The
fundamental differences between freshwater and saltwater
fish lie in the two environmental extremes in which
they live. In general, the freshwater species of fish
are hardier than their marine counterparts, having evolved
to withstand the rapid and dramatic changes in water
conditions that occur on land. On the other hand, most
marine species have lived in constant environmental
conditions; they have not evolved the mechanisms to
adapt to sudden changes, such as those that may occur
in the home aquarium. This, of course, renders these
fish more difficult to maintain in captivity.
Obviously,
saltwater contains much higher concentrations of salt,
sodium chloride, than freshwater. In addition, many
others dissolved elements occur in higher concentrations
in saltwater than they do in freshwater. The amount
of these dissolved salts in water is referred to as
its salinity. All living things must balance their internal
chemistry within very precise limits in order to survive.
In general, the salinity of cells must be maintained
in the face of external salinity gradients. In the process
called osmosis, pure water flows through cell membranes
from areas of low salinity to areas of high salinity.
Fish in freshwater are constantly subjected to an influx
of water because their cells are more saline than their
environment. On the other hand, marine fish are always
threatened by the loss of water from their cells because
their environment is more saline.
Although
marine and freshwater fish are anatomically similar
in appearance, they have evolved very different ways
of living in their respective environments. As a means
of maintaining their internal salinity, freshwater fish
drink very little water and produce large quantities
of dilute urine. In contrast, most marine fish drink
large quantities of water, and eliminate salts in small
amounts of highly concentrated urine and feces, as well
as at the gills. Sharks and their close relatives, rays,
are exceptions to this pattern in marine fish. These
species concentrate urea in their tissues and blood
to offset the loss of water.
Invertebrates
Invertebrates
are another extremely popular species for many aquarium
hobbyists. The term invertebrate is a convenient catch-all
title, loosely covering all those animals that do not
have a backbone or vertebral column, and an internal
skeleton. Invertebrates range in size for microscopic
plank tonic animals to giant squid, fierce predators
that Roman deep, colder waters of the world.
The
first vital steps to success with invertebrates is to
use a high-quality salt mix that closely matches the
composition of natural seawater. Throughout the world,
the chemical composition of seawater is remarkably similar.
Although the total weight of salts in a given volume
of water may very slightly, particularly in comparatively
land-locked waters such as the Red Sea, the proportions
of each are largely the same.
In
the early years of marine hobby there were many Sea
salts of varying qualities. Some were acceptable and
others were certainly not. So much so, but the many
early books available he detailed formulae so the aquariums
and by the various chemicals required, blend them and
hopefully produce something approaching seawater. Fortunately,
those days are long gone and now there is a wide range
of professionally produced salt mixes, the vast majority
of which are perfectly suitable. As a general rule,
it is a good idea to use the same salt mix as your supplier;
although most salt mixes are virtually indistinguishable,
there is no point in subjecting your livestock to any
unnecessary environmental stress.
Generally
speaking, any reputable salt mix can be dissolved in
cold tap water to produce a satisfactory solution. One
word of caution, however; in some areas, particularly
of high population densities or where there is intensive
arable farming, the tap water may contain nitrates at
concentrations above those considered safe for some
of the more delicate invertebrates. If there is any
doubt as to the quality of your tap water, it is worth
carrying out a simple nitrate test before mixing up
new salt water. If it gives the reading of much above
25 mg per litre, either filter the tap water through
a nitrate removing resin before using it or find a safer
source of fresh water.
The
main ingredients of seawater are various sodium, magnesium,
calcium and potassium salts. In addition, natural seawater
contains small amounts of every known naturally occurring
element. Examination of a bag of prepared salt mix will
show that many other chemicals are also present in very
small quantities. Certain of the so-called trace elements
are known to play a vital role in the well-being of
both marine invertebrates and fishes, and that they
are extracted from the surrounding water and helped
to sustain the animals metabolic processes. In the wild,
the concentration of trace elements is continually replenished
through decomposition of dead animals in the Rosen of
minerals from the land into the sea. Sub-oceanic volcanic
activity may also be significant in this respect. Clearly
none of these forces are at work in the domestic aquarium,
yet trace elements are still being abstracted by livestock
and various algae in the tank.
Aquarium
Supply and Google Ad Directory for
1.
2.
