Multispecies Probiotics Relieve High Temperature–Induced Growth Obstruction and Stress on Rohu ( <i>Labeo rohita</i> ) by Activating GH/IGF Axis

ABSTRACT Global warming is upsetting for aquatic species, and probiotic treatment may help to diminish its impacts. In order to counter the negative consequences of elevated temperature on growth and well‐being, rearing water of rohu ( Labeo rohita ) was supplemented with multispecies probiotics (1.0 mL/L). For 6 weeks, fingerlings weighing 10.08 ± 0.13 g were raised in triplicate at normal temperature (30°C) and higher temperatures (33°C and 36°C) with or without probiotics. Fish treated without probiotics showed substantial decreases in weight gain (WG) and specific growth rate (SGR) at 36°C in contrast to normal temperature (30°C). However, fish reared with probiotics showed enhanced WG and SGR at the highest temperature (36°C) compared to fish maintained without probiotics. In the group of fish supplemented with probiotics under high‐temperature conditions, haemoglobin levels increased while glucose levels decreased. The number of irregularities in cells and nuclei of erythrocytes was dramatically reduced in probiotic‐treated fish at 36°C. The relative mRNA level of three growth‐relevant genes (growth hormone, gh , in the pituitary; insulin‐like growth factor 1 and 2, igf‐1 and igf‐2 , in the liver) decreased with increasing temperature but rose after probiotic addition. Fish at 36°C revealed a notable upregulation regarding the expression of genes for stress‐associated heat shock protein 70 and 90 ( hsp70 and hsp90 ), whereas their expressions were lowered following probiotics administration. Considering as a whole, the addition of probiotics to water improved blood biochemistry and cellular structure of blood and increased the expression levels of GH and IGF which consequently relieved growth retardation and stress in rohu.