The relative abundance, diversity and micronutritional value of small fish species in the Kamutjonga floodplain, Kavango river, Namibia

Abstract

Floodplains are among the most productive ecosystems on earth, serving as biodiversity hotspots and critical resources for ecological and human communities. They provide essential seasonal habitats for fish migrating from the mainstream to nutrient-rich areas for feeding, spawning, and refuge. These fish not only play a pivotal role in the ecological balance of floodplains but also serve as a primary source of nutrition for riparian communities, where alternative food sources are often limited. Despite their importance, significant gaps remain in understanding fish diversity and abundance in floodplain ecosystems of southern Africa, and the value of their nutritional contribution to local populations. This study addressed these knowledge gaps by investigating the dynamics of fish abundance and diversity in the Kamutjonga Floodplain and the nutrient composition of small, commonly consumed fish species. The study focused on barbs (Enteromius spp.), Zambezi bream (Pharyngochromis acuticeps), redbreast tilapia (Coptodon rendalli), and threespot tilapia (Oreochromis andersonii). It evaluated their contributions to the Recommended Nutrient Intake (RNI) for vulnerable groups, including pregnant and lactating women and young children between one to three years of age. These populations are articularly at risk of nutrient deficiencies, making understanding these fish species' nutritional value crucial for public health. Fieldwork was conducted during the flood seasons of 2018 and 2019, employing throw trap nets and seine nets at a total of 20 sampling sites across the floodplain. The data collected in 2018 was analysed to assess fish abundance and diversity, while the 2019 samples were subjected to mineral analysis. A total of 1,389 fish, representing nine families and 35 species, were documented. The Cyprinidae, dominated by hyphen barb (Enteromius bifrenatus), accounted for 28.2% of the Index of Relative Importance (IRI), while the Cichlidae, led by southern mouthbrooder (Pseudocrenilabrus philander), comprised 12.3%. Seasonal patterns revealed the highest fish diversity during the receding flood phase, whereas fish abundance (measured as Catch per Unit Effort, CPUE) peaked during the rising phase. Juvenile cichlids were particularly abundant during this phase, highlighting the floodplain’s critical role as a nursery habitat. This finding reinforces the ecological significance of the floodplain in supporting the early development and growth of fish populations. Nutritional analyses focused on the mineral content of the four most commonly consumed species. Composite samples were tested for macrominerals (sodium, potassium, phosphorus, calcium, and magnesium) and microminerals (iron, copper, zinc, and manganese). Results showed that small fish, particularly Enteromius spp. and P. acuticeps, are nutrient-dense, providing significant proportions of essential minerals. For instance, a standard portion (200g for women, 100g for children) of Enteromius spp. can meet over 30% of the recommended daily calcium intake and 35% of the recommended zinc intake for both women and young children. Oreochromis andersonii stood out for its iron content, with a standard portion capable of fulfilling 70–90% of the daily recommended intake for vulnerable groups. These results highlight the substantial role of small, locally available fish in combating micronutrient deficiencies and enhancing food security. In conclusion, this study underscores the dual ecological and nutritional value of the fishes of the Kamutjonga Floodplain. By serving as a key nursery habitat, it supports the life cycles of diverse fish species, while the consumption of these fish can significantly address nutritional deficiencies in vulnerable human populations. The findings have direct implications for floodplain fisheries management, emphasizing the need to sustain fish biodiversity while optimizing their role in food security. Future research should focus on understanding the longterm impacts of environmental changes, such as climate variability and land-use shifts, on fish populations and their nutritional contributions to riparian communities.