RESUMO
Isotopic values of two Caribbean sharpnose shark Rhizoprionodon porosus litters (Poey, 1861) with two and three embryos and one litter of 11 smalltail shark Carcharhinus porosus embryos showed enriched 15 N and 13 C compared to their mothers. In R. porosus, embryonic isotope values were 3.06 ± 0.07 and 0.69 ± 0.15 greater than their mothers' for δ15 N and δ13 C, respectively, whereas in C. porosus, δ15 N and δ13 C were 1.79 ± 0.09 and 1.31 ± 0.17 greater in embryos than their mothers.
Assuntos
Isótopos de Carbono/análise , Embrião não Mamífero/metabolismo , Isótopos de Nitrogênio/análise , Tubarões/embriologia , Animais , Região do Caribe , Embrião não Mamífero/química , Tubarões/metabolismoRESUMO
This study describes the fetal mummification process in two embryos of a 310 cm total length scalloped hammerhead shark Sphyrna lewini caught in southeastern Brazil, in December 2017. Fourteen embryos were observed in total, in which two males in the left uterus presented different stages of mummification. Both mummified embryos were covered by an exudate (i.e., a mucous substance), indicating a hematic mummification process. All embryos were at the placentotrophic stage of development, indicating that they were close to parturition. An intrinsic characteristic is suggested as possible etiology for this condition, such as umbilical torsion, because both embryos were at different sizes and, therefore, at different development stages. In addition, the sample size did not allow the authors to presume any pollution effect once only one female was observed. Finally, fetal mummification and other embryonic development disorders might have populational impacts due to reduction in embryo survival and, consequently, recruitment. For this reason and considering that S. lewini is categorized as a "critically endangered species," this study's results have conservational relevance.
Assuntos
Ovoviviparidade/fisiologia , Tubarões/embriologia , Animais , Brasil , Espécies em Perigo de Extinção , Feminino , Morte Fetal , MasculinoRESUMO
The reproduction of the sandbar shark Carcharhinus plumbeus in the U.S. south-eastern Atlantic Ocean including the Gulf of Mexico was examined using a combination of histological and morphological characteristics of C. plumbeus collected through fishery-dependent and -independent sampling programmes (n = 1,567). Indices of maturity were constructed using measurements of gonads, reproductive tracts and claspers, and sandbar sharks exhibited 50% maturity sizes of 140 and 148 cm fork length for males and females respectively. Gonado-somatic indices and variation in reproductive tract condition were used to determine seasonal trends in reproduction of mature C. plumbeus. Sandbar sharks have discrete seasonal reproductive cycles in which males produce sperm from January to May with a peak in May and females develop eggs from January to May with ovulation occurring in June. Females were shown to exhibit a >2 year reproductive cycle. Embryonic development was assessed through measurements of masses and lengths of uterine contents. Gestation was 12 months, from July to the following June, with parturition in late June. This research highlights a difference from previously reported data on the periodicity of female reproduction in C. plumbeus in the U.S. south-eastern Atlantic Ocean and Gulf of Mexico, which may have major effects on future C. plumbeus stock management.
Assuntos
Reprodução , Tubarões/anatomia & histologia , Animais , Oceano Atlântico , Desenvolvimento Embrionário , Feminino , Gônadas/anatomia & histologia , Golfo do México , Masculino , Caracteres Sexuais , Maturidade Sexual , Tubarões/embriologia , Tubarões/fisiologia , Estados UnidosRESUMO
This study reports the first bicephalic embryo of smalltail shark Carcharhinus porosus, which was removed from a pregnant female in coastal waters of the tropical eastern Pacific Ocean. The observation suggested that although the individual's body was well formed, the malformation of the head would have affected it survival.
Assuntos
Embrião não Mamífero/anormalidades , Tubarões/anormalidades , Tubarões/embriologia , Animais , Feminino , Masculino , GravidezRESUMO
Uteri from four pregnant females and two newborn of shortfin mako, Isurus oxyrinchus, were collected in the southeastern region of Brazil, during September, October, and November of 1993 and 1994. All embryos were near-term with developing dentition and inner organs. Total length ranged from 64.5 to 72.0 cm, and the maximum number of embryos observed in a litter was 20. These observations further confirmed oophagy as a form of nutrition in this species, and its periodicity. The presence of teeth in the embryos' stomachs suggest that tooth replacement begins in the uterine phase.