| Abstract |
The increasing demands of large-scale aquaculture production across the world tend to
prioritize quantity over the welfare conditions of the reared animals and the quality of the
final products. Body shape is among the critical parameters of fish quality, especially
concerning the species which are marketed as a whole (Fragkoulis et al., 2017a). Beyond the
dependence on genotype and environment, body shape is susceptible to increased variability
induced by the appearance of skeletal deformities. Therefore, optimizing fish skeletal quality
is an emerging issue, especially for aquaculture species (Boglione and Costa, 2011). This
emergence is mainly correlated with the increased prevalence of skeletal abnormalities
affecting not only farmed fish species but also the laboratory raised (Boglione et al., 2013b;
Dietrich et al., 2021; Printzi et al., 2021b). Concerning the Mediterranean hatcheries, the
mean abnormalities frequency is reported between 7-20% of the annual production with the
possibility of reaching even higher levels under certain conditions (Georgakopoulou et al.,
2010; Koumoundouros, 2010). In the case of gill-cover deformities for example, they have
been reported to affect up to 80% of the farmed gilthead seabream (Sparus aurata) (Andrades
et al., 1996; Verhaegen et al., 2007). Skeletal abnormalities development has been correlated
with downgraded biological performance of the individuals (e.g., growth, survival, swimming
performance, feed conversion ratio, susceptibility to stress and diseases; Basaran et al., 2007;
Kent et al., 2004; Koumoundouros et al., 2002; Lijalad and Powell, 2009; Matsuoka, 2003;
Schwebel et al., 2018), which therefore can negatively affect the production cost and market
value (Gavaia et al., 2002; Koumoundouros, 2010). As a result, nowadays, skeletal
deformities represent a valuable index of animal welfare (Huntingford et al., 2006). By
successfully copying with skeletal abnormalities development, the aquaculture sector could
not only optimize the product quality but simultaneously comply with the European
legislation about animal-friendly husbandry practices (fish farming with respect to the
biological characteristics and different species-specific needs; Giménez-Candela et al., 2020).
Thus, a better understanding of the development of skeletal deformities in fish is of
increasing necessity. Extensive research over the last decades has identified several causative
factors acting upon specific developmental windows for the induction of skeletal deformities
(Boglione et al., 2013b). Beyond the extended awareness of the aquaculture sector today, the
latter continue to appear even in well-studied species (e.g., seabass, Dicentrarchus labrax and
seabream), as a result of inappropriate rearing procedures (Loizides et al., 2014b). To copy
with their unpredictable development, new tools are available today (e.g., morphometrics for
skeletal deformities prediction, Fragkoulis and Koumoundouros, 2021; key-performanceindicators for identification of skeletal quality predictors, Kourkouta et al., 2022) targeting the
early identification of the skeletal deformities and therefore a cost-efficient management of
the hatchery production. Moreover, utilizing recent knowledge over skeletal abnormalities
induction in a standardized way (e.g., swimming challenge test for haemal lordosis induction;
Kihara et al., 2002; Printzi et al., 2021a), can emerge as a valuable method of rearing
parameters evaluation. Through this controlled introduction of a specific deformity under
standard conditions, it is possible to evaluate the effect of nutritional and/or abiotic stimuli on
the skeletal development and integrity of the individuals by a simple comparison.
Consequently, the examination of the nutritional and/or abiotic effects on fish skeletal
development and integrity is now possible even after the end of the larval stage. Thus,
reversing the role of deformities from results to accurate tools allows current research to move
towards their prevention or recovery. Within this frame, an early evaluation of the possible
nutrient effects on larval and post-larval skeletal elements could be achieved, enabling the
development of appropriate diets for optimal skeletal development.
The following sections introduce the skeletal abnormalities in fish, with a description of
the main typologies observed, their causative factors and their recovery potential. Increased
attention is then drawn into the tools of skeletal abnormalities induction that are available
today, with emphasis on the swimming challenge tests (SCT) for evaluating the vertebral
columns’ integrity in post-larval individuals. A detailed insight into the main teleosts skeletal
tissues and their plasticity is provided afterwards. Finally, the last sections are dedicated to
early fish nutrition, revealing the main challenges that larval finfish production faces today.
Soon after establishing the basic key-points in early larval digestive function, the nutritional
effects on teleost musculoskeletal development are also discussed according to the nutrient
group (lipids, proteins, vitamins, minerals).
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