Cypermethrin toxicity to aquatic life: bioassays for the freshwater prawn Palaemonetes argentinus

Cypermethrin (CY) effects were evaluated in freshwater prawn Palaemonetes argentinus, a common member of the aquatic fauna in the vegetated littoral of lotic and lentic environment of La Plata basin. LC50 was calculated, and oxygen uptakes together with ammonia-N excretion were related to biocide concentrations. Behavioral and growth changes were analyzed, and a unique application of CY was evaluated in P. argentinus micropopulations. LC50 and their 95% confidence limit were 0.0031 microg CY L(-1) (0.0023-0.0039) for 24 h and 0.0020 microg CY L(-1) (0.0014-0.0027) for 96 h. Oxygen uptake and ammonia-N excretion increased in the prawns kept in CY solutions. The behavioral effect was hyperactivity. Although prawns in biocide groups have null or negative growth, the intermolt period was 246% larger than in the control group. Moreover, the mortality in the second cycle was 100%. A unique application of pyrethoid provoked high mortality after 50 days. The low concentrations of this biocide affected the survival and altered the prawn metabolic activity, behavioral and ecdysis cycle. These results suggest that juveniles of P. argentinus are much more sensitive to CY pollution than other crustaceans, fish, and tadpoles.