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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING GREAT LAKES AQUACULTURE PRODUCTION Title: Acute handling disturbance modulates plasma insulin-like growth factor binding proteins in rainbow trout (Oncorhynchus mykiss)

Authors
item Shepherd, Brian
item Aluru, Neelakanteswar -
item Vijayan, Mathilikath -

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2010
Publication Date: April 1, 2011
Repository URL: http://handle.nal.usda.gov/10113/55690
Citation: Shepherd, B.S., Aluru, N., Vijayan, M. 2011. Acute handling disturbance modulates plasma insulin-like growth factor binding proteins in rainbow trout (Oncorhynchus mykiss). Domestic Animal Endocrinology. 40:129-138.

Interpretive Summary: Rainbow trout are an important aquaculture species and much is known about production parameters and how these affect important traits such as disease and growth. However, many routine production practices (cleaning, sorting, netting and handling) can adversely affect growth by influencing the stress response. The stress response is primarily mediated by cortisol (a steroid hormone), which can reduce levels of the hormones that control growth, mainly Insulin-like growth factor-I (IGF-I) which is stimulated by growth hormone (GH). IGF-I is released into the blood at which time it is bound to specific binding proteins called IGF-binding proteins (IGFBPs), which distribute and control the effects of IGF-I. Often, in culture situations, routine disturbances can be of a short duration, but the effects of brief stressors (less than 5 minutes) on the hormones that control growth have not been examined. To evaluate this, we subjected rainbow trout to a 5-minute netting and chasing disturbance. Following this disturbance, blood was taken from these animals and undisturbed controls at 0 (before disturbance), 1, 4, and 24 hours after stressor exposure. Cortisol levels peaked at 1 and 4 hours and then decreased to baseline levels at 24 hours after disturbance. Growth hormone levels were unaffected by the stressor, whereas levels of IGF-I were depressed at 1 and 4 hours post-disturbance. Four IGF-binding proteins were identified in the blood of rainbow trout. There was no effect of stressor, nor was there a daily pattern in undisturbed animals on the two smaller IGFBPs. By contrast, we found that levels of the larger IGFBPs decreased over the 24-hr sampling interval (a daily pattern) in the unstressed animals. However, this daily decrease was not present in the stressed animals. Instead, we found that the larger IGFBPs were generally elevated in response to stressor exposure. These findings suggest that short-term disturbances (similar to those routinely encountered in hatchery operations) impact hormones important to growth and well-being in rainbow trout.

Technical Abstract: The effects of acute stressor exposure on proximal (growth hormone; GH) and distal (insulin-like growth factor-I; IGF-I and IGF-binding proteins) components of the somatotropic axis are poorly understood in finfish. We exposed rainbow trout (Oncorhynchus mykiss) to a 5-minute handling disturbance to mimic an acute stressor episode, and measured levels of plasma GH, IGF-I and IGFBPs at 0, 1, 4 and 24-h post-stressor exposure. An unstressed group was also sampled at the same clock times (09:00, 10:00, 13:00 and 09:00) as the acute stress sampling to determine diel changes in the above somatotropic axis components. The acute stressor transiently elevated plasma cortisol and glucose levels at 1- and 4-h post-stressor exposure, while no changes were seen in the unstressed group {Aluru, 2006 #1932}. Plasma GH levels were not affected by handling stress or sampling time in the unstressed animals. Plasma IGF-I levels were significantly depressed at 1- and 4-h post-stressor exposure, but no discernible diel pattern was seen in the unstressed animals. Using a western ligand blotting technique, we detected plasma IGF-binding proteins (IGFBPs) of 21, 32, 42, and 50 kDa in size. The plasma levels of the lower molecular weight IGFBPs (21 and 32 kDa) were unaffected by handling stressor, and there was no discernible diurnal pattern in the unstressed animals. By contrast, the higher molecular weight (42 and 50 kDa) IGFBPs were affected by stress and/or time of sampling. Levels of the 42-kDa IGFBP levels significantly decreased over the sampling period in the unstressed control animals, but this temporal drop was eliminated in the stressed animals. Levels of the 50-kDa IGFBPs also decreased significantly over the sampling time in the unstressed trout, while handling disturbance transiently increased this IGFBP levels at 1 h but not at 4- and 24-h post-stressor exposure compared to the control group. Overall, our results suggest a role for the high molecular mass IGFBPs (42 and 50 kDa) in acute stress adaptation in trout.

Last Modified: 12/26/2014
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