of major importance in industrial wastewater treatment
and aquaculture. They reside in the sediment and other
substrates, and in the water of aquaculture facilities,
as well as in and on the culture species. Microorganisms
may have positive or negative effects on the outcome
of aquaculture operations. Positive microbial activities
include elimination of toxic materials such as ammonia,
nitrite, and hydrogen sulfide, degradation of uneaten
feed, and also providing nutrition to aquatic animals
such as shrimp, fish etc. These and other functions
make microorganisms as key players in the health and
sustainability of aquaculture. Yet, microorganisms are
among the least known and understood elements in aquaculture.
Like other areas in aquaculture, microorganisms require
management and manipulation.
The world of microorganisms
is made of bacteria, fungi, algae, protozoa, and viruses.
They are grouped together only because of their small
size, and not by their function. If, for example, the
same taxonomical rules were applied to larger animals,
some fish, shrimp, green plants, birds and mammals would
be grouped together. Some microorganisms such as viruses,
bacteria, and protozoa are notoriously small (one mm
in diameter). Others, like algae and fungi, have large
sized relatives (such as the brown algae that is among
the largest living organisms). Unlike larger organisms,
the morphology of microorganisms is poorly known, and
is confined to a few shapes and colors. However, their
poor morphology is compensated by great physiological
Viruses are very small,
ranging between 0.01 and 0.03 microns, and only visible
by using an electron microscope. They cannot live independently,
and only multiply inside the cells of other organisms.
However, their demand for a host is fairly specific.
For example, it is unlikely that a crustacean virus
will attack humans or fish. Viruses are also the simplest
of all organisms and are made of nucleic acid (either
DNA or RNA), frequently coated with a protein layer.
Algae are photosynthetic
organisms (contain chlorophyll) and obtain their energy
from the sun and their carbon from carbon dioxide. Their
size ranges from one micron to many meters. All organisms
that use carbon dioxide for their carbon requirement
are called autotrophs. Algae are generally beneficial
in aquaculture by supplying oxygen and as a natural
food base for the cultured animals. However, such as
dinoflagellates cause red tide when blooms formed.
Fungi are similar
to algae, but they do not contain chlorophyll and require
pre-formed organic matter as energy and carbon sources
(e.g., sugars, fat, protein, and other carbohydrates).
Such organisms are called heterotrophs. Fungi, ranging
in size from a few microns to several centimeters, grow
either independently by feeding on decaying matter,
or in association with plants and animals.
Protozoa are heterotrophs,
mostly free-living, feeding mainly by devouring smaller
microorganisms. Their size ranges between 2 and 200
micron meters. A large group of protozoa, the Sporozoa,
are parasites. Small numbers of protozoa contain chlorophyll
and can switch over from autotrophic to heterotrophic
mode of feeding, based on light conditions.
Bacteria range in
size from 0.1 to 15 micron, with some "giants"
that may reach half a millimeter. They make up the most
metabolically diverse group of living organisms. Although
some are parasitic to animals and plants, the majority
of bacteria are free-living, having either a neutral
or beneficial relationship with humans and other animals
and plants. Their metabolic versatility is incredible;
while most are heterotrophs, using either light or chemical
energy. One of their most remarkable characteristics
is their ability to multiply rapidly, with generation
times usually ranging between minutes to hours.
Bacteria and other
microorganisms, most notably fungi, are able to metabolize
and transform numerous organic and inorganic compounds.
Therefore, man has used them for thousands of years
for making yogurt, pickles, bread, cheese, wine, and
more recently for wastewater purification. The Process
controlled by microorganisms can occur aerobically or
anaerobically. The starting materials and the end products
of such processes vary based on the microorganisms'
capabilities (as reflected in their genetic makeup),
and the environment in which these processes occur (e.g.,
availability of oxygen, temperature, salinity, pH, etc).
microbial process in aquaculture
microbial processes yield compounds which can be beneficial,
and are either not toxic or have low toxicity levels
in aquaculture ponds or tanks. Oxidation of organic
matter to carbon dioxide is a process that is the main
consumer of oxygen in aquaculture ponds or tanks. Oxidation
of ammonia to nitrate via nitrite, also consumes large
quantity of oxygen, oxidation of reduced sulfur compounds
(such as hydrogen sulfide and elemental sulfur) to sulfate,
a process that generally has low oxygen demand in aquaculture.
Conversion of carbon dioxide to biomass by autotrophic
bacteria (such as the nitrifying bacteria) with a relatively
small amount of biomass produced in aquaculture facilities,
when compared to the conversion of carbon dioxide to
biomass by algae.
Conversion of carbon dioxide to biomass by algae depending
on the availability of light. Excluding feeding, the
photosynthetic process in aquaculture is the main input
of carbon source and natural food for aquatic animals.
microbial process in aquaculture
processes, if not controlled, can produce compounds
that are highly toxic to cultured animals. These processes
are included: Consumption of organic matter, without
the utilization of free oxygen, resulting in products,
which are usually not fully oxidized (such as alcohols,
organic acids). Reduction of nitrate and nitrite, which
can yield either nitrogen gas or ammonia. In aquaculture,
due to toxicity of ammonia and nitrite, ammonia production
is not welcomed, while nitrogen gas production is beneficial.
However, in agriculture, the opposite is true the conversion
of nitrate and nitrite to nitrogen has result in a loss
of fertilizers. Reduction of sulfur compounds to hydrogen
sulfide as a final product, a compound, which is toxic
to most animals at even very low concentrations.