Uncoupling Thermotolerance and Growth Performance in Chinook Salmon: Blood Biochemistry and Immune Capacity.

Ronald Lulijwa,Andrea C Alfaro,Seumas P Walker,Tim Young,Natalí J Delorme,Jane E Symonds

doi:10.3390/metabo11080547

Abstract

Ocean warming and extreme sea surface temperature anomalies are threatening wild and domesticated fish stocks in various regions. Understanding mechanisms for thermotolerance and processes associated with divergent growth performance is key to the future success of aquaculture and fisheries management. Herein, we exposed Chinook salmon (Oncorhynchus tshawytscha) to environmentally relevant water temperatures (19–20 °C) approaching their upper physiological limit for three months and sought to identify blood biomarkers associated with thermal stress and resilience. In parallel, blood biochemical associations with growth performance were also investigated. Temperature stress-activated leukocyte apoptosis induced a minor immune response, and influenced blood ion profiles indicative of osmoregulatory perturbation, regardless of how well fish grew. Conversely, fish displaying poor growth performance irrespective of temperature exhibited numerous biomarker shifts including haematology indices, cellular-based enzyme activities, and blood clinical chemistries associated with malnutrition and disturbances in energy metabolism, endocrine functioning, immunocompetence, redox status, and osmoregulation. Findings provide insight into mechanisms of stress tolerance and compromised growth potential. Biochemical phenotypes associated with growth performance and health can potentially be used to improve selective breeding strategies.

Highlights

Chinook salmon (Oncorhynchus tshawytscha) are large anadromous fish native to North America and regions in the northwestern Pacific
The current study extends this research by investigating the influence of thermal stress on a targeted suite of 47 blood parameters with potential clinical significance, and their associations with highly divergent growth trajectories
A three-month thermal challenge at 19–20 ◦C resulted in 20% cumulative mortality and hampered the overall growth of surviving fish (Figure 1)

Summary

Introduction

Chinook salmon (Oncorhynchus tshawytscha) are large anadromous fish native to North America and regions in the northwestern Pacific. Valued for their high-quality fillet, global fishery landings peaked in the late 1980s, but have since declined markedly to less than 5000 tonnes in 2019 [1]. Salmon are reared only in the South Island of New Zealand where cooler water temperatures are more favourable. Sea surface temperatures (SSTs) around New Zealand have been rising at a rate of approximately 0.2 ◦C per decade over the past forty years, and end-of-century forecasts predict a 1.1–2.5 ◦C increase above the current average [2,3]. Plasticity in thermotolerance and growth performance is well documented among fishes [13], which affords an optimistic outlook to build potential thermotolerance into New Zealand’s Chinook salmon stocks

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