GAIAPRESS continues to shed new light on the wonders of nature, including theories that used to be considered unscientific or have long been ignored, in order to gain a new perspective on science.
Rock-climbing goby swim against strong currents and ascend the slippery, overhanging rocks of high waterfalls using mouth and pelvic suckers.
While some other fish species are known for their waterfall-climbing feats, none of them jump onto and over dry rocks like the rock-climbing goby.
What is it that drives rock-climbing goby to fight their way upstream over waterfalls and dry rocks?
Rock-climbing goby is a species of goby that lives in fresh water and has a life history very similar to sweetfish.
After laying eggs downstream, the young fish hatch and make a straight line for the ocean where they spend winter.
The ecology of these young fish living out at sea is not yet fully understood.
It is assumed that they feed off animal plankton around sand spits at the river mouth.
In spring, these goby form schools in estuaries and head upstream in groups, only eating algae once they enter the river system.
Starting out in schools of small fish, rock-climbing goby gradually begin to dominate single rocks and mark out their territory as they grow in size.
It’s not difficult to imagine that fish able to monopolize the algae supply will grow larger and head further upstream where there is less competition.
In this respect, rock-climbing goby are extremely similar to sweetfish.
But, there are several critical differences between the two species.
Sweetfish are annual fish that only live for one year.
After heading upstream in search of algae, they go back downstream to lay their eggs in Autumn, unlike rock-climbing goby that breed in early summer.
Rock-climbing goby are thought to have a lifespan of 5 to 6 years.
After the long winter, they head back to the same area to lay eggs around the same time young fish head upstream.
Rock-climbing goby are destined to head back downstream after fighting their way against the current and over high waterfalls.
But, we still don’t know when exactly it is that this takes place.
Some species of rhinogobius, a member of the goby family, are also known for waterfall climbing.
Rhinogobius is still the subject of classification, but it is believed that waterfall-climbing species such as the rhinogobius flumineus most likely lay eggs upstream where there are fewer fish in order to reduce the risk of their eggs being eaten.
There is no advantage for rock-climbing goby to lay eggs in this way, and they make the arduous journey upstream and over waterfalls later than sweetfish and rhinogobius flumineus.
It would seem that rock-climbing goby use their sense of smell to detect algae upstream, or have a lateral line with which they detect minute increases in water temperature that trigger their exodus upstream. Unfortunately, neither theory has yet been proven.
Algae in upstream areas rely on rises in water temperature and extended sunlight to grow.
It would therefore be dangerous to venture upstream should the river dry up, exposing this algae.
Sweetfish and rhinogobius are believed to head upstream early to preserve the species, or to grow large and gain an advantage during egg laying.
For reasons largely unknown, rock-climbing goby mysteriously lay their eggs at a different time and appear to confirm algae growth before making their way upstream.
Rock-climbing goby are widespread on the Pacific side of Japan south of the Kanto region.
While there’s no accepted theory as to why they inhabit certain rivers and not others located nearby, many of these rivers have well-developed sand spits at the river mouth.
In the case of the well-researched sweetfish sharing a similar life history, sand spits are not regarded as having any bearing on their journey upstream.
A proper understanding of the life history and sensor mechanism of rock-climbing goby may very well serve to overturn such theories.
Humans do not have such refined sensors with which to measure the natural world.
However, humankind posses the power of analysis, one that goes beyond our natural limitations.
The protection of this diverse and beautiful earth through the analysis of nature is a mission that has been entrusted to humankind.