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In-Depth Information
Fish may not demonstrate the same level of bonding or create distinct
community identities or individual identities within a community as
some mammals and birds, but they do often live in large groups and are
interdependent on one another and occasionally on other species. Most
species of fish do not possess the tendencies to bond as pairs in the same
way many birds do. Swans not only select a mate, a common process in birds,
but this pairing often lasts for life. Furthermore, some fish species go to some
lengths to attract females. Male sticklebacks are territorial, selecting the
sites most favored by females to build nests made from filamentous algae
and water plants to entice the female to lay her eggs. The male alone then
carefully tends the eggs by wafting his tail, creating a flow of oxygenated
water over the surface of the eggs.
There is a selection process of sorts during the mating of salmon. Cock salmon
demonstrate aggressive behavior toward other males as they jostle for
position alongside the hen salmon as she deposits her eggs in a depression in
the gravel bed (known as a
redd
), though this more often than not still results
in a group mating activity.
Despite the exceptions to the rule, fish often tend to breed en masse, with
many males gathering together in an attempt to fertilize the eggs of the
females. The majority of fish fertilize their eggs externally, but sharks and
rays are among the fish that fertilize eggs internally—a strategy that results
in the laying of egg capsules or the female bearing living fish. The external
fertilization of eggs is a process that for some species has led to a tendency
toward hybridization. For those fish capable of hybridization, and indeed
in some waters this has become a tendency to hybridize, the process may
present some danger for the preservation of original fish stocks.
Such a strategy negates the need for males to compete for a mate in the same
way as birds and mammals do.
Fish seldom demonstrate the same tendency as animals to live in identifiable
family groups with hierarchies, nor do they tend to have a capacity for the use
rudimentary tools, like some mammals and some birds. However, unlike birds,
some fish regularly eat smaller fish, including the young of the same species,
which may even include their own young. Despite the odd exception, once
fish are born there is very little aftercare; they are on their own.
The diversity, distribution, and morphology of fish are hugely varied, with the
greatest range of diversity found in sea fish. The wide variety of morphology
found in fish is very different from that of birds. Birds share, in a very general
way, a common physiognomy, but fish vary a great deal in both size and shape.
The classification of fish is a rather complex matter and has been subject
to many modifications since this branch of science began. It continues to
offer ichthyologists a challenge. For the purposes of this text we can safely
ignore many of these complications, though it might be useful for us to
recognize that fish seem to share a common ancestry. Some of the earliest
