The Mimicry and Life Cycle of Freshwater Mussels

On the surface, this is just a small fish,

but if you look closely,

you’ll find it is a freshwater mussel’s

disguised lure.

This form of mimicry is exactly what

carnivorous bass love to eat.

When a bass approaches to attack, the female mussel instantly

opens its shell, spraying millions of glochidia

at the bass’s face. These micron-sized larvae

have two tiny shells and use powerful

adductor muscles to firmly attach to the bass’s gills,

drawing nutrients from its blood.

Even more incredibly,

these freshwater mussels have no eyes at all,

so they cannot see how lifelike

the little fish they mimic actually looks.

In ancient times, freshwater mussels did not

have these fake lures. Due to random

genetic mutations, some freshwater mussels’

mantles unexpectedly developed patterned folds,

attracting fish while increasing their offspring’s

chances of survival. Through continued evolution,

the mantle gradually formed the outline

of a small fish. Individuals without this lure

were gradually eliminated by natural selection,

and this ingenious disguise became encoded in their genes.

From then on, freshwater mussels became

masters of deception in nature. To avoid being swept away,

glochidia that fail to parasitize a host

anchor themselves with a byssal thread

to vegetation, quietly waiting for the next

host to pass by.

A small number of parasites will have no effect

on the bass at all,

but if there are too many, the bass may

suffocate to death from impaired breathing.

In about two to four weeks, all the larvae

complete their metamorphosis. Once they become juvenile mussels,

they actively detach from the fish’s gills

and use the bass’s mobility to settle

in new waters. If you think freshwater

mussels have perfected the art of deception,

then the next creature is the true master

of turning the tables.

From April to June each year, male bitterlings

actively search for suitable freshwater

toothless mussels. During the breeding season,

males will fight fiercely over an ideal freshwater mussel,

but they do not intend

to mate with it. They are after the mussel’s two

hard shells.

In fast-flowing, dangerous waters,

fish eggs can easily be swept away by the current.

Freshwater mussel shells not only protect against predators,

they also make ideal nurseries.

Once a female approaches, the male

shows off the freshwater mussel he has claimed

by trembling his body to attract her attention.

If the female accepts the match,

the male continues to the next step.

The mussel has no eyes and no brain,

and its every movement is guided by

Following its genetic instructions.

Once it has confirmed it is safe,

the freshwater mussel opens its shell slightly,

letting water flow into its chamber to breathe

and filter food from the water.

To allow the female fish to lay her eggs,

the male fish desensitizes the freshwater mussel

by constantly swimming around the freshwater

mussel and harassing it. At first, the mussel

instinctively closes its shell,

but as this stimulation is repeated,

the freshwater mussel gradually gets used to it

and stops defending itself.

Meanwhile, female bitterlings temporarily grow

an ovipositor about three centimeters long during

breeding season. As the shell opens slightly,

they insert the ovipositor directly into the mussel.

The whole process takes about one second.

Without slow motion, it is hard to see

exactly what happens.

After the female has laid her eggs, the male waits

for the freshwater mussel to open its shell again

and releases his sperm.

As the freshwater mussel filters water,

it draws some of the sperm into its chamber,

fertilizing the eggs inside.

The bitterling couple think their breeding plan is

flawless, unaware that they are already

covered in the mussel's glochidia larvae.

Thirty hours after fertilization, the fish egg embryos

begin developing into fry, making this

the safest time of their lives.

After developing in the freshwater mussel's gills for three

to four weeks, their swim bladders gradually inflate,

and the fry become able to move freely.

Once fully developed,

the fry slip out through the mussel's opening

as it opens and closes. Little do they know, the river

mussel has already used this current

to send its mature glochidia larvae

out along with them.

As the saying goes, free things are often

the most expensive.