Smale and Goosen: Reproduction and feeding of Thakis megalopterus 



991 



50 100 150 200 250 300 350 400 450 

 Embryo total length (mm) 



Figure 3 



The relation between embryo mass (EM) and 

 total embryo length ( TL ) was BM = 2.397 x 10-« 



 rL"«i|r=0.99, ;!=275). 



1.400 1,500 1,600 1,700 

 Total length (mm) 



1,800 



Figure 4 



The relation between the number of normal 

 embryos (?2 ) and total length (TL I of pregnant 

 females was n = -21.74 + 0.020 x TL (r=0.52. 

 n=38). 



(paired t test; P>0.5). Of the 244 embryos that were 

 ■sexed, 122 were male and 122 were female. 



The relation between wet body mass and total 

 length of embryos was described by a power curve 



(Fig. 3): 



W = 2.397 X 10-6 X TL^ 



089 



[r2=0.994; /7=275] 



where W 

 TL 



embryo weight; and 

 embryo total length. 



Weight of near- term embryos ranged from 300 to 362 g 

 ( .v=331.4g;«=23). 



During all stages of development, the embryos 

 within a uterus often differed in size; the largest 

 embryos were as much as SO^c longer than the small- 

 est. Greater differences were found in early stages 

 of embryonic development. Larger embryos usually 

 occupy a more posterior position, suggesting that they 

 are older than litter mates in more anterior positions. 

 The embryos in both uteri were at equivalent devel- 

 opmental stages in all the samples. Embryo orienta- 

 tion within the uteri was normally head forward. 

 Only two embryos from one batch lay head backward. 

 Description of the developmental morphology of em- 

 bryos was given by Goosen ( 1997 1. 



Average observed embryo length in females be- 

 tween 19 May and 25 August was 425 mm ( /? =30 ). A 

 female caught on 19 May had an embryo length range 

 of 416-443 mm ( .v=431 mm;7i = 15), whereas another 

 female, caught on 25 August, had embryos in the 

 length range of 412-440 mm ( .v =425 mm; n =8). Yolk 

 sacs were barely visible in the smaller of these em- 

 bryos, and the largest had closed umbilical scars be- 

 tween the pectoral fins. Denticles and teeth of larger 

 ones had erupted from the skin; one or two black 

 spots were noted on some embryos. Their large size 



and eruption of teeth and denticles suggested that 

 they had developed approximately to term. No em- 

 bryo examined during this study showed any sign of 

 a placental attachment between embryonic and ma- 

 ternal tissue. Embryos were readily removed from 

 the uterus at all stages of development. Embryos are 

 separated from each other in the uterus by envelop- 

 ing uterine membranes, from which they apparently 

 emerge shortly before birth. The largest embryo 

 measured 443 mm and weighed 341 g. Based on avail- 

 able information, size at birth is estimated at 420- 

 450 mm; birth probably occurs between May and 

 August. The smallest free swimming individual, 576 

 mm in length, was taken in August. 



Careful examination of embryos and uterine eggs 

 showed that some of the uterine eggs failed to de- 

 velop. Of 39 pregnant females, 11 (289f) had some 

 nondeveloping uterine eggs. The greatest number of 

 nondeveloping uterine eggs carried by a single fe- 

 male was 4 out of a total of 11, but most had only one 

 or two. Of these pregnant females, 10 (267r ) contained 

 empty egg cases (no yolk). The largest number of 

 empty egg cases carried by a single female was 12 

 (out of a total of 121. Occasionally, one embryo in a 

 litter was deformed or retarded in growth. Because 

 of the nondevelopment of a small proportion of uter- 

 ine eggs, the number of developing, apparently nor- 

 mal embryos is a better measure of reproductive out- 

 put than the number of uterine eggs. The relation 

 between number of normal embryos and total length 

 of the mother may be described by a linear regres- 

 sion (Fig. 4): 



n = -21.74 + 0.02 TL, 



[n = 381 



where /; = litter size; and 



TL = the total length of the mother in mm. 



