Maintenance of good fish health is critical to
profitable fish culture. Slow growth, poor feed conversation, low yields,
increased disease incidence and mortality, consequently, low profitability are
the results of poor fish health. Physiological stress is the fundamental cause
of most fish health problems. The best way to manage fish health is through
prevention. Practical health management is based on stress management. This
involves preventing and minimizing stress to the fish in the culture
environment through:
- Good water quality management. This begins by picking a farm site with good water quality and quantity. Maintain water quality at non-stressing levels.
- Good nutrition: Feed high quality feed (nutritional and physical aspects) in the proper size and amounts.
- Catfish do not have scales to protect them so rely on mucous to protect their skin. When the mucous is rubbed off, the catfish are very prone to infection and parasites.
- Fish do not have eyelids and cannot protect their eyes when they are being rubbed against each other or being poured from a basket or net.
Fish Stress
Stress is
an abnormal physiological condition of fish that results when the fish’s
collective adaptive responses to environmental factors are extended to, or
approach its limit of tolerance when fish are stressed.
THE CAUSES OF STRESS
There are dozens of potential stresses to fish, but some of
the most common causes are:
•
Elevated ammonia
•
Elevated nitrate
•
Improper PH level
•
Fluctuations in temperature
•
Low oxygen levels
•
Harassment's from other fish
•
Lack of hiding places
•
Inadequate tank size
•
Overstocking of tank
•
Medications and water treatment
•
Improper nutrition
•
Sorting and shipping of fish
•
Harvesting and shipping of fish
Signs Sick Fish Posses
Signs Possible
Causes
Bloated
body resulting
from bacterial infection
Gasping Parasites
in low dissolved oxygen
Not eating
Signs
of ill health
Upside
down swimming Bladder
problem
Peeling
skin PH
problem
PREDATORS AND THEIR CONTROL
Predators
are a major source of stress of fish and can also cause significant losses.
NOTE: Large African catfish can predate on smaller ones; so,
maintaining uniform sizes within ponds is critical.
Predators:
•
Consume the fish in the pond,
•
Consume the fish’s feed,
•
May transmit parasites and other infections to fish
•
Scare the fish when they are chasing them up, and
•
Cause physical injury to several fish in the process of
hunting.
•
May Trans-locate fish to a different pond
The
wounded fish left in the pond consequently cannot get to the feed as well as
the other normal fish. This is because, for example, their eyes might be
injured or their open wounds might get infected, etc. Consequently, their
growth rate slows and chance of survival drops. Controlling predators is
therefore important in commercial production.
The most common predators are:
- Human Beings
Provide
security to your premises by fencing off and keeping the place active. Some
places have gotten local authorities to recognize how harmful theft is to the
development of commercial fish farming in their area and have enlisted their
help in prosecuting fish farm thieves. As well, be a good neighbour and make
sure others appreciate the fact your farm is there. This can create “social
pressure” to reduce their.
•
Birds
•
Wading birds (such as the heron, marabou stork, and hammer
kop) walk into the pond to catch fish. To control wading birds, ensure pond
average water depths of 1 meter so that the birds are unable to stand in the
pond.
•
Diving birds (such as the king fisher’s, ducks) fly over or
swim on the water surface then dive down to pick the fish. Tying string at
close intervals over the pond prevents them from being able to fly away once
they have come down or dive through the strings.
•
Avoid setting your ponds near places where birds can perch,
such as having pond under telephone or electricity wires/poles, trees, etc.
These provide a sport for birds of prey to sit, watch the fish and time when
best to hunt them. Tall sticks placed in ponds are excellent perches for
kingfishers. If sticks are required in a pond, they should be kept as short as
possible. (d). Scarecrows or sudden
loud noises may be used to scare away birds. However, if this option is used, change
the tactics at least every two weeks. This is because the scarecrow or noise. (e).
Learn at what time birds come to hunt fish. Most times, birds come down to get
fish soon after feeding, early in the mornings or late in the evening. Be
around at such times to scare away the birds. Human activity helps to keep
birds away.
Predators Control
• Minimize the amount of vegetative growth around ponds as
these act as a refuge for many potential predators e.g. Birds, snakes, otters,
monitor lizards, thieves.
•
Keep the place around farm active and be observant.
•
Keep area around ponds clean.
•
In the case of plastic pond or concrete tanks cover with
net.
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