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Imidacloprid, a neonicotinoid pesticide that was once thought to be a solution to environmental pollution caused by previous pesticides like organophosphates and organochlorines has raised global concern recently. The present study aimed at assessing the effect of Imidacloprid on the behaviour of a commercially important fish species, Oreochromis niloticus. The study involved a 48 h sub-lethal toxicity test which was carried out with 0, 5, 10, 20, and 40 ppm of Imidacloprid. Fingerlings of O. niloticus weighing between 18 and 32g were exposed to these concentrations in a static bioassay with continuous aeration. Regular observation of the clinical signs revealed that fish exposed to higher concentrations of Imidacloprid displayed behavioural abnormalities such as erratic behaviour, respiratory stress, and irregular nervousness. The findings of this study revealed that Imidacloprid is toxic and causes behavioural distress on O. niloticus fingerlings. Therefore, there is urgent need for further studies to determine safe limit of Imidacloprid and other pesticides in the environment. Unregulated disposal of toxic pesticides should be avoided, to ensure human safety and environmental sustainability.

The estuarine croaker (Pseudotolithus elongatus, Sciaenidae) has long‐term socio‐economic and ecological significance in tropical and subtropical regions of the world, but little has been reported on the population demographics of this species. In this study, a traditional morphometric approach was used to test the hypothesis that island samples are morphologically distinctive from adjoining estuarine waters. The study involved a total number of 612 specimens from four islands (Alligator, Tobacco, Parrot and James) of the lower Cross River, Nigeria as well as from the mouth of the Cross River estuary, sampled from January to July 2020. Each specimen was subjected to morphometric measurements consisting of 14 allometrically modified characters. Results of principal component analysis explained 85.6% of the total variance. The pooled between‐groups discriminant function analysis correctly classified 66.0% of individuals into two distinct stocks (Island and Estuary mouth). The present finding demonstrates that the Cross River Islands hold a unit stock of P. elongatus that is morphologically separable from the adjoining estuarine waters. We therefore recommend that the croaker population in Cross River should be managed as separate stocks.