The largest animal on Earth of all time is the 30.5-meter long blue whale and the largest fish is the whale shark which reaches almost 12-meter long. However, besides sharks, the largest fish that can now be found is the famous sunfish, Mola mola, which reach 3.1-meter long. The Canadian researchers examined why there are no large fish nowadays, in a recent study conducted on a huge marine beast, an ancient fish called Leedsichthys problematicus.
The researchers, whose study has just been published in Palaeontology, have assessed the hypothesis that suggests that there are no such large fish today because their high metabolic rate would simply not be compatible with larger sizes because an increase in volume would mean that for every gram of tissue there would be less oxygen available.
However, the authors have concluded that the limits are actually well above the maximum size a modern-day fish can reach and, therefore, there should be larger fish.
Leedsichthys problematicus, an ancient fish, has been studied
Scientists at the University of Guelph in Canada have tried to estimate the metabolic rate of the Leedsichthys problematicus, a marine beast believed to have reached 16.5 meters in length and to have weighed 45 metric tonnes, a mass similar to that of a modern tank.
L. problematicus is believed to have lived about 165 million years ago in European and South American seawaters and to have fed on plankton in the oceans of the Middle Jurassic.
The authors have used this extinct ancient fish as a reference to estimate the metabolic rate, both the energy expenditure and oxygen consumption, that such a large fish would have had.
The researchers calculated the characteristics of L. problematicus
The Canadian researchers stated that this marine beast would have reached a surprisingly high cruising speed of about 17.8 kilometers per hour, while modern-day fastest fish reach 30.
According to them, by moving at these higher speeds, the extinct ancient fish Leedsichthys problematicus’ tissues would have been perfectly oxygenated.
This suggests that fish of 16.5 meters long and about 45 tons are not currently theoretically impossible. That’s why the metabolism is not the factor that can answer the question of why there are no such huge fish specimens today, the Canadian researchers concluded.