Early Life Stages Of Rainbow Trout Research Articles

Exploring Yersinia ruckeri (O1 Biotype 2) infection in three early life-stages of rainbow trout.

Enteric redmouth disease (ERM) caused by the enterobacterium Yersinia ruckeri poses a significant threat to salmonid aquaculture globally. Despite decades of experimental infection studies, key knowledge gaps remain regarding the onset of disease susceptibility and mechanisms of immunity during early developmental stages, undermining disease management efforts in all susceptible life-stages. In this study, a series of immersion challenges were conducted, challenging and re-challenging rainbow trout Oncorhynchus mykiss (Walbaum) at 7, 14 and 51 d post-hatch (dph; mean weights = 0.085, 0.1 and 2.0 g respectively) to high concentrations (1.72 × 107-1.1 × 108 CFU) of Y. ruckeri at 15°C. This study indicates the hitherto unknown initial point of susceptibility to infection as the time of first ingestion of exogenous food (14 dph), and shows that individuals surviving primary challenge at 14 dph are significantly more likely to survive re-challenge at 51 dph compared with naive individuals (hazard ratio = 1.446, p = 0.032). Other key findings include large variation in mortality between different development-stages, from 21.1% at 14 dph to 81.2% at 51 dph, and novel age-dependent symptoms not reported previously. Results from this study enhance our understanding of ERM in juvenile rainbow trout and inform the development of improved aquatic animal health management strategies, thereby contributing to the productivity and sustainability of salmonid aquaculture into the future.

Subchronic Exposure to Environmental Concentrations of Chlorpyrifos Affects Swimming Activity of Rainbow Trout Larvae.

Chlorpyrifos (CPF), an organophosphorous pesticide, can be found in aquatic ecosystems at concentrations of up to several hundred nanograms per liter because of water runoff from treated crops. While some studies have shown that low concentrations of CPF may have adverse effects on aquatic species, comparatively little is known about its effect on fish embryos and larvae. To investigate the developmental effects of CPF, rainbow trout (Oncorhynchus mykiss) eyed-stage embryos were exposed in semistatic conditions to 0.3 and 3 µg/L of CPF up to the end of the sac-fry stage, 3 weeks, at 12 °C. Several endpoints were analyzed including survival, hatching delay, hatching success, biometry, swimming activity, DNA damage, lipid peroxidation, protein carbonyl content, acetylcholinesterase (AChE) activity, and gene expression. At the end of the 3-week exposure, larvae exposed to the highest concentration of CPF were less mobile compared to the control and the lowest CPF conditions. No significant differences in AChE activity were observed in either set of CPF conditions compared to control, but it was significantly reduced for larvae exposed to 3 µg/L compared to those exposed to 0.3 µg/L of CPF. Expression of genes that encoded estrogen receptor beta was downregulated for larvae exposed to both CPF concentrations. Expression of cytochrome P450 family 19 subfamily A member 1 was also significantly repressed but only on larvae exposed to the highest concentration of CPF. Our results indicated that subchronic exposure to environmental concentrations of CPF could lead to sublethal effects on early-life stages of rainbow trout, especially effects on swimming activity that could affect foraging activity and escaping from predators. Environ Toxicol Chem 2021;40:3092-3102. © 2021 SETAC.

Acute exposure of larval rainbow trout (Oncorhynchus mykiss) to elevated temperature limits hsp70b expression and influences future thermotolerance

As poikilotherms, fish health is compromised by exposure to elevated temperatures (e.g. climate change-related warming, anthropogenic thermal pollution, and/or hatchery processes). While fish thermotolerance has been demonstrated to be plastic, the downstream impacts of early life-stage high temperature exposure are not known. In the present study, we investigated the thermotolerance of rainbow trout (Oncorhynchus mykiss) fry 2 months after being exposed to elevated temperature (22°C) for 96 h. Exposed fry demonstrated a reduced critical thermal maxima (CTmax) in comparison to control fish. Using the RNase H-dependent quantitative PCR method, expression of rainbow trout hsp70 isoforms was determined immediately after the acute thermal stress and immediately following the thermotolerance trials. The lowered CTmax was associated with a reduced ability to upregulate the hsp70b gene during the thermotolerance trials, whereas no changes in hsp70a were observed. Overall, these results indicate that exposure to thermal stress in early life-stages of rainbow trout can have negative effects on future physiological function.

Expression stability and selection of optimal reference genes for gene expression normalization in early life stage rainbow trout exposed to cadmium and copper

Gene expression analysis represents a powerful approach to characterize the specific mechanisms by which contaminants interact with organisms. One of the key considerations when conducting gene expression analyses using quantitative real-time reverse transcription-polymerase chain reaction (qPCR) is the selection of appropriate reference genes, which is often overlooked. Specifically, to reach meaningful conclusions when using relative quantification approaches, expression levels of reference genes must be highly stable and cannot vary as a function of experimental conditions. However, to date, information on the stability of commonly used reference genes across developmental stages, tissues and after exposure to contaminants such as metals is lacking for many vertebrate species including teleost fish. Therefore, in this study, we assessed the stability of expression of 8 reference gene candidates in the gills and skin of three different early life-stages of rainbow trout after acute exposure (24h) to two metals, cadmium (Cd) and copper (Cu) using qPCR. Candidate housekeeping genes were: beta actin (b-actin), DNA directed RNA polymerase II subunit I (DRP2), elongation factor-1 alpha (EF1a), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), glucose-6-phosphate dehydrogenase (G6PD), hypoxanthine phosphoribosyltransferase (HPRT), ribosomal protein L8 (RPL8), and 18S ribosomal RNA (18S). Four algorithms, geNorm, NormFinder, BestKeeper, and the comparative ΔCt method were employed to systematically evaluate the expression stability of these candidate genes under control and exposed conditions as well as across three different life-stages. Finally, stability of genes was ranked by taking geometric means of the ranks established by the different methods. Stability of reference genes was ranked in the following order (from lower to higher stability): HPRT<GAPDH<EF1a<G6PD<RPL8<DRP2<b-actin in gills of fish exposed to Cd; b-actin<GAPDH<G6PD<DRP2<RPL8<HPRT<EF1a in gills of fish exposed to Cu; RPL8<HPRT<GAPDH<G6PD<EF1a<DRP2<b-actin in the skin of fish exposed to Cd; and EF1a<GAPDH<RPL8<HPRT<G6PD<b-actin<DRP2 in the skin of fish exposed to Cu. The results demonstrated that the stability of reference genes depended on the metal, life-stage and/or organ in question. Thus, attention should be paid to these factors before selection of reference gene for relative quantification of the gene expressions.

Effects of Sodium Chloride on Chronic Silver Toxicity to Early Life-Stages of Rainbow Trout (Oncorhynchus Mykiss)

Effects of Sodium Chloride on Chronic Silver Toxicity to Early Life-Stages of Rainbow Trout (Oncorhynchus Mykiss)