68 SEPTEMBER 2019 • WORLD AQUACULTURE • WWW.WAS.ORG Red Blood Cell Indices At the end of bioassay, blood of red tilapia cultured at low density in seawater (C1) had the highest total erythrocycte counts compared to fish in other other groups (Fig. 4A). However, hemoglobin and packed cell volume were not different between fish at low density in seawater (C1) and fish from high density with biofloc plus probiotics (B+P2) (Figs. 4B and C). The mean corpuscular volume and mean hemoglobin concentrations (Fig. 4D and E) of fish cultured at both densities with biofloc with or without probiotics were significantly greater than those of fish from the low-density control (C1). The mean corpuscular hemoglobin concentration (Fig. 4F) of fish cultured at low density with or without biofloc and probiotics was not different and lowest in fish from the high-density control (C2). The interaction of density and system significantly influenced almost all red blood cells parameters of red tilapia juveniles, except mean hemoglobin concentration, which was mainly influenced by the presence or absence of biofloc (Table 1). Low erythrocyte counts in healthy fish are related to a high oxygen demand caused by high activity or increased metabolism (Hrubec and Smith 2010, Maciak et al. (2011). In our work, erythrocyte count was lower in fish from biofloc and probiotics at both densities compared to control at low density. Although Abduljabbar et al. (2015) did not find a significant effect of biofloc on the blood of Nile tilapia O. niloticus, our results agree with Telli et al. (2014), who found erythrocyte counts were low in Nile tilapia that received probiotics. On the other hand, because the low hemoglobin concentration and high mean corpuscular volume found in fish from C2, our study indicated the presence of a greater amount of immature erythrocytes (which are larger in volume than mature erythrocytes). Decreases in hemoglobin, erythrocyte count or packed cell volume in the absence of their regeneration indicate suppressed production of red blood cells, which may be impaired by factors like chronic inflammatory diseases, decreased food intake and protein deficiency (Hrubec and Smith 2010). Stress and Nutritional Condition Indices The concentration of glucose (Fig. 5A) in blood of fish at low density in seawater (C1) and both B+P groups were not different. Glucose in fish reared at high density (C2 and B2) was significantly less than glucose in fish reared at low density (C1 and B1). The interaction of density and system significantly influenced glucose of blood plasma juveniles of red tilapia (Table 2). Glucose increases in response to an increase of stress or high metabolism related to a high energy requirement (Martinez-Porchas et al. 2007). In this study, glucose content was affected significantly by the interaction of density and system, where glucose decreased at high density but recovered with probiotics. These results may be related to probiotics promoting better use of nutrients in feed and biofloc. The total protein in the blood of fish in C1 was greatest, while that from B+P treatments at both densities had the lowest total protein concentration (Fig. 5C). The albumin concentration of C1 and B+P fish at both densities were not different and C2 fish had the lowest values (Fig. 5D). Although total protein was not significantly influenced by main factors or their interaction, albumin was strongly influenced by density. An adequate intake of protein is essential for normal synthesis of albumin (Mazzaferro et al. 2002). The albumin concentration in blood of red tilapia in this study decreased at high density but recovered with the addition of probiotics. Probiotic supplementation reduces the impact of stress in fish at high density (Telli et al. 2014). Red tilapia in biofloc systems with probiotics had the lowest total protein values and normal albumin values. The cholesterol concentration in the low-density control (C1) was greatest, except for B+P2 (Fig. 5B). Cholesterol concentration was mainly influenced by system type. Cholesterol is the most common steroid in body tissues and acts as a precursor to the synthesis of steroidal hormones. It is also the main structural component of cell membranes. Most cholesterol is synthesized in the liver and the remainder is derived from the diet (Ma et al. 2016). In this study, blood of red tilapia cultured at low density in biofloc with probiotics had the lowest cholesterol concentration. Abduljabbar et al. (2015) reported similar results in Nile tilapia cultured with biofloc. Although high stocking density generates significant stress in red tilapia, biofloc with probiotics improves physiological regulation and therefore health condition. TABLE 2. Two-way ANOVA results blood biochemistry of juveniles of red tilapia Oreochromis spp. cultured in sea water with biofloc and probiotics. Group Density System DensityxSystem GLU 0.21 0.37 0.02 CHOL 0.83 0.01 0.25 TP 0.93 0.92 0.23 ALB 0.00 0.44 0.68 Values presented are significant when P < 0.05. from red tilapia cultured at low (114 fish/m3) and high (228 fish/m3) densities with biofloc (B) and probiotics (P). C were the control from each density without B and P. GLU, glucose; CHOL, cholesterol; TP, total protein; ALB, albumin. TABLE 1. Two-way ANOVA results for red blood cells indices of juveniles of red tilapia Oreochromis spp. cultured in sea water with biofloc and probiotics. Group Density System DensityxSystem EC 0.06 0.02 0.01 HB 0.00 0.28 0.00 PCV 0.00 0.13 0.00 MVC 0.00 0.25 0.03 MCH 0.27 0.01 0.72 MCHC 0.49 0.02 0.01 Values presented are significant when P < 0.05 from red tilapia cultured at low (114 fish/m3) and high (228 fish/m3) densities with biofloc (B) and probiotics (P). C were the control from each density without B and P. EC, total erythrocytes count; HB, hemoglobin; PCV, Packed cell volume; MCV, mean corpuscular volume; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration.
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