Peres and Vooren: Sexual maturation, reproductive cycle, and fecundity of Galeorhmus galeus 



665 



TOTAL LENGTH (cm 



Figure 15 



Relationship between total body length and uterine fecundity 

 of the school shark Galeorhmus galeus, of (1) southern Brazil; 

 (2) southern Australia, according to Olsen (1984); and (3) 

 California, according to Ripley (1946). 



Australian animals, the HSI ranged from 6.0 to 11.0 

 in GR females, and from 15.0 to 24.0 in NGR-2 females 

 (Olsen 1954). Since these values are similar to those 

 of comparable eastern South Atlantic females, it is con- 

 cluded that the liver cycle of adult females observed 

 in the present study is characteristic of the species. 



When estrogen was administered to the female of the 

 spotted catfish Scyliorhinus canicula, the liver in- 

 creased in size and produced vitellogenin and released 

 it into the blood (Craik 1978). Estrogen is produced by 

 the granulosa of the maturing ovarian follicle of the 

 spiny dogfish Squalus acanthias, and by the mature 

 testis of Torpedo marmorata, Scyliorhinus canicula, 

 Squalus acanthias, and Raja clavata (Lance and 

 Callard 1969, Craik 1978, Dodd 1983). This explains 

 why in the western South Atlantic school shark the HSI 

 increases in both sexes after sexual maturation and 

 varies with the cycle of the adult ovary, reaching a max- 

 imum during the NGR-2 stage. Ripley and Bolomey 

 (1946) show that in spring the proportion of oil in the 

 liver of the eastern North Pacific adult is about 60% 

 in males and NGR-1 females, 40% in GR and post- 

 partum females, and 70% in NGR-2 females and those 

 with uterine eggs. Thus, the changes in HSI of the adult 

 female reflect a major variation in the quantity of lipids 

 in the liver during the reproductive cycle. 



The submerged weight (SWj) in seawater of an ob- 

 ject i can be determined by the model 



SWj = m;(l - d s /d,), 



where m t is the mass of the object in g, and d s and 

 dj are the specific densities of seawater and of the 



object, respectively, in g/cm 3 . A negative submerged 

 weight indicates buoyancy. Using this model, sub- 

 merged weight for the eviscerated body and the oil 

 reserve in the liver was calculated for males and 

 females of 130 cm TL in all three reproductive stages. 

 For submerged weight of the body, m, was calculated 

 from the regressions in Table 1, and dj was estimated 

 at 1.065 g/cm 3 , which is the mean of the liver-free 

 body density of 13 species of sharks (Baldridge 1970). 

 For submerged weight of the oil reserve, the liver mass 

 calculated from the HSI in the present study was 

 multiplied by the percentage of oil in the liver in the 

 eastern North Pacific school shark. For the specific 

 density of the liver oil in the different reproductive 

 stages, values from Bone and Marshal (1982) were 

 used: GR females, non-metabolizable lipids, 0.860 

 g/cm 3 ; NGR-2 females, metabolizable lipids, 0.930 

 g/cm 3 ; NGR-1 and males, the median of these values, 

 0.895 g/cm 3 . To calculate the submerged weights of 

 the mature ovaries of NGR-2 females 130 cm TL, the 

 regression of ovarian fecundity on total length was 

 combined with data on mass and volume of 14 follicles 

 (4.0cm in diameter). This resulted in an ovary mass of 

 665. OOg and a specific density of 1.108g/cm 3 . The 

 specific density of seawater was taken as 1.024 g/cm 3 , 

 according to Baldridge (1970). 



The results are summarized in Table 4. In males and 

 NGR-1 females, the buoyancy of the liver is about one- 

 fourth the submerged weight of the eviscerated body. 

 In NGR-2 females, the increased liver buoyancy com- 

 pensates for 60% of the submerged weight of the yolk 

 mass in the ovary. Through the production of estrogen, 

 the maturing ovary also controls, simultaneously, the 

 vitellogenic and hydrostatic functions of the liver. 

 Besides providing buoyancy when this is most needed, 

 the metabolic reserve of the NGR-2 female guarantees 

 resources for vitellogenesis and maturation of the fol- 

 licle, thus ensuring the timing of reproduction. 



The specific density of embryos, for example, 1.035 

 g/cm 3 in the sandbar shark Carcharinus milberti 

 (Baldridge 1970), is much less than that of yolk. Dur- 

 ing gestation of aplacentary sharks, some organic 

 matter in the yolk reserve is lost but water is ab- 

 sorbed, and the full-term embryo weighs twice as 

 much as the yolk (Ranzi 1932). The specific density of 

 the uterus decreases during gestation because of the 

 increase of intrauterine liquid and embryos and the 

 decrease of egg yolk. This enables the gestating female 

 to metabolize her lipid reserves without loss of buoy- 

 ancy, and explains the low liver buoyancy in this stage. 

 The reduction in liver volume also provides space for 

 the gravid uteri. Such a trade-off between lipids and 

 water without change in overall buoyancy also occurs 

 during the winter fasting of Clupea harengus (lies 

 1984). 



