The Hylian Loach is a fish that appears in Ocarina of Time and Twilight Princess.
Ocarina of Time
The Hylian Loach makes its debut in Ocarina of Time. It is found in the Fishing Pond both as child and adult. The Hylian Loach is found around the lilypads, and can only be caught when using the Sinking Lure. Link has to pinpoint the lure between the Loach and the center of the pond. Once every minute or so the Hylian Loach swims to the center of the pond, and is at that time Link's only chance to catch it. This is the easiest way to catch it. Link cannot set records with them, but only grants 50 Rupees of subsequent catches.
As child, the Hylian Loach can weigh over 15 pounds, and as an adult it weights over 30 pounds.
The Hylian Loach in Twilight Princess is found in Hena's Fishing Hole around the lilypads, which are located at the back cave only in the summer, (the season changes every time Link exits and re-enters the area), same as it were in Ocarina of Time. This time around, Link has to use the Frog Lure or the Sinking Lure in order to catch it. The Hylian Loach may also be found in the Kakariko Graveyard, Sacred Grove, or Lanayru Spring as a smaller fish (Around 15 inches). If caught in the Fishing Hole, it may be as large as 30 inches.
Hylian Loach from Ocarina of Time
Link with the Hylian Loach in hand in Ocarina of Time
Link holding the Hylian Loach in Twilight Princess