Worldwide, herbicides are used to control weeds to boost crop productivity, however, they could harm non-target species like fish if misapplied. This study evaluates the effect of Orizoplus®, a commonly used herbicide on the behaviour, haematology, blood biochemistry and kidney histology of juvenile catfish, Heterobranchus bidorsalis. Juvenile fish weighing 12.6.01±5.43g were exposed to sublethal concentrations of Orizoplus® for 96h. Thereafter, the water quality and behavioural, blood biochemistry and histopathological changes of the fish were monitored. The results showed concentration-dependent changes in behaviour. The white blood cell increased significantly (p<0.05) by 107-112% while red blood cells, haemoglobin, mean cell corpuscular volume, mean corpuscular haemoglobin concentration and mean cell haemoglobin content reduced non-significantly (p>0.05) in the test organisms compared to the control. The activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) increased significantly (p<0.05), however, changes in the serum glucose, protein and bilirubin were not significant (p>0.05). Histopathological changes in the exposed fish were moderate shrinking of the glomerulus, eosinophilic appearance of the tubules, focal distortion of the glomerulus and severe loss of renal tissues. These show that Orizoplus® is toxic to fish and proper regulation and education are required to guide against misuse.