1. What Are the Three Kinds of Names a Japanese Fish Can Have?
The first kind is the everyday name. The same fish can be called one thing in one port and something else in the next, and the same fish may be called by different names at different stages of its life. The second kind is the hyojun wamei, or "standard Japanese name." The Ichthyological Society of Japan, a group of fish scientists, describes it as a name for a kind of fish that is easy to pronounce and remember, an academic name that helps make up for Latin names, which are unfamiliar to many people [1]. The third kind is the Latin scientific name, which is the same in every country.
The society's guideline does not try to replace the first kind. It says the standard names are meant for science, education, law and government, where everyone must be sure which fish is meant, and that this does not limit the use of local names or market names [1]. So "aji" in a fish shop and "aji" in a field guide can both be right. They just do different jobs.
2. How Does a Japanese Fish Get Its Official Name?
Nobody holds a naming ceremony. According to the society's 2020 guideline, a new standard name is proposed in a scientific publication, such as a society journal, a university or museum bulletin, or a specialist field guide. A press release or a personal website does not count [1]. The guideline says the person proposing it should describe the fish well enough that others can recognize it, should say what the name means, and should usually write it in katakana, one of the Japanese writing systems [1].
The same guideline admits something interesting: until then there had been no written rules at all. New names, duplicate names and renamings had been handled by custom, which often made problems hard to settle fairly [1]. In other words, for these matters the written rules came only after a long period of custom.
3. Why Do Scientists Around the World Use a Latin Name Too?
Common names differ from language to language, and sometimes from place to place inside one language. The article on binomial nomenclature in the English-language encyclopedia explains that the system exists for this reason: short, stable names that can be understood internationally, unlike common names, which are usually different in every language [2]. Each name has two parts, the genus and the species, as in Homo sapiens.
According to that encyclopedia article, the system began in plants in 1753 through the work of the Swedish naturalist Carl Linnaeus. For animals, the official rule book, the International Code of Zoological Nomenclature, fixes a starting date: 1 January 1758, the date on which Linnaeus's tenth edition of Systema Naturae is treated as published. Names published before that date do not count as official scientific names [3]. So whenever a scientist writes a fish's Latin name, it can be traced back along one shared chain to that date.
A good example of why this matters is the word "frogfish." In Australia the frogfish family has a different common name, anglerfish, and "frogfish" there means a different, unrelated family [4]. Without a Latin name, a scientist in Sydney and one in Tokyo could not be sure they were discussing the same animal.
4. Is the Horse Mackerel Really Called Aji Because It Tastes Good?
This is the claim we started with. The online dictionary Wiktionary says the fish's name likely comes from the ordinary word aji, "flavor," in reference to its tastiness. It also says the fish name is found in writing since at least the late 800s, in the old spelling adi [5]. So "tastes good" is a serious explanation, and the one that entry leans toward.
Notice the word "likely." Nobody wrote down who first called the fish aji, or why, so the word cannot be proved by a record. I treat "tastes good" as the best available idea, not a settled fact. This is a common situation with very old words.
5. Is the Sea Bream Called Tai Because It Is "Medetai," Meaning Happy?
Another popular story says that tai, the red sea bream, got its name from medetai, meaning "joyful, auspicious." The major Japanese dictionary Nihon Kokugo Daijiten gives a slightly different explanation. It says the red sea bream is treated as the "king of fish" in Japanese cooking, and that because its name sounds like part of medetai, it has long been served at celebrations [6]. The dictionary entry gives a Man'yoshu poem from the 700s that mentions catching tai, so the word was already in use then [6].
That difference matters. The entry shows that the name tai reminds people of medetai and that the fish has long been served at celebrations. As I read it, the entry does not say the name itself came from the pun, and I did not find a source here that explains where tai originally came from.
Both cases teach the same lesson. A name that sounds as if it explains itself may be a later story added to an older word.
6. Can the Official Name of a Fish Be Changed?
Yes, and one case is well documented. Until 2007, a small fish that moves along the seabed on its fins, almost like legs, had the standard Japanese name izariuo. The first part, izari, was an old word used for people who had trouble walking, and it is now considered offensive. A fish writer explains that the Ichthyological Society of Japan announced a new name in 2007 for that reason [7].
The society's own list of proposed changes is online. It shows that the name kaeruankou, "frog anglerfish," was chosen as the base name for the whole group because the fish's shape recalls a frog and because the English name is "frogfish." It also records that the committee considered another option, but preferred a name that would not remind people of the old one [8]. The same document lists many other fish names as candidates for change, not just this one [8].
So the answer to our opening question is that people decide, and they can decide again. A standard name is a tool made by a group of scientists, and in this case they replaced it when they saw that it hurt people.
7. How Can You Look Into Fish Names Yourself?
Pick one fish you know and find its three names: what people call it where you live, its standard Japanese name from a field guide or fish database, and its Latin scientific name. Do the names agree? Then ask one more question: does each name describe the fish's looks, its taste, its behavior, or something else? You may find that some of them, like aji, come with a story that sounds neat but cannot be fully proved. If you find a Japanese fish guide at a library or an aquarium, check whether it lists the standard Japanese name next to the Latin one. That small detail shows you which kind of name you are looking at.