Page 62 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

60 FRESHWATER FISH: BREEDING

Reproductive behavior

Fish can be divided into two broad categories on the basis of their
breeding behavior. Egg-layers, which form the majority, practice
external fertilization, while in livebearers the eggs are fertilized in
the female’s body and emerge as fully formed young. Some species
show little regard for their offspring and cannibalize their own eggs
or fry. Others display surprisingly high levels of parental care.

When fish mate, it is known as spawning. In egg-layers, this
involves the male’s releasing sperm into the water at roughly
the same time that the female expels her eggs This temporarily flooded forest in the Amazon region of
nearby so that fertilization occurs outside South America provides a spawning ground for egg-laying
fish such as discus. Breeding behavior in the wild is often
the female’s body. This is a rather seasonal and influenced by rainfall patterns.

The male Siamese Fighting Fish uses haphazard method of reproduction, and, not surprisingly,
his elaborate fins for display purposes, a significant proportion of the eggs fail to become
not just to entice potential female fertilized. In order to maximize the chances of
mates, but also to intimidate
rival males. fertilization occurring, some egg-layers attempt to
maneuver their genital openings as close to each other as
possible before spawning occurs, and there is occasionally
contact between the fish, such as embraces with the fins.

Reproduction in livebearers
The likelihood of successful fertilization is greatly
enhanced in livebearing species, which practice
internal fertilization. The male livebearer introduces
his sperm directly into the body of the female
using his anal fin, which is typically modified
into a tubelike projection called a
gonopodium. The eggs are fertilized
inside the female and then develop in
the relative safety of her body.
The male’s gonopodium carries
sensory organs that help him to
guide it into the female’s genital
pore. The shape of the gonopodium
varies between different livebearing species, and
its appearance is used by zoologists as a means
of distinguishing between them. Males with a
long gonopodium are able to mate easily. Spawning
is more intimate for males with a short gonopodium,
and courtship plays a greater role in such species, helping
the female to feel comfortable with the male being so close.
During mating, sperm are transferred into the female’s
body in the form of a sperm packet. This dissolves within
about 15 minutes, freeing the sperm. Any sperm that fail to

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