Biotecnologia na aquicultura: efeitos da exposição crônica à temperatura fria sobre o crescimento, expressão de genes relacionados à ingestão de alimentos e imunidade de tilápias-do-Nilo (Oreochromis niloticus)

Abstract

Nile tilapia (Oreochromis niloticus) is the fourth most produced species in the world aquaculture scene. A particularity of this species is the need for water with a temperature above 16ºC for development and survival. Little is known about the effects of low temperature on genes related to food intake and the inflammatory response in this species. The present study provides information regarding the modulation of genes in tissues collected from the brain, liver, kidney and spleen when tilapia is exposed to low temperatures. Sixty animals were divided into two groups, where one remained at the optimum temperature (24ºC) and the other at a low temperature (15ºC), during an exposure period of 28 days. Biometric evaluations were performed before and after the experimental period. Blood samples were used to perform flow cytometry while brain, spleen, liver and kidney were collected, RNA was extracted, and qRT-PCR was performed. Lower final weight and specific growth rate were observed in the group exposed to low temperature. There was a 2-fold increase in Pyy gene expression and a 0.5-fold decrease in Npy and Cart genes, indicating that low temperatures modulate food intake genes. The coding genes for pro-inflammatory cytokines were modulated in the spleen, kidney and liver with higher expression of Il-1b and Tnfa genes and reduced expression of Il-8 and Nf-kb genes in the group exposed to 15ºC. Analyzes performed with blood cells revealed a lower level of membrane fluidity, DNA fragmentation and cell disruption were higher in the cold exposed group. The observed results suggest a reaction caused by the stress generated by the cold. The present work is important, as it brings new information about the well-being of tilapia exposed to low temperature. This, by elucidating molecular and cellular effects that occur in this condition, is a first step towards a better understanding of the management of this species, helping to find alternatives to deal with the impacts of cold on aquaculture.