Functional diversity of the fish fauna in the Nyong estuary (Atlantic Coast, Cameroon), and its correlation with environmental variables.

Archaic fishing, anthropogenic pollution linked to demographic and economic growth stand to be a real threat to the richness and abundance of the aquatic fauna of estuaries in Sub-Saharan Africa. The knowledge of the Nyong estuary ichthyofauna's ecology in Cameroon is particularly essential to establish a management plan and sustainable management of this important ecosystem. The Nyong estuary ichthyofauna was composed of 13 families, 20 genera and 22 species, from February to June 2020. Eleven species had a marine affinity while11 others were from the freshwater dirivation. Mormyridae (14%), Cichlidae (14%) and Clupeidae (14%) were the most represented families. Also, Chrysichthys nyongensis was the most abundant species with a frequency of 30.26%. Despite the low diversity in the study area, the specific diversity index showed that Dikobe was the most diverse station (H' = 2.98 and J = 0.46), contrary to Donenda's station (H' = 2.30 and J = 0.22). In general, significant correlations were noted between physico-chemical parameters and the total abundances of the different fish species (P < 0.05). Thus, in Behondo, characterized by polyhaline waters, Gnathonemus petersii in contrary Pellonula vorax was positively and significantly correlated with salinity, electrical conductivity and total dissolved solids. This study clearly illustrates that the distribution of ichthyofauna in the Nyong estuary mainly depends on the environmental variables. The data obtained would therefore allow the implementation of a sustainable fisheries development and management plan in the localities concerned by this study, and sensitize fishermen on the need to respect the fishing code.

Four new species of Hysterocinetida (Protozoa: Ciliophora) from the digestive tract of earthworms collected to the lower Nyong estuary (South Coast, Cameroon).

Hysterocinetida are a large assemblage of ciliates characterized by sucker and buccal apparatus. They have a wide distribution in the digestive tract of oligochaete annelids of the genus Alma that inhabit hydromorphic parts of non-anthropic hydrosystems. On the basis of morphological, morphometric and infraciliature characteristics revealed by ammoniacal silver carbonate and 4',6-Diamidino-2-Phenyl Indole (DAPI) staining techniques, four forms were identified as new members belonging to three genera: Preptychostomum, Proptychostomum and Thurstonia. Preptychostomum donendaensis n. sp. is ovoid with a slightly narrowed anterior part and is commensal to the digestive tract of Alma emini and A. nilotica. There are 20-23 kineties on the lower side and 42-45 on the upper side. Proptychostomum gigas n. sp. is pear-shaped, with a narrowed anterior part and a wide posterior part (125-138 µm × 80-85 µm). There are 40 to 44 kineties, equally distributed on both sides of the ciliate. Its sucker is circular and measures 31-34 µm in diameter. The peristome follows the contour of the cell and the infundibulum has a turn of spire. Thurstonia emini n. sp. is identified in the digestive tract of A. emini. The cell is elongate, with the anterior pole narrower than the truncate posterior pole (90-115 µm × 40-55 µm). The kineties are equally distributed on both sides of the ciliate. The sucker is in the shape of an inverted U. Thurtonia nilotica n. sp. is commensal of the digestive tract of A. nilotica. The cell is pear-shaped, with the anterior part narrowed and the posterior part swollen (110-114 µm × 85-92 µm). 46 to 50 kineties are unevenly distributed on both sides of the ciliate. The sucker is shaped like an inverted lunar crescent.