Expansion of the geographic distribution and morphological aspects of Braga patagonica (Isopoda: Cymothoidae) to Eastern Amazon, Brazil.

The Amazon rainforest and its rivers host a vast biodiversity, including many unique yet undiscovered species, particularly among Amazonian fish. These organisms can be susceptible to ectoparasites, such as isopod crustaceans. This study describes the presence of the isopod Braga patagonica parasitizing Hoplias malabaricus in the state of Maranhão, located in the eastern Amazon region of Brazil. Isopod specimens were collected from the fish bodies in two sampling periods conducted between 2021 and 2022 and identified using dichotomous keys based on morphological analysis and measurements of the parasites. Furthermore, parasitological indices were calculated, including prevalence rate (P%), mean intensity (MI), and parasite abundance (PA). A total of 25 parasites, including females and males, were found fixed in the gill cavity, on the integument, and near the pectoral and pelvic fins. During the first collection period, the hosts exhibited a prevalence rate of 100%, with MI and PA of 1.0 ± 0.00. In contrast, during the second collection period, the prevalence rate decreased to 66.67%, with MI of 1.0 ± 0.04 and PA of 0.64 ± 0.49. Females were larger, measuring approximately 2.09 cm in length and 1.09 cm in width, while males reached 1.96 cm in length and 0.86 cm in width, and displayed a lighter coloration compared to the females in both collections. This study establishes a new geographical occurrence of Braga patagonica in the state of Maranhão, in Northeast Brazil, providing a comprehensive analysis of the morphological characteristics of this isopod. The results provide valuable insights into the distribution of the Cymothoidae family in the Eastern Amazon.