The synergistic interaction of thermal stress coupled with overstocking strongly modulates the transcriptomic activity and immune capacity of rainbow trout (Oncorhynchus mykiss)

Abstract

The objective of the present study is to identify and evaluate informative indicators for the welfare of rainbow trout exposed to (A) a water temperature of 27 °C and (B) a stocking density of 100 kg/m3 combined with a temperature of 27 °C. The spleen-somatic and condition index, haematocrit and the concentrations of haemoglobin, plasma cortisol and glucose revealed non-significant differences between the two stress groups and the reference group 8 days after the onset of the experiments. The transcript abundance of almost 1,500 genes was modulated at least twofold in in the spleen of rainbow trout exposed to a critical temperature alone or a critical temperature combined with crowding as compared to the reference fish. The number of differentially expressed genes was four times higher in trout that were simultaneously challenged with high temperature and crowding, compared to trout challenged with high temperature alone. Based on these sets of differentially expressed genes, we identified unique and common tissue- and stress type-specific pathways. Furthermore, our subsequent immunologic analyses revealed reduced bactericidal and inflammatory activity and a significantly altered blood-cell composition in challenged versus non-challenged rainbow trout. Altogether, our data demonstrate that heat and overstocking exert synergistic effects on the rainbow trout’s physiology, especially on the immune system.

Catastrophic mass mortalities caused by Photobacterium damselae affecting farmed marine fish from Deeba Triangle, Egypt

“…Antibiogram of the retrieved bacterial isolates tidal force for water exchange. In the current research, diminished dissolved oxygen, high water temperatures inconsistently high salinity and remarkably high ammonia concentration together with other erratic managerial issues have staggeringly jeopardized the fish integumentary and systemic immune barriers (Eissa et al, 2013;Rebl et al, 2020). Such structural and functional breakdown of the fish immune barriers have facilitated intense invasion with ubiquitous (Vibrio spp.)…”

Blood Will Tell: What Hematological Analyses Can Reveal About Fish Welfare

“…An initial test for assessing immunocompetence is to record the bacterial growth rate in blood plasma from treated vs. control fish (173)(174)(175)(176). For example, the growth of the bacterium Aeromonas salmonicida after a 24-h incubation was significantly enhanced in plasma from O. mykiss with impaired immune capacity due to the exposure to high temperature coupled with crowding (177). By contrast, the non-stressed fish clearly showed potent bactericidal mechanisms that depended mainly on the concentration of a range of immunocompetent macromolecules known as humoral factors.…”

Uncoupling Thermotolerance and Growth Performance in Chinook Salmon: Blood Biochemistry and Immune Capacity

“…The limited influence of temperature on activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lipase (LIP) enzymes suggests that the chronic thermal regime applied was unlikely associated with liver, bone, or pancreatic damage in surviving fish (Figure 3A: 10-12). Low thermal impact on numerous other plasma proteins (Figure 3A: [13][14][15][16]) and metabolites (Figure 3B: 5-12) indicate robust homeostatic regulation of various physiological processes.…”

“…20%) over the 2017/2018 and 2018/2019 austral summers due to unprecedented SSTs reaching 2-5 • C above the species' preferred upper threshold (17 • C) where peak health and growth can be maintained [6][7][8][9]. Temperaturestressed salmon generally have increased metabolic rates and somatic maintenance costs, grow slower with lower condition factors, have suppressed appetite, experience reproductive issues, display compromised immunity, and exhibit increased sensitivity to other stressors [10][11][12][13][14]. However, plasticity in thermotolerance and growth performance is well documented among fishes [13], which affords an optimistic outlook to build potential thermotolerance into New Zealand's Chinook salmon stocks.…”