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The oocyte structure of jumbo squid (Dosidicus gigas) female gonads was analyzed to validate morphochromatic sexual maturation stages based on a six-phase scale. Samples were obtained fortnightly from the Santa Rosalía area, Baja California Sur, from June 2001 to November 2002. Histological preparations were obtained from each gonad to count the number of oocytes at each level of development. The frequency of oocytes at each level was then used to estimate a maturity index (MI) to assess the correspondence between morphochromatic maturation stages and the oocyte structure in the gonad tissue. The histological analysis showed that morphochromatic stages I, II and III were ruled by oocytes in developmental level 2 or less (i.e., secondary growth has not yet begun), and thus correspond to sexually immature juveniles. Stages IV, V and VI were ruled by oocytes in more advanced developmental levels and correspond to mature or maturing adults. According to the analysis of variance, the morphochromatic maturity scale allowed sexually immature individuals to be readily and reliably distinguished from mature ones. A detailed analysis of MI confidence intervals showed that each morphochromatic maturity stage had a specific oocyte structure, except for stages II and III, which presented morphological differences.
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