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INTRODUCTION
LENGTH-WEIGHT DATA on fishes collected from various locations can be used
to calculate typical average weights for fishes of specific lengths. Differences
in weight of fishes of similar length is best expressed in terms of a relative
condition factor (4) which is calculated by dividing an observed weight by
a typical average weight for fishes of a certain length.
Relative condition (Kn) = W/^W where
W = weight of an individual or the average weight of individuals
of a certain length
^W = the calculated average weight for the same length from
the equation W = aLb where a and b are constants derived from fitting the
equation
log W = log a + b log L
A relative condition (Kn) value greater than one indicates that
a fish or fishes of a specific length weigh more than the average weight,
or are in better condition. This
condition could indicate an aquatic system of greater productivity I), or
that the fish populations are structured (predator-prey ratio) to allow rapid
growth. The weight per unit length of a fish is greater when it is growing
rapidly. A Kn value of less than one indicates that a fish is growing slowly,
which may be attributed to overcrowding, parasites, diseases, or low productivity.
Seasonal changes as well as state or sexual maturity may also affect the condition
of fish. Godoy (2) observed that the weight change per unit of length is greater
for female curimatff {Prochilodus cearensis) than for males; also the condition
index for this species varies between seasons. However, Silva (5) determined
that the condition of Pescado do Piauf {Plagioscion squamosissimus) is not
sex related.