Featuring the ovarian morphological of Cichla kelberi Kullander & Ferreira, 2006 introduced in a Basin adjacent to the Lençóis Maranhenses National Park, Northeastern Brazil.

Background: Peacock bass (Ciclha kelberi) has been introduced in reservoirs in Brazil; however, information about its reproductive aspects and gonadal maturation remains scarce. Studies on this field carried out in Maranhão State, Brazil mainly address information from lakes and specific regions. The aims of the present study are to feature the gonads and female germ cells of C. kelberi captured in a basin by Lençóis Maranhenses National Park. Thirty specimens were collected, euthanized and weighed. Their gonads were subsequently removed and taken to histological processing. Females were classified as synchronous in multiple batches. Germ cells were featured as Primordial Follicles, Primary Development, Cortical Alveoli, Lipid Vitellogenesis, Lipid-Protein Vitellogenesis and Complete Vitellogenesis. Post-ovulatory and Atretic Follicles were also observed. The smallest cell (in diameter) was observed in primordial follicle cells (16.7 µm) and the largest one was recorded for atretic follicle cells (453.5 µm). The smallest cell area was 580.9 µm2 and the largest one was 300,240.7 µm2. The collected data differed from those recorded other reservoirs in Maranhão State and for other locations in Brazil. This finding points out that this species remains under adaption to the lotic environment in Preguiças River, at Lençóis Maranhenses National Park. Additional research is necessary to help better understanding the long-term reproductive and ecological aspects of the assessed species in order to support the sustainable management of this basin.