The influence of water temperature on the immune function of Nile tilapia (Oreochromis niloticus) when challenged with Saprolegnia parasitica

Crynodeb

Disease results in large production losses within fish farming worldwide, estimated to cost aquaculture production $6 billion (USD) per year. Saprolegniasis is one example of an infectious disease that impacts the culture of important production species, including tilapia. Unfortunately, control options for saprolegniasis are extremely limited, so understanding the mechanisms behind disease outbreaks is increasingly important. Consistent with reports of
saprolegniasis outbreaks in tilapia aquaculture, an infection challenge study showed juvenile Nile tilapia (Oreochromis niloticus) are more susceptible to Saprolegnia parasitica infection when housed at sub-optimal temperatures (19 and 23°C) compared to optimal production temperature (27°C). Although it is widely accepted that temperature influences teleost physiology, including immune function, knowledge on the mechanisms underpinning increased saprolegniasis susceptibility during cold-weather remains limited. Whole transcriptome and DNA methylation analyses (Reduced Representation Bisulphite Sequencing) of tilapia skin samples 24 hours post-infection challenge revealed differential gene expression and methylation between S. parasitica infected and sham-control tilapia housed at 19 and 27°C. An extensive differential gene expression response was identified in S. parasitica infected tilapia challenged at 19°C, including strong upregulation of numerous pro-inflammatory genes. Consistent with previous studies exploring fish gene expression response to saprolegniasis, a downregulation of Major Histocompatibility Complex class II components was identified in infected tilapia. A greater degree of suppression was detected in tilapia challenged at 19°C relative to 27°C, suggesting that at lower temperatures tilapia may be more vulnerable to the potential immunosuppressive actions of S. parasitica. Furthermore, a multi-omics approach integrating both transcriptomic and methylation data revealed a number of temperature and or infection-driven CpG methylation changes that were correlated with gene expressions. These included a number of genes predicted to code for immune-related transcription factors which may underpin tilapia’s increased susceptibility to saprolegniasis when housed at sub-optimal temperature.

Dyddiad Dyfarnu	2019
Iaith wreiddiol	Saesneg
Sefydliad Dyfarnu	Prifysgol Aberystwyth
Goruchwyliwr	Paul Shaw (Goruchwylydd) & Peter Brophy (Goruchwylydd)