Effects of temperature and photoperiod on rainbow trout (Oncorhynchus mykiss) smoltification and haematopoiesis

Bernat Morro,Pablo Balseiro,Amaya Albalat,Simon Mackenzie,Cindy Pedrosa,Tom O Nilsen,Shotaro Suzuki,Munetaka Shimizu,Harald Sveier,Marnix Gorissen,Lars O.E Ebbesson,Sigurd O Handeland

doi:10.1016/j.aquaculture.2019.734711

Abstract

• nkaα1a , nkaα1b and nkcc1a provide relevant information that the NKA activity does not reflect. • While nkaα1a and nkcc1a transcription are mainly regulated by temperature, nkaα1b is regulated mainly by photoperiod. • High water temperature could potentially compromise the adaptive and innate immune response of rainbow trout. • Increased water temperature (8 °C) during winter does not provide clear advantages for smoltification or size at harvesting.

Highlights

Most freshwater fish would not be able to cope with the osmotic stress intrinsic to seawater, quickly dehydrating and dying, and so are bound to freshwater ecosystems (Quinn et al, 2016)
Once anadromous salmonids reach a threshold size (Kendall et al, 2015), smoltification is triggered by environmental cues, such as changes in photoperiod, water temperature and salinity, which in turn alter the pituitary, thyroid and inter-renal tissues (Prunet et al, 1989)
NKA α-subunit isoform 1a (NKAα1a) is a freshwater pump present in lamellar chloride cells, the function of which is to generate a hyper-osmotic gradient that results in ion uptake, and is highest during the parr stage of the fish

Summary

Introduction

Most freshwater fish would not be able to cope with the osmotic stress intrinsic to seawater, quickly dehydrating and dying, and so are bound to freshwater ecosystems (Quinn et al, 2016). Once anadromous salmonids reach a threshold size (Kendall et al, 2015), smoltification is triggered by environmental cues, such as changes in photoperiod, water temperature and salinity, which in turn alter the pituitary, thyroid and inter-renal tissues (Prunet et al, 1989) These tissues are key orchestrators of many biochemical (e.g. haemoglobin, Fyhn et al, 1991), physiological (e.g. increased metabolism, Björnsson et al, 2011), morphological (e.g. dark and rounded to silvery and streamlined, Winans and Nishioka, 1987) and behavioural changes (e.g. bottomdwelling, aggressive and territorial to pelagic, schooling and downstream migrating, McCormick et al, 1998; Riley et al, 2014), all designed to improve seawater performance and survival. If the fish do not reach seawater during the smolt window, these changes are lost in the process known as desmoltification (Stefansson et al, 1998)

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