OBJECTIVE: To study the monogeneans gill parasites of Heterobranchus bidorsalis (Siluriformes, Clariidae) fish of economic interest in the Bagoue River.
METHODS: Fifty-five specimens of H. bidorsalis were caught with gillnets in the Bagoué River from August 2018 to January 2019. The monogeneans were individually isolated from the gill and transferred directly onto a slide in a drop of glycerin ammonium picrate mixture (GAP).
RESULTS: The new species differ from the previously described Quadriacanthus spp. mainly by the morphology of their sclerotised vagina: Quadriacanthus tanoyaoi sp. nov having a V-shaped, widely open vagina with a central protuberance, and Quadriacanthus bidorsalisi sp. nov having a pear-shaped vagina, composed of a tubular part with a ring near the aperture and a swollen portion. Q. tanoyaoi sp. nov and Q. bidorsalisi sp. nov are different in the shape of the dorsal and ventral anchors (more sturdy for Q. tanoyaoi), of the dorsal and ventral cuneus (triangular vs Y-shaped, respectively), and that of the vagina (V-shaped, widely open with a central protuberance vs pear-shaped, respectively).
CONCLUSIONS: To date, only Quadriacanthus mandibulatus Francová & Řehulková, 2017 were recognised parasitizing from H. bidorsalis from the Nile River Basin (Sudan) and Lake Turkana (Kenya). The present study with the description of 2 new species expands the number to 3 species of monogeneans for this fish.

The dearth of African giant catfish Heterobranchus bidorsalis seeds poses great threat to its aquaculture and biodiversity, hence detailed knowledge and understanding of its embryology is indispensable for its artificial propagation and conservation programmes. Photomicrographs of extruded oocyte through all developmental cell stages of live embryo to larval stage are documented with the aid of a light microscope. The optical transparency of the developing embryo enabled us to describe its deep structures, distinctive features and characterize the stages pictorially. Extruded oocyte had a mean diameter of 1 ± 0.1 mm, ~20% increase when hydrated, and bounded by double thin perivitelline membranes. The first mitotic cleavage occurred at 69 min post-fertilization (pf) resulting in 2, 4 (2 × 2 array of cells), 8 (2 × 4), 16 (4 × 4), 32 (4 × 8), 64 (2 × 4 × 8) blastomeres, then developed to morula, blastula and gastrula stages. Blastula was featured by formation of enveloping layer and yolk syncytial layer. Onset of epiboly at 3 h 57 min depicted the commencement of gastrula while closure of blastopore at 11 h 8 min marked its completion. Neurulation period was distinct from segmentation where organogenesis was fully active. Embryo sudden muscular contraction was noticed at ~17 h pf, increased prior to hatching with caudal locomotion firstly at 42 s interval. Heartbeat of embryo commenced at ~1 h before its unique eclosion at average of 72 beats/min while first larva emerged at 21 h at a controlled temperature of 28.5 ± 0.5°C. Mean total length (TL) of larvae and their pouch thickness were 5 ± 1 mm and 0.05 ± 0.02 mm respectively. 1 -day old larvae revealed 8 distinctive neuromeres and by day 3, epicanthus folds of the eyes were fully uncovered; and thereafter commenced exogenous feeding. At day 4, larvae recorded mean TL of 9 ± 1 mm and 15 caudal fin rays. The fin bifurcation to dorsal and adipose fins was observed at third and half weeks post-hatchability with the dorsal fin length to adipose fin was 1.7:1. This study, for the first time, presents significant morpho-sequential developmental stages of H. bidorsalis and registers its unique form of eclosion.