The credit of the figure: FAO, the artificial propagation of warm-water finfishes
Review: Abdel Rahman El Gamal
The Dubisch method was named after Thomas Dubisch, the fishery inspector who introduced this system which has been used afterwards based on its practically, efficiency, and cost.
The Dubisch method includes facilities, fish and management. The key facility in this method is the “Dubisch Pond”. Often this pond is of relatively small pond with an area of about 100m2. The design and size of this pond help to stimulate the spawning of common carp, Cyprinus carpio.
In order to secure the above conditions, the small size of the pond allows a quick filling and draining as required. Also, this small size implies the use of only one or two spawning set.
The pond has typical structures for water filling and draining. Also, a spawning pond of about 100-m2 area would require a peripheral ditch of about 50 cm deep that is dug adjacent to the main dyke of the pond, to serve as a refuge for the breeders.
The main area of the pond is made to slope slightly toward the ditch and is covered with short grass. When the pond is filled, water will cover the grassy area with a depth of about 30-50 cm water.
Management of the spawning operation:
Pond preparation: this includes the elimination of any left-over organisms. This is done through sun-drying and/or use of disinfectants. The proper screening of water inlet is essential to prevent any entry of unwanted organisms. The long and especially soft grass in the pond should be mowed off before the spawning begins.
Pond filling: in order to avoid the accumulation of predatory insect larvae, the ponds are filled up only shortly before the spawning starts. Water used should be of optimum quality for the spawning operation.
Stocking the broodfish: The ready-to-spawn broodstock are selected based on established criteria. Two sets of spawners are stocked in the individual 100-m2 Dubisch pond; each set consists of one female and two males. To avoid any disease transfer from the spawners to the embryos and larvae of carp, the spawners receive a prophylactic treatment. The spawners are stocked in the filled ditch and then after the water are gradually allowed into the pond till fully filled. By doing this, the triggering factors to induce the spawning become available which are summarized in:
Good water quality
Availability of grass
Bringing the two sexes together (note that before the stocking, males and females must have been stocked separately)
The spawning usually begins shortly after the stocking of broodfish or at maximum in the following day and this could be observed in the vigorous spawning on the grassy area to which the laid adhesive eggs stick to.
Immediately after the spawning, the pond water is lowered and hence the broodstock are directed to the ditch where they are carefully netted out from the pond which is filled up again. Hatching will take place in few days/hours depending on water temperature. The removal of broodstock provides enough safety to the offspring against possible disease transfer from parents and also facilitates the handling of hatched fry which are moved few days after to be nursed in nursing facilities.
These simple facilities have been found effective in the spawning of other fish species such as pike, tench, crucian carp and others.