Immune and stress regulation under light and dark conditions in both central neuroendocrine and peripheral tissues of gilthead seabream (Sparus aurata L.) after vaccination

Circadian rhythms are present in all living organisms, participating in many physiological regulations including immune, stress and anti-oxidant responses. However, in fish the mutual influences between immune and circadian systems, either in wild or farmed scenarios, are still poorly analyzed. In farmed fish, vaccination strategies rely on memory immune responses to elicit a secondary boosted response to a previous immunisation, and, in doing so, may induce mild stress on fish associated to husbandry procedures, but also to species-specific circadian patterns of activity. Here we aim to elucidate the effects of diurnal vs. nocturnal vaccination on the short-term (1, 6, and 24 h) responses of immune-, stress-, oxidative and circadian-related transcripts and biochemical markers in several lymphoid and metabolic organs of gilthead seabream (Sparus aurata L.), a widespread commercial fish species. Immune responses after vaccination were generally evoked to an extensive degree in all tissues tested including brain, pituitary, head kidney, spleen, liver and intestine. The immune responses presented tissue-specific patterns, but intestine showed higher alterations in day- than in night-vaccinated fish. In terms of the responses, stress markers were moderately modulated, but a significant down-regulation of antioxidant genes were observed in most immune tissues after vaccination. The expression of genes related to circadian clock function were suppressed in almost all tissues, but much more extensively in the peripheral tissues, especially in liver, and lymphoid organs (head kidney and spleen).