8142

• UCREFRP Catalog Number: 8142
• Author: Horn, M. J.
• Title: Nutritional Limitation of Recruitment in the Razorback Sucker ‎(
• USFW Year: 1996.
• Copyright Material: NO

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62

As such a becomes the intercept and b the slope of a regression line (Laurence 1978).

From length-weight relationships several types of condition factors have been developed,

the most gen~ral being the Fulton index of condition (Fulton 1911):
K = w/13 ,

In this case a (the intercept) is 1, and b (the slope), is assumed to be 3. When b equals 3

fish are assumed to be growing proportionally with mass increasing as a cube of length.

Because growth is generally allometric, however, K can only be used to compare

individuals of similar length (Anderson and Gutreuter 1983), and misinterpretations can

occur when individuals of different sizes are compared (LaCren 1951). More recent

metrics known as relative condition factor (Kn) and relative weight (Wr) have been

developed to address this problem (LaCren 1951; Wege and Anderson 1978). They differ

from the Fulton-type condition factor in that b is now species (Wr)- or population (Kn)-

specific, which given certain assumptions, should allow comparison across more than one

length class and across populations (Murphy et al. 1991).

Ideally, a condition index is based upon a population of "known" optimal

condition, where differences among populations examined do not have a genetic basis but

are instead purely environmental in nature (Anderson and Gutreuter 1983; Murphy et al.

1990). Problems arise, however, when relative weights are derived from length-weight

relations for a series of populations across a species' range (Willis 1989). Chances are,

not all populations are living under optimal conditions. Thus the value of the index may

be somewhat lower than it should be, and consequently, give misleading results. For

example, a condition index derived for New York largemouth bass (Micropterus