Abstract
Skeletal deformities, one of the major threats for aquaculture, have been studied extensively. These include opercular malformations in gilthead sea bream (Sparus aurata), a key fish species for Mediterranean aquaculture. What is causing it and at what morphogenetic level it arises, however, is still unclear. Here we focus on bone formation, at the level of bone mineralization. Several methods have been used to study bone mineralization density (BMD), however, these are frequently limited when targeting a high-resolution, three-dimensional mapping of BMD. We used micro-computed tomography (micro-CT) data to perform such a 3D quantification of BMD levels in gilthead sea bream that showed different levels of opercular bone deformations. This approach has the advantage of not having to rely on calibration phantoms, as long as relative BMD values are needed. The results show an increased BMD in deformed opercles compared to normal ones, especially in a bilaterally-deformed specimen. Furthermore, we show that opercular deformations are not necessarily associated with similar mineralization patterns in other mineralized cranial elements, except for the otoliths. Also, mineralization seems to occur left-right independently, matching earlier observations of such an independency of the opercular phenotype as a whole. This study confirms that a quantitative characterization of BMD patterns in 3D is feasible, even in smaller specimens, and that it has several advantages over other commonly used approaches.
Highlights
Skeletal deformities are currently one of the major threats for farmed fish production, especially those at early stages of the fish development
Malformation of the opercular complex could affect up to 80% of the reared population in gilthead sea bream (Paperna 1978; Francescon et al 1988; Andrades et al 1996). This rate nowadays has become reduced to 5-20% of the production in commercial hatcheries (Beraldo & Canavese 2011), opercular deformation is still one of the most frequent skeletal deformities observed in this species (Verhaegen et al 2007; Castro et al 2008; Prestinicola et al 2013; Boglione et al 2013a)
Our results corroborate the qualitative observations of Morel et al (2010), that higher bone mineral density (BMD) can be observed in deformed opercles, especially in the region that shows the inward folding of the bone
Summary
Skeletal deformities are currently one of the major threats for farmed fish production, especially those at early stages of the fish development Many studies have focused on the biology of bone development in fish, trying to tackle aspects of bone morphogenesis, possible causal factors related to rearing conditions, or just the categorization of deformity types resulting from intensive fish culture (e.g., Villeneuve et al, 2005; Lall & Lewis-McCrea 2007; Darias et al 2011; Holmes 2012). Many questions remain, including the level at which impaired bone morphogenetic processes result in deformed skeletal phenotypes. Impaired bone mineralization is one such an example, where proper insights are mainly constrained because of methodological limitations or accessibility, especially considering the non-medical context for studying fish skeletal deformities
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