Introduction
Juvenile quality is a major determinant of productivity, fish welfare, and economic sustainability in Mediterranean aquaculture. Among quality-related traits, skeletal abnormalities remain one of the most persistent challenges in marine fish hatcheries, affecting biological performance, morphology, and commercial value of the final product (Boglione et al., 2013). Since the early development of Mediterranean aquaculture, significant progress has been achieved through improvements in larval rearing protocols, selective breeding programs, and morphological quality control. As a result, the prevalence of malformed fish has substantially decreased during the last decades. Nevertheless, important variability among hatcheries, production cycles, and fish populations still occurs, while novel deformity phenotypes continue to emerge under standard commercial conditions (Kourkouta et al., 2022; Kourkouta et al., 2025). In this presentation, emphasis will be placed on the major factors contributing to the quality downgrading of reared fish larvae, the critical ontogenetic stages involved, and the proposed management practices for addressing the problem in hatcheries. In addition, recent research findings will be presented regarding the assessment of the severity of skeletal deformities at the production level.
Anatomical and ontogenetic differentiation of skeletal abnormalities
Skeletal abnormalities differ considerably in terms of affected anatomical structures, developmental timing, and biological severity (Boglione et al., 2013). Most abnormalities develop during skeletogenesis up to metamorphosis, whereas others, such as haemal lordosis and Ray-Resorption Syndrome (RSS), may appear after completion of skeletal development on initially normal skeletal elements (Sfakianakis et al., 2006; Kourkouta et al., 2025). Each deformity type is characterized by a specific critical ontogenetic window associated with the developmental pattern of the affected skeletal structures (Koumoundouros, 2010). This ontogenetic specificity highlights the strong developmental plasticity of marine fish larvae and partly explains the difficulty in defining universally optimal rearing conditions for normal skeletal development.
Causative factors and hatchery variability
The development of skeletal abnormalities is multifactorial, involving nutritional, abiotic, and genetic determinants (Boglione et al., 2013, Fragkoulis et al., 2018). Despite extensive research efforts, the identification of widely used optimal environmental and nutritional conditions remains challenging because larval physiological requirements vary substantially throughout ontogeny (Mazurais et al. 2009, Georgakopoulou et al. 2010). In commercial hatcheries, skeletal abnormality incidence is additionally characterized by high variability both among production batches and among populations within the same production cycle, suggesting that small deviations in complex production protocols may substantially influence larval skeletal quality (Kourkouta et al., 2022).
Emerging management approaches and future perspectives
Recent findings are progressively changing the traditional perception that skeletal abnormalities represent irreversible developmental defects. Experimental and commercial-scale studies have demonstrated that some abnormalities, including haemal lordosis and upper jaw deformities, may partially recover during ongrowing (Fragkoulis et al., 2019, 2022; Geladakis et al., 2025). In parallel, advances in morphometric tools provide new opportunities for early diagnosis and severity-based classification of skeletal abnormalities (Geladakis et al., 2025). Recent nutritional approaches aiming to enhance skeletal resilience and mineralization capacity further support the development of preventive management strategies (Printzi et al., 2024). At the production level, integration of automation systems, benchmarking approaches, certified raw materials, and large-scale production data may improve protocol standardization and reduce within-hatchery variability. Future improvements in skeletal quality management will likely depend on combining precision hatchery practices with selective breeding programs incorporating morphological quality traits.
Conclusions
Current evidence indicates that skeletal abnormalities should be viewed as dynamic phenotypes influenced by developmental plasticity, recovery capacity, and hatchery management. Integrating precision phenotyping, resilience-oriented nutrition, and standardized production protocols may substantially improve skeletal quality, fish welfare, and production sustainability in Mediterranean aquaculture.
The research was supported by the Research Funding Program of the University of Crete (Project Number ΚΑ-12554).
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