Strange Facts or ... Did you know?

Habits:

Did you know that some fish can shoot water 4 metres away with a 3 cm accuracy?
Did you know that some fish spend most of their life OUT of the water?
Did you know that some fish can walk miles to go from one lake to another?
Did you know that many fish – not just the so called "flying fish" jump long distances out of the water? Many of them use their fins, much like a paper airplane to stay "flying" longer and further.
Did you know that most fish are meat eaters? Not just piranhas.
Did you know that some infant fish have to eat the slime off their parents body to survive?
Did you know some fish can breath air from above the surface – and that some of them will die if they can't get to the surface – they can't get enough from the water?
Did you know that some fish will "drown" if they don't get a quick breath of air right after they are born? They use this air to fill up their swim bladder.
Did you know that some fish look like plants, and may never walk around?
Did you know that many corals do walk around – mostly when you aren't watching of course!
Did you know that some fish "talk"? Technically most of them either take a bubble of air and pop it, or they rub two parts of their bodies together like a grasshopper.
Did you know many catfish roll their eyes so quickly, it looks like they are blinking?
Did you know that almost all fish sleep with their eyes open?
Did you know that fish eyes adapt slowly to changes in light intensity?
Did you know that many fish create a mild electrical pulse for various reasons including trying to get irritants off their skin? Not just electric eels.
Did you know in most species the male is more aggressive than the female?
Did you know there are special fish and animals that are "fish cleaners"? They walk all around the fish looking for dead, diseased, dying skin and parasites. Some are even allowed to go inside the mouth and gills of the fish. This is like letting a bug with pinchers go up your nose! We know it is sometimes painful to the fish being cleaned because it will jerk as something is being removed, but it stays and lets the cleaners do their job. The fish know that to do the cleaning, they must come and usually lower their head, then wait patiently until the cleaner is done.
Did you know that some fish eat only the scales of other fish?

SEX:

Did you know that some fish start out as females and become males as they get older?
Did you know that many of the fish die when they are partly female and partly male? This seems to be because they still have the female "non-aggressive" attitude, but the males in the area recognize them as "males" and attack them until they kill them.
Did you know that some schooling fish have 1 and only one male, and when the male dies, one of the females (usually the biggest) decides "OK, I'll be the male now" – and changes into a male? It is easy to get breeding fish from these types – just put a bunch of females in the tank and wait a while. Poof. You've got yourself a male and a "bunch minus one" females.
Did you know some schools of fish will have 1 alpha male, lots of females, and a few "near-males" that are neither male nor female, when the alpha male dies, usually the largest "near-male" completes the change into a male. Other times the "near-male" will try to convince several females to break away from the school with it. If it succeeds, the "near-male" then turns into a male.
Did you know that some fish start out as males and become females as they get older? Not as many as the other way however. Starting out as females is more common.
Did you know that some fish switch back and forth from male to female depending on the needs of the group? This is even more rare than the ones that start out as males.
Did you know that the reason fish tend to be less "sexed" than animals is because they carry the male and female gene information on several chromosomes, not just one? (ie – mammals have X & Y XX = female XY = male and very seldom do things get mixed up with mammals because of this. i.e, you aren't going to see many YY's)
Did you know that some livebearers have no males? They are all females! A male of a different species is usually required to get the egg dividing – but in most, none of the donor male genetic material are found in the resulting female babies! The female provides the chromosomes, the male is just the catalyst.
Did you know that most fish are egglayers?
Did you know that despite that, 1000's of varieties of fish give birth to fully formed babies? They are called livebearers.
Did you know that some livebearers have a placenta type system?
Did you know that in a few fish, it is the MALE that gets pregnant? Seahorses are the most commonly known. And they really are pregnant, the female put unfertilized eggs in the males pouch and they are fertilized internally. So this is true pregnancy. Not only that but the babies are born live and the male goes through severe contractions to give birth.
Did you know that some fish keep the eggs and young in their mouths, for weeks, for protection until they grow big enough? And the adults can lose lots of because weight because they don't eat for this entire time? The eggs are fertilized before they go in the mouth or the mother deposits the eggs, then takes them in the mouth, then has them fertilized so this is not a true pregnancy/livebearer regardless whether it is the male or female or both.
Did you know that some fish are "annuals" – they lay their eggs as the water is drying up, then they die. These fish actually wait until the water is so low that they will die soon before they will breed.
Did you know the eggs of many annuals will only hatch after enough time is elapsed?
Did you know that the eggs of many annuals require one or more dry/wet cycles before they will hatch This way if there is a "freak" rainstorm too soon, or if the ponds dry up too quickly one year, only some of the eggs will hatch and produce babies that don't have time to grow up and breed themselves.
Did you know that some of the "annual" fish and their longer lived cousins are some of the most brightly coloured fresh water fish? They are called Killifish.
Did you know that some females breed by swimming full speed into the bottom of the tank, smashing their heads into the ground, then the males fertilize the eggs that come out of the dead female? Don't try this twice – it only works the first time.
Did you know that some males kill the female after they breed?
Did you know that some females kill the male after they breed?
Did you know that some males "squeeze" the eggs out of the females by wrapping their bodies around them? If the female isn't ready to deliver her eggs, this process will often kill her.
Enough about deadly breeding, did you know that some fish build bubble nests and the eggs are placed, one per bubble, where they stay until they hatch?
Did you know that some fish jump out of the water to lay their sticky eggs above the water surface? … and the eggs that get placed where water covers them (perhaps because the water rises slightly) end up drowning! When the eggs hatch, the fish that don't fall or bounce into the water die because they need their gills wet to breath!
Did you know that some livebearers are designed as "right or left" handed sex? Their sex organs can be found on either the right or left side, so you have 4 sexes: Left Male, Right Male, Left Female, Right Female. And you need the right combination for pregnancies to result! (This last sub-fact is recently being debated in scientific circles. It may be it just appears to be this way or it may be fact.)
Did you know that some livebearer mothers feed their babies before they are born? We aren't talking about the ones with a placenta here – we are talking about secretions that the mother releases into the womb and her young ingest it through their mouths until they are big enough to be born. This is called uterus lactation (or the Latin equivalent.)
Did you know some fish can't seem to decide whether they are livebearers or egg layers? The eggs are fertilized inside the mother. They develop to some degree (about 50%) inside the mother, then they are laid as eggs to complete their development and then hatch.
Did you know that some fish have simple plain males and females and conception and eggs and everything else just seems "normal"? Of course … now that you have learned all these other interesting options … you may find it hard to ever decide what "normal" is for fish.

Visual Characteristics:

Did you know that some fish look almost exactly like other poisonous fish? (They are designed to look that way presumably so that other fish won't eat them.)
Did you know that some fish look like plant leaves, typically floating head down, and when food swims by they suddenly "wake up" and eat?
Did you know that some fish look like crabs – and even swim sideways to look like they are walking like a crab? (The crab is more feared of course because of its claws)
Did you know that some fish look like a discus? The kind you throw. Interestingly enough, they are called "discus" fish and, though expensive and somewhat difficult to keep, their beauty has earned them the title "King of the freshwater fish." We've kept them and we love them.
Now of course you know that some fish have heads that look like a horse … but did you know that sea horses have their skeleton on the OUTSIDE? Most fish have them on the inside!
Did you know that the pencil fish (yes, it looks much like a pencil) is closely related to the seahorse?
Did you know that most fish will turn pale when put into an environment that does not have dark background and bottom? This is why most natural aquariums have dark gravel – the fish look the best that way.
Did you know that most fish can lose most of their colour when scared and some when they are angry?
Did you know there are true albinos among fish? One of most popular fish for tanks is an Albino Corydoras catfish. (Look for white fish with pink eyes – a white fish with coloured eyes is not Albino.)
Did you know there are fresh water sting rays?

Plants:

Did you know that some aquarium plants only grow when they are out of the water and then slowly die (perhaps over a period of several years) while they are underwater?
Did you know that most aquarium plants use their roots primarily for anchoring, and they get most of their nutrients through their leaves?
Did you know we fertilize aquarium plants so they can grow?
Did you know that most fertilizer for houseplants will kill your fish and not help your aquarium plants much? The fish create the nitrogen & phosphates (ever heard of fish fertilizer? Your aquarium plants usually have all the fish fertilizer they can use), what they are mostly missing is trace elements.
Did you know too much of the trace elements can kill fish & cause algaes to grow?
Did you know that algae in a tank is usually a sign that the tank is healthy? We control most forms of algae to keep the tank looking good – and so visitors can see through the glass, not because it is bad for our pets.
Did you know we sometimes enlist the help of special fish and invertebrates to clean the algae off the glass?
Did you know that not ONE of the ones we use to remove algae has the word "algae" in its name?
Did you know that almost every fish with "algae" or "algae eater" in its name … will NEVER eat a bite of algae? And that the remaining one only eats algae when it is very young, later it switches to eating things like your plants and small fish?
Did you know that even the "best" algae eaters will, on an individual basis, suddenly decide they don't like algae anymore?

Poisons:

Did you know that some fish inject a poison into the water to "stun" fish around it so it can get away?
Did you know that the fish that inject the poison can themselves be poisoned by their poison? (In the wild there is enough water to dilute it quickly, in an aquarium, for some species, there isn't enough water to dilute it. When they release the poison towards their enemy, they swim the other way and are safe.)
Did you know that the octopus ink can kill the octopus (it is a poison – again in the wild this would be very rare because of the dilution ability of the ocean and the fact the octopus swims away from the ink.)
Did you know there is a blue jelly fish that can kill a human in a few moments with just a tiny drop of poison? No, you should not have this one in your aquarium – and yes we were asked – no you should not put this one in your mother-in-law's aquarium!
Did you know that chorine (this includes household bleach of course) is one of the most deadly poisons for fish … not to mention many other animals. It can kill in minutes because it prevents breathing. It can also kill over several days or weeks if it only partly destroys the ability of the fish to breath.
Did you know that Windex is probably the second most potent fish killer? (It contains ammonia, when sprayed, the ammonia gets on to the surface of the water. It gets into the air, the air pump pumps it into the water. Once in or on the water, the water distributes it to the gills of the fish, the fish can't breath, the fish dies – slowly under normal circumstances – quickly if there was a lot of it.) Do NOT use Windex or other ammonia cleaners anywhere near your aquariums. Lets say keep them 30 or 40 feet 10metres) away. Use vinegar and paper to clean your aquarium and windows near the aquarium. (You may like it enough you will use it on all your windows.)
Did you know that a copper penny, dropped into a marine aquarium, may end up killing most of the invertebrates? Did you know that lots of pennies dropped into an aquarium or pond can cause copper poisoning of fish? Don't let your visitors use your aquarium or pond as a "wishing well". And if your pond attracts coins despite signs put out, be sure you remove the money regularly to avoid poisoning the fish. Also, stuff on the coins can kill. And fish that pick up a shiny dime or bigger coins can die by having the coin get stuck in the mouth. It happened 2000 years ago too! So, if people must throw coins, try to find a fish free "safe" location for them to throw them.

Legal & Dangerous:

Did you know it is legal to keep piranha's in many provinces and states? States where a piranha might live & breed if were released into the wild don't seem to be as willing to allow them anywhere in their state – including aquariums! I wonder why… Currently Alberta is fine.
Did you know that most varieties of piranha's are not human eating monsters? There are a couple varieties that are the ones that eat mammals, most varieties of piranhas wouldn't eat a mammal unless they are starving (the fish – not the mammal). Of course a couple varieties, like the red-bellied piranha… well, more than one owner has lost part of a finger to its "well fed - there was no reason to bite off my finger" or "this variety doesn't eat mammals" pets. Talk about biting the hand that feeds you!
Did you know that the cut of the piranha is almost surgical? Most fish "tear" when they bite, the piranha is one of the few that "snips off" a pieced of flesh.
Did you know that piranha's are very similar to neon tetras? (Actually to all tetras – big and small.)
Did you know that piranha's are mostly schooling fish and they seldom eat each other?
Did you know that piranha's that have schooled together for years can suddenly decide that their $500 school buddies look like a delicious meal – even when there is lots of other food to choose from?
Did you know, that if you decide you want piranha's, having a lid that locks is 2 really good ideas? 1. It discourages putting hands in. 2. Do you really want to pick up a mad piranha flopping around on the floor? If you want one at work, you may want to check with restrictions that your insurance company places on you first. Or better yet – pick a less vicious pet.
Did you know the Pacu looks just like a piranha, including the teeth, but it is strictly a vegetarian? Well, at least that's all it tries to eat. If something gets in the way, it may be ripped and eaten accidentally It can use its teeth to rip apart very tough foliage. And a friendly nibble on your fingers can still be accidentally disastrous (for you that is - your meat won't hurt the Pacu).
Did you know that the Convict Cichlid was so named because it was considered one of the meanest fish. Of course, that was before a lot of varieties of cichlids were found. Turns out the Convict Cichlid is actually one of the more peaceful cichlids, but the name has stuck.
Did you know that most people who keep stingrays (fresh or salt or brackish water) snip off the "sting" to avoid being stung or having other tank inhabitants stung.
Did you know that almost all sharks outgrow any practical home or office aquarium? We're talking the real sharks here, the ones with rows and rows of deadly teeth, not the fake freshwater sharks that simply have the body shape of a shark. These fake sharks are mostly of the loach family.
Did you know that some livebearers eat siblings BEFORE they are born! They are cannibals while still in the womb. (These are most common in livebearers that do not have a placenta, and it is not common in most livebearers without a placenta. Some sharks are among the best known for this method of womb cannibalism.)
Did you know many loaches are great at controlling snails? Did you also know that if you put more peaceful fish like Angelfish or Discus in with them, once the snail population is down a bit, they decide they like Angelfish and Discus meat better than snails? (Note: Anglefish, especially in small numbers are not all that nice either, they will eat full sized guppies for example.)

Misc:

Did you know that when fish doctors operate surgically on fish, they may keep the fish out of the water for even a couple hours? They keep them wet, especially their gills so that they don't die from being out during the surgery. (But muzzle and sedate your piranha before you try this!) In one case, we had a skunk loach that spent an hour out of the water. It was stuck to the carpet because it was so dry, its top side was leathery, but its gills were still wet. A couple days of careful care and it was completely back to its mean old self.
Did you know that some fish spend most of their lives out of the water? (Some mudskippers are reported to do this.)
Did you know the "Mystery" snail was so named because they didn't know where it laid its eggs? Turns out they were laid above the surface of the water at nighttime. That was why it took so long to solve the mystery.
Did you know most people think a guppy is a plant eater but that the guppy and some of its relatives are deployed for mosquito control? Given the choice between mosquito larvae and a plant, the guppy chooses the mosquito every time.
Did you know that the silicone on a large tank, like one with ¾" glass takes 2 months for the glue to dry? This means if you order a large custom tank and they deliver it 2 weeks later, you are going to let it sit for several weeks before you fill it with water. Trust those that learned the hard way (not us fortunately, but we know of a couple others) – you want the glue to dry before you fill the tank with water!
Did you know that clear silicone is the popular choice for tanks in North America, and black silicone is the popular choice in Europe? The clear ends up looking "ugly" sooner as algae grows on it, but "in the store" it looks better at a lower cost. That is why stores here prefer clear silicone while, for aquariums for viewing, "we" usually prefer the slightly more expensive black silicone. The cost is for the extra labour – a mistake in clear silicone hardly shows up so most tanks until after you have had it home for a while – they frequently have lots of smudges – often very sloppy, but with black you have to do the job more carefully, and that is where the extra cost comes. Funny thing too – manufacturers claim the black silicone is actually stronger than the clear. And remember, the clear, while nearly unnoticed in the store may look sloppy once algae starts to grow on it, especially in the edges and creases where you can't clean.
Did you know that some fish like water very calm and slow moving and will die if the water is fast moving, while other fish need water that is rushing past and will die if the water is slow moving? Some people have reported that when their fish of the latter variety appear "tired and lethargic" they go to the pump inlet and swim very hard for awhile – sometimes days on end – to revive themselves. They seem to be relaxing by swimming as hard as they can. So some fish are couch potatoes and will die of exhaustion if they have to move for more than a few minutes in a row, and others die if they aren't doing the iron-man-triathalon most of the time.
Did you know that lethargic fish typically require less oxygen? So you can usually have more grams of lethargic fish than active fish in a given tank, except that the constant water flow for active fish often introduces significantly more oxygen into the water. So it's still a balancing act.
Did you know that some fish have been arguing with Evolutionary Scientists? Seems that some fish and amphibians that "have" to be extinct for 100's of millions of years are turning up quite alive thank you very much! Since they aren't found anywhere in the fossil record between now and rocks that were assumed to me 100's of millions of years old, they are forcing scientists to reconsider their conclusions and assumptions.
On this topic, several scientists have stated recently that the Cichlid population couldn't possibly evolved the way "they did" according to theories of continental drift. Of course, the Cichlids, being very alive are completely unconcerned that they cause so much consternation among their "much smarter" human observers. Ah well, theories should adapt themselves to the facts (at least in theory.)
Did you know that some fish have compound eyes designed where the top half work in air, the bottom half work in water and … when they are at the surface, they can use all 4 lenses at the same time? They are often called "4 eyes" just as inaccurately as when the school bully calls a kid with glasses "4 eyes."
Did you know that some legless amphibians are commonly mistaken for fish? (By humans of course – not by the fish.)

Man Made

Moving from the God designed to the man-made: Have you heard about the Mood ring fish? The National University of Singapore in 2003 genetically engineered several versions of zebra danios (Brachydanio rerio) that glow different colours to indicate the presence of different pollutants.
Did you know there is NO correct way to pronounce the scientific names of fish or plants? (TFH May 2003. pg 9) The names are more or less based on classical Greek and Latin, but no one knows how either of these languages were pronounced and they probably had local variation just like some modern languages. So, like the Chinese can "draw" their language to each other no matter what variation they speak, we can write scientific names to each other but pronunciation is up to each speaker. Personally, I learned "the most popular" version of classical Greek pronunciation so that tends to highly bias how I speak the scientific names. Others vary depending on their classical language training (or lack) and friends and pronunciation of their own native languages.

Final thoughts

Did you know that at least one fish is fairly occasionally (but not necessarily advisedly) available in the aquarium trade for each and every one of the items noted above? So if you like any one or more of these characteristics, you can have them in your tank? Some characteristics are only available in "hard to keep fish".

Footnote:
1. In doing work with some Chinese friends, I found that this is not completely true anymore. For those that know the "simplified" Chinese character set it is true. Older Chinese of most dialects can read the older Chinese, but the simplified Chinese is mostly for Mandarin and "educated" others.