Temperature affects settlement success of ectoparasitic salmon lice (Lepeophtheirus salmonis) and impacts the immune and stress response of Atlantic salmon (Salmo salar)

Abstract

In this study, the effect of temperature on Atlantic salmon (Salmo salar) stress and immune response to the ectoparasitic salmon lice (Lepeophtheirus salmonis) was investigated. We found that infestation affected the expression of several immune and wound healing transcripts in the skin especially at the site of lice attachment compared to un‐infested control fish. Moreover, expression patterns in the skin of infested fish suggest that host immune responses towards salmon lice are impaired at low temperatures. However, reduced lice infestation success and survival at the lowest investigated temperatures suggest that cold water temperatures are more detrimental to the lice than their fish hosts. Finally, temperature affected the stress response of the fish and infected fish had a higher increase in cortisol levels in response to handling (a stressor) than un‐infested controls.

Repeated exposure affects susceptibility and responses of Atlantic salmon (Salmo salar) towards the ectoparasitic salmon lice (Lepeophtheirus salmonis)

“…Most differential gene expression was observed in the skin at the site of lice attachment, while much fewer transcriptional changes were observed at non-lice sites. Hence, lice infection tended to result in more local than systemic immune responses in the skin of salmonids, confirming earlier findings (Øvergård et al ., 2018; Dalvin et al ., 2020; Ugelvik et al ., 2022). Considering that salmon lice are ectoparasites in contact with the host only at the attachment site is unsurprising.…”

“…Here we address this question using the salmon louse ( Lepeophtheirus salmonis ), an ectoparasite of salmonid fishes. Infection with the parasite causes a well-described immune response in the skin also in susceptible species such as Atlantic salmon ( Salmo salar ) and rainbow trout ( Oncorhynchus mykiss ) (Braden et al ., 2015; Dalvin et al ., 2020; Ugelvik et al ., 2022; Ugelvik and Dalvin, 2022; Øvergård et al ., 2023). Salmon lice display aggregation on wild Atlantic salmon hosts in the northern Atlantic Ocean (Jacobsen and Gaard, 1997; Torrissen et al ., 2013).…”

A Review of Factors Affecting Farmed Atlantic Salmon (Salmo salar) Welfare in Australia and Beyond

“…Conversely, ultraviolet light has been shown to suppress the reproduction of sea lice, albeit to the detriment of salmon health (Barrett et al 2020a). Temperature mediates salmon-parasite relationships, with lower ambient temperatures perhaps affecting sea lice more than salmon (Ugelvik et al 2022). The most obvious negative temperature effects on fish welfare are found following delousing at high temperatures, e.g., ≥28 °C (Nilsson et al 2019), suggesting such parasite control approaches need to be re-evaluated in the context of welfare (Nilsson et al 2023).…”

Louse‐induced mortality thresholds in Atlantic salmon of wild‐origin

“…Grazing of the epidermis can cause wounds leading to secondary infections and osmoregulatory issues, and louse infections may affect the immunological capabilities of the fish (Barker et al, 2019; Llewellyn et al, 2017; Øvergård et al, 2023; Ugelvik & Dalvin, 2022; Wootten et al, 1982). Salmonids display a range of responses toward this parasite but many, including all the Atlantic species, have a limited immunological response toward the parasite resulting in low rates of clearance (Braden et al, 2017; Dalvin et al, 2020; Fast et al, 2002; Jones, 2011; Ugelvik et al, 2022). Meanwhile, the effects of sublethal infections, which have implications especially for the fitness of wild individuals, such as reduced growth and condition (Fjelldal et al, 2022; Susdorf, Salama, Todd, et al, 2018), indirect delayed maturation (Vollset et al, 2014), reduced growth of reproduction organs in mature males (Fjelldal et al, 2022), reduced swimming performance (Bui et al, 2016; Wagner et al, 2003), stress tolerance, and maturation timing remains under‐scrutinized.…”