Growth and size variation of Senegalese sole (Solea senegalensis)
- Autores: Pablo Sánchez Fernández
- Directores de la Tesis: Pedro Pablo Ambrosio Jiménez (dir. tes.), Rosa Flos (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2012
- Idioma: inglés
- Tribunal Calificador de la Tesis: Lluís Tort Bardolet (presid.), María Lourdes Reig Puig (secret.), Bari Howell (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Senegalese sole (Solea senegalensis) is a flatfish of high commercial importance in Southern Europe that has been a promising species for diversifying Mediterranean aquaculture since early 1980's. It has failed to reach successful farming development due to lack of full control over spawning, poor fry quality and high mortality during the weaning stage. Furthermore, optimization of production has not been possible due to high heterogeneity in growth rates within cultured stocks that result in high body size variance at harvest. Among the several aspects needing wider knowledge in order to reach optimization of sole aquaculture, the ongrowing stage from juveniles to the commercialization size has been overlooked until the last years. It includes the relationships between individual growth and rearing parameters as stocking density, or the size composition of stocks. It is also important to evaluate growth according to the feeding rhythms, offering feed at adequate times for this species. Not less important is to assess the genetic variability of farmed stocks, and compare it to the wild populations, as a stepping stone to link genetic traits to the performance of aquaculture stocks. The aims of this thesis were to take an individual-based approach to growth, and growth sexual dimorphism, of Senegalese sole reared at high and low densities, with different levels of initial size variation, and under different feeding strategies. Moreover, the level of genetic variability of this species was compared between farmed and wild stocks through molecular genetic markers, and their sibship relationships were also assessed. Three experiments were conducted, involving a) rearing soles under high density (180% of bottom coverage) and low density (60% of bottom coverage); b) rearing soles under the same high and low densities, but also under homogeneous or heterogeneous initial size composition; c) rearing soles under a medium/high initial density (130% of bottom coverage) fed either during nocturnal hours, similar to their natural feeding rhythms, or during daylight hours. Additionally, the genetic variability of a farmed sample was compared to its wild donor population. Stocking density affects growth of Senegalese sole in two ways. First, sudden and steep increases in density could lead to poorer or no growth of fish until re-acclimatization to new high density conditions. Second, it seems that there is a sizedependent component on how stocking density affects growth, with smaller fish (sub-adults) growth being suppressed by high stocking density. Size composition of reared Senegalese sole does not affect individual growth. Sole doesn¿t show aggressive behavior and apparently, competition between individuals is low and size independent. Grading Senegalese sole does not guarantee the improvement of growth, and if so, it would be in high density conditions. Senegalese sole females grow faster than males, but after attaining certain body weight (between 40 and 80 g). It could be hypothesized that sexual maturation may be involved in the onset of sexual growth dimorphism in this species. Besides being an eminently nocturnal species, Senegalese sole fed during the light phase may yield specific growth rates and feed conversion ratios that are comparable to those of fish fed during the dark phase, suggesting the feasibility of feeding during normal business hours in commercial facilities. There is a loss in genetic variability in a single generation of Senegalese sole rearing, as evidenced by lower values of mitochondrial haplotypic diversity and nuclear diversity in the farmed sample compared with the wild donor population. Comparing wild Atlantic and Mediterranean samples suggests a limited gene flow between the populations inhabiting these basins. An accurate knowledge of the genetic composition of farmed stocks is essential both for maintaining the cultured stocks and for potential future restocking purposes. Castelldefels 17/
