Investigating the Impact of Higher Acclimation Temperatures on Growth Process through the Expression of hsp70, hsp90 and ghrelin Genes in Nile Tilapia (Oreochromis niloticus)

Abstract

The physiological response, metabolic rate, and growth of aquatic organisms can be influenced solely by water temperature. To know the impact of increased acclimation temperatures governing the stress response, feed intake, and growth, juvenile Nile tilapia (Oreochromis niloticus) were acclimated to three different temperature conditions (31ºC, 34°C and 37°C) for a duration of 30 days. The quantitative real- time PCR method was used to quantify the relative expression levels of genes associated with heat shock proteins (HSPs) (hsp70 and hsp90) and ghrelin from the brain of Nile tilapia. The findings indicated a significant elevation in the expression of hsp70 in the brain of O. niloticus subjected to a temperature of 37ºC. The relative mRNA level of hsp90 mRNA in the brain of Nile tilapia was higher at 34°C and 37°C compared to the 31°C acclimation temperatures with no statistically significant differences among the three acclimation temperatures. In contrast, a lower expression of ghrelin in the brain was observed at higher acclimation temperature (37ºC) actuating lower feed intake and decreased appetite. Higher acclimation temperature (37ºC) also led to a reduction in weight gain (WG) and specific growth rate (SGR) with a significant increase in the blood glucose level. Conversely, an increase in WG and SGR was observed at 34ºC in contrast to fishes at 31ºC and 37ºC. The present study implies that a slight elevation in temperature can enhance the physiological processes and growth of juvenile O. niloticus and the higher acclimation temperature induces stress response, decrease appetite and hinder their overall growth performance.