RNA profiling identifies novel, photoperiod-history dependent markers associated with enhanced saltwater performance in juvenile Atlantic salmon.

Marianne Iversen,Børge Gellein Blikeng,Even Hjalmar Jørgensen,David Hazlerigg,Teshome Mulugeta,Simen Rød Sandven,Alexander Christopher West

doi:10.1371/journal.pone.0227496

Marianne Iversen, Børge Gellein Blikeng + Show 5 more

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https://doi.org/10.1371/journal.pone.0227496

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Abstract

Atlantic salmon migrate to sea following completion of a developmental process known as smolting, which establishes a seawater (SW) tolerant phenotype. Smolting is stimulated by exposure to long photoperiod or continuous light (LL) following a period of exposure to short photoperiod (SP), and this leads to major changes in gill ion exchange and osmoregulatory function. Here, we performed an RNAseq experiment to discover novel genes involved in photoperiod-dependent remodeling of the gill. This revealed a novel cohort of genes whose expression rises dramatically in fish transferred to LL following SP exposure, but not in control fish maintained continuously on LL or on SP. A follow-up experiment revealed that the SP-history dependence of LL induction of gene expression varies considerably between genes. Some genes were inducible by LL exposure after only 2 weeks exposure to SP, while others required 8 weeks prior SP exposure for maximum responsiveness to LL. Since subsequent SW growth performance is also markedly improved following 8 weeks SP exposure, these photoperiodic history-dependent genes may be useful predictive markers for full smolt development.

Highlights

In anadromous salmonids, the transformation of freshwater resident juvenile fish into a migratory form which will migrate downstream migration and enter the sea is known as smoltification or smolting
The LL group maintained this capacity for hypo-osmoregulation throughout the experiment
Fish that were transferred to short photoperiod (SP) lost their osmoregulatory capacity by day 32, but underwent a partial recovery when exposure to SP conti nued to the end of the study

Summary

Introduction

The transformation of freshwater resident juvenile fish (parr) into a migratory form (a smolt) which will migrate downstream migration and enter the sea is known as smoltification or smolting. Smolting entails a complex combination of physiological and behavioural changes, critical amongst which is the acquisition of the ability to efficiently maintain water and ionic balance upon entering the sea [1, 2]. In natural systems smolting is stimulated by the increasing day length (photoperiod) in spring, causing a cascade of physiological responses mediated by changes in circulating. Photoperiodic history affects novel smolt-markers and quality and analysis, decision to publish, or preparation of the manuscript

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