Abstract
In this paper, 981 reared juveniles of gilthead seabream (Sparus aurata) were analysed, 721 of which were from a commercial hatchery located in Northern Italy (Venice, Italy) and 260 from the Hellenic Center for Marine Research (Crete, Greece). These individuals were from 4 different egg batches, for a total of 10 different lots. Each egg batch was split into two lots after hatching, and reared with two different methodologies: intensive and semi-intensive. All fish were subjected to processing for skeletal anomaly and meristic count analysis. The aims involved: (1) quantitatively and qualitatively analyzing whether differences in skeletal elements arise between siblings and, if so, what they are; (2) investigating if any skeletal bone tissue/ossification is specifically affected by changing environmental rearing conditions; and (3) contributing to the identification of the best practices for gilthead seabream larval rearing in order to lower the deformity rates, without selections. The results obtained in this study highlighted that: i) in all the semi-intensive lots, the bones having intramembranous ossification showed a consistently lower incidence of anomalies; ii) the same clear pattern was not observed in the skeletal elements whose ossification process requires a cartilaginous precursor. It is thus possible to ameliorate the morphological quality (by reducing the incidence of severe skeletal anomalies and the variability in meristic counts of dermal bones) of reared seabream juveniles by lowering the stocking densities (maximum 16 larvae/L) and increasing the volume of the hatchery rearing tanks (minimum 40 m3). Feeding larvae with a wide variety of live (wild) preys seems further to improve juvenile skeletal quality. Additionally, analysis of the morphological quality of juveniles reared under two different semi-intensive conditions, Mesocosm and Large Volumes, highlighted a somewhat greater capacity of Large Volumes to significantly augment the gap with siblings reared in intensive (conventional) modality.
Highlights
Gilthead seabream (Sparus aurata L.) is a species of high commercial value, especially in the Mediterranean region, where it was one of the first species to be intensively cultivated
This study represents the first attempt to compare the effects of varying rearing methodology on the morphological quality of juveniles of gilthead seabream (S. aurata), in many replicae and on a commercial scale: larvae from the same egg batch were split into two lots and reared in intensive or semi-intensive conditions (n = 459), in different farms, periods and countries
The observation of pattern and frequencies of skeletal anomalies occurring in reared fish at a commercial level is important, because in this way, the multilevel factors interacting with developing organisms in an unknown way, as happens in farming conditions, and that are not reproducible under experimental conditions, can be included in our approach
Summary
Gilthead seabream (Sparus aurata L.) is a species of high commercial value, especially in the Mediterranean region, where it was one of the first species to be intensively cultivated. In the last few years, the drop in the gilthead seabream market price due to overproduction is forcing the aquaculture industry to reduce production costs and enhance fish quality. The latter goal is seriously affected by the presence of skeletal anomalies, one of the most important bottlenecks in current aquaculture production, as they require manual sorting [1]–[2] and are associated with a general lowering of performance (i.e. swimming ability, conversion index, growth rate, survival, and susceptibility to stress, pathogens and bacteria) [1], [3]–[14]. Even automatic fillet processing is impaired by the presence of vertebral deformities, reducing economic return [25]
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