This study proposes eight stages according to the main discernible changes recorded throughout the embryonic development of Jenynsia multidentata. The development of morphological embryo structures, pigmentation, and changes in tissues connecting mother and embryo were included in the stage characterization. From the fertilized egg (Stage 1), an embryo reaches the intermediary stages when presenting yolk syncytial layer (Stage 2), initial pigmentation of the outer layers of the retina and dorsal region of the head (Stage 3), and the sprouting of the caudal (Stage 4), dorsal and anal fins (Stage 5). During the later stages, the ovarian folds enter the gills, and the body pigmentation becomes more intense (Stage 6), the body becomes elongated (Stage 7), and there is a greater intensity in body pigmentation and increased muscle mass (Stage 8).The dry weight of the batches varied between 0.6 ± 0.3 mg (Stage 3) to 54.6 ± 19.7 mg (Stage 8), but the dry weight of the maternal-embryonic connecting tissues remained almost constant. After controlling the effect of those reproductive tissues, the gain in dry weight of the batches throughout development increased exponentially from Stage 6, reflecting the increase in size and weight of the embryos due to matrotrophy.Keywords: Developmental stages, Dry weight, Matrotrophy, Morphology, Viviparity.Este estudio propone una clasificación constituida por ocho etapas, establecidas con base en los principales cambios macroscópicos registrados a lo largo del desarrollo embrionario de Jenynsia multidentata. El desarrollo de estructuras embrionarias, los patrones de pigmentación y los cambios en los tejidos de conexión entre la madre y el embrión fueron incluidos en la caracterización de cada etapa. Inicia con el huevo fertilizado (Etapa 1), siguiendo con etapas intermedias del embrión en las cuales es visible la capa sincitial del vitelo (Etapa 2), la pigmentación inicial de las capas externas de la retina y el dorso de la cabeza (Etapa 3), y la aparición de las aletas caudal (Etapa 4), dorsal y anal (Etapa 5). En las etapas posteriores, los pliegues del tejido ovárico se introducen por las branquias y se intensifica la pigmentación corporal (Etapa 6), el cuerpo se extiende (Etapa 7) y hay un marcado aumento en la pigmentación corporal y masa muscular (Etapa 8). El peso seco de los lotes varió entre 0,6 ± 0,3 mg (Etapa 3) y 54,6 ± 19,7 mg (Etapa 8); sin embargo, el peso seco del tejido que conecta a la madre con el embrión se mantuvo prácticamente constante. Después de controlar el efecto del peso seco de estos tejidos, la ganancia de peso seco de los lotes de embriones a lo largo del desarrollo aumentó de forma exponencial a partir de la Etapa 6, evidenciándose en el aumento en tamaño y peso de los embriones debido a la matrotrofia.Palabras clave: Etapas del desarrollo, Matrotrofia, Morfología, Peso seco, Viviparidad.
The reproductive strategy of a species must be adjusted to variations in environmental conditions to guarantee population balance. Hydrological fluctuations in Amazonian streams of terra firme (non-flooded) are controlled primarily by local rainfall. Fish assemblages are composed predominantly of species of small size. We investigated the reproductive strategy of the cryptic catfish Helogenes marmoratus and assessed the influence of environmental variables (e.g., rainfall, conductivity, habitat descriptors) on its reproductive activity in a catchment of the Guamá River in the eastern Brazilian Amazon. Through monthly collections between March 2019 and March 2020, we identified an extended reproductive period between July 2019 and March 2020. Males mature at smaller sizes than females (♂ = 27.41 mm; ♀ = 31.36 mm). We confirmed batch spawning, low fecundity (59.55 ± 22.76 stage IV oocytes), and large oocytes (1.24 ± 0.15 mm). Our results indicated that H. marmoratus strategy occupies an intermediate place between opportunistic and equilibrium gradient. Multiple regressions showed that thalweg depth, electrical conductivity, leaf litter, and rainfall are important drivers of reproductive activity of females of H. marmoratus, explaining 32% of the variation of the GSI. Our study provides evidence of differentiated reproductive response between the sexes to environmental variables.
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