Page 286 - Agriculture_Form_Three

Agriculture for Secondary Schools

(v) Fertilise only on sunny days
Fertilisers are generally less active if applied on a cloudy or rainy day.
(vi) Remove aquatic plants from the pond
The fertiliser benefits are reduced if there are aquatic plants in the pondwater
because aquatic plants comparatively absorb more nutrients than phytoplankton.
(vii) Wean fish on pellets
Small amounts of feed should be provided to ponds to train fish on feeding
from the beginning of the seventh week or according to the guidelines provided
by extension worker or other agricultural experts. In fish farming, weaning is
used to describe the transition in the feeding of fingerlings from live foods to
dry artificial diet such as pellets.

Management of water quality in fish pond
The aquatic environment is a complex ecosystem consisting of multiple water
quality variables. The critical parameters in the pond environment, in order of
importance, are the Dissolved Oxygen (DO) concentration, temperature, pH, un-
ionised ammonia concentration, CO , nitrite, suspended solids and alkalinity. Each
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individual parameter is important; however, it is the aggregate and interrelationship
of all the parameters that influence the health and growth rate of the fish. Water
quality within fish ponds can determine the health of the fish and consequently the
success or failure of a fish farming enterprise. In managing water quality in fish
pond, the following aspects have to be adhered to.

(a) Measure water quality parameters regularly
Ideally, water quality is monitored on a daily basis. The following water quality
parameters should be monitored:

(i) Temperature: The optimum growth for most tilapia species is achieved at
24 - 30 °C. Temperature can be measured with a hand-held thermometer.

(ii) Dissolved oxygen (DO): A level between 5.0 mg/L and 7.5 mg/L is recommended.
Growth and Feed Conversion Ratio (FCR) will be affected by chronically low
DO concentrations below 3.5 mg/L. Signs of low DO (i.e., gasping fish, fish
at surface, low transparency, fish swim sluggishly) should be checked in the
morning.
(iii) pH: Fish like tilapia can survive a wide range of pH, from 5 - 10, but are said
to grow best at pH 6 - 8. pH can be measured using the method you have learnt
in Chapter Two.
(iv) Transparency: Transparency is an indicator of water clarity and gives an
indication of the amount of suspended solids in water. It can be measured using
a Secchi disc or with the hand method (when submerging arm in water to the

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