Abstract
The condition factor is a parameter which acts as a general indicator of the "well-being" of a species, and it can be obtained through the analysis of width vs. weight relationships. The present work aims to investigate size vs. weight relationship and the condition factor of the crab Goniopsis cruentata (Latreille, 1803). The study area was the Mundaú/Manguaba estuarine complex, Maceió, state of Alagoas, Northeast Brazil. Samplings were monthly accomplished from August 2007 to July 2008. A total of 626 individuals were analyzed, being 309 males and 317 females. Males were larger and heavier than females, what is expected in many brachyuran. The growth was positive allometric to both males (b = 3.42) and females (b = 3.30), not obeying the "cube law". The condition factor of female was higher than that of male crabs, probably due to the gonad weight of females. It also varied seasonally for both sexes, being higher in the autumn and winter in males, and in the autumn and spring in females, and related to the molt and period of spawning intensification.
Highlights
The equation that best fits the size vs. weight relationship is the power function (y = axb), the same typically used in allometric studies in brachyurans (Le Cren, 1951; Atar & Seçer, 2003; Branco & Fracasso, 2004)
According to Froese (2006), if b = 3, small specimens have the same form and condition as large specimens; when b > 3, large specimens may presents ontogenetic changes in body shape with size, which is rare, or they are fatter than small specimens, which is not uncommon; in the case of b < 3, large specimens may have changed their body shape to become more elongated or small specimens are in better nutritional condition
The cube law states that when the humid weight (HW) of an animal is related with its size, a tridimensional variable is compared to a linear one
Summary
The condition factor may vary among seasons, gonad cycle and annual differences in environmental conditions (Froese, 2006) It results from different size vs weight relationships obtained in each case. According to Froese (2006), if b = 3, small specimens have the same form and condition as large specimens; when b > 3, large specimens may presents ontogenetic changes in body shape with size, which is rare, or they are fatter than small specimens, which is not uncommon; in the case of b < 3, large specimens may have changed their body shape to become more elongated or small specimens are in better nutritional condition These types of weight increase are termed isometric, positive and negative allometric, respectively (Hartnoll, 1982). In the relation HW vs. CW, the value of b is isometric when equal to tree, as well as allometric, when b differs from three (Le Cren, 1951; Froese, 2006; Ahmad Dar et al, 2012)
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