Dichlorvos is an organophosphate pesticide used for the control of pests in crops and stored products, while primextra is a commercial herbicide formulation generally used in agriculture for weed control. The present study was designed to evaluate and compare the acute toxicity of dichlorvos and primextra pesticides and assess their effects on mortality and behavioural changes of Clarias gariepinus juveniles. The 24, 48, 72 and 96 h LC 50 of dichlorvos were 6.06, 4.96, 1.65 and 1.29 mg l −1 , while those of primextra were 9.34, 6.50, 5.41 and 4.67 mg l −1 , respectively. The safe levels estimated by different methods varied from 1.29 × 10 −1 to 1.29 × 10 −5 mg l −1 in dichlorvos and from 4.67 × 10 −1 to 4.67 × 10 −5 mg l −1 in primextra. Behavioural changes, such as hyperactivity, gulping of air, skin discoloration, loss of balance, convulsion, erratic swimming and mucous secretions, were observed in fish exposed to both pesticides. Our study indicated that dichlorvos (96 h LC 50 = 1.29 mg l −1 ) was more toxic to C. gariepinus compared with primextra (96 h LC 50 = 4.67 mg l −1 ). The use of these pesticides in both terrestrial ecosystems and aquatic environments should be subject to strict control and monitoring to prevent potential ecotoxicological hazards to aquatic lives.Darbo tikslas -įvertinti ir palyginti dichlofoso ir Primextra ūminį toksiškumą bei poveikį Clarias gariepinus jauniklių mirtingumui ir elgsenos pokyčiams. Dichlofosas -organinis fosforo junginys, naudojamas vabzdžių naikinimui laukuose ir sandėliuose, Primextra -herbicidas, dažniausiai naudojamas piktžolių naikinimui žemės ūkyje. Paveikus žuvis tiriamąja medžiaga 24, 48, 72 ir 96 valandas, dichlofoso LC 50 koncentracija buvo 6,06, 4,96, 1,65 ir 1,29 mg l −1 , Primextra LC 50 koncentracija -9,34, 6,50, 5,41 ir 4,67 mg l −1 atitinkamai. C. gariepinus saugios dichlofoso koncentracijos buvo nuo 1,29 × 10 −1 iki 1,29 × 10 −5 mg l −1 , Primextra -nuo 4,67 × 10 −1 iki 4,67 × 10 −5 mg l −1 . Abiem medžiagomis paveiktoms žuvims buvo būdingi elgsenos pokyčiai: hiperaktyvumas, žiopčiojimas ryjant orą, odos spalvos pakitimai, pusiausvyros sutrikimai, konvulsijos, chaotiškas plaukimas ir gleivingos išskyros. Šis tyrimas parodė, kad dichlofosas (96 val. LC 50 = 1,29 mg l −1 ) C. gariepinus yra toksiškesnis negu Primextra (96 val. LC 50 = 4,67 mg l −1 ). Dichlofoso ir Primextra naudojimas turi būti griežtai kontroliuojamas dėl galimo ekotoksikologinio poveikio vandens gyvūnams.

Asu River is one of the major tributaries of Cross River, a tropical reforest river in southeast Nigeria. The climate of the region is divided into the wet and dry seasons. Human activities such as fishing, bathing and washing go on in the river especially during the dry season. Farming also takes place at the fringes of the river. Some important physicochemical parameters of the river were investigated at two designated sites comprising the downstream and the upstream for nine (9) months, from October, 2013 to June, 2014. Temperature, carbon (iv) oxide, conductivity, total dissolved solids, nitrate and phosphate recorded maximum values during the dry season while dissolved oxygen and pH recorded maximum values in the wet season. The physicochemical variables evaluated showed that the river is not in a critical condition as most of the variables recorded are within the WHO permissible limit. However, the paper therefore recommends the need for public enlightenment on environmental management and control of household and industrial wastes in order to sustain the usefulness of Asu River.