This study evaluated growth performance, hematological parameters, histological liver analysis, and production costs of Nile tilapia fed increasing levels of digestible protein, digestible energy, and choline. Twelve thousand Nile tilapia (148 ± 6.7 g) were randomly distributed into 80 1 m 3 net cages, in a 5 × 2 × 2 factorial design with five digestible protein (DP) levels (24, 26, 28, 30, and 32% DP), two digestible energy (DE) levels (13.4 and 14.65 MJ DE kg −1 diet), and two choline levels (0.0 and 1000 mg kg −1 diet), with four replicates per treatment. Fish fed the higher energy level showed a sparing effect of protein; the higher protein level determined the highest fillet yield. Fish fed diets with 24% DP showed the highest liver lipid, and independently of treatment all analyzed fish showed hepatocyte degeneration. The best benefit cost ratio for whole fish production was achieved with 28% DP/13.4 MJ DE kg −1 , and for fillet production with 30% DP/13.4 MJ DE kg −1. The results of the hematological assay showed alterations in red blood cells, mean corpuscular volume, albumin, Albumin:Globulin ratio, and glucose after size-sorting stress. Overall, these results indicate a lower resistance to stress, mainly for fish fed with no choline and oil supplementation. In this study we determined that the best performance was achieved with DP:DE ratios of 21.45 g MJ −1 (28.74% DP/13.4 MJ DE kg −1) and 18.60 g MJ −1 (27.25% DP/14.65 MJ DE kg −1). The highest fillet yield was obtained with 30% DP, regardless of the dietary energetic level. Sustained homeostasis was observed in this setting, and even though size-sorting stress altered some hematological parameters, they were still within the range recognized as healthy. Choline was not effective in protecting the liver against hepatic steatosis, but was able to buffer some of the negative effects of stress under these rearing conditions. Statement of Relevance: This research has been approved by the Ethics Committee of our Institution. Our team has been working with nutrition and fish health since 2000. According to the NRC (2011), only a few studies have been conducted to estimate the dietary nutrient requirements of farmed fish under intensive culture conditions. Moreover, a number of factors may affect the dietary and nutritional requirements of fish differentially in the laboratory and under intensive culture. For example, climatic conditions may fluctuate widely in the field, directly affecting physiological responses, hence nutritional requirements. Similarly, fish densities are much higher under intensive farming. Establishing the appropriate nutritional requirements in these settings must also consider the trade-off between growth performance and production costs. Based on this, we investigated the effect of different levels of digestible protein and digestible energy on growth performance and hematological responses of the Nile tilapia in a commercial fish farm in Brazil, where fish farmers are known to use diets with excessive levels of crude protein through...

Nutritional strategies can help fish manage stress, and functional feedstuffs are an interesting nutritional option. Therefore, this study evaluated the potential functional effect of spray-dried plasma (SDP) on Nile tilapia growth performance and the capacity of SDP to improve fish health under cold-induced stress (CIS). A total of 440 fish (12.64 ± 0.64 g) were randomly distributed into 40,250-L aquaria and fed five diets containing graded levels of SDP (0, 16.6, 33.2, 49.7 and 66.3 g kg − 1) for 60 days. The growth performance, villus height:crypt depth ratio, and hematological parameters were analyzed, and the same hematological parameters were then analyzed after 7 days of CIS. Based on the broken-line analysis of the FBW, SGR, RWG and FCR, the optimum dietary level supplementation of SDP was determined to be 49.70, 50.16, 51.83 and 41.83 g kg − 1 diet, respectively. The crypt depth and villus:crypt ratio were positively affected by SDP supplementation. After CIS, hematocrit of fish fed 16.6 g kg − 1 of dietary SDP was significantly lower than fish fed 66.3 g kg − 1 level (P < 0.05). The supplementation level of dietary SDP and the CIS affected the leukocyte, lymphocyte and neutrophil counts. The monocyte count was affected by the dietary SDP supplementation level both before and after CIS (P < 0.05). Total plasma protein concentration in the fish fed 49.7 and 66.3 g kg − 1 SDP were significantly higher than fed 16.6 g kg − 1 SDP after CIS (P < 0.05), and CIS led to a higher Albumin:Globulin ratio (P < 0.05). Dietary SDP supplementation improved the growth performance, intestinal health, hematological profile and CIS resistance of the studied fish. Based on our results, we recommend a dietary supplementation level of 51.83 g kg − 1 SDP for Nile tilapia.

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The effect of the ethanolic extract of propolis (EEP) on Aeromonas hydrophila was analyzed by determination of minimum inhibitory concentration (MIC). Then, the effects of crude propolis powder (CPP) on growth, hemato-immune parameters of the Nile tilapia, as well as its effects on resistance to A. hydrophila challenge were investigated. The CPP (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0%) was added to the diet of 280 Nile tilapia (50.0 ± 5.7 g fish -1 ). Hemato-immune parameters were analyzed before and after the bacterial challenge. Red blood cell, hematocrit, hemoglobin, mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), and hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) were evaluated. The MIC of the EEP was 13% (v/v) with a bactericidal effect after 24 hours. Growth performance was significantly lower for those fish fed diets containing 2.5 and 3% of CPP compared to the control diet. Differences in CPP levels affected fish hemoglobin, neutrophils number and NO following the bacterial challenge. For others parameters no significant differences were observed. Our results show that although propolis has bactericidal properties in vitro, the addition of crude propolis powder to Nile tilapia extruded diets does not necessarily lead to an improvement of fish health.