The true size of Arapaima gigas

[kydsexy]

freshwater stingrays are the largest freshwater fish.

http://news.nationalgeographic.com/news/2008/04/photogalleries/stingray-pictures/index.html


at 4.3 meters, a gigas would easily dwarf this ray and a claim such as "There are accounts of freshwater stingrays growing as large as 1,000 pounds (450 kilograms), which could make them the largest freshwater fish in the world, Hogan said" probably would not be made by any accredited biologist, especially fishing in Asian waters. I have to agree with Acheelos that minus freak species, which none have been verified, A. gigas probably reaches around 3m and 200kg.

Does anyone have any proof that they are capable of growing larger?

 

[kydsexy]

i do disagree with Acheelos on at least 1 fact, fish do grow their entire lives, even if it seems untraceable

 

[Acheloos]

Some species like many sturgeons or catfish will grow for a long time, but the older they become, the lesser they grow. Very old fish often even loose body weight and have no possibility to invest further energy in length growing.
A lot of fish will reach a distinct size during a distinct time and won´t grow much larger, even after many years. Dependent on their size, they will possibly grow some millimetres or centimetres, but does this really count?
Many people believe that fish and reptiles can grow for their whole lifes and are therefore able to reach nearly every size if the life long enough, but that´s not true. There are very good studies for example about eels from Ireland, which shows that even under optimum conditions and exceptional good growth they have a biological maximum size, even if they will (very slowly) grow untill the end of their lives. This case is especially interesting, because several thousand eels were examined, some of them older than a half century. You can see this study here: http://www.ria.ie/cgi-bin/ria/papers/100439.pdf

 

[kydsexy]

not arguing that the growth will dramatically slow down, but growth is growth when you're talking about what's involved considering a fish's life. whether it's a mm of growth or feet of growth, the belief is, and evidence proves that if a fish was to live infinitely, then it would grow infinitely.

 

[Acheloos]

No, that´s not true. Please check the article I posted. The growth rate of the eel for example would reach its asymptote when it would be around 200 years old (older than any eel could be), that means there would be no growth any more, and it could not reach bigger sizes, even if it would grow for some more centuries. It´s similar to records in sport. Even the the best runners will once and again break a record for 0,01 or eben 0,1 seconds, they will never come over a distinct limit.

 

[kydsexy]

ok maybe "infinite" was exaggeration but no eel will age to 200 years old, which only goes to prove that they grow their entire lives. and runners top speeds differ greatly because it will top off during their lifespan. top speed of an individual as well as group is dependent on many more factors than growth of an animal. i can control the growth of my fish in one year based on amount of food, quality of food, frequency of feedings, optimal water conditions all of which are in our control. genetics play a minor but still somewhat significant role in fish growth. humans are affected by genetics at a much greater rate, which is why Usain Bolt is such a freak of nature!!! If human top speeds followed the same path as fish growth then there would be millions more individuals like Usain running at insanely fast speeds. Just saying, apples to oranges.

also with athletes .01 and .001 and .1 are all drastic differences

 

[kydsexy]

has anyone read up on the exponential curve of human athletes and that a person of usains caliber wasn't supposed to appear til like 2030!

 

[Acheloos]

Okay, sport records were probably not the best example, but I think you know what I mean. As the growth slows down it will come close to a maximum which can´t be beated.
To make a (simplyfied) example lets assume that the growth of a 1m long fish will slow down for 50 percent per year. If it would still grow for 10cm in a year at 1m length it would be 110cm, the next year 115cm, the next year 117,5cm, the next year 118,75cm and so on. In a mathematical sense it will never ever reach 120cm, even if it would grow for millions of years. In nature it would be that it would probably come once to 120cm or even some milimetres more, but it would be never able to reach much larger sizes like 200cm.
I have some very good books with information aoout the growth of animals, for example pikes and wels catfish, but also about big snakes like anacondas. It is true, in such animals the available amount of food and its quality is very important. But genetics are also very important. Even among same conditions some specimens will grow more or lesser than others, even at the same amount of food they consume. This can even cause comparably drastic differences.
To produce a really monstrous specimen you need one with extraordinairy good genetics for growth and optimum conditions too, even for a fish or reptile.

 

[kydsexy]

haha i love math and a note that if growth slows down 50% a year then it will grow infinitely as the only number you can't take half of is 0. when i mentioned genetics, i simply meant that if 100 3' foot pikes breed, then you can pretty much predict the size of the future offspring, very close to 3' with a few exceptions. on the other hand if 100 humans breed together then size can be predicted but at a very low percentage rate

my dad was 5'3" and mommy was 5'5" im 6'5", my sis is 5'4", and my bro is 6'0" which is why i said that genetics play a more important role in some species more than others--humans compared to fish

 

[Acheloos]

The cells of a living body always reproduce themeselves. If they preproduce faster than they die, the tissue and the whole organism will grow (very simplified), if only as much reproduce as die, it won´t grow anymore. I suppose that at one time this will be also the case at very old fish.
Humans´growth is for about 10% dependent from food supply, i.e. people with get only very few and bad food when they grow will in general stay small and people with good food supply will grow in general taller. In animals like (most) fish the supply of food can cause more drastic changes, but even here genetics have a bigger impact than you will perhaps think.
At my guppys I saw also some drastic differences in the growth of the females even among those with the same parents.