Abstract
The aim of this study was to evaluate the effect of slow reduction in water level during Nile tilapia (Oreochromis niloticus) harvest on growth performance, condition factor, hemato-biochemical parameters, genetic polymorphism, and genomic template stability. During tilapia harvest, water level was reduced from 150 to 30 cm in different duration as follows: group one (control), in 72 hours (h); group two, in 48 h; and group three, in 24 h. There was a significant correlation between length and weight of fish among all experimental groups. Condition factor showed significant differences (P<0.05) among all experimental groups. Hemato-biochemical parameters showed no significant differences in PCV % and lymphocyte/RBC ratio. Moreover, significant differences were recorded in total protein, albumin, globulin, A/G ratio, cholesterol and triglycerides among the experimental groups. To evaluate genetic polymorphism, eleven RAPD primers generated a total of 67 DNA bands, out of which 31 (46.27%) were polymorphic. Cluster analysis and Principal Coordinate Analysis indicated high dissimilarity degree between the control and treatment groups. Genetic fingerprint for all experimental groups was performed by DNA barcoding, which revealed that the number of bands differed among all experimental groups with an average of 52.3 bands. Percentages of genomic template stability were 56.5 and 54.3 for the 48 and 24 h treatment groups, respectively. RAPD technique identified some specific unique markers for the treatment of water level reduction in Nile tilapia harvest and indicated that the rapid reduction (24 h) could reduce the bad effects of crowding stress and improve tilapia welfare during harvest.