Abstract :
Grading fish into groups of similar individual sizes is a common management practice in fish farming. Grading has several advantages: reducing fish losses through cannibalism, improving supplementary feeding efficiency through adequate food ration, increasing the accuracy of stock estimates for monitoring, reducing the proportion of small fish at harvest of fattening ponds and increasing production, for example by increasing the proportion of faster growing males in tilapia ponds. The aim can be achieved by the some objectives (easing of harvesting fish, decreasing of harvesting time fish and decreasing of harvesting costs). All experiments were carried out at different combinations of water speed (0.6, 0.8 and 1.0 m/s), grading sieve depth (50, 70 and 90 cm) and grading sieve holes area (12, 20 and 28 cm2). In each experiment, a test was carried out in Manzala Lake to determine the dead fish ratio, grading efficiency and fuel consumption rate. The experimental results revealed the following:1- Increasing water speed decreased grading efficiency and increased both dead fish ratio and fuel consumption rate.2- Increasing grading sieve depth decreased dead fish ratio and increased both grading efficiency and fuel consumption rate.3- Increasing grading sieve holes area decreased dead fish ratio and increased both grading efficiency and fuel consumption rate.
