Effects of spirulina Spirulina platensis meal as a feed additive on growth performance and immunological response of Gangetic mystus Mystus cavasius

Abstract

The aim of this study was to investigate the effects of dietary Spirulina platensis supplementation on the growth and immunity of Mystus cavasius. Fish were fed on the experimental diets, where the fish meal was replaced with S. platensis meal at 0%, 2.5%, 5.0%, 7.5%, and 10% levels, respectively. Triplicate groups of fish were fed with each diet twice a day near satiation and reared for 10 weeks. After the trial, serum lysozyme levels, whole-body composition, feed utilization, growth performance, and blood characteristics were examined. The pathogenic Aeromonas hydrophila was administered intra-peritoneally to 10 fish from each group and monitored for daily mortality rate. Metagenomics analysis was used to investigate the gut microbiota. When more than 7.5% of fish meal in the diet was replaced with S. platensis meal, the body weight, and specific growth rate were higher than in the control diet. The protein efficiency and feed conversion ratio were also positively affected by dietary S. platensis meal supplementation. The replacement of 7.5–10% fishmeal with S. platensis increased the whole-body protein and ash contents more than the control. The red blood cells, white blood cells, hemoglobin, hematocrit, and mean corpuscular hemoglobin levels of M. cavasius rose when fish were fed 7.5–10% S. platensis compared with the control. The serum lysozyme test result showed an increase in the lysozyme value as dietary S. platensis supplementation was gradually increased. The abundance of bacterial composition was found to be higher with gradually increasing S. platensis supplementation, especially up to 5–10% supplementation level. The total mortality of fish was decreased with higher inclusion of S. platensis when challenged by A. hydrophila. These findings suggest that dietary S. platensis has positive effects on the growth and immune system of M. cavasius, and maintaining dietary replacement of 7.5–10% fish meal with S. platensis can be suggested for feed formulation of M. cavasius.