Nezha is not a myth? It was already three years and six months old when it was born in the deep sea!

“It was three years and six months old when it was born.”

This is not talking about the mythical figure Nezha, but the spiny-tailed deep-sea ray/𝑩𝒂𝒕𝒉𝒚𝒓𝒂𝒋𝒂 𝒑𝒂𝒓𝒎𝒊𝒇𝒆𝒓𝒂 which is distributed in the deep sea of ​​the North Pacific Ocean. The water depth they live in can reach 1450m.

The water temperature in the deep sea tends to be stable. It has been reported that in an environment of about 4.4°C, it takes nearly 1,290 days for the small-tailed deep-sea ray in the egg case to hatch.

Figure 1: Spinytail deep-sea ray © Alexei Orlov

The deep-sea ray genus/𝑩𝒂𝒕𝒉𝒚𝒓𝒂𝒋𝒂 can be said to hold the record for the longest egg incubation time in the animal kingdom, and more than 1,000 days is already commonplace.

But an incubation time of thousands of days is not a good thing for the population. We must find a way to shorten the incubation time as much as possible.

Figure 2: Egg case of a spinytail ray © Gerald Hoff.

You should know that the time required for incubation is related to the average temperature during the incubation period. Within a certain range, the higher the average incubation temperature, the shorter the incubation time. This is called the "effective accumulated temperature law" in biology.

However, deep-sea rays distributed in the deep sea can neither incubate eggs themselves like chickens, nor expose the eggs to sunlight, so how to increase the incubation temperature becomes a problem.

But some time ago, they seemed to have found a solution...

Figure 3: Thornytail deep-sea ray © Jackson WF Chu

The scientific journal Scientific Reports published an article in 2018 titled "Deep-sea hydrothermal vents as natural egg-case incubators at the Galapagos Rift."

Scientists have discovered some deep-sea ray egg cases near deep-sea hydrothermal vents in the waters of the Galapagos Islands.

Figure 4: Hydrothermal vents, spiny-tailed deep-sea rays and their egg cases photographed by ROV at a depth of 1600m ©Salinas-de-León, P., Phillips, B., Ebert, D. et al. SciRep (2018)

After molecular identification, these egg cases were found to be laid by the spiny-tailed deep-sea ray/𝑩𝒂𝒕𝒉𝒚𝒓𝒂𝒋𝒂 𝒔𝒑𝒊𝒏𝒐𝒔𝒊𝒔𝒔𝒊𝒎𝒂.

After comparing the distances of these egg cases to the hydrothermal vents and the number of egg cases, scientists discovered that these egg cases were not randomly laid by the spiny-tailed deep-sea rays, but were related to the hydrothermal vents.

Figure 5: Statistics of the number of egg cases of the spiny-tailed deep-sea ray and the distance from the hydrothermal vent ©Salinas-de-León, P., Phillips, B., Ebert,D. et al. Sci Rep (2018)

Subsequent measurements found that the water temperature at these spawning locations was higher than the ambient temperature. Therefore, scientists believe that the spiny-tailed deep-sea ray uses the temperature near the hydrothermal vent to speed up the hatching of eggs.

Thus, this behavior of using the heat from hydrothermal vents in the deep sea to accelerate the hatching of eggs was recorded by humans for the first time.

Figure 6: Ambient water temperature and egg case number statistics (the red vertical line is the average background water temperature) ©Salinas-de-León, P., Phillips, B., Ebert,D. et al. Sci Rep (2018)

Well, in this place where the sun doesn't shine, you always have to find new support.