Worlds largest freshwater fish

[Acheloos]

Wyomingite, sorry, I have sometimes really problems to calculate with non-metric systems.
I am also highly interested in outsized animals, no matter if the are giant fish, giant crocs or snakes or for example giant squid. In general it turns out after a closer examination, that the alleged sizes over a distinct limit aren´t true. For example the great white shark. For decades you could read they reach 11m, but those reports were highly questionable (for more info look for example here: http://www.jawshark.com/great_white_recorded_sizes.html ). Or take the whale shark. This often cited lengths of 18 or even 20m are not confirmed records, but only estimated lengths of swimming specimens. Big animals are very often highly overestimated in size. At snakes there is the same phenomen, a lot of allegedly highly outsized freaks, but the actual records are far below them. I wrote some time ago a very long article for a magazine about the alleged monster anacondas. I used a lot of scientific dates of their growth rates and life-spans, as well as the dates of the actual known record specimens and their proportions. To make it short, it is just completely impossible that an anaconda could reach much more than 10m. At crocs there are also a lot of tales of giant freaks. But either there is no physical evidence, or if, it turned always out that the super-giant crocodiles were smaller in life than in the stories of their hunters ( for more look here: http://madrascrocbank.blogspot.com/2008/08/worlds-biggest-crocodiles.html ). At the end, the very largest modern crocs on records were about in the 7m range, what is already monstrous.
Something I really hate is the fact that even many scientists used and still use old unconfirmed dates of alleged records as facts. Just take the arapaima. Why did nearly nobody wonder why there is not a single photographic evidence for one of the alleged 4,5m and how on earth such an animal could weigh only 200kg? There are very much similar cases.

 

[Wyomingite]

Well, no need to apologize about converting U.S to metric. It confuses me sometimes. I actually do most of my DIY projects using metric 'cuz the math is easier to do in my head.

Sounds like we have a common interest, and have reached the same conclusions. I was a romantic about these things through high school, but a bachelors degree in Zoology toned down the romanticism and forced me to start looking at things from an objective point of view. Thanks for the links. I think I've stumbled onto the crocodile one before, the great white one was new.

......Something I really hate is the fact that even many scientists used and still use old unconfirmed dates of alleged records as facts.

Ditto. The past few years I've started looking at it from the psychological aspect. Humans NEED monsters, even scientists. The wonder of the unknown.

...Just take the arapaima. Why did nearly nobody wonder why there is not a single photographic evidence for one of the alleged 4,5m and how on earth such an animal could weigh only 200kg? There are very much similar cases.

Well, people have wondered, for example yourself and I.

A fish that large would have found it's way into a museum collection or a private trophy room, especially if the genetic potential of the species is such that most individuals should reach that size. In that case, there would have been many fish that size and documentation would be relatively easy to come by; there should be photographic evidence, or even an old mounted specimen, somewhere. (BTW, I agree completely on the alleged weight for a 4.5 meter specimen, its ridiculous).

Nope, if a 4.5 meter arapaima has ever existed, it was a rare example of gigantism and not representative of the average population. Possible? Maybe. Likely? Nope. Claims like that need to be verified, and no authentication exists.

WYite

 

[Acheloos]

I think one problem is that many people don´t care about biological limits and believe that many animals can grow to every size within a very wider range. But if you look at actual growth rates, possible life-spans and confirmed records of exceptional large specimens (and their numbers in populations) you can exclude some size-claims with nearly 100% certainity. At the case of the arapaima we have the further fact, that the 4,5m comes from a more than 150 years old SECOND-HAND-report. Perhaps this was nothing but a mistranslation. Schumburgk was a german, his guides spoke probably spanish, and how knows what language the people spoke from whom he get this dates? The weight of 200kg could be actually come close to the very largest specimens, and I would predict a possible maximum length somewhere around 3m for this species.
There are limits even for freak specimens. For example at crocs. We have a small handfull of specimens which most probably were about 7m long. That is really monstrous, and nearly 50% longer than what we would already call very big. Given this fact, stories of 10m long crocs are practically not based on facts.

 

[nishant_datta]

I think one problem is that many people don´t care about biological limits and believe that many animals can grow to every size within a very wider range. But if you look at actual growth rates, possible life-spans and confirmed records of exceptional large specimens (and their numbers in populations) you can exclude some size-claims with nearly 100% certainity. At the case of the arapaima we have the further fact, that the 4,5m comes from a more than 150 years old SECOND-HAND-report. Perhaps this was nothing but a mistranslation. Schumburgk was a german, his guides spoke probably spanish, and how knows what language the people spoke from whom he get this dates? The weight of 200kg could be actually come close to the very largest specimens, and I would predict a possible maximum length somewhere around 3m for this species.

sounds plausible.

Also, recently i saw a documentary on great white sharks in which the camera man (or someone else part of film crew) of JAWS said that when they shot the movie years back 4+ meter sharks were a common sight but now hardly any above that mark are seen and are considered rare. causes attributable were stated to be over fishing and plundering of prey and habitat (pollution perhaps ?). So even if there were 3 m + arapaimas earlier, in our lifetime we may not see one.

 

[Acheloos]

But exploitation of a species is not everything. In the case of the arapaima, there are still good reasons why we could even today see specimens very near the maximum biological size. At first the arapaima has a huge geographical distribution, and there are still a lot of regions where this species occurs, without any commercial fishery. Furthermore, has been farmed in ponds, without much competition and with a lot of food. It is well possible that the largest ever documented arapaimas will come at the end not from a stream in South-America but from a fishing-or fish-farm-pond somewhere in Asia.
And even if there is overfishing, there are in general still some specimens of extraordinairy size left. For example the beluga sturgeon, which is highly endangered and over-exploited. But there were still in the last decades some specimens in the 4-5m range.
In the case of the wels we have today even larger confirmed (and not just big-fish-tales) specimens than in the past.

 

[Zoodiver]

In my opinion, the wild is where we will find the largest animals. That competition that captive life lacks is key to bigger, stronger, healthier animals.

 

[BloodredOscar]

This sounds kinda newbie, but I FORGOT HOW TO MAKE A THEARD! Help?

 

[Acheloos]

The reason why we find in general most records specimens of a species in the wild is mainly because there are normally much more wild than captive specimens, and the chance that one of exceptional size is found in a zoo or something like this, is just much smaller. Genetics play a big part in the size of most animals, and if only let´s say one in 10.000 soecimens of a population reaches monster-size (let´s say more than 50% more than most other bigger adults), the chance is very low that such a specimen is born and raised in captivity. Furthermore it would not be easy to house most of the bigger species. For a fish of more than 1m, you need a really big aquarium, and that´s very expensive.

 

[Eoibio]

What about the nile perch?

 

[Ramesh]

In my opinion, the wild is where we will find the largest animals. That competition that captive life lacks is key to bigger, stronger, healthier animals.

In general the aquatic literature and studies have shown time and time again fish kept in closed reservses or pondages grow larger than fish in streams or rivers. It is the lack of competition and a constant supply of food to predators that allow fish to flourish there.
Arapaima in Asian ponds and other species farmed or stocked in large lakes for sport fisherman are prime examples of this larger size abundence. Streams and rivers seem to allow by the nature of their flow of resouces far less density of large predators along their length than large closed bodies of water.
Aquaria seem to be the opposite for maximum speciems.