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Pesticide residues pose a significant risk to aquatic ecosystems, fauna and human health.
Yet, the physiological impact on aquatic organisms, especially fish exposed to pesticide
residues in the dry season, remains unexplored, and even data on chronic exposure to
pesticide residue mixtures under natural environmental conditions remains scarce.
This study evaluated the immune, haematological and growth responses of Oreochromis
niloticus exposed to cotton field effluents under in-situ conditions during the dry season in
the Batran water reservoir. A 56-day experiment was conducted during the dry season
using a 2 × 1design (pen culture system × two environments). The Batran water reservoir
in Benin’s cotton basin (effluent-exposed site) was used as a test (polluted) environment,
and a concrete tank at the Station de Recherche et d’Innovation en Aquacultures (SRIA) of
the University of Parakou represented the controlled environment. The results revealed that
O. niloticus exposed to the polluted environment showed significantly lower macrophage
activity compared to the control (p > 0.05). The haematological analysis showedelevated
eosinophil and heterophil levels in the polluted environment compared to the controls
(p < 0.05). On the growth parameters, generally, O. niloticus exhibited higher growth performance
in the polluted environment compared to the control, with a significant difference only with the
final average weight (83.61 ± 16.61 g; 69.44 ± 5.73 g, respectively) (p < 0.05) at the end of the experiment.
These findings imply that the absence of pesticide application during the dry season at Batran likely reduced
pollutant-inducedphysiologicalstress, thereby enhancinggrowthdespitecomparableimmunemetrics.
These findings suggest the needtocontextualiseaquaculturemanagementstrategieswithinseasonalagrochemicalusecycles,
asnon-applicationperiodsmay offer critical recovery intervals for farmed species.
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University of Cape Coast