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Reproductive aspects of the Jenynsia multidentata.

43

October-November achieved maturation fast, probably due the abundant food in spring, and they reproduce altogether with their mothers (in 2nd pregnancy at this moment) in January-February. The females born in January-February have taken nine months to achieve the maturity and they have shown the first pregnancy in October-November, only in the next reproductive period and, consequently, their 2nd pregnancy will occur just in the following year.

(a)

Sexual stage (%)

100 80 60 40 20 0

Rest With eggs With embryos

Gonadossomatic relation Mean and standard deviation

20 16 12

8 4 0

Salinity Temperature ( C)

o

30 25 20 15 10 5 0

(c)

1 0.8 0.6 0.4 0.2 0

transparence (m)

M A MJ

J

AS Months

  • O

    ND

J

F

Figure 3. (a) Monthly variation of frequency of occurrence (in percentage) in each stage of gonad maturation of Jenynsia multidentata colleted in the estuary of Patos Lagoon, between March 2000 and February 2001; (b) Monthly variation of average values of gonadossomatic index for females of J. multidentata in the estuary of Patos Lagoon; (c) Variation of abiotic variables in the sampled period.

Period

(n)

(n)

:

January

81

6

13.5

February

30

10

3

March

205

82

2.5

April

235

156

1.51

May

47

45

1.04

June

11

1

11

July

---

---

---

August

2

---

---

September

28

38

0.74

October

4

1

4

November

105

76

1.38

December

141

26

5.42

Total

889

441

2.02

Table I. Number of females’ specimens, males and sexual ratio of Jenynsia multidentata collected at Patos Lagoon estuary between March 2000 and

February 2001.

Discussion

Reproductive season and relationship with abiotic factors

Fontoura et al. (1994) and Garcia et al. (2004), for a freshwater lake and for the Patos Lagoon estuary, respectively, suggested this species has two reproductive peaks, in which females born in December to March comprises the first cohort, reproducing at the end of winter and beginning of spring (September-November). The second cohort (September-November) will reproduce for the first time in summer and fall (December-May). Our results indicate a reproductive period extending from September to May, which encompass both reproductive peaks reported by the above mentioned studies. The low GSR value we observed in December did not fit this hypothesis but it could be explained by the absence of females with eggs and to the low fecundity (average of 16 embryos, n= 5) showed in this month.

60

Fecundity (number of embryos)

40

20

F = 1,015TL - 33,165 R2 = 0,6571

0

40

45

50

55

60 Size (mm)

65

70

75

80

Figure 4. Relationship between the number of embryos and the total length (TL) Jenynsia multidentata’s females colleted in the estuary of Patos Lagoon, between March 2000 and February 2001.

Temperature seemed to be the factor that better explained the GSR variations along the year, which have been previously noted by Garcia et al. (2004). In contrast, there were no significant correlations among water transparency and salinity with reproductive aspects. The fact that temperature was the only abiotic factor measured showing significant correlation with GSR is not surprising, considering that temperature variation is much more predictable in this region when compared with water transparency and salinity. These latter factors have a more stochastic pattern along the year due to their relationships with wind patterns (Costa et al. 1988).

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

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