Transcriptomic response to parasite infection in Nile tilapia (Oreochromis niloticus) depends on rearing density

Abstract

BackgroundCaptive animal populations, be it for food production or conservation programmes, are often maintained at densities far beyond those in natural environments, which can have profound effects on behaviour, immune and stress levels, and ultimately welfare. How such alterations impact transcriptional responses to pathogen infection is a ‘different kettle of fish’ and remains poorly understood. Here, we assessed survival and gene expression profiles of infected fish reared at two different densities to elucidate potential functional genomic mechanisms for density-related differences in disease susceptibility.ResultsUtilising a whole-transcriptome sequencing (RNAseq) approach, we demonstrate that rearing density in tilapia (Oreochromis niloticus) significantly impacts susceptibility to the oomycete Saprolegnia parasitica, via altered transcriptional infection responses. Tilapia held at low densities have increased expression of genes related to stress, likely due to increased aggressive interactions. When challenged with Saprolegnia, low-density fish exhibit altered expression of inflammatory gene responses and enhanced levels of adaptive immune gene suppression compared to fish reared at higher density, resulting in significantly increased mortality rates. In addition, Saprolegnia infection substantially perturbs expression of circadian clock genes, with fish reared at low-density having higher levels of molecular clock dysregulation.ConclusionsOur results reveal the wide-scale impact of stocking density on transcriptional responses to infection and highlight the need to incorporate circadian biology into our understanding of disease dynamics in managed animals.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-5098-7) contains supplementary material, which is available to authorized users.

Acting locally - affecting globally: RNA sequencing of gilthead sea bream with a mild Sparicotyle chrysophrii infection reveals effects on apoptosis, immune and hypoxia related genes

“…To our knowledge, only one microarray study is available in the literature on the host response against a monogenean [33]. Thus far, RNA-seq has been used only recently to analyse the host reaction against some fish parasites [34][35][36][37][38] and no transcriptomic study on the response against a polyopistocothylean has been performed. Therefore, the current study on the reaction of GSB to S. chrysophrii is the first comprehensive transcriptomic analysis of a polyopistocothylean infection.…”

Social Behavior and Welfare in Nile Tilapia

“…There are several studies regarding the effects of stocking density on the Nile tilapia production, but only a few suggesting the effects of social behavior, although they do not quantify aggressive interactions. For instance, according to Ellison et al [48], Nile tilapia reared at low stocking densities (fry LD = 94 individuals at 1.5 kg m −3 vs. fry HD = 366 individuals at 6 kg m −3 ) have an increased expression of genes related to stress which is likely due to increased aggressive interactions; moreover, they are more susceptible to the consequences of infection by Saprolegnia parasitica, and have higher mortality rates. Overall, these authors showed that Nile tilapia reared at low densities have a higher susceptibility to negative effects than those reared at higher densities.…”

The Complex Interplay of Parasites, Their Hosts, and Circadian Clocks

“…Knowledge of the effect of Leishmania infection on host clocks is even scarcer: the only study that has addressed this question showed that L. amazonensis does not alter melatonin levels or rhythms in hamsters up to 21 days post infection (Laranjeira-Silva et al, 2015). A manipulation of clock mechanisms may also occur in fish: in a transcriptomic analysis of Nile tilapia infected with Saprolegna parasite vs. non infected controls, one of the most prominent category of modified genes was that of clock genes and regulators (Ellison et al, 2018).…”