Nesting and Reproduction
Most fishes reproduce by external fertilization—a female fish releases
eggs into the water, where they are fertilized by sperm from a male.
This process is called spawning. Some fishes, such as sharks, reproduce
by internal fertilization— the male deposits sperm into the female fish,
where the eggs are fertilized. These fishes are called “livebearers,”
which means that they give birth to live young.
Fish
Eggs
Fish eggs range in size from a barely visible dot to the size of
a pea. Some eggs float in the open water, while others are
heavier than water and sink to the bottom. Eggs on the bottom
may clump together in masses, or they may stick to sand grains
or to hard objects. Some fishes carefully place eggs on the
undersides of rocks or on sticks in the water. Some eggs are not
sticky at all and simply fall into the spaces between pebbles.
Fish eggs may hatch within several days of spawning or many
weeks later, depending on the species and the water temperature.
Fish Attraction
Many fishes develop bright colors during their breeding seasons.
Usually it is the male that is more colorful. He uses his bright
colors to attract females. Color also makes it easier for fishes
to recognize members of their own species.
Spawning Run
Many fishes move to special areas where conditions are just right for
spawning and protecting their eggs. For some minnows and sunfishes, this
is a matter of moving a few yards in a stream or into shallow water in a
lake. But for salmons and shads, it can mean a journey of thousands of
miles.
Salmon Life Cycle
Coho Salmon spend part of their lives in the salt water of the
Pacific Ocean, but they travel many miles into freshwater
streams and rivers to spawn. Along the journey, their bodies
change to a brilliant red color. Females release eggs along the
gravel bottom, where they are fertilized by males. Both males
and females die after spawning. The young fish hatch and spend a
year in the fresh water before traveling out to sea. Two to
three years later, the salmon return to the river as breeding
adults. They spawn, and the cycle continues.
Fish
Nests
Many fishes simply release their eggs and sperm into the water
and pay no attention at all to the fertilized eggs, but other
fishes build nests and guard the eggs and young. Fishes usually
spawn during a particular time of year. In freshwater ponds and
lakes, late spring and early summer are excellent times to
observe fishes making nests and laying eggs. It’s also a good
time to observe hatchlings (baby fishes) schooling together.
Fish Parenting
Most fish parents spend little time caring for their offspring.
But some, such as certain catfishes, guard the nests and young
for a few days after the eggs hatch. In a few species the adults
carry eggs on their bodies. Some fishes actually keep the eggs
in their mouths until they hatch.
Baby
Fishes
When young fishes hatch they may look very different from adult
fish of their species. Newly hatched fishes may be nearly
transparent, but in a few days they develop color patterns.
Juvenile freshwater fishes tend to resemble their parents, but
most saltwater fishes have larval stages. These larval fish
drift freely in the open sea and many are bizarre-looking, with
odd shapes or long trailing fins.
