Consumption of baits containing sodium fluoroacetate (1080) by the New Zealand freshwater crayfish (Paranephrops planifrons)

Native freshwater crayfish (koura: Paranephrops planifrons) were exposed to baits containing sodium fluoroacetate (1080) to determine whether they consumed baits in the presence of other food (detritus and invertebrates), and whether such consumption was lethal. Crayfish were collected from streams and placed individually into 50 cages in a large "stream simulator", divided into a riffle and pool habitat. A single 1080 bait (mean weight = 6.4g) containing c. 0.15% 1080 (i.e., 9.6 mg) was added to each of 20 cages in each habitat. Non-toxic baits were added to five additional control cages within each habitat. A further five crayfish were placed in aquaria to act as double controls. Replicate crayfish exposed to 1080 baits were collected from both habitats after 1, 2, 4, and 8 days and analysed for 1080 in their viscera and tail muscle. Crayfish exposed to non-toxic bait, and double control crayfish were collected after 8 days and analysed for 1080. The highest concentration of 1080 (1.1 μg litre -1 ) in water collected from the simulator occurred after 2 days, and no residual 1080 was detected after 8 days. Crayfish consumed baits, even in the presence of other food items, but no mortality was observed. The highest 1080 concentrations were 3.3 μg g -1 body tissue in the viscera, and 5 μg g -1 in tail muscle. 1080 concentration in the viscera was positively related to that in the tail muscle. 1080 concentrations declined in the tail muscle between days 4 and 8, suggesting that sub-lethal doses of 1080 could be successfully metabolised. The potential risk to humans consuming crayfish containing 1080 is considered virtually nonexistent, as an 85 kg person would need to consume over 40 kg of contaminated crayfish tails in a single sitting to receive an LD50 dose.