Reproduction in fishes is regulated
by external environmental factors
that trigger internal mechanisms
into action. The final event of the
reproductive cycle, the release of
eggs and sperm resulting in
spawning, can be controlled by
either placing the fish in an appropriate
environment or by changing
the fish’s internal regulating factors
with injected hormones or
other substances. The internal
mechanisms that regulate spawning
are similar for most fishes. The
external environmental factors
that control reproduction, however,
vary considerably among
species. For this reason, more is
known about the internal regulatory
mechanism of fish reproduction
than the specific environmental
requirements for spawning
each species.
Many fish spawn in environments
that are nearly impossible to simulate
in a hatchery. Hormone-induced
spawning is the only
reliable method to induce reproduction
in these fishes. Hormoneinduced
spawning of fish has been
used for almost 60 years. Surprisingly,
the same procedures, with
only minor modifications, have
been used to spawn an entire