How Can Human Urine Make Fish And Reptiles Change Their Sex?
Human urine and thus wastewater treatment plant output can contain hormones.
Some of this is natural output,
but some comes from medical hormone treatments.
Scientists are discovering that populations of fish and reptiles are
changing their sex because of hormones in the water.
And, in some cases, fish populations are crashing because almost all of
the males are changing to females and the females can't produce viable eggs.
Is It A Boy Or A Girl?
Chromosomes determine the sex of many, but not all, animals.
In humans and most other mammals, plus some insects,
females have two of the same sex chromosome (XX)
while males have one of each (XY).
Chickens and some other birds, some reptiles, and some insects are
the other way around with their ZW system.
Males are ZZ while females are ZW.
Other animals use schemes including XX/X0,
where there is only one sex chromosome.
Females have XX and males have only one X
(several species of insects plus a few mammals including some
rats, shrews, and voles).
The platypus has
10 sex chromosomes,
which seems needlessly complicated.
Males have XYXYXYXYXY and females have XXXXXXXXXX.
If you find this confusing, consider the
That protozoan exists in seven different sexes and
they can reproduce in twenty-one different combinations.
For many animals, their chromosomes control their development.
Male chromosomes lead directly to development into a distinctively male form,
female chromosomes to a female form.
However, with some animals you can't see any difference between
males and females.
Amphibians, reptiles, birds, and some fish have
A cloaca is a common opening shared by the digestive, urinary,
and reproductive tracts.
Cloaca Maxima, Rome's grand sewer
Cloacina, Goddess of the Sewer
Cloaca means "drain".
These three diverse systems share a common drain in these animals.
It's the same word the Romans used for their municipal wastewater system.
was Rome's grand sewer, and
Cloacina was its goddess.
The platypus also has a cloaca, and it lays eggs.
And don't forget those 10 sex chromosomes.
Plus, any group of two or more demand to be called "platypi."
They're just weird.
Don't pay any attention to them, it will just encourage them.
The males of a few bird species have an external phallus,
but for the rest of the species with cloacae there's
nothing external to this single shared opening.
For some species, adult males and females have distinctive overall forms.
But for young birds and the reptiles, you have to closely inspect the cloaca.
Some fish and gastropods display sequential hermaphroditism,
changing their sex during their lifespan.
Clownfish, for example, are protandrous hermaphrodites,
born male and changing their sex to female when they become the largest
and dominant individual in their social group.
The prequel to
should be interesting.
Protogynous hermaphroditism is more common among fish.
Three out of every four of sequential hermaphrodite fish species are
the other way around, they are born female and turn male at some point.
Wrasses, for example, plus the groupers, porgies, gobies, parrotfish,
and swamp eels.
How Did The Animal Get This Way?
Some species develop quickly, like the biology student's pal the
fruit fly or Drosophila melanogaster.
Fruit flies become sexually differentiated as soon as the egg is fertilized.
In other species, such as humans, there is no sexual differentiation
for some time into development.
Human embryology is complicated and strange.
Humans first develop a cloaca, which is right next to the tail.
The cloaca and surrounding structures later develop into specifically
male or female reproductive organs plus an anus,
while the tail disappears.
This is very early, around the time when human pharyngeal grooves
look like gill slits.
Tail and cloaca of a human embryo at 32-33 days,
from Gray's Anatomy.
Temperature-Dependent Sex Determination
For reptiles and fish, the temperature during a critical stage
of development can determine the offspring's sex.
Turtles, crocodiles, and alligators don't have sex chromosomes.
Their sex is controlled by the temperature during the
middle third of embryonic development.
You have to carefully examine the interior of the cloaca to determine
the sex of an adult.
That's a hazardous undertaking with alligators and crocodiles.
Sexing the alligator can be a dangerous job.
But then there are the endocrine disruptors,
molecules that interfere with the body's hormone systems.
These can cause cancerous tumors and developmental disorders.
They can also change the male/female balance of individuals,
especially when they involve sex steroids such as estrogens and androgens.
Endocrine disruptors may be used intentionally.
Groupers are commonly raised in fish farms in Asia.
Adults take several years to change from female to male,
so male-stage groupers are especially valuable members
of the operation's broodstock.
Aquaculture operations may use artificial hormones to adjust the sex ratio.
Tilapia are raised on food containing high levels of
17α-methyltestosterone is given to humans for a variety of
and abused to enhance athletic performance and bodybuilding.
Added to tilapia feed in large quantities,
it changes the females into faster-growing males.
The Sex-Changing Crocodiles and Fish
that American crocodiles in Costa Rica's Palo Verde National Park
had a strange sex ratio, with males outnumbering females four to one.
The warming climate should be pushing the ratio the other way,
with more females resulting from warmer temperatures during development.
The park is surrounded by fish farms that raise tilapia using feed
filled with the synthetic hormone 17α-methyltestosterone.
The fish farms want to skew the sex ratio of their tilapia heavily male.
It appears that their overflow and runoff are getting into the water in
the park and changing the crocodile sex.
The crocodiles' tissues contained 17α-methyltestosterone.
That same article reported that scientists in the 1990s found that
male alligators in Florida's Lake Apopka were femininized, with
shrunken genitalia and reduced testosterone levels.
That lake is polluted by chemicals that mimic estrogen.
Trenbolone or 19-nor-δ9,11-testosterone,
very similar to 17α-methyltestosterone.
Cattle have trenbolone acetate pellets implanted in their ears while
they are in U.S. feedlots being prepared for market.
Trenbolone, or 19-nor-δ9,11-testosterone,
is an anabolic-androgenic steroid that increases muscle growth
At the Sochi Winter Olympics in 2014,
Russian officials gave their athletes a mixture of
including trenbolone, metenolone, and oxandrolone.
Regulations are supposed to limit runoff from feedlots into streams,
but compliance and enforcement are lax.
Endocrinologists have found intersex minnows downstream from feedlots.
That is, females with male characteristics and vice-versa.
Meanwhile the E.U. banned growth hormone use in both domestic and imported
meat in 1990.
Human Hormonal Runoff
Enough people are taking hormones, especially testosterone and its
derivatives, that sewage treatment plant output can be a significant
source of contamination.
article in Scientific American
reported that only about half of the prescription pharmaceuticals and other
newly recognized contaminants are removed by sewage treatment plants.
This comes from a study by the International Joint Commission,
a consortium from the United States and Canada studying the Great Lakes.
The European Union may restrict hormone use in cattle,
but humans still use it and excrete it into the wastewater flow.
study in Galicia in northwestern Spain
found three hormones
(estrone, 17β-estradiol, and 17α-ethinylestradiol, used
in birth-control pills)
plus other pharmaceuticals in the output of a municipal wastewater
different study in Spain
examined the sludge at two sewage treatment plants.
They found nine hormones and their derivatives, plus 20 pharmaceuticals
including anti-inflammatories, lipid regulators, and antibiotics.
study in northwestern Ontario
found that natural estrogens (estrone or 17β-estradiol)
and the synthetic estrogen used in birth-control pills
(17α-ethinylestradiol) led to feminization of male fishes
and disruptions in the egg production of female fishes.
This led to the near extinction of fathead minnows from a lake
over a 7-year period.
For this study they added the hormones to an isolated lake,
using estrogens that are not completely broken down in
typical municipal wastewater treatment plants.
Treatment plant upgrades can help.
study in Canada
measured the incidence of intersex fish downstream from a large
wastewater treatment plant that had gone through an upgrade of its
sludge treatment process.
When the larger of two treatment plants at Kitchener, Ontario used
carbonacious activated sludge treatment, 70% to 100% of nominally male
rainbow darter found downstream in the Grand River were intersex.
After an upgrade to nitrifying activated sludge treatment, the
intersex rate dropped to less than 10%.
Work is underway to measure and control pharmaceuticals
in sewage treatment output in
and many other countries.
Scholarly papers on:
pharmaceuticals in sewage
hormones in sewage
Could The Chicken Sexers Be Spies?
Family lore tells how everyone was fascinated when three Japanese men
moved into the boarding house across the street in Corydon, Indiana,
The three men from Japan were exotic newcomers for a town in southern
Indiana, where just 1,865 people lived that year.
The new neighbors were chicken sexers,
poultry specialists skilled at determining the sex of newly born chicks.
Males are useless for egg production operations,
and so most of them are killed immediately.
Just a few are kept for meat production.
By 2018, around 7 billion day-old male chicks were killed daily,
with most of them in the U.S. killed in industrial macerators,
The poultry industry in Japan had rapidly progressed in the 1920s.
In 1925 Dr Masui of the Veterinary Division of the University of Tokyo
published an initial report on sex determination of 60-day-old chickens.
He followed this up with a later paper,
"The Rudimentary Copulatory Organs of the Male Domestic Fowl
and the Difference of the Sexes of Chickens".
It was thought to be of academic interest only, until Professor Kojima
improved the technique, achieving high accuracy in day-old chicks.
In 1933, Professors Masui and Hashimoto published a book
describing methods for sexing newborn chicks based on cloacal vent features.
It was translated into English, and quickly came to the interest of the
North American poultry industry.
The Masui-Hashimoto technique quickly became the way to do this.
Some poultry breeders sent representatives to Japan for specialized training.
Chick sexers who knew the technique were in demand.
1933 article in Canadian Poultry
for much more the Japanese development of chick sexing.
And so, the three men from Japan arrived in Corydon in 1940
to work with the surrounding poultry industry.
They were skilled in biology, but deeply interested in technology.
The three of them had a car, and every weekend they explored the area.
They visited and examined and photographed the bridges across the Ohio River
around Louisville, Kentucky,
the dams and locks on the Ohio River and the shipping passing through them,
the roads and railways leading to and from Fort Knox,
electrical power plants,
Then one day in early November, 1941, they were gone.
They had left no word, they simply disappeared.
Coffee, Tea, or Coliform?