3.2 Fry Rearing Ponds and Basins

The small fry are reared from the age of 4-5 days to 3-4 weeks in the fry rearing ponds and basins. These should be arranged in places sheltered from wind, on impervious soil and close to the hatching house and road.

The preferable size of the fry rearing ponds ranges from 100 to 1 000 m² . Within this range the actual size of the fry rearing pond depends on the number of fry which can be introduced within 1-2 days. The pond size should therefore be adjusted to the capacity of the hatching house.

The water supplied to the fry rearing ponds should be rich in oxygen and must contain no chemical or biological pollution. Water containing much suspended sediment must be allowed to settle first. The supply system should be dimensioned to permit the water in the pond to be exchanged twice daily. In densely populated ponds, a distribution network of perforated pipes should be provided at the bottom for the uniform distribution of inflow water. The fry rearing ponds are lined with stone or concrete.

Circular basins are made with diameters from 4 to 6 m and about 1 m depth. The freshwater is introduced tangentially through nozzle pipes to maintain the water in permanent circulation. The effluent is withdrawn from the centre of the basin.

Rectangular basins should have a ratio of short to long sides from 1:2 to 1:4. The water is introduced to, and withdrawn from, these basins along the short sides. The drainage system of the fry rearing ponds should be dimensioned hydraulically to permit each basin or pond to be drained in four hours. Sluices equipped with box traps should be used to collect the fry. For a guideline to determine the total area of all fry rearing ponds, as a general rule 100 to 200 feeding larvae require 1 m² of water surface area.