Introduction
Aquaculture continues to face challenges in producing high-quality larvae and early developmental deformities, often leading to high mortality and reduced production efficiency (Boglione et al., 2013; Chandra et al., 2024), are among major concerns. Variation in the type and occurrence of deformities across species, populations, and even within families complicates efforts to study and understand their underlying causes. While deformities are generally linked to genetic, biological, and external factors, those occurring immediately after hatching are more likely to result from genetic or non-genetic parental influences (Adrian-Kalchhauser et al., 2020). Among others, heart oedema is one of the most common deformities and is often expressed as a lethal trait. In Eurasian perch (Perca fluviatilis ), this condition, marked by fluid build-up around the heart, is often observed in larvae obtained from spawners grown in recirculating aquaculture systems (RAS), impairing their cardiovascular function (Alix et al., 2017) . Despite its prevalence, its underlying mechanisms remain poorly understood. This study aims to compare the within-family transcriptomic profiles of normal-shaped newly hatched larvae with those exhibiting heart oedema , offering insights into its molecular basis and potential strategies for improving broodstock management and larval quality.
Materials and Methods
Eurasian perch larvae from 8th-generation domesticated broodstock reared in RAS were used. Eggs were fertilized in vitro using cryopreserved milt and incubated under controlled conditions. On the day of hatching, larvae showing heart o edema and normal-shaped siblings were selected from 5 different families . Total RNA was extracted from each family and phenotype, and sequenced (10 libraries, 150 bp paired-end, 40M reads per library). Differentially expressed genes analysis was performed using DESeq2. G ene ontology enrichment (GO) was conducted with ShinyGO . Heart-specific genes were identified using PhyloFish database and further validated by RT-qPCR.
Results
Heart oedema has been found to be a lethal trait in Eurasian perch. Transcriptomic analysis revealed 507 differentially expressed genes (DEGs; p < 0.05, log2FC>1). GO analysis of DEGs indicated strong enrichment in metabolic regulation, stress response, and DNA repair. Seventeen heart-specific DEGs (τ >0.85) were selected for RT-qPCR validation. Their expression was tracked across key embryonic developmental stages to assess their role in cardiac development. Among these, arl14, hbz and c18orf21 has been positively validated with qPCR . Developmental profiling showed lack of these genes in unfertilized eggs, low expression levels shortly after fertilization, with a noticeable increase around 100 hours post-fertilization (tail detachment stage), followed by a sharp rise at approximately 7 days post-fertilization, corresponding to the eyed- egg stage.
Discussion
This study provides novel insights into the processes underlying larval cardiac deformities and offers a foundation for developing strategies to mitigate mortality and improve aquaculture outcomes. The presence of both heart-oedema and normal larvae within the same family, sharing the same genetic background, suggests complex interactions between parental gametes, which we term ‘parental dispute’ (Debernardis et al, 2024). This highlights the crucial role of gamete-derived non-genetic factors underlying heart oedema. Additionally, the genes validated through qPCR emerge as strong candidate marker s for further investigation into cardiovascular development and stress responses in fish embryos. Profiling their expression at critical embryonic stages revealed that their expression starts after zygotic genome activation and is associated with further heart morphogenesis (Alix et al., 2015). Our results suggest that disruptions in gene regulation during these stages may contribute to heart oedema.
Overall, these findings enhance our understanding of larval deformities, emphasizing the role of non-genetic inheritance factors in shaping larvae quality in E. perch.
Acknowledgment
This work was funded by National Science Center of Poland (SONATA BIS project, number UMO-2020/38/E/NZ9/00394).
References
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