Behavioural and ultrastructural activity relationship as early warning signs in fish species
Larvicides when applied repeatedly to effectively kill mosquito species often accumulate in water bodies affecting nontarget aquatic organisms including fish species. It is hypothesised that the behavioural responses from exposure of Poecilia reticulata to tolerable concentration of larvicides is unconnected to the ultrastructural alterations found in the exposed fish species. Heterogeneous sexes of fish consisting of 18 females (gravid and non-gravid), and 9 males, in three replicates, were separately exposed to spinosad (49 and 110 μgL-1) and chlorpyrifos (0.4 and 0.8 μgL-1) at dosages that did not cause physical death for 28-days under static renewal bioassay with control. Ultrastructural analysis was performed for control and treatment in 3 replicates each, on randomly selected pre-treated fish species with evidence of behavioural changes or deformities including reduced feeding, loss of equilibrium, hypoactvity and pectoral fin forward. Behavioural changes were consistent with the ultrastructural damage observed in the fish, and demonstrated the strength of each larvicide as fish toxicant. At higher spinosad concentration, reduced feeding in fish manifested as ruptured lysosomonal cells. Fish in lower spinosad concentration behaved similar to control with minimal cellular damage characterised by increased secretory vesicles and mucin. Opercular haemorrhage and skeletal deformities, more likely to be responsible for loss of equilibrium and pectoral fin forward, were mostly found in the chlorpyrifos treated fish. These were as evidenced by mitochondria rupture, gross dead cells and loss of grey area in cytosol. Behavioural changes are reliable diagnostic warning signs of early, and ongoing cellular damage in exposed fish species necessary for rapid detection and prompt intervention against non-target larvicidal effects on aquatic organisms.
Keywords: Poecilia reticulata; chlorpyrifos; spinosad; ultrastructural; behavioural