Andrew stated:
"Birds are thought to be more susceptible to tetrodotoxin than mammals.
The lethal dose of tetrodotoxin for a pigeon is estimated at 50 ug/kg,
so 1/10000 of a gram might kill a gull. How much tetrodotoxin the fish
contains I don't know and probably varies significantly."
Table 1 in the following paper summarises the results of investigations into
tetrodotoxin concentrations in marine organisms.
http://www.int-res.com/articles/meps/136/m136p147.pdf
Tetrodotoxin concentrates in various organs of puffer fish (e.g. liver and
ovaries). Average measured concentrations in the livers of puffer fish range
from 67-187 ug/g wet weight (depending on species of puffer fish), and in
the ovaries the average concentrations ranged from 32-157 ug/g wet weight.
Maximum values ranged from 1000-1960 ug/g wet weight in the liver (depending
on species of puffer fish) and from 200-520 ug/g wet weight.
So based on Andrew's earlier comments about the intolerance of birds to
tetrodotoxin, I expect that concentrations within the liver and ovaries of
puffer fish to be toxic to birds. It would be interesting to know if some
seabirds avoid being poisoned by puffer fish by avoiding the consumption of
internal organs of the fish where tetrodotoxin is concentrated.
It is also interesting to note that the scientific paper quoted above shows
that tetrodotoxin also occurs in other marine organisms (e.g. marine worms,
molluscs, crustaceans), but at much lower concentrations than in puffer
fish. This is because tetrodotoxin moves up the food chain and becomes more
concentrated in higher-order predators. But it made me wonder whether
shorebirds consume large amounts of tetrodotoxin as a result of consuming
large amounts of benthic organisms on mudflats and sandflats, especially
when they are foraging intensively to build up or replenish body reserves
prior to or after long-distance migration. If so, have they evolved a
tolerance to high concentrations of this poison?
Stephen Ambrose
Ryde, NSW
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