Dr. Akinyemi, A. A.
Aquaculture and Fisheries Management
University of Agriculture, Abeokuta,
• Microorganisms is the existence of every
minute living organisms or they are living
features that can be seen with the aid of
microscope, most of them are normally singlecelled while some may exist in multicellular forms.
• These microorganism, though minute and
microscopic, are a very powerful group of
• They can make healthy animals sick, destroy
plantations, decay food (e.g fish) and cause
• Some of them however, are very useful in that
they can be used for the manufacture of drugs
capable of destroying harmful microorganisms
while a few can convert certain fruit juices into
wine, vinegar and alcohol(Ramalingam,1987).
• Microorganisms are found everywhere except
in a vaccum that is, they are ubiquitous; on
and inside living organisms.
• These organisms vary in sizes from certain
algae just large enough to be seen by the
naked eye to viruses which are too small to be
seen by normal microscope but can be
discerned by an electron microscope.
• Microorganisms are chief agents of spoilage of
food especially fish.
• These microorganisms responsible for food
spoilage especially fish include bacteria, fungal
• These are unicellular microscopic organisms
smaller in size than mould and yeasts
• different from one another in size and shape,
• widely distributed in the environment-air,
• water and soil,
• on the surface of all living features,
• on the moist lining of the mouth, nostril and
• inside intestinal tract of almost all animals.
• Their natural habitat is the soil.
• They are varied requirement for growth.
• Some bacteria are thermophilic; they grow
best at a temperature range of 450C – 550C.
• Others are mesophilic which grow best at
room temperature (200- 300C) and
• pyschrophilic which grow best at refrigeration
temperature between 40C – 100C
• Moreso, some bacteria will grow in the
presence of oxygen (aerobic)
• while other grow in the absence of oxygen
• Therefore, bacteria are classified based on
temperature on oxygen preference.
• Bacteria do not generally grow at low pH
especially below 3.5.
Bacteria exist in four typical shapes:
Spherical in shape (cocci),
cylindrical or rod shaped (bacilli),
long coiled thread or spiral shape (spirillae)
• comma shaped (vibrio or filamentous
• They possess cell wall which sometimes may
be surrounded by capsule or slime layer.
• Some bacteria are motile (capable of
movement) through the use of flagella.
• They normally produce asexually by a process
of binary fission.
• Bacteria spore with a very resistance bodies
are produced for protection in unfavourable
• These are microscopic plant, most of which are
• although yeast and some aquatic species are
• Fungi living in a variety of habitat aquatic ranges
to moist situation on land however,
• some of them are able to withstand drier/dried
condition e.g Aspergillus sp, Penicillum spp).
• Fungi by nature are heterotrophic organisms that
is they require an organic source of carbon for
energy and depend upon this source for their life.
• Some fungi can be found feeding on non-living
organic matter that is, dead or decaying organic
matter called saprophytes (this is important for
• Many other fungi obtain their organic nutrient
from the host and live as parasites.
• Some are also plants and animal pathogens they
cause diseases (Young et al., 1984).
• The two main group of fungi important in food
spoilage are mould and yeast which is made up of
Laboratory Investigation of Microorganisms
Associated Fish Production