The effect of digestible protein to digestible energy ratio and choline supplementation on growth, hematological parameters, liver steatosis and size-sorting stress response in Nile tilapia under field condition

Abstract

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...

<b>Digestible protein requirement for Nile tilapia fed with rations based on soybean meal and corn

“…The results of FY were similar to those found by Fernandes et al (2016), who did not observe differences in the diets with 30 and 32% of DP. Koch et al (2014) evaluated the sales profitability of Nile tilapia fillets and recommend the use of 32% of DP to increase the FY and consequently the sales profitability.…”

The evaluation of energy in fish feed

“…This suggests that the optimal DP/ DE ratio is either not present or lower than 16 g MJ -1 for Nile tilapia. The current finding of an optimal DP/DE ratio below 16 g MJ -1 is a very low estimate compared to other studies on Nile tilapia having reported optimal values between 18 and 26.3 g MJ -1 (Al Hafedh, 1999;Ali et al, 2008;El-Sayed and Teshima, 1992;Fernandes et al, 2016;Kaushik et al, 1995;Li et al, 2012;Van Trung et al, 2011). The value is also low compared the optimal DP/DE ratio reported for other fish species e.g.…”

“…An alternative explanation might be differences in feeding level (restricted vs. satiation) between studies. Most studies assessing the impact of dietary protein to energy ratios are done at satiation feeding (e.g., tilapia (Ali et al, 2008;Fernandes et al, 2016;Kaushik et al, 1995) Salmon (Einen and Roem, 1997); gilthead sea bream (Lupatsch et al, 2001). The optimal 2 DP/DE ratio in various response criteria other than feed intake might still be a reflection of the impact of DP/DE ratio on the voluntary feed intake.…”

Dietary protein:lipid ratio changes growth, digestive enzyme activity, metabolic profile and haematological parameters in hybrid surubim (Pseudoplatystoma fasciatum × Leiarius marmoratus)

“…The use of dietary protein by fish for body growth should be maximized (Chatzifotis et al., ). Therefore, evaluation of protein:lipid ratio on protein‐sparing effect has great importance (Arslan, Dabrowski, Ferrer, Dietrich & Rodriguez, ; Bicudo, Sado & Cyrino, ; Fernandes et al., ). When dietary lipid levels are above metabolic and growth requirements for the fish, it might be stored as visceral fat (Chatzifotis et al., ; Martino, Cyrino, Portz & Trugo, ).…”