Rainbow trout
Otolith description
The otolith is triangularly shaped. The sulcus is straight and runs along the length of the otolith. The sulcus is open and well developed. Ostium and cauda are clearly visible and separated by a narrowing of the sulcus. The ostium is shorter and wider than the cauda. The inside of the ostium is irregular. The surface of the inside and outside is smooth. The margins are relatively smooth, with an indistinct indention at the posterior end of the otolith, at the cauda. The posterior end is rounded. The rostrum of the otolith is well developed and pointed. The antirostrum is indistinct. The otolith is thin and flat at both the inside and outside.
Rainbow trout otoliths are difficult to distinguish from sea trout Salmo trutta. Otoliths of sea trout are not as round, especially at the ventral side. The rostrum of sea trout otoliths is larger. The posterior end of sea trout otoliths is pointed unlike rainbow trout, which is rounded. The outside of rainbow trout otoliths is slightly concave compared to the outside of sea trout otoliths.
When eroded the sulcus becomes less distinct, with the ostium remaining longer visible than cauda. The rostrum is smoothed but remains pointed.
Fish length and distribution
Rainbow trout can grow up to 100 cm. Rainbow trout is a pelagic roundfish from fresh waters. In Asia and North America this is a migratory species that only comes to spawn in fresh water. In Europe the migratory subspecies does not survive but introduced sedentary stocks are found throughout the continent. (Wheeler, 1978, De Nie, 1996, Muus et al., 1999).
Sample origin
Commercially, from unknown freshwater bodies.