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44

A. C. G. MAI. ET AL.

(%)

50 40

30 20

OCTOBER, n=11

40

(%)

30 20 10

FEBRUARY, n=14

10 0

0

(%)

100 75 50 25 0 100

(%)

75 50 25

NOVEMBER, n=3

DECEMBER, n=5

%)

%)

(%)

(%)

60

40

20

0

60

40

20

MARCH, n=26

APRIL, n=7

(%)

0 40

30 20

10 0

JANUARY, n=11

0

(%)

100 75

50 25 0

MAY, n=1

42.5 47.5 52.5 57.5

62.5 67.5 72.5 77.5

Size class (mm)

4 2 . 5 4 7 . 5 5 2 . 5 5 7 . 5 6 Size class (mm) 2 . 5 6 7 . 5 7 2 . 5 7 7 . 5

Figure 5. Monthly distribution (in percentage) Jenynsia multidentata’s females with embryos per 5 TL mm size classes, colleted in the estuary of Patos Lagoon between March 2000 and February 2001.

The second pregnancy

We observed a second pregnancy for some females along the reproductive period. In January, we verified the occurrence of the smallest reproductive females, probably born in October- November. Also in this month, we observed the occurrence of large reproductive females and they have showed a large empty space inside the abdominal region, which suggests that these females would be in their second pregnancy in the reproductive period. Or rather, females that have given birth in October-November would be in their second reproductive cycle in January-February.

This second pregnancy has not been reported in the previous reproductive study of this species in the same estuary by Garcia et al. (2004). Probably, this is because their studied was based on indirect reproductive evidences (abundance per size class plots) that did not involved dissection and examination of reproductive status of each specimen. Another confounding factor in this previous study was the higher variance in their dataset, since the analyzed individuals came from a larger number of sampling stations, encompassing not only the estuary but also freshwater sites in the northern reaches of the lagoon.

Fontoura et al. (1994) have observed that J. multidentata reaches smaller sizes in fresh water

environments when compared with brackish ones. Experimental studies tested this hypothesis, confirming that individuals reared in brackish water presented higher growth and less mortality than those reared in freshwater (Mai et al. 2005). It seems plausible to expect, therefore, that higher growth and survival rates in brackish water would allow a second pregnancy for those females inhabiting an estuarine zone, as we have reported in this study.

Fecundity and sex ratio The positive relation between the number of embryos and the total length of females corroborates the previous analysis of Betito (1984), which suggest that females limit the space of ovaries and, consequently, their fecundity. The minimum female size (43 mm) observed in this work was similar to the values described by Betito (1984) and Fontoura et al. (1994) of 42 e 45 mm, respectively.

Previous studies using this species have shown a higher number of females in relation to the males (Fontoura et al. 1994, Betito 1984, Garcia et al. 2004). Many hypotheses have been suggested to explain this pattern. For example, some authors have hypothesized the existence of an asymmetric predation between genders to due the peculiar reproductive behavior of this species. The copulation in the one-sided livebearer happens without the

Pan-American Journal of Aquatic Sciences (2007) 2 (1): 40-46

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