There has been some confusion regarding my use of the word "fishes." My use of this word is completely intentional. "Fishes" has a particular use among ichthyologists and fisheries scientists. "Fish" can be singular or plural. We use it as a general plural, as in, "there are 20 fish over there." "Fishes" is used when one is discussing multiple types (species, genera, whatever), as in, "a red fish and a blue fish makes two fishes". When I say "fishes", I am referring to more than one type. When I say "fish", I am referring to multiple fish of the same type." https://www.reddit.com/r/explainlikeimfive/comments/4vqkuq/eli5why_cant_most_freshwater_fish_survive_in/
2 the_original_Retro Some fish do, given a period when they can "transform" from one water type to another. Salmon are an example; they mostly live at sea but spawn way up in fresh water streams. But the reason is how the salt itself interacts with gills, which are pretty much a fish's lungs where its blood exchanges oxygen and carbon dioxide as part of breathing. Our human bodies need a certain balance of salt or they start having electrical problems. So if we ingest too much salt our kidneys try and filter it out, and if they don't - such as if we're on a liferaft at sea and drink sea water - we go mad (the classic line "water water everywhere and not a drop to drink" comes from this). Fish don't just DRINK water, they breathe it. So they get used to breathing salt water and their chemistry compensates for contact with all the salt, or they get used to breathing fresh water and their chemistry compensates for not enough salt. Flip the switch too completely and too rapidly, and the fish dies because there's too much or tool little salt in its "lungs".
2 bertnod We often use freshwater as a treatment for saltwater fish and vice versa.  Some fish live their lives, at different stages, in one then the other.  Some fish move back and forth on a more regular basis and some fish are either completely freshwater or completely saltwater.  So, when you put that saltwater fish into freshwater here is how it goes.  Assuming you have matched the pH and temperature and have removed any other toxic compounds like chlorine, the fish is primarily dealing with a major change in the salt gradient between the inside of their body and the outside.  Many parasites and bacteria cannot tolerate this rapid change and will “absorb” water until they rupture and die.  This is driven by osmosis where the water wants to be equally diluted with the “salts” on either side of a semi-permeable membrane (cell walls).  The water begins to move through the cell walls and the parasite or bacteria are not equipped with a mechanism to deal with all of the water intruding and they explode.  Your fish on the other hand, is capable of dealing with this issue for various amounts of time depending on the species of fish.  This time (think minutes in most cases) in the freshwater is a wonderful treatment for external parasites and is not a severe stress for many saltwater fish.  If on the other hand, you do not match the pH or other parameters then the reaction is very different and other chemical/biological reactions take place generally being highly stressful for the fish and usually killing it.
1 [deleted] [removed]
16 0 taggartism Well, I typed out an explanation, but then did a quick search to see if I could phrase things better. I am an aspiring marine biologist, but this fisheries scientist put it pretty well a year ago. I suggest you read his explanation. @mynameismrguyperson --- "Fisheries scientist here. I am seeing a lot of incomplete or partially correct answers here. This might be more ELI15. Freshwater fishes tend to have much higher concentrations of ions (like sodium) in their blood compared with the concentrations in the water. Their bodies are designed to expel large volumes of very dilute urine frequently. This works to their advantage in a freshwater environment because they are surrounded by water with low salt concentrations. So, just pee a lot and hang onto what little salts you have. They also have specialized cells in their gills to allow them to directly take up sodium and chloride from the water to fine-tune the salt balance in their blood and cells. Saltwater fishes face the opposite problem. They need to maintain salt concentrations in their blood that are much lower than the surrounding environment. To do this, they actively drink water and form a highly-concentrated urine to expel the excess salts. They also actively expel salts at their gills. So the basic freshwater strategy is to pee like hell and absorb salt. The basic saltwater strategy is to drink and hold it so they can absorb as much of the water (while leaving behind the salts) as possible. Put either of these fishes in the opposite environment, and these critical systems fail to function. The "pee like hell" strategy will quickly deplete cells of water in a saltwater environment, while the "drink and hold it" strategy will completely water-log them. These salt concentrations are critical to many bodily functions. Just think about what happens to people when they get dehydrated or, in some cases, drink TOO MUCH water. They are at real risk of death. Same for these fish. What about things like salmon? Or sharks? Many salmon and their relatives live in both fresh and saltwater at different points in their lives. Pacific salmon (e.g., Chinook salmon) are born in freshwater. They have nice, normal freshwater adaptations. However, when they reach a certain age and are ready to leave their rivers, they go through dramatic physical transformations during which they develop the necessary adaptations to live in a marine environment. When they are old enough, and are ready to breed in freshwater as adults, they undergo yet another transformation. This, and the energy required to to migrate and produce eggs/sperm, exacts such a toll on the fish that they almost always die immediately after spawning. Moving between fresh and saltwater is not easy. What about sharks, like bullsharks? How do they move between fresh and saltwater? Sharks are very different from what people normally call "fish". They also have a completely different strategy for surviving in saltwater, which will inform us about how some survive in freshwater. Rather than deal with the threat of constant water loss by drinking saltwater and excreting the extra salt, a shark's blood is filled with urea (a nitrogen-based compound that makes your pee stink [EDIT: the stink is actually from the urea decomposing into ammonia; urea is odorless on its own]). In fact, they store so much of it that their blood ion concentrations are actually close to that of sea water. Sharks that can spend time in freshwater are able to expel excess urea (which is just a metabolic waste product, hence why it's in your pee) rather than retain it in their blood. This allows them to adjust the levels of dissolved ions in their blood so that they can flexibly move between salt and freshwaters. Now, this doesn't cover everything (there are 25,000+ fish species), but hopefully it gives a more complete overview... EDIT: There has been some confusion regarding my use of the word "fishes." My use of this word is completely intentional. "Fishes" has a particular use among ichthyologists and fisheries scientists. "Fish" can be singular or plural. We use it as a general plural, as in, "there are 20 fish over there." "Fishes" is used when one is discussing multiple types (species, genera, whatever), as in, "a red fish and a blue fish makes two fishes". When I say "fishes", I am referring to more than one type. When I say "fish", I am referring to multiple fish of the same type." https://www.reddit.com/r/explainlikeimfive/comments/4vqkuq/eli5why_cant_most_freshwater_fish_survive_in/
2 0 the_original_Retro Some fish do, given a period when they can "transform" from one water type to another. Salmon are an example; they mostly live at sea but spawn way up in fresh water streams. But the reason is how the salt itself interacts with gills, which are pretty much a fish's lungs where its blood exchanges oxygen and carbon dioxide as part of breathing. Our human bodies need a certain balance of salt or they start having electrical problems. So if we ingest too much salt our kidneys try and filter it out, and if they don't - such as if we're on a liferaft at sea and drink sea water - we go mad (the classic line "water water everywhere and not a drop to drink" comes from this). Fish don't just DRINK water, they breathe it. So they get used to breathing salt water and their chemistry compensates for contact with all the salt, or they get used to breathing fresh water and their chemistry compensates for not enough salt. Flip the switch too completely and too rapidly, and the fish dies because there's too much or tool little salt in its "lungs".
2 0 bertnod We often use freshwater as a treatment for saltwater fish and vice versa.  Some fish live their lives, at different stages, in one then the other.  Some fish move back and forth on a more regular basis and some fish are either completely freshwater or completely saltwater.  So, when you put that saltwater fish into freshwater here is how it goes.  Assuming you have matched the pH and temperature and have removed any other toxic compounds like chlorine, the fish is primarily dealing with a major change in the salt gradient between the inside of their body and the outside.  Many parasites and bacteria cannot tolerate this rapid change and will “absorb” water until they rupture and die.  This is driven by osmosis where the water wants to be equally diluted with the “salts” on either side of a semi-permeable membrane (cell walls).  The water begins to move through the cell walls and the parasite or bacteria are not equipped with a mechanism to deal with all of the water intruding and they explode.  Your fish on the other hand, is capable of dealing with this issue for various amounts of time depending on the species of fish.  This time (think minutes in most cases) in the freshwater is a wonderful treatment for external parasites and is not a severe stress for many saltwater fish.  If on the other hand, you do not match the pH or other parameters then the reaction is very different and other chemical/biological reactions take place generally being highly stressful for the fish and usually killing it.
1 0 [deleted] [removed]