Teratogenic processes in an embryo without gills and low yolk absorption of Zapteryx brevirostris (Elasmobranchii: Rhinobatidae)

Abstract

This is the first report of morphological anomaly in embryos of Zapteryx brevirostris (Lesser guitarfish), a very common species in Brazil. The gills were absent, and the pectoral fins were not fully formed nor were they completely fused to the head. They were asymmetrical, with the larger left pectoral fin projecting more toward the head (almost at the height of the eyes). The pelvic fin was absent, making sexing impossible. The cause of the morphological deformity is uncertain, although a nutritional problem of the embryo is evoked. Este é o primeiro relato de anomalias morfológicas em embriões de Zapteryx brevirostris, espécie comum no Brasil. As brânquias estiveram ausentes, e as nadadeiras peitorais mostraram-se assimétri-cas e não totalmente formadas e fundidas à cabeça. A nadadeira esquerda, a maior, se projetou destacadamente em direção à cabeça, quase alcançando a altura dos olhos. A nadadeira pélvica esteve ausente, não foi possível a determinação do sexo do animal. A causa da deformidade morfológica é incerta, mas sugere-se que possa estar relacionada a problema nutricional durante o desenvolvimento do embrião. AbstrAct

Embryonic malformations in an offspring of the shortnose guitarfish

“…To date, congenital anomalies have been described only for viviparous species, given the greater maternalfetal interaction in this reproductive mode. However, occurrence is not restricted to matrotrophy, since reports in lecithotrophic species are also common (Ribeiro-Prado et al, 2008;Bornatowski and Abilhoa, 2009;Carmo and Fávaro, 2015). Zapteryx brevirostris (Müller and Henle, 1841) is a small-sized guitarfish, endemic to the Southwest Atlantic, with a lecithotrophic viviparous mode and up to 6 embryos per litter (Figueiredo, 1977;Batista, 1991).…”

“…In Southern Brazil, the embryonic development period occurs during spring, with birth occurring in warmer months (December to March) (Batista, 1991;Abilhoa et al, 2007). Reports on Z. brevirostris malformations are recent, with only two occurrences described in the literature, one related to an embryo malformation (one in a litter of five embryos) (Carmo and Fávaro, 2015) and another being a case of anophthalmia in an adult female (Ribeiro-Prado et al, 2008). Here, we report for the first time an occurrence of congenital malformation in multiple embryos of the same offspring, compare them with abnormalities commonly found in other elasmobranchs and discuss possible causes for the alterations observed.…”

“…The offspring of the present study indeed presented the most commonly observed deformities in elasmobranchs, however at a frequency never reported in the literature, since 80% of embryos had morphological alterations. Such a phenomenon, although occurring in elasmobranchs that have more than one developing embryo at the same time, appears to have low occurrence in the same offspring, with usually only one or two embryos exhibiting significant morphological alterations (Bornatowski and Abilhoa, 2009;dos Santos and Gadig, 2014;Carmo and Fávaro, 2015;Lamarca et al, 2017). This fact is of significance, since all embryos are exposed to the same uterine conditions and maternal-fetal interactions, thus future studies aiming to understand why malformations are not prevalent within an offspring should be carried out.…”