Video credit: Charles Bernard Makuya (Malawi)
Review: Abdel Rahman El Gamal (Founder of the video channel)
Cannibalism is a common phenomenon which starts early in the life of African catfish (Clarias gariepinus) and usually causes significant losses. The phenomenon of cannibalism is encouraged by some environmental factors such as insufficient food, high stocking density and others. The situation becomes worse along with the spotting of few individuals of exceptionally large sizes (shooters). In order to minimize the losses due to cannibalism, periodic grading should be carried out as an essential practice in catfish hatcheries. As the cannibalistic behavior has been observed among catfish fry upon their first feeding, the grading is usually performed periodically during the nursing of fry to juveniles with higher frequency in case of fry (could be weekly) to bi-weekly grading in case of advanced fingerlings and in regard to juveniles, a monthly grading would be sufficient.
Catfish fry and fingerlings are usually graded into 2 or 3 sizes using proper graders which could be made of nets with varying mesh sizes and/or bar graders. In fact, hand sorting could be performed especially for the exceptional large size specimens (shooters).
The relative uniformity of graded fry does not only minimize the occurrence of cannibalism, but is also in their management especially in regard to feeding whether in ratios or frequency.
The 5-min video has been filmed as a part of training program carried out in Egypt. The grading targets three size grades whereas the medium size represents the largest portion (retained above), the smallest size which passes through the mesh of the grader –along with debris- are retained by the underneath net of small mesh in addition to few specimens of largest size which were picked by hand and placed in the red bucket. Of course, as fish grows, nets with larger mesh would be in use.