The Midsummer Day of the Ox
In Japan, today is called "the midsummer day of the ox." There is a custom of eating eel on the day. According to one theory, this custom appeared in the Edo era. Eel isn't summer-seasonal food and it was too fatty to eat in summer. So someone started to advertise that eel was nutritious against summer heat.
Nowadays, there is a problem that a lot of ells are overfished even though they are one of the endangered species.