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A. C. G. MAI. ET AL.

A total of 247 females were dissected in laboratory, and for each individual we recorded: total length (TL, mm), total weight (WT, g), weight of the full and empty gonad (g) and reproductive stage (rest, with eggs or embryos), number and weight (g) of eggs and embryos. These measurements were obtained using a microscopy stereoscopic, a caliper rule (precision on decimals of millimeters) and a precision balance Kern 410 (precision of 10-3 grams).

The maturation stages of gonads were distinguished as: rest, with eggs and with embryos. The reproductive season was estimated based on analyses of monthly frequencies of gonadal maturation stages (Santos 1978), and also by variation in the average values of the gonadossomatic relation (GSR) (Vazzoler 1996). The GSR was obtained for each individual using the total gonad weight/WT*100 and for each month we calculated the value’s average and its respective deviation. This relation was used to balance the subjectivity of data over the stages of maturity (Vazzoler 1996). The Spearman test (Hamilton et al. 1977) was performed to verify possible correlations

between GSR and abiotic factors temperature and water transparence) simultaneously with fishes sampling.

(salinity, collected

winter (June, July and August) all captured specimens were in sexual rest stage, but in September 42.9% of specimens presented eggs, and in the following month, 63.5% of females were found with embryos. The females with embryos were dominant along spring and summer (October until March), showing a decline in fall (April and May) (Fig. 3a). A temporal variation of gonadossomatic relation (GSR) showed an increase tendency starting in September and, although variable, it seemed to extent until February and March (Fig. 3b). The species reproductive cycle presented a larger correlation with water temperature (r = 0.76) than to water transparency (r= 0.52) and salinity (r= 0.04) (Fig. 3c).

Average number

50

Eggs

40

Embryos

30

20

10

0

M

A

M

J

J

A Months

S

  • O

    N

D

J

F

Figure 2. Average number of eggs and embryos per month for females of Jenynsia multidentata colleted in the estuary of Patos Lagoon, between March 2000 and February 2001.

sexual

The monthly variation in abundance

ratio

(number

of

females/males)

and was

calculated based on the total of number specimens collected in the sampling locations (n= 1330). The Chi-Square test ( 2) was performed in order to verify the significant differences in the sex ratio. At last, we analyzed the distribution of female with embryos, broke down by length classes of 5mm. The

fecundity

was

calculated

based

on

distribution

of

average

number

of

eggs

and

embryos

per

month

and

also by the number of embryos 5 mm size classes (SC).

per

female

divided

in

Results

The periods of highest abundance of J. multidentata in the Patos Lagoon estuary occurred between March-April and November-December, when, in most cases, females predominate in relation to males. The sex ratio showed monthly variations with peaks in January (:: 13.5:1, n= 86) and June ( : : 11:1, n= 12) and had an average of 2.02:1 during the sampling period (Tab. I). The Chi-Square

test (:

showed a significant difference in : 2 = 1171.42; d.f. = 48; p < 0.01).

this

ratio

The average number of eggs and embryos changed along the year. September and January had the largest number of eggs per female (Fig. 2). In

Based on the monthly average distribution of number of eggs and embryos, frequencies (in percentage) of gonad maturation stages and average values of the gonadossomatic index, we may ascertain that this species has a reproductive season between September and May, which is coincident with local higher water temperatures (> 15°C) (Fig. 2 e 3).

The fecundity, estimated from the number of embryos, was directly proportional to the length of females (Fig. 4). The fecundity average was estimated in 30 embryos per female, and the female that presented the lowest number of embryos (n=9), measured 51 mm in Total Length (TL). The most fecund female (74 eggs, TL = 72 mm) was collected in January 2001 at Saco da Mangueira, and the smallest mature female observed measured 43 mm TL.

Pregnant females were recorded in January and February, with growing gonads and the abdominal region extended, presenting an empty space, which characterize a second pregnancy in the reproductive period.

The largest and smallest reproductive females (SC = 72.5 e 77.5 mm e SC = 42.5 mm, respectively) were observed in reproduction in January (Fig. 5). This suggests that females born in

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

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