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This experiment was conducted to examine the effect of dietary nucleotides (NT) on fish performance and acute stress response on fingerling rainbow trout (23 g ± 0.01, mean weight ± SEM). Five experimental diets according to different levels of supplemented nucleotides (0, 0.05, 0.1, 0.15, and 0.2%) were assayed on experimental fish for 8 weeks. Growth, hematological parameters (hematocrit, hemoglobin, erythrocyte, lymphocyte, and neutrophil count), serum proteins (globulin, albumin), and plasma enzymatic activity (alkaline phosphatase, ALP; aspartate transaminase, AST; lactate dehydrogenase, LDH; alanine transaminase, ALT) were assayed. At the end of feeding trial, fish fed the control and 0.2% diets were subjected to handling and crowding stress. Modulatory effects of nucleotides on acute stress response (cortisol and glucose) and plasma electrolytes (Na(+), Cl(-), K(+), and Ca(2+)) were studied. The percentage of body weight gain (WG) and feed efficiency (FE) of fish were better when the fish were fed 0.15-0.2% diets. Fish fed the nucleotide-supplemented diets tended to have lower levels of serum enzymes including ALP, AST, LDH, and ALT. Plasma cortisol levels of fish fed on 0.2% diet under handling and crowding stress were significantly lower than fish fed the control diet at all post-stress time intervals. In our study, fish fed nucleotide-supplemented diet had significantly lower concentrations of glucose compared to those fed the basal diet. The concentrations of sodium, chloride, calcium, and potassium of fish fed the control diet were significantly lower than in fish fed nucleotide-supplemented diet. Dietary nucleotides administration seems to promote growth and to enhance resistance against handling and crowding stress in fingerling rainbow trout.

This experiment was conducted to compare the effects of different sources of selenium (Se) on growth, muscle Se concentration, muscle proximate composition, blood enzymes and antioxidant status of common carp, Cyprinus carpio. Organic Se (selenomethionine, SeMet), inorganic Se (sodium selenite, Na2SeO3), or nanoselenium were each added to the basal diet at 0.7 mg Se kg−1 diet. Four groups of fish with an average weight of 9.69 ± 0.12 g were fed one of the experimental diets for 8 weeks. Nano‐Se diet resulted in better growth performance (P < 0.05). Fish fed with Se‐supplemented diets showed a higher (P < 0.05) Se content in the muscle and liver tissues. Fish fed nano‐Se had the highest liver glutathione peroxidase, superoxide dismutase and catalase activities (P < 0.05). Liver malondialdehyde level was significantly (P < 0.05) lower in fish fed on SeMet and nano‐Se diets as compared to control. The carp fed on nano‐Se diet had the lowest values of aspartate transaminase and alanine transaminase. Lactate dehydrogenase activity was significantly lower in fish fed on SeMet and nano‐Se diets. This study shows that nano‐Se acts more efficiently on growth performance and antioxidant defence system of common carp than organic and inorganic sources of Se.

An 8-week feeding trial was conducted to compare the effects of supplementing (0.7 mg kg) different dietary selenium (Se) sources including organic [selenomethionine (SeMet)], inorganic [sodium selenite (NaSeO)], and nanoparticulate Se (nano-Se) on physiological responses of common carp, Cyprinus carpio juveniles (9.7 ± 0.1 g). Basal diet without Se supplementation used as control. Fish fed nano-Se supplemented diet had the highest weight gain (97.2 ± 10.8%) and feed efficiency ratio (42.4 ± 0.8%). Intestinal villi height was significantly taller in fish fed nano-Se diet than in the control group in both foregut and midgut sections. Serum glutathione peroxidase and superoxide dismutase activities were significantly higher in nano-Se and SeMet groups than in control and sodium selenite groups. Fish fed Se-supplemented diets had greater red blood cell counts and hematocrit and hemoglobin values than the control group (P < 0.05). Nano-Se and SeMet groups showed a significant increase in white blood cell counts, neutrophil percentage, and serum lysozyme activity than the other groups. Fish fed nano-Se diet had the highest serum hemolytic activity, total immunoglobulin, and total protein and albumin contents, as well as the lowest serum total cholesterol and low density lipoprotein levels (P < 0.05). Overall, significant improvements in growth performance, feed utilization, intestinal morphology, and hemato-immunological and serum biochemical parameters of common carp juveniles suggest nano-Se as an efficient source for providing dietary Se in this species.

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