EFFECT OF AGE AND WEIGHT-SPECIFIC RESPIRATION RATE ON TOXICITY OF ESFENVALERATE PULSE-EXPOSURE TO THE AUSTRALIAN CRIMSON-SPOTTED RAINBOW FISH (MELANOTAENIA-FLUVIATILIS)

The acute toxicity of a 1-h pulse-exposure with the synthetic pyrethro id pesticide, esfenvalerate, to Australian crimson-spotted rainbow fis h (Melanotaenia fluviatilis) of different ages was measured. The effec ts of esfenvalerate were measured on embryos 1, 2, 4, 8, 24, 72, and 1 44 h post-fertilisation, and on larvae <2 days, 3-4, 7-8, 14-16, 28-32 , and 90 (sexually mature) days old. The effects of rainbow fish age a nd esfenvalerate exposure on weight-specific metabolism were also reco rded and we tested the hypothesis that there was a significant correla tion between the 1-h pulse-exposure 96-h LC(50), and weight-specific r espiration rate. The eggs of the rainbow fish were not sensitive to es fenvalerate, although the pesticide was highly toxic to larvae less th an 1 week old. The mean (s.e.) 96 h LC(50)'s following a 1-h pulse-exp osure to esfenvalerate were 2.32 (0.70), 1.07 (0.26), 28.11 (14.46), 3 3.42 (10.21), 48.04 (13.34) and 3960 (157) mu g l(-1) for rainbow fish <2 days, 3-4, 7-8, 14-16, 28-32, and 90 days old, respectively. There was a significant negative correlation between weight-specific respir ation rate and the toxicity of pulse-exposed esfenvalerate, although e sfenvalerate did not affect the respiration rate directly. We postulat e that the observed decrease in toxicity of esfenvalerate with increas ing age was due to lower uptake of the pesticide on a weight basis.