Abstract
The present study aimed to investigate the effect of fish grading on the growth performance of common carp Cyprinus carpio cultivated in floating cages located in the Al-Mashab River northwest of Basrah. A total of 4896 fishes were transferred from storage cages to culture cages (3×4×2 m), and distributed at a rate of 816 fishes per cage with a culture density of 34 fishes/m3 into six cages, three of which were classified into large (GL), middle (GM) and small (GS) individuals, whereas three cages were left without grading (UG). The graded and ungraded cages were chosen depending on the standard deviation for each cage. The fishes were fed for both treatments on a standardized, locally made diet. The results of the study were evaluated according to the criteria for total weight gain (WG), daily growth rate and specific growth rate. In the first grading process, significant differences (P<0.05) were recorded between graded (GL) and ungraded in final weight and specific growth rate (SGR) but not in weight gain and daily growth rate (DGR), while in the second grading, significant differences (P<0.05) were recorded between graded (GL) and ungraded in final weight and weight gain but not in SGR and DGR. At the end of the second grading period, the daily and specific growth rate of graded fishes were ranged between 3.26-4.73 g/day and 0.22-0.46%/day, respectively, while for ungraded fishes there were 2.35 g/day and 0.23%/day, respectively. The survival rate (SR) was not different very much in all treatments and ranged between 94.34 to 95.49% in small graded and ungraded fishes, respectively. The study results recommend at least two grading processes should be established during the culture season in two or three months intervals.
Published Version
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