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Docosahexaenoic acid (DHA); a driving force regulating gene expression in bluefin tuna (Thunnus thynnus) larvae development.

ABSTRACT: This study elucidated the role of DHA-modulated genes in the development and growth of bluefin tuna (Thunnus thynnus) larvae ingesting increasing levels of DHA in their rotifer prey. The effect of feeding low, medium, and high rotifer (Brachionus rotundiformis) DHA levels (2.0, 3.6 and 10.9 mg DHA g-1 DW, respectively) was tested on 2-15 days post hatching (dph) bluefin tuna larvae. Larval DHA content markedly (P < 0.05) increased in a DHA dose-dependent manner (1.5, 3.9, 6.1 mg DHA g-1 DW larva, respectively), that was positively correlated with larval prey consumption, and growth (P < 0.05). Gene ontology enrichment analyses of DEGs demonstrated dietary DHA significantly (P < 0.05) affected different genes and biological processes at different developmental ages. The number of DHA up-regulated DEGs was highest in 10 dph larvae (408), compared to 5 (11) and 15 dph fish (34), and were mainly involved in neural and synaptic development in the brain and spinal cord. In contrast, DHA in older 15 dph larvae elicited fewer DEGs but played critical roles over a wider range of developing organs. The emerging picture underscores the importance of DHA-modulated gene expression as a driving force in bluefin tuna larval development and growth.

ORGANISM(S): Thunnus thynnus

PROVIDER: GSE263473 | GEO | 2024/10/09

REPOSITORIES: GEO

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Project description:Introduction: A major economic impediment to the aquaculture of marine finfish in land-based recirculating systems is maintaining the system salinity at a range for optimal growth. Florida Pompano (Trachinotus carolinus) are warm water, euryhaline, marine finfish shown to be a suitable candidate for low-salinity culture. Due to its popularity among sport and commercial fishers, high market value, and ability to readily consume pelleted feeds, the Florida Pompano has become a renewed target for commercialized aquaculture. Although the Florida Pompano has been successfully grown at various salinities, its optimal growth salinity has not yet been established. Studies have shown culturing at different salinities has an effect on digestion rates, feed utilization, and lipid biosynthesis. Identifying the optimal salinity for growth would result in decreased energy expenditure on maintaining homeostasis, since osmoregulation is a highly demanding process. This would allow for energy to be spent on the efficient use of nutrients. Methods: Our study was designed to determine how Florida Pompano larviculture at various salinities affects fish health with transcriptomics (RNA-seq) and fatty acid analysis. RNA-seq was used to identify genes actively transcribed and expressed at the time of sampling. After hatching in a salinity of ~ 30 ppt, larvae were reared in 345 L tanks at one of three salinities (10, 20, 30 ppt) in triplicate. Larvae samples for RNA-seq and fatty acid analysis were collected every three days until weaning. Samples for fatty acid composition were analyzed using a gas chromatography-mass spectrometry (GC/MS). RNA was extracted from homogenized whole-body samples using the Qiagen RNeasy Mini kit. Total RNA was sequenced on the Illumina HiSeq 4000 System. Raw sequences were filtered for low-quality sequences, aligned to the S. dumerili reference genome (NCBI Genome: 12614), and quantified. Each sampling day was compared across salinities to establish the differentially expressed genes (DEGs) between salinities. Results & Discussion: The numbers of DEGS in pooled samples was minimal (less than 15 total in each comparison) and the number of DEGS at each dph was variable. There were no significant differences between pooled samples or at each dph according to PERMANOVA analysis, but each dph was statistically different on pairwise analysis. Gene set enrichment analysis revealed that there was a downregulation of immune related genes in lower salinities versus higher salinities suggesting larvae may be dealing with less stress at lower salinities. Most osmoregulation, fatty acid, and immune related genes tested were not significantly different across salinities. This is likely be cause the Florida pompano is euryhaline and has a tolerance to the salinities selected. There was an increase in the expression levels of several immune related genes that may indicate an increase exposure to pathogens at later days post hatch likely related to feeding schedule. There was also an increase in fatty acid biosynthesis genes that corresponded with levels of fatty acids indicating a possible synthesis of essential fatty acids from precursors. Conclusions: From a transcriptomics perspective, the larvae did not show a negative response to lower salinities in comparison to higher salinities, which in fact showed upregulation of immune related genes. Further exploration of Florida pompano’s ability to biosynthesize essential fatty acids is necessary. This study will help enable the optimization of Florida Pompano larviculture using information on the optimal salinity and fatty acid content for growth and facilitate more cost-effective rearing methods.

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Docosahexaenoic acid (DHA); a driving force regulating gene expression in bluefin tuna (Thunnus thynnus) larvae development.

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