Cryptotomus roseus, lives in naturally protected shallow areas, with vast meadows of Thalassia testudinum
associated with coral systems. In order to know some population parameters of this species, monthly samples were taken from
November 2006 until October 2007, using a beach seine 60 m long x 4 m high, with a mesh size of 25,4 mm in the wings and
6,4 mm in the central portion. Cryptotomus roseus showed yearly unimodal distributions with respect to size and weight, with
a percentage of females (53.22%) and individuals with indeterminate sex (27.49%) higher than that of males. In general, the
size ranged between 5.50 and 14.40 cm Lt, with average 10.45 ± 1.62 cm Lt, while the weight varied from 1.40 to 43.10 g,
with average 15,28 ± 7,71 g. The size range of females varied between 6,60 and 14.40 Lt cm, with average 10.45 ± 1.29 cm
TL, while the weight ranged from 1.80 to 32.80 g, with average 14.62 ± 6,18 g. On the other hand, the size range of males
varied from 8.50 to 14,20 Lt cm, with average 11,80 ± 1.34 cm TL, with a weight that ranged from 6.40 to 43.10 g, with
average 22,33 ± 9.05 g. The comparison of intercepts and slopes of the relationship between weight and lenght showed lack
of significant differences between sexes and individuals with indeterminate sex (Chi2 = 0.1139; p = 0.7357), being the best
describing equation: W= 0,005TL3,383 (r2 = 0.9525, n = 171), showing a positive allometric growth. From a group of 124
specimens, 73.39% were females and 26.61% males, it was shown that the proportion of females was higher throughout the
year (2.75:1) (Chi2 = 27.14, p=<0.05). Similarly, the monthly variation in sex ratio showed significant differences, with a
greater proportion of females in May, June and September. Monthly averages of physiological condition ranged from 0.92 to
1.17; with an annual average of 1.02 ± 0.08, indicating good physiological in this species. The higher values of this parameters
are associated with the reproductive season, which may be taking place during the upwelling period in the first quarter of the
year.