Video credit: Zanou Dossou (Togo)
Review: Abdel Rahman El Gamal (Founder of the video channel)
Before starting any fish farming operation, it is essential that culture unit is free of aquatic organisms which could be accidently left-over from earlier operation whether in fry nursing or grow-out. While this matter is simple in completely drained tanks and/or ponds, it turns a real concern in situations where culture units cannot be completely drained. Small water buddies scattered in earthen ponds could be sufficient to host various organisms including fish fry, fingerlings, molluscs, insects, snails and others. In fact, the adults of some hardy species can survive un-noticed in watery footprints (e.g. tilapia and African catfish). These left-over organisms –depending on their types and densities- may threaten the following crops, and so the eradication of such organisms is a must to ensure a safe crop.
There is a long list of compounds which can be used for such disinfection process. The effectiveness, availability and cost are criteria used in choosing a given disinfectant. Moreover, the easiness of neutralizing the applied substance is an important criterion to consider.
The video shows the use of chlorine solution for the eradication of possible left over organisms. As the remained water scattered in the pond is not easy to estimate, the volume and concentration of chlorine required for such task would depend on personal experience as well as the immediate reaction of organisms that may occur in shown water buddies. In such situations, fish farmers may lean more to overdosing than under-dosing.
It is often recommended to allow water sufficient to cover the whole pond bottom before the application of chlorine. Doing so will ensure a better mixing of chlorine solution with the entire bottom water. Afterwards, and before stocking the fish, no sign of life should be observed in treated water otherwise, repeating the process is possible.
The most common chlorine source used in aquaculture ponds are calcium hypochlorite whether in the form of powder or tablets.
After a day or two of the chlorine applications, pond water is raised and the dead organisms are netted out before stocking the new batch of farmed organisms.