【Reading】きすいぎょ

【English Name】Brackish water fish

Fish that dwell in estuarine zones—the boundary between seawater and fresh water, that is, "brackish-water zones"—are collectively called kisuigyo (brackish-water fish).

Within Japan, mullet (bora), sea bass (suzuki), and yellowfin goby (mahaze) are representative presences, and the majority of fish dwelling in brackish-water zones are thought to be species that were originally saltwater fish and changed so as to be able to tolerate fresh water as well.

The degree to which a fish is connected to the brackish-water zone has gradations by species.

• "Sojourner fish" (gurai-gyo), whose main habitat is the saltwater zone but which also enter the brackish zone
• "Amphidromous fish" (ryosoku-kaiyu-gyo), which use the brackish zone only in their juvenile period
• "Peripheral freshwater fish," which make the brackish zone their principal living sphere
• "Euryhaline fish" and "secondary freshwater fish," which advance even into freshwater zones

Geographically, diversity is high from the subtropics to the tropics, and abundant species have been confirmed from Southeast Asia to the estuary of the Amazon River. In Japan too, the coasts of Kyushu, Shikoku, and the Kii Peninsula, where warm currents strike strongly, have comparatively many records of brackish-water fish.

The points of contact with sushi cannot be overlooked either. Sea bass is popular as a refined white-fleshed sushi topping, and "karasumi"—made by salting and drying the ovaries of mullet—is counted among the high-grade delicacies.