Abstract
The quality and relative amounts of dietary lipids may affect the health and growth of cultured Atlantic salmon. So far, little is known about their effects on the performance of the fish immune system during early life stages and, in particular their importance in the transition from endogenous nutrition (yolk) in the alevin stage to exogenous nutrition in the later fry stage. We investigated the immunomodulatory effects of fish oil, vegetable oil and phospholipid-rich oil in feeds for farmed Atlantic salmon using a transcriptomic approach. The experiment allowed a fine-scale monitoring of gene expression profiles in two tissues, the pyloric caeca of the intestine and the liver, in a 94 days-long first feeding experiment. The analysis of transcriptional profiles revealed that first feeding induced a strong immunomodulation in the pyloric caeca after 48 days of feeding, lasting up to day 94 and possibly beyond. On the other hand, the differential effect of the three dietary regimes was negligible. We interpret this upregulation, undetectable in liver, as a potentiation of the immune system upon the first contact of the digestive system with exogenous feed. This process involved a complex network of gene products involved in both cellular and humoral immunity. We identified the classical pathway of the complement system, acting at the crossroads between innate and adaptive immunity, as a key process modulated in response to the switch from endogenous to exogenous nutrition.
Highlights
The feeding regime in fish farming is a crucial factor in ensuring the health of animals and improving the quality of product for human nutrition
Vegetable oil is devoid of LC-PUFA, but often contains high amounts of linoleic acid (LNA) or alpha-linolenic acid (ALA)-rich, which serve as sources of n-6 and n-3 fatty acids, respectively[4]
Several studies are concordant in supporting the use of feed supplements as nutraceuticals in fish aquaculture, due to their ability to modulate the immune system since the early life stages[15], The Atlantic salmon has been the subject of extensive studies on the effects of nutrients intake and frequency of feeding on the innate immune response[7,9,16]
Summary
The feeding regime in fish farming is a crucial factor in ensuring the health of animals and improving the quality of product for human nutrition. Several studies have pointed out that the quality of diet, in terms of phospholipid and fatty acid (FA) contents, may have important effects on the immune response of fish This can be conveniently tracked by investigating the modulation of expression profiles of immune genes[7,8,9]. The biological interpretation of gene expression data in the context of feeding is not straightforward, as the intensity and significance of modulation depends on various factors These include dietary ingredients, the duration of the experimental study, as well as the species, developmental stages and tissues studied[10,11,12,13] and, crucially, the effects on gut microbiota[14]. It can serve as a reference for transcriptome profiling, with a broad range of applications[27,28,29,30,31]
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