Danilewicz et al.: Reproductive biology of male Pontoporia blainvillei from Rio Grande do Sul, southern Brazil 



587 



a subsample of 10 mature males were 

 examined histologically, we did not find 

 any sign of spermatozoa. 



Discussion 



The high bilateral uniformity in tes- 

 ticular weight and length presented 

 by the franciscana is a characteristic 

 shared with many other cetacean spe- 

 cies. Studies on the striped dolphin, 

 Stenella coeruleoalba (Miyazaki, 1977), 

 the common dolphin, Delphinus delphis 

 (Collet and Saint Girons, 1984), the 

 sperm whale, Physeter macrocephalus 

 (Mitchell and Kozicki, 1984), and the 

 dusky dolphin, Lagenorhynchus obscu- 

 rus (van Waerebeek and Read, 1994), 

 among others, demonstrate the same 

 pattern of testis symmetry. Given the 

 similar dimensions of both testes in 

 franciscanas, it is possible to extrapo- 

 late the combined-testes weight by 

 weighing only one testis without intro- 

 ducing bias in the analysis. It is recom- 

 mended, however, that the weight of 

 the testes should be presented without 

 the epididymis weight, as it was pre- 

 sented in the most extensive compara- 

 tive study on the subject (Kenagy and 

 Trombulak, 1986). 



There is a negative allometry of the 

 seminiferous tubule diameter in rela- 

 tion to testis length, standard length, 

 and total weight. This pattern is ac- 

 centuated in immature males, in which 

 the tubule diameters remain almost 

 unchanged with the increase of the 

 other variables. The lack of values for 

 tubule diameters in the testes weight 

 interval (2.5-6.0 g) and testes length 

 interval (34-42 mm) just before the 

 attainment of sexual maturity (Figs. 

 2 and 3) indicates that the increase in 

 tubule size in relation to sexual matu- 

 rity must occur very quickly, probably 

 when the tubules are between 85 and 

 125 urn in diameter. 



Attainment of sexual maturity 



Length and weight at attainment of 

 sexual maturity of male franciscanas 

 in Rio Grande do Sul are very similar 

 to those values estimated in previous 

 estimates for Uruguay (Table 2). In con- 

 trast to the present study, Kasuya and 

 Brownell (1979) calculated mean length 

 at sexual maturity for Uruguay as the 



Figure 8 



Relationship between month and relative testes weight in mature male 

 franciscanas (Pontoporia blainvillei) (7j=31) (l = January, 12 = December; 

 filled boxes=the nonreproductive months, open boxes=reproductive months). 

 Bars indicate 25^ and 75% percentiles. 



