1. Why the Yellowfin Goby Is Easy to Catch: It Chases Almost Any Food Near the Shore
The yellowfin goby lives in river mouths, tidal flats, and shallow bays, places where fresh water and sea water mix and the water is salty but not as salty as the open sea. Such water is called brackish. A Japanese seafood guide says the fish is common there and that it keeps chasing bait from the time it is small, which is why it is a classic first fish for children [1].
What it eats changes as it grows. According to the Toyosu fish museum, newly hatched larvae drift in open water and eat tiny animals called zooplankton. At about 1.5 cm (0.6 in) they settle on the bottom and eat small crustaceans such as amphipods. At about 2 cm (0.8 in) they start eating marine worms. Once they reach about 10 cm (4 in), their big mouths take crabs, shrimp, and even young fish [2]. The museum calls the species a hungry omnivore. The seafood guide adds that larger goby also eat seaweeds such as green laver [1]. So it is not a picky fish, which is part of why a hook with a bit of worm on it works so well. Feeding is busiest around sunset and just before dawn, and the museum says its sense of smell is probably what helps it find food in dim light [2].
2. Why Cooks in Edo Loved It: Clear, Mild White Flesh That Fries Well
"Edo" is the old name for Tokyo, used until the 1860s. The seafood guide describes the goby's flesh as clear white, with no strong or unpleasant flavor, only a faint taste in the skin, and it does not get hard when cooked [1]. The guide says the fish was long a standard ingredient of Edo-style tempura, a food of lightly battered, deep-fried pieces that was sold from street stalls to ordinary people [1].
The fishing tools of the time reflected this popularity. A craft magazine about water culture says that Edo-style bamboo rods were made for particular fish found near the city, such as goby, sillago (called kisu in Japan), and crucian carp. It names a maker called Taichiya Tosaku, who opened a shop in the Tenmei era (1781 to 1789), as the founder of this tradition [3].
One question the sources I read do not answer is why the flesh is so mild when the fish lives in murky water. The guide describes how the fish tastes, and the museum describes what it eats, but neither tests a link between the two for this species. So the taste and the habitat are both well described, while the reason for the mildness is still an open question.
3. How a One-Year Life Works: Fathers Dig the Nursery and Guard the Eggs
Most yellowfin gobies are born in spring, grow through summer, and spawn (lay eggs) at about one year old. A few grow slowly and spawn a year later, and anglers call these extra-large fish hine-haze in Japan; the museum says they appear more often when there is too little food per fish [2] [1].
Spawning runs from winter to early summer, with the season starting earlier in warmer places [1]. The male digs a V-shaped burrow in a sandy-muddy seabed near a river mouth, about 2 to 10 m (7 to 33 ft) deep. A female picks a male, and according to the museum the quality of the burrow matters more than the size of the male. She lays about 30,000 eggs on the ceiling of a chamber inside, and then she dies [2].
The father stays. He guards the eggs in the burrow until they hatch. Then his job is finished and he dies too [2]. The museum says many goby species guard their eggs this way [2]. This is why a goby that lives only a year is not a fish of no importance: it spends its short life growing, digging, and protecting the next generation.
4. Why Gobies Became Harder to Find in Tokyo Bay, and How Anglers Help Count Them
The seafood guide says the goby was once caught in great numbers and used for dried fish and a sweet simmered preserve. It attributes a sharp decline to development and pollution of rivers and river mouths, and calls the goby a pricey fish today [1]. A newspaper report on the same subject shows an old photograph of goby fishing boats in the shallows of inner Tokyo Bay in the 1960s and says the commercial catch from the bay has stopped. I could read only the opening of that report, so I use it only for those points [5].
The "Edo-mae Goby Revival Project" is an effort to find out how many gobies the bay holds. A leaflet from Japan's national land and infrastructure research institute describes its survey for anglers. From July to December, ordinary people fish in Tokyo Bay, with an adult, and report each fish's length and the number they caught. In 2014, 102 people sent in data from about 120 places, covering more than 2,800 fish. The average lengths in July, August, and September were 82, 88, and 98 mm (about 3.2, 3.5, and 3.9 in), and an average of 21.4 fish per person per hour was the most in the survey's history. The leaflet notes that the fish seemed to be getting smaller year after year, and asks anglers to release gobies smaller than average [4].
The goby has also moved. The museum and the seafood guide both say it now lives in Australia and the United States (the guide lists California), possibly carried in ships' ballast water, which is sea water pumped in to keep a ship steady [2] [1]. A fish counted with care in one country is treated as a pest in others, which shows how much a fish's role depends on where it lives.
5. How to Learn More About Gobies Near Your Own Shore
If you want to look for yourself, ask an adult to take you to a quiet harbor, river mouth, or fishing pier where fishing is allowed. Read the posted rules first. Rules on size, season, and where you may fish differ from place to place. A seafood guide lists a parasite risk from brackish-water fish, so never eat a fish you caught unless a knowledgeable adult has confirmed it is safe in that water and cooked it thoroughly [1]. You can also search for your local fish and wildlife agency's page on gobies, which may tell you whether yellowfin gobies or other gobies live nearby. Note the fish's length and when and where you saw it. That is the same kind of record the Tokyo Bay survey collects [4].