Brachyhypopomus draco, Giora, Malabarba & Crampton, 2008, Giora, Malabarba & Crampton, 2008

Schaan, Andrea B., Giora, Júlia & Fialho, Clarice B., 2009, Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil, Neotropical Ichthyology 7 (4), pp. 737-744 : 738-739

Results

A total of 300 specimens - 150 females with total length ranging from 55.5 to 176.8 mm and 150 males ranging from 68.2 to 212.3 mm - were analyzed. The estimated reproductive period lasted from August to December for females and from July to December for males ( Fig. 1 ).

The GSI of B. draco males did not exhibit a significant relation with the feeding indexes analyzed (IR and HSI), whereas the GSI of females showed significant positive relation with HSI ( Table 1 ). Among the six abiotic factors that were considered, temperature, oxygen saturation, and water depth positively influenced male GSI, while female GSI was affected only by water depth ( Table 1 ). Monthly data of RI and HSI variation are presented in Figs. 2 and 3 respectively. Monthly data of water temperature, conductivity, depth, dissolved oxygen, rainfall, and photoperiod for the study site are summarized in Fig. 4 .

The absolute fecundity of the species analyzed showed an average value of 935.8 vitellogenic oocytes (ranging from 576 to 1391 oocytes) for females with total length from 113.9 to 174 mm ( Table 2 ). The average relative fecundity was estimated as 0.17 vitellogenic oocytes per mg total weight ( Table 2 ). Analysis of the absolute frequency distribution of oocyte diameter conforms to that of a species with synchronous oocyte development in more than two groups, and with fractional spawning, the species being estimated to spawn at least twice during a reproductive period ( Fig. 5 ). A high frequency of pre-vitellogenic (reserve) oocytes can be observed. These are the smallest germinative cells that are visible under a stereomicroscope, have a large and central nucleus, and contain no yolk vesicles. The reserve oocytes will only mature in the next reproductive period, but are followed by oocyte stores in successive maturation stages ( Fig. 5 ), which are released at different times in the current reproductive period. The presence of reserve oocytes and more than one store of oocytes in successive developmental stages provide evidence that B. draco is an iteroparous species.

The sex ratio established for the B. draco studied population was 1: 1 in each month, as well as in the global sample. Sexual dimorphism related to total body length was determined for the species, with males growing to greater lengths than females ( Fig. 6 ). The largest male and female sampled had total lengths of 212.3 mm and 176.8 mm, respectively. Males of B. draco with hypertrophy of the distal portion of caudal filament - vertical broadening and lateral compression, which give the caudal filament a paddle-like shape - were sampled during all months of the year, with male caudal filament depth ranging from 0.96 to 6.88 mm, representing 1.14% to 3.47% of total length. Caudal filaments grouped in level one (n = 32) were found in all months of the year, except November and December, but with higher frequency in April and July ( Fig. 7 ). Caudal filaments in level two (n = 94) were found in all sampled months, showing a higher frequency in November ( Fig. 7 ). Filaments in level three (n = 7) were found from August to January except in September and November ( Fig. 7 ). The χ 2 test indicated a significant difference between the three levels during the whole sampled year, except in February and July, with the highest values occurring from August to December and in March ( Table 3 ). No individuals with level three filaments were found from February to July of the year studied, suggesting a regression of the caudal filament hypertrophy after the reproductive period months ( Fig. 7 ).

Figures

Fig. 1. Monthly variation of mean gonadosomatic index (GSI) for Brachyhypopomus draco males (above) and females (below) from September 2003 to August 2004. Vertical bars represent the standard deviation and the values between the brackets are the sample size.

Fig. 2. Monthly variation of mean repletion index (RI) for Brachyhypopomus draco males (above) and females (below) from September 2003 to August 2004. Vertical bars represent the standard deviation and the values between the brackets are the sample size.

Fig. 3. Monthly variation of mean hepatosomatic index (HSI) for Brachyhypopomus draco males (above) and females (below) from September 2003 to August 2004. Vertical bars represent the standard deviation and the values between the brackets are the sample size.

Fig. 4. Monthly variation of light photoperiod (min) (above); water temperature (ºC), depth (cm) and oxygen saturation (%) (middle); conductivity (µS/cm) and rainfall (mm) (below). Values in lagoa Verde from September 2003 to August 2004.

Fig. 5. Distribution of relative frequency of 150 oocyte diameters of 10 Brachyhypopomus draco females with highest GSI values sampled from September 2003 to August 2004. Vertical bars represent the standard deviation.

Fig. 6. Relative frequency distribution of Brachyhypopomus draco males (n = 175) and females (n = 175) for total length classes sampled from September 2003 to August 2004.

Fig. 7. Relative frequency distribution of caudal filament depth levels for Brachyhypopomus draco males. Caudal filaments depth Level 1 = from 0 to 1.5%; Level 2 = from 1.51% to 2.5%; Level 3 = from 2.51% to 3.50%.