Mary, Basically the literature indicates that cyanide concentration and exposure duration are the main factors accounting for acute mortality of marine aquarium fish. There may be a concentration where fish are not killed outright. An early paper by Ireland and Robertson (1974) assumed that the collectors were using a concentration near 5 mg/L (ppm) in their squirt bottles. This cyanide ion concentation might allow fish to be captured without serious acute mortality.
However, the actual amount of cyanide being used far exceeds 5 ppm. This was first pointed out by Johannes and Riepen (1995) who stated the concentrations being used exceeded 25,000 ppm. Most MO collectors use 1 or 2 cyanide tablets and food fish collectors 3-5 NaCN tablets in a one liter squirt bottle during collection (Rubec et al. 2001). Ferdinand has stated that some collectors only use a 1/2 tablet. Since, one 20 gram sodium cyanide tablet is equivalent to 11,000 ppm cyanide ion, the concentrations being used far exceed what is safe for both the fish and the corals. Even a half tablet is equivalent to a concentration of 5,500 mg/liter (ppm) in a one liter squirt bottle.
Hanawa et al. (1998) demonstrated that a 50 ppm cyanide ion concentration for a 10 second exposure resulted in 0% mortality, 50 ppm for 60 seconds caused 0% mortality, but 120 seconds was 100% lethal to humbug damselfish (Dascyllus aruanus).
With cyanide exposure + stress (being chased or placed in a plastic bag) the following results were found. There was 0% mortality with exposure to 25 ppm after being either chased, bagged, or bagged and chased. With a concentration of 50 ppm CN ion exposed for 60 seconds, there was 0% mortality with the control, and for being chased, but a 100% mortality after being bagged.
There is no evidence that concentrations of cyanide ion less than 50 ppm are being used by the collectors, or that they can ensure that the exposure time does not exceed 120 seconds.
Hanawa et al. (1998) also did experiments on oxygen consumption by the liver that indicated impairment for longer time periods. Under non-stressed conditions, pulse exposures of 25 ppm or 50 ppm cyanide ion for 10 and 60 seconds respectively, significantly reduced liver oxygen consumption rates measured 2.5 weeks post-exposure. Under stressed conditions, liver oxygen consumption rates were significantly higher in cyanide-exposed fish than with control fish. The combined effects of cyanide exposure plus stress increased the mortality and placed an appreciable metabolic load on the fish. Hence, cyanide exposure in combination with handling stressors could partly explain the high delayed mortality in the marine aquarium trade (Hanawa et al. 1998, Rubec et al. 2001).
Hanawa, M., L. Harris, M. Graham, A. P. Farrell, and L.I. Bendall-Young. 1998. Effects of cyanide exposure on Dascyllus aruanus, a tropical marine fish species: lethality, anaesthesia, and physiological effects. Aquarium Sciences and Conservation 2: 21-34.
Rubec, P.J., F. Cruz, V. Pratt, R. Oellers,B. McCullough, and F. Lallo. 2001. Cyanide-free net-caught fish for the marine aquarium trade. Aquarium Sciences and Conservation 3: 37-51.
The other references are in the above paper. I can email the Rubec et al. (2001) paper to you if you wish. If you provide me with your fax number I can fax the Hanawa paper.
Peter Rubec
