St. Lynott et al., MONTHLY AND SIZE-RELATED CHANGES IN THE DIET OF RAINBOW-TROUT IN LAKEOAHE, SOUTH-DAKOTA, Journal of freshwater ecology, 10(4), 1995, pp. 399-407
We analyzed the food habits of rainbow trout (Oncorhynchus mykiss) fro
m Lake Oahe, South Dakota, from May through September, 1993-1994. Rain
bow trout were captured in surface, suspended and bottom monofilament
gillnets. Diets were analyzed using the relative importance index (RI)
. Composition of the diet differed among months and among size categor
ies of rainbow trout. Greatest RI values for zooplankton prey occurred
during May, July and August. Terrestrial invertebrates had the highes
t RI value during June and September. Overall, RI values for aquatic m
acroinvertebrates and rainbow smelt (Osmerus mordax) were lower than t
he other two prey categories. Zooplankton were the most important prey
for rainbow trout < 330 mm and decreased in importance as rainbow tro
ut increased in length. Rainbow trout between 330-459 mm fed predomina
ntly on terrestrial invertebrates. Rainbow smelt were incorporated int
o the diet of rainbow trout between 201-330 mm and increased in import
ance as rainbow trout length increased. Rainbow smelt dominated the di
et of rainbow trout > 460 mm.