Effect of water source and trout strain on expression of stress-affected genes in a commercial setting

Authors: Welker, Thomas; Overturf, Kenneth - Ken; Abernathy, Jason

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2018
Publication Date: 2/14/2018
Citation: Welker, T.L., Overturf, K.E., Abernathy, J.W. 2018. Effect of water source and trout strain on expression of stress-affected genes in a commercial setting. North American Journal of Aquaculture. 80(3):249-262. https://doi.org/10.1002/naaq.10028.
DOI: https://doi.org/10.1002/naaq.10028

Interpretive Summary: The majority of rainbow trout produced in the United States is in single pass, flow-through raceway systems with water being used multiple times before exiting into a quiescent zone. Water quality is initially determined by the source water (1st use) and is degraded as it moves through successive raceway passes. Stocking densities are typically high in these systems, which can also lower water quality by reducing dissolved oxygen (DO) and increasing particulate and dissolved material loads in effluent, which can adversely affect fish growth and elevate stress levels. We examined the effects of water from a commercial rainbow trout farm of varying quality (1st use [source spring], 3rd use [two raceway passes], and 5th use [four raceway passes]) on the physiological stress response (plasma cortisol levels), stress-affected gene expression (after 10 and 90 days), and growth (after 90 days only) in rainbow trout. Water quality, especially DO, turbidity, and total dissolved solids (TDS), was poorer in 5th use water, which corresponded to reduced growth, elevated stress, and differential gene expression (typically upregulated; regulator of G-protein signaling [REGPS], growth arrest and DNA-damage-inducible protein [GADD45a], glutathione peroxidase 1 [GPX1], and FK506-binding protein [FKBP2]). Superoxide dismutase [SOD] was down-regulated, and expression of catalase [CAT] was variable. Expression of most genes was also affected by the length of 5th use water exposure (10 vs. 90 days) but not trout strain. The uniformity of response of these genes makes them candidates as potential biomarkers for identification of adverse water quality conditions and for further understanding effects on rainbow trout performance in intensive culture systems.

Technical Abstract: Reduced water quality is a common problem in intensive fish culture that limits production and can affect fish mortality. In this study, two strains of juvenile rainbow trout (approximately 210 g initial weight) were exposed to 1st, 3rd, and 5th use water from raceways (the source spring and after two and four raceway passes) at a commercial rainbow trout farm for 90 days. Fish were sampled at 10 and 90 days post-stocking to examine the effect of water source on the stress response and stress-affected gene expression (gill, kidney, liver, and spleen). Water quality, especially dissolved oxygen, turbidity, and total dissolved solids, was poorer in 5th use water causing significantly lower growth performance and an elevated stress response in rainbow trout. All six “stress-affected” genes examined, superoxide dismutase (SOD), regulator of G-protein signaling (REGPS), growth arrest and DNA-damage-inducible protein (GADD45a), glutathione peroxidase 1 (GPX1), FK506-binding protein (FKBP2), and catalase (CAT; unchanged in gill and spleen), were differentially expressed as water quality deteriorated from 1st to 5th use water, and the length of exposure also affected expression of most genes. The uniformity of response of these genes to water quality stress makes them candidates as potential biomarkers for identification of stressful conditions and for further understanding effects on rainbow trout performance in intensive culture systems.