The most biggest freshwater fish in the world is the arapaima gigas arowana , it can reach more than 4 meters . if you want to keep one of these guys youd have to get a 6 ton pond . the type of arowanas you usually see in a pet store is the silver arowana witch will reach at least 3 feet in captivity. lets say you went to a petstore and saw one of these fish , you brought a baby one and you put it in a 20 gallon tank , but it eats all your community fish , they get hard to take care of and the food bill goes up. You'd have to get a 200 galon tank to raise one because they get very , very big , the cruel thing about these fish is that people buy them and they think they are easy to take care of so they keep them in a cramp tank , and feed them unhealthy food such as feeder fish . this is very cruel . If you were in asia , the most expensive fish ever paid for is the asian arowana , the red asian arowana is the rarest , the price for a first grade full grown one would probably be a quarter million dollars , although now it is illegal to import the asian arowana it will always be the raest and expensivist fish in the world . Why are these fish the most expensive ? , because they are rare , they are almost extinct and they are prehistoric . This fish has live in the jurasic period and has come back like the coelacanth fish . I raise one myself , a silver arowana . he is very hard to take care of and he , like all arowanas must have crystal clear water . i feed him pellets so his aggresive level is low and give him lots of room . I would recomend this fish only for experts that can afford the food bill , gat a 200 gallon tank , no a lot of info on this fish , and can keep the tank crystall clear by cleaning the water once a week . The only arowana known to be to be in captivity is the asian , black , autralian , and silver .why do people keep this fish , because of good luck , as i already said this fish is prehistoric and has come back to life for us to take care of but it is endangered. The reason people raise these fish is because they bring good luck , if you die you become this fish if you treated your well , brings good health , cast out evil , uphold families togatherness , vital buisness success , and prediction of buiness affairs . I would like to give a very important part about raising fish that eat fish , please do not feed your fish feeder fish , they contain diseases , they make your fish die , they cause trouble with the digestion system , so I recomend feeding them with pellets .for any ifo or comments please reply here .