Studies on microplastic contamination in african catfish (clarias gariepinus) and tilapia (oreochromis niloticus) marketed in Lokoja, Kogi state

Abstract

Microplastic contamination has been documented in environments and organisms across the world, but the exposure arising from fish sold in Nigerian markets remains poorly characterised. This study analysed the occurrence of microplastics in two species widely marketed and consumed in Lokoja, Kogi State: Clarias gariepinus and Oreochromis niloticus. Ten specimens of each species were purchased from New Market, Lokoja, and their gastrointestinal tracts were subjected to wet peroxide oxidation followed by density separation in saturated sodium chloride, with a procedural blank run for every five samples. Recovered particles were classified microscopically as fibres, fragments or pellets. Microplastics were recovered from every specimen examined, giving a prevalence of 100 percent in both species. A total of 224 particles was recovered, 108 from C. gariepinus and 116 from O. niloticus, with burdens ranging from 7 to 15 particles per individual. Mean burden was 10.8 ± 2.30 particles per fish in C. gariepinus and 11.6 ± 1.90 in O. niloticus, and the difference between species was not statistically significant, t(18) = 0.83, p = 0.418. The distribution of morphotypes likewise did not differ significantly between species, χ 2 (2) = 2.01, p = 0.367. Morphotype did differ within each species. Pellets were the most abundant form in C. gariepinus, at 47.2 percent of its load, whereas fragments and pellets were equally abundant in O. niloticus at 37.9 percent each; fibres were least abundant in both, at 21.3 and 24.1 percent respectively. These differences among morphotypes were significant in both species, with p = 0.004 for C. gariepinus and p = 0.002 for O. niloticus. Because both species are commonly prepared with some viscera retained, the gastrointestinal burden reported here represents a direct route of human exposure.