Effects of transportation stress and addition of salt to transport water on the skin mucosal homeostasis of rainbow trout (Oncorhynchus mykiss)

Abstract

Transportation of live fish is a common practice among aquaculture facilities. Many studies have previously reported how transport elicits physiological stress responses and increases disease susceptibility in farmed fish. The aim of this work is to investigate the changes that the skin of rainbow trout (Oncorhynchus mykiss) experiences due to stress. Since NaCl is commonly added to transport water as a stress mitigator, the effects of salt addition on the skin mucosa and skin-associated bacteria were also examined. Three experimental groups (Control, post-transport no salt (PTNS) and post-transport with salt (PTS)) were analyzed in a 5-hour transport acute stress model. Results indicate that the skin mucosa and the skin-associated bacteria are affected by transport stress. Total numbers of culturable skin-associated bacteria increased by ~10-fold and ~50-fold in the PTS and PTNS groups, respectively. Compared to controls, MUC2 expression was increased by 5-fold and 2-fold in the PTNS and PTS groups, respectively. Claudin-7, 8d and 12 expression levels were higher in both PTNS and PTS groups whereas antimicrobial peptide gene expression was lower than controls. Expression of the anti-inflammatory cytokine TGF-β but not IL-1β, IL-6 and TNF-α was up-regulated 2-3 fold in both the PTS and PTNS groups. The addition of salt diminished some of the physiological responses measured including the numbers of skin-associated bacteria. The responses recorded here appeared to be efficient at controlling bacterial translocation since stress did not lead to significant presence of bacteria in the liver or spleen of rainbow trout. When examining the ability of skin mucus to inhibit or promote growth of the bacterial pathogen Vibrio anguillarum, the skin mucus of PTS trout was more efficient at inhibiting V. anguillarum growth (20% inhibition) compared to control or PTNS mucus (11-12% inhibition). Our data clearly indicate the skin and skin microbiota of rainbow trout undergo important physiological responses during stress. The reduction in the magnitude of the skin responses recorded when salt was added to the transport water explains a new mechanism by which salt is an effective stress mitigator in some fish species. Aquaculture specialists will benefit from the present study by taking into consideration the importance of skin health during live transport.

Effect of temperature and diet on wound healing in Atlantic salmon (Salmo salar L.)

“…*Transcription levels significantly different than those observed at time 0 (p \ 0.05) for each diet (different colour code) Fish Physiol Biochem dynamics. It is known that stress leads to changes in mucous cell production in teleost skin (Tacchi et al 2015;Esteban 2012;Vatsos et al 2010), and a variation in mucous cell coverage in the epidermis related to temperature has been described for salmon (Jensen et al 2014). Increased production and hypertrophy of mucous cells is also described as a response to ecto-parasitism attacks in fish (Fast et al 2002a;Nolan et al 1999).…”

Influence of native catfish mucus on Flavobacterium columnare growth and proteolytic activity

“…In another host–pathogen system, Tacchi et al. () documented an alteration of mucosal homoeostasis in stressed rainbow trout ( Oncorhynchus mykiss ) skin showing a fivefold increase in Muc‐2 activity and subsequent decrease in antimicrobial activity against Vibrio anguillarum in vitro. Although we used mucus collected from apparently healthy fish, the importance of stress and mucosal immune homoeostasis in F. columnare disease has been suggested (Liu, Li, Su, Beck, & Peatman, ; Shoemaker & LaFrentz, ).…”

Methodological issues affecting the study of fish parasites. I. Duration of live fish storage prior to dissection

“…Ectoparasite abundance, and especially that of ciliates and monogeneans, is dependent on the environmental conditions of their hosts (Lester 1990). Stress suffered by fish during sampling, transport and holding can induce the release of catecholamines and corticosteroids and increase glucose levels in blood, which influences skin mucosal homeostasis (Pottinger 2008, Pankhurst 2011, Tacchi et al 2015. Skin epithelium and mucous secretions are passive physical barriers and form part of a fish's innate protective mechanism (Davis et al 2002).…”