Sensitivity of brain cholinesterase activity to diazinon (BASUDIN 50EC) and fenobucarb (BASSA 50EC) insecticides in the air‐breathing fish Channa striata (Bloch, 1793)

Abstract

With the expansion of agricultural areas within the Mekong River Delta in Vietnam, a concurrent, dramatic increase has occurred in agrochemical usage. To date, little consideration has been given to the negative impacts of this agricultural activity on the aquatic resources of the region. Both acute toxicity and subacute effects on brain cholinesterase (ChE) of two of the most commonly used insecticides, diazinon and fenobucarb, on adult native snakehead (Channa striata) were evaluated in a static, nonrenewable system, the environmental parameters of which, such as dissolved oxygen, water temperature, and pH, fluctuated similarly to field conditions. Four levels of insecticides, from 0.008 to 0.52 mg/L (for diazinon) and from 0.11 to 9.35 mg/L (for fenobucarb), were tested to assess the effects on the brain ChE activity of the snakehead up to 30 and 10 d for diazinon and fenobucarb, respectively. Diazinon was highly toxic to this fish species, with a 96-h median lethal concentration (LC50) of only 0.79 mg/L, and it also caused long-term ChE inhibition, with activity still significantly inhibited by 30% after 30 d for the three highest concentrations. Fenobucarb was less toxic to this species, with a 96-h LC50 of 11.4 mg/L. Fenobucarb caused more rapid ChE inhibition but also rapid recovery. The results of the present study indicate an urgent need to regulate the usage of these pesticides in the Mekong River Delta.

Effects of sublethal concentrations of diazinon on surfacing and hanging behaviors of snakeheadChanna striata

“…The snakehead significantly increased its oxygen consumption from the air while decreasing uptake from the water 4 when the gills had sustained substantial damage from exposure to the lethal concentration (5 mg/L) of metasystox for 48 h 11 . In the present study, however, the fish were exposed to concentrations well below the the concentration causing 50% mortality during 96 hours of exposure (LC 50−96 h ), which is 0.79 mg/L, 12 and exposure lasted only for 5 h. It is therefore more likely that the behavioral change in the present study is avoidance rather than the result of gill damage. This behavior may also help the fish to reduce the uptake of diazinon.…”

Effects of fenobucarb based-Excel Basa 50EC on brain cholinesterase of juvenile snakehead fish (Channa striata) in the Vietnamese Mekong Delta’s rice fields

“…An average temperature range of 27.7 to 30.6 °C is suitable for the survival of snakehead fish [ 15 ]. According to Cong et al [ 16 ], the temperature from 23 - 36 °C did not affect the ChE activity of snakehead fish. In this experiment, the temperature difference between morning and afternoon was not more than 3 °C.…”

“…Fenobucarb belongs to the carbamate pesticide group, and its mode of action is ChE inhibition [ 20 ]. Fenobucarb is moderately toxic to snakeheads with LC50-96h 11.6 ppm [ 16 ]. The water concentration of fenobucarb in the experimental plots was far lower than LC50-96h.…”

Effect of Chlorpyrifos Ethyl on Acetylcholinesterase Activity in Climbing Perch (Anabas testudineus, Bloch, 1972)

“…With a water level in the rice field of 20 cm and assuming that 50 % (Cong et al 2006) of the sprayed insecticide reaches the water, the concentration of CPF in water would be approximately 80 lg/L. This concentration is 4.6 % of the 96-h LC 50 value.…”