In higher vertebrates, Tripartite Motif (TRIM) proteins modulate the immune response by coordinating processes related to inflammation such as antiviral restriction, autophagy and inflammasome activation. In fish, TRIM proteins have been reported mainly in cyprinids (e.g., carp—Cyprinus carpio and zebrafish—Danio rerio) and salmonids (i.e., rainbow trout—Oncorhynchus mykiss). However, their molecular mechanisms and functions are still being described in aquatic animals. Thus, our study focused on characterizing novel TRIM proteins involved in the innate immunity of gill cells from rainbow trout (RTgill-W1 and primary cultures) stimulated with lipopolysaccharide (LPS) or polyinosinic–polycytidylic acid (poly I:C). Furthermore, an in vivo experiment with rainbow trout was performed to detect TRIM proteins after the challenge with Flavobacterium psychrophilum (a major bacterial pathogen affecting Chilean salmonid industry). In vitro results showed that OmTRIM25 triggered an LPS-induced expression of pro-inflammatory cytokines such as TNF-α2 and IL-1β. Moreover, in the fish experiment, OmTRIM25 and finTRIM2 were up-regulated in the gills two days post-infection (dpi), whereas IL-1β and TNF-α2 had a higher gene expression at four and six dpi, respectively. To investigate the immunological role of OmTRIM25, a gene silencing strategy using RNA interference (RNAi) was used, confirming the immunomodulatory function of OmTRIM25.

Chilean salmon farming still suffers from high mortality rates due to Salmonid Rickettsial Septicemia (SRS) caused by Piscirickettsia salmonis genogroups (LF-89 and EM-90). To modulate fish immunity against bacterial pathogens (without compromising host growth), we investigated the bioactive properties (e.g., iron-chelating or antioxidant activity) of sixteen peptides that were pre-selected from public databases and chemically synthesized following an Fmoc strategy. Then, prior to a four-week small-scale experiment with pre-smolts Atlantic salmon (Salmo salar), two synthetic peptides were chosen based on DPPH-radical scavenging activity, oxygen radical absorbance, antioxidant or iron-chelating function, as well as the modulation of immune-related biomarkers (e.g., ifny, nlrc3, il1b) in RTS11 cells or head kidney leukocytes (HKLs) from rainbow trout (Oncorhynchus mykiss). Peptides (p4426: antioxidant; p4429: iron-chelating) were microencapsulated and added (at 150 μg kg^-1) into a commercial-like diet (CD) to produce three other experimental feeds (AD: antioxidant, ID: iron-chelating, AID: p4426 and p4429 at equal concentration). After four weeks of feeding, data showed that fish's body weight and length increased with ID and AID diets (compared to CD), while ID also increased the number of red blood cells per mL. Furthermore, HKLs from fish fed synthetic peptides and stimulated with protein extracts of P. salmonis genogroups (LF-89, EM-90 or a mixture of both) modulated innate immune biomarkers such as chemokine il8 and effector molecules (i.e., arg1, sod1), compared to CD group. Therefore, the use of microencapsulated peptides with iron-chelating or antioxidant activities should be explored as potential feed additives to strengthen host immunity against P. salmonis.

Global aquaculture faces increasing threats from declining oxygen levels, with several key aquaculture regions now classified as hypoxic. The gills, responsible for oxygen uptake, pathogen-sensing, and immune responses, are the primary interface for this stress. However, the comparative effects of different hypoxic regimes on the gill resilience of Atlantic salmon (Salmo salar) remain poorly understood. In this study, Atlantic salmon were exposed during a 7-day trial to two different moderate hypoxic stress models, chronic hypoxia and cyclic hypoxia. A whole-genome oligo-microarray revealed that both hypoxic stress regimes cause transcriptomic shifts, driven in the chronic hypoxia group by upregulation of PRRs and other immune components and downregulation of DNA repair and cell cycle maintenance. On the other hand, the cyclic hypoxic group focused on physiological plasticity and rapid cellular adjustments. Additionally, RT-qPCR was used to evaluate key gene expression of hypoxia and immune response. The chronic hypoxia group was characterized by downregulation of hif2a, gshpx, and gr-anx1 signaling, with a continuous upregulation state of tnfa2, suggesting an unresolved inflammatory state, often associated with apoptosis and gill damage. In contrast, the cyclic hypoxia group displayed an increased epo expression and recovery of antioxidant enzymes (e.g., gsphx), accompanied by normalized levels of tnfa2 at the end of the 7-day trial. Therefore, chronic hypoxic stress imposes a significantly higher burden on the gills of Atlantic salmon than cyclic hypoxic stress, compromising their ability to respond to secondary stressors and impairing immune homeostasis.