|Abstract or Summary
- This investigation explored the use of microcosms as a tool for
studying the dynamics of tropical aquaculture ponds. The potential use
of rabbit excreta as a pond fertilizer in integrated farming systems was
Twelve insulated fiber glass tanks were utilized as microcosms to
simulate earthen ponds. Seven hand-sexed Nile Tilapia O. niloticus)
were stocked per tank, and microcosm performance was observed for a 90-
day experimental period. Three rabbit excreta loading rates
corresponding to 50 and 75 kg/10,000 m³ /day, and a continuously adjusted
manure loading rate were assessed. The fertilizer treatments were
compared to a control treatment where fish were fed on a prepared food.
Water quality variables and fish performance were regularly monitored.
Nitrogen and phosphorous content of rabbit excreta were measured.
The dynamics of the microcosms were similar to warm water earthen
ponds with respect to physical and chemical characteristics.
Statistical differences were detected between control and fertilized
treatments in relation to dissolved oxygen levels, net primary
productivity, total alkalinity, total ammonia and orthophosphate levels.
Primary productivity was influenced more by light intensity and
penetration than by nutrient limitation. Rabbit excreta overloading was
observed in the 75 kg treatment. Fish growth was greatest in the
control treatment, but it was not statistically different from the
continuously adjusted fertilizer treatment (Pondclass) (0.0065 and
0.0056, respectively). Low daily fish gains were observed in the 50 and
75 kg treatments. Low dissolved oxygen and high total ammonia were
concentrations resulted in low weight gains and condition indices of
fish in the 50 and 75 kg treatments. Extrapolated fish yields
corresponded to 6,205, 4,563, 3,686, 4,869 kg/ha/year for control, 50
kg, 75 kg and Pondclass treatments, respectively. The observed yields
are comparable with field experiences in real ponds. The continuously
adjusted treatment showed the lowest manure conversion ratio (3.85) in
the fertilized treatments.
The nitrogen content of rabbit excreta varied according to rabbit
size, presence or absence of urine plus water waste, and food droppings.
Urine plus water waste provided 28 % of the total nitrogen content in
rabbit excreta, whereas food droppings provided 12 %. Rabbit urine may
play an important role in aquacultural systems because it contains a
large fraction of nitrogen in inorganic forms which are readily utilized
for algal growth. Other rabbit excreta characteristics such as buoyancy
may be advantageous in aquacultural systems. Rabbit excreta is a
potentially rich source of fertilizer for use in fish ponds.