SEASONAL-AND HABITAT-SPECIFIC GROWTH OF SHORTHEAD REDHORSE IN THE
UPPER MISSISSIPPI RIVER.  

Carey Hale and Michael D. Delong.   Large River Studies Center
and Biology Department, Winona State University, Winona, MN
55987.  

Two primary models that describe trophic dynamics in large river
are the Flood Pulse Concept (FPC) and the River Productivity
Model (RPM).  The major difference between these two models is
the timing of production in the river.  The FPC is flood-oriented
and is, therefore, associated with the spring season for the
upper Mississippi River.  The RPM emphasizes autochthonous
production and is, therefore, associated with the summer and
autumn seasons.  The objective of this study was to: (1)
determine if seasonal growth of fish could be measured by using
the annuli of scales obtained from the fish; and (2) to examine
the habitat-specific differences in growth.  Fish samples were
taken near shore at main, side and backwater sites through the
months of April to October using a boat electroshocker.  Length,
weight, and scales were taken for each fish.  Growth of shorthead
redhorse (Moxostoma macrolepidotum) was determined from analysis
of scales.  Fish collected in the spring were used to establish
age classes and initial size.  Measurements were taken from the
last annuli to the outer edge of the scale on fish collected in
the summer and fall.  Preliminary results suggest that growth is
similar between the main and side channel habitats, and that
growth is higher in the latter part of the growing season, in
conjunction with peak periods of primary production.  

Keywords:  fish, growth, habitat, seasonal patterns, Mississippi
River, redhorse, Moxostoma macrolepidotum