Life Cycle Development of Anacanthorus spathulatus and Notozothecium janauachensis (Monopisthocotyla), Parasites of the Gills of Colossoma macropomum (Osteichthyes: Serrasalmidae) Raised in Glass Aquariums in the Peruvian Amazon

Introduction: This study describes the life cycle development of two monopisthocotyls gill parasites, Anacanthorus spathulatus Kritsky, Thatcher & Kayton, 1979 and Notozothecium janauachensis Belmont-Jégu, Domingues & Martins, 2004 (Monopisthocotyla), infecting Colossoma macropomum (Cuvier, 1816) reared under controlled aquarium conditions in the Peruvian Amazon. Materials and Methods: Twenty naturally infected fingerlings were collected from a fishpond and maintained in glass aquariums under controlled conditions. Fish showing typical clinical signs of monopisthocotyls infestation were selected. Eggs were obtained from adult parasites isolated from the gill arches and monitored using stereomicroscopy and light microscopy to characterize embryonic development, oncomiracidium morphology, and early post-hatching stages. Additional gill samples were processed to mean study juvenile, subadult, and adult morphology. Results: In A. spathulatus, development from egg to hatching oncomiracidium required approximately 72 h, followed by an active swimming phase of approximately 10 h before loss of cilia and immobilization. In contrast, N. janauachensis completed embryonic development in approximately 48 h, with free-swimming oncomiracidia remaining active for about 12 h. In both species, a sequence of well-defined developmental stages was documented, including egg (time 0), early and advanced embryo, fully developed oncomiracidium with four ocelli and ciliation, early and developing juvenile, subadult, and adult forms, accompanied by progressive differentiation of the haptor and copulatory complex. Conclusions: This study provides a detailed morphological and temporal characterization of the life cycles of A. spathulatus and N. janauachensis under experimental conditions, identifying critical windows of larval infectivity. These findings contribute to a better understanding of host–parasite dynamics and provide essential information for the development of monitoring and control strategies for monopisthocotyls infections in C. macropomum aquaculture in the Peruvian Amazon.