Temporal Variability in Gonadal Development and Reproductive Indices of African Lungfish (Protopterus annectens) across Seasons in Northern Nigerian Rivers

Ndekimbe Mamndeyati Uruku¹ and Rose Oyibinga Ameh²

¹ Lecturer, Department of Fisheries and Aquaculture, Federal University Wukari, P.M.B 1020, Taraba State, Nigeria.

² MSc Graduate, Department of Fisheries and Aquaculture, Federal University Wukari, P.M.B 1020, Taraba State, Nigeria.    

Abstract

Seasonal environmental changes profoundly influence the reproductive biology of tropical freshwater fishes. This study assessed how temporal fluctuations affect gonadal development and reproductive performance in Protopterus annectens, a resilient species of ecological and aquacultural relevance. Fieldwork was conducted across the Lower and Upper river Benue in Northern Nigeria over a 12-month cycle, capturing both dry and wet seasons. A total of 240 specimens (120 males and 120 females) were collected using baited traps and gill nets. Morphometric parameters, including total length and body weight, were recorded. Gonadosomatic index (GSI), condition factor (K), fecundity, and sex ratio were calculated. Gonadal tissues were processed histologically using hematoxylin and eosin staining to determine reproductive phases. The results revealed significant seasonal variation in reproductive parameters. GSI and fecundity peaked during the wet season (July–September), indicating a distinct reproductive period aligned with hydrological conditions. Female GSI increased from 0.89 ± 0.15 during the dry season to 5.12 ± 0.37 in the wet season (p < 0.001). Relative fecundity values were also significantly higher in the rainy months, while histological observations showed mature oocytes and spermatozoa predominantly in this period. Condition factor was highest at the onset of the rains, suggesting optimal physiological condition for reproduction. The sex ratio remained approximately 1:1 throughout the study period. This study concludes that P. annectens displays a well-synchronized seasonal reproductive pattern, closely regulated by hydrological cycles. These findings highlight the need for seasonally adjusted fishery regulations. It is recommended that closed seasons be implemented during peak breeding months, and key floodplain habitats be conserved. The outcomes are critical for managing inland fish populations and guiding the aquaculture of underutilized indigenous species in sub-Saharan Africa.    

Keywords: Aquatic reproductive cycles, Flood-induced breeding, Inland fisheries sustainability, Sex differentiation, Spawning regulation

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