Aquaculture America 2020

February 9 - 12, 2020

Honolulu, Hawaii

DIFFERENTIAL REGULATION OF HYPOXIA RESPONSIVE GENES IN ATLANTIC SALMON SUBJECTED TO LOW OXYGEN STRESS DURING EARLY DEVELOPMENT

Erik Burgerhout* ,  Tara Kelly, Nicholas Robinson, Helge Tveiten,  Erica Leder, Hanne Johnsen
 
Nofima AS
Muninbakken 9-13,
9019 Tromsø, Norway
 erik.burgerhout@nofima.no
 

During the on-growth phase in sea cages, Atlantic salmon are subjected to a large variability in dissolv ed oxygen  (DO)  concentration.  Low  DO concentrations are known to limit food utilization , growth,  production performance and welfare, and may contribute to  some of the mortalities observed at sea.  The environment (e.g. temperature, oxygen, photoperiod) during an organism's embryonic development can shape its phenotype at later life stages, through modifications in the epigenetic machinery.  The aim of the present study was to determine the effects of different DO levels during early  ontogeny on the transcriptomic and methylomic profiles in later life stages.

Until start feeding, salmon eggs and larvae were subjected to 30%, 60% and 100% DO levels.  Development was  monitored based on embryonic stages.  Whole embryos and l arvae were sampled  at consecutive time points to investigate differential gene expression and  DNA methylation using qPCR and RNA-sequencing, and  pyrosequencing and  Reduced Representative Bisulfite Sequencing (RRBS), respectively.

Growth was affected especially in the 30% DO group, such that the occurrence of s tart feeding was delayed ca. 8 days  compared  with the 60% and 100% DO groups.  The 60% and 100%  showed no  clear differences with regard to development and growth, suggesting that 60%  DO  may  not visibly affect larval development. However, on the molecular level clear differences were observed between all groups . Preliminary data shows that b etween the three groups, 69 genes were differentially expressed , and had biological functions relating to, for example, oxygen transport (e.g. haemoglobin subunits),  and  major energetic metabolic processes (e.g. cytochrome c oxidase, p450 subunits).

Further, t he expression  levels  of prolyl hydrogenase-domain (PHD ) genes,  which are  essential  regulators in  maintaining  oxygen homeostasis , were  significantly increased with decreasing oxygen levels . Moreover, t wo putative CpG sites in the promoter of PHD 3 were found differentially methylated and showed a negative correlation with its expression.  It is hypothesized  that through  the  inhibitory effects of these PHD  genes on hypoxia inducible factor (HIF) the potentially harmful effects of hypoxia may be reduced during early development.