A delicious plate of hamachi kama (‘yellowtail collar’ [or ‘sickle’]), pictured below, serendipitously led me to discover that hamachi (魬) and buri (鰤) are merely different sizes of the same fish, the Japanese amberjack (Seriola quinqueradiata). Yellowtail is the usual translation in Japanese restaurants, but that name can also apply to a whole lot of other fishes (as well as other animals). You can tell you’re dealing with a highly commercialized and regulated industry when the difference between the smaller and larger fish is defined so precisely: hamachi weigh less than 5 kg, buri weigh 5 kg or more. The fry are called by yet another name, mojako.
According to Japanese Wikipedia, buri has a plethora of synonyms that vary by size and region. The term hamachi seems to come from Kansai; its match in Kanto seems to be inada. The names used on Japan Sea side are even more varied. (See here for a romanized glossary of Japanese fish names.)
This put me in mind of other types of jackfish (Jp. 鯵科 ajika, Carangidae) that have different names at different sizes in Hawaiian. Ulua refers to several types of large jackfish weighing 10 lbs or more, including the white ulua, or giant trevally (Caranx ignobilis); the omilu, or bluefin trevally (Caranx melampygus); and the kagami [< Jp. ‘mirror’] ulua or African pompano (Alectis ciliaris). At smaller sizes, the same fish are called papio. (Papio papio is also the genus and species name of the Guinea baboon.) In older Hawaiian usage, the smallest ones were called pāpio(pio); the somewhat larger ones, pā‘ū‘ū; and the largest ones, ulua.