How Embryo Temperature Affects Young Salmon's Response to Bacterial Infections

Jim Crocker
20th November, 2024

How Embryo Temperature Affects Young Salmon's Response to Bacterial Infections

Following a bacterial challenge, the pathogen Yersinia ruckeri was localized in the gills of Atlantic salmon (Salmo salar) alevins from all embryonic temperature groups at 24 (a–c) and 72 hours (d–f), confirming a successful mucosal infection that resulted in temperature-dependent differences in survival and immune response.

Image adapted from: Malik et al. / CC BY (Source)

Key Findings

  • The study by Nofima AS examined how different embryonic temperatures affect the immune responses of Atlantic salmon alevins to bacterial infection
  • Salmon embryos reared at 4°C and 6°C had higher survival rates post-infection compared to those reared at 8°C
  • Lower embryonic temperatures enhanced the immune responses of salmon alevins, as indicated by distinct gene expression patterns and increased survival rates
Atlantic salmon (Salmo salar) are a critical species both ecologically and economically. Understanding how environmental factors, such as temperature, affect their immune responses is essential for effective management and aquaculture practices. A recent study by Nofima AS investigated the effects of embryonic temperature on the immune responses of Atlantic salmon alevins when challenged with the bacterial pathogen Yersinia ruckeri[1]. This research is particularly relevant given previous findings on the influence of temperature on fish physiology and immune function[2]. The study reared salmon embryos at three different temperatures: 4°C, 6°C, and 8°C, from fertilization until the eyed-egg stage. After hatching, the alevins were exposed to Yersinia ruckeri, and their survival rates and early immune responses were monitored. The results showed that alevins from the 4°C and 6°C groups had higher survival probabilities 72 hours post-infection compared to those from the 8°C group. This suggests that lower embryonic temperatures may enhance the resilience of salmon alevins to bacterial infections. Histopathological analysis revealed mild changes in the gills and skin across all temperature groups. Bacterial antigens were detected in the secondary lamellae of gills and the epithelial and basal layers of the skin, indicating that the pathogen was present in these tissues. The study also examined gene expression profiles to understand the immune responses at the molecular level. Notably, gelsolin (gsn) expression increased in the skin across all temperature groups at 72 hours post-infection, indicating a role in the immune response to infection. Interestingly, the study found distinct immune gene expression patterns between the low-temperature groups (4°C and 6°C) and the 8°C group. For example, claudin (cldn4) and collagen (col1a) were upregulated only in the skin of the 4°C group, while heat shock protein 70 (hspa1a) was downregulated in the gills of infected fish at 72 hours compared to controls. Additionally, toll-like receptor 13 (tlr13) expression increased in infected fish at 24 hours compared to controls, highlighting its potential role in early immune recognition of pathogens. These findings align with previous research showing that suboptimal temperatures can impair fish immune systems[2]. The study expands on this by demonstrating that lower embryonic temperatures can actually enhance certain immune responses, potentially through epigenetic mechanisms. This is consistent with earlier research on the epigenetic effects of temperature on muscle development and growth in Atlantic salmon[3]. The study also ties into previous work on the role of antimicrobial peptides, such as cathelicidins, in fish immune responses[4]. While the current study did not focus on cathelicidins specifically, the observed changes in gene expression and survival rates suggest that similar innate immune mechanisms may be at play in the alevins' response to bacterial infection. In conclusion, this study by Nofima AS highlights the importance of embryonic temperature in shaping the immune responses of Atlantic salmon alevins. By demonstrating that lower temperatures can enhance survival and modulate immune gene expression following a bacterial challenge, the research provides valuable insights for improving aquaculture practices and managing wild salmon populations. The findings underscore the need for further investigation into the complex interactions between environmental factors and fish immune function.

BiochemAnimal ScienceMarine Biology

References

Main Study

1) Embryonic Temperature Influences the Mucosal Responses of Atlantic Salmon Alevins to a Bacterial Challenge.

Published 19th November, 2024

https://doi.org/10.1007/s10126-024-10386-w

Related Studies

2) Impacts of Low Temperature on the Teleost Immune System.

https://doi.org/10.3390/biology6040039

3) Genetic background and embryonic temperature affect DNA methylation and expression of myogenin and muscle development in Atlantic salmon (Salmo salar).

https://doi.org/10.1371/journal.pone.0179918

4) Evidence of an antimicrobial-immunomodulatory role of Atlantic salmon cathelicidins during infection with Yersinia ruckeri.

https://doi.org/10.1371/journal.pone.0023417


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