Effects of Dietary Nucleotide on Performance and Stress Response in Rainbow Catfish, Pangasianodon hypophthalmus
This study was conducted to determine the effect of dietary nucleotides on growth performance, hematological and biochemical parameters and resistance to stress of Rainbow Catfish, Pangasianodon hypophthalmus. Five experimental diets were applied for 10 weeks. Nucleotides were supplemented with 0, 0.25, 0.5, 0.75 and 1%. 750 fish (average weight±SE 1.52±0.03g) were acclimatized to the laboratory conditions for two weeks and then randomly divided in to five triplicate groups of fish. Each group was kept in a 150 L aquarium for ten weeks. At end of the experiment, growth parameters, hematological and biochemical parameters (hematocrite, hemoglobin, white blood cell, red blood cell, total protein, glucose, triglyceride, cholesterol, albumin, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), lactate dehydrogenase, aspartate transaminase, alkaline phosphatase and alanin transaminase) was recorded. The control group and fish fed highest nucleotide concentration were subjected to handling and crowding stress. Blood samples from stressed fish were taken 1, 3, 8, 24 and 48 hours after stress and cortisol, glucose, Na+, K+ and Ca+ were assayed. Results indicated that fish fed 0.75 and 1% had the highest condition factor (P<0.05), but other parameters did not show significant difference (P>0.05). Dietary NT could significantly change the Hb and Hct levels in the stripped catfish (P<0.05), but there were no significant different in WBC, RBC, MCHC, MCV and MCH (P>0.05). Dietary NT could significantly decrease LDH level in the Rainbow Catfish (P<0.05), but other enzymes not affected by nucleotide. The Rainbow Catfish fed with 0.75% or 1% NT had significantly higher triglycerides in comparison to other groups, while other blood biochemical parameters (TP, Alb, Glb, Chol and Glu) were not affected by dietary NT(P>0.05). Fold and entrocyte heights of the gut increased significantly in fish fed 0.75, 1% and 0.25% nucleotide respectively (P<0.05). There were no significant differences in cortisol levels among different sampling times between two groups (P>0.05). erum glucose and calcium levels showed elevation trend in fish subjected to stress in both groups and decreased after 3 and 1 hours respectively. In both groups, the levels of sodium and potassium concentrations decreased after stress challenges and reached the lowest amount at 3 and 48 h post stress. In conclusion, the results of the present study demonstrated that the dietary NT has very limited positive effects on Rainbow Catfish welfare, growth parameters, hematological and biochemical parameters and stress responses while nucleotide improved condition factor, triglyceride, fold height and entrocyte height.
Keywords: Nucleotide, Rainbow Catfish, Pangasianodon hypophthalmus, growth parameters, hematology indeces, acute stress.