Red blood cell indices for rainbow trout (Oncorhynchus mykiss Walbaum) reared in cage and raceway culture

Abstract

In this study, 161 immature female rainbow trout of weight 331 ± 30 g, raised in cage culture 291 m above sea level at water temperature 17 ± 3°C, were used to calculate reference (physiological) haematology values for red blood cell indices. Red blood cell counts (RBCc), haematocrit values (Hct), haemoglobin concentrations (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were measured and analyzed. The calculated intervals of the reference ranges between the lower and upper quantiles were: RBCc 0.87-1.34 T·l-1, Hct 0.36-0.554, Hb 64-107 g·l-1, MCV 347-501 fl, MCH 60-92 pg and MCHC 0.15-0.21. Multiple correlation indices obtained from cage culture fish to determine effects of time (Day), water temperature (WT), dissolved oxygen (O2), oxygen saturation level of the water (OSW), chemical oxygen demand (CODMn), biological oxygen demand (BOD5) and NH4+ were the following: RBCc was explained by Day and QOSW with coefficient of correlation r = 0.611, Hb was explained by QBOD5 and QNH4+ with correlation r = 0.783 and MCHC was explained by CODMn, QDay and QO2 with correlation r = 0.743. Fish from cage culture had significantly greater red blood cell indices (P = 0.01 and P = 0.0000, respectively) than fish from flow-through tanks 651 m above sea level, water temperature 9 ± 2.5°C and equal nutrition. The results have shown that fish farming technology, varying physical and chemical properties of water and availability of natural food may influence erythropoiesis in caged fish.