Desarrollo de un programa piloto de mejora genética en dorada (Sparus aurata L.): efecto del origen de los reproductores y estimación de parámetros genéticos para caracteres de crecimiento y de calidad

Abstract

[ESP] El objetivo de esta Tesis fue obtener información relevante para el desarrollo de un programa de mejora genética en dorada. Con este fin, se obtuvo una población de alevines de dorada, a partir de tres lotes de reproductores diferentes [Mar Cantábrico (CAN); n = 59, 2?:1?; Océano Atlántico (ATL); n = 98, 1?:1? y Mar Mediterráneo (MED); n = 47; 1?:1?]. Los alevines fueron marcados para su identificación individual con Passive Integrated Transponder y criados bajo las mismas condiciones industriales hasta su sacrificio. Esta población fue analizada para desarrollar diversos objetivos concretos que se centraron en estudiar algunos aspectos escasamente tratados o desconocidos en dorada. Inicialmente se estudió la variabilidad y la estructuración genética de esta población, caracterizando genéticamente, mediante marcadores microsatélites, tanto reproductores como descendientes. Además se establecieron sus relaciones de parentesco y se estudiaron las contribuciones a la puesta. Los resultados mostraron que los tres orígenes estudiados presentaron una alta variabilidad genética y fueron diferentes genéticamente entre sí. Además, las contribuciones de los reproductores de los diferentes orígenes fueron desiguales por lo que su tamaño efectivo disminuyó. Se formaron un total de 201 familias de hermanos completos, más 21 familias de medios hermanos paternos y 9 familias de medios hermanos maternos. Seguidamente se analizó el efecto del origen de los reproductores sobre caracteres de interés comercial, lo que proporcionaría información fenotípica relevante para la adquisición de un stock. Así mismo, se estimaron parámetros genéticos (heredabilidades y correlaciones genéticas) y correlaciones fenotípicas para dichos caracteres con el fin de determinar posibles criterios de selección. Los caracteres crecimiento y presencia de malformaciones esqueléticas externas fueron analizados a diferentes edades iniciales (163, 368 y 516 días) así como a la edad de sacrificio (690 días). Se observó un efecto del origen de forma que los individuos del MED presentaron un mayor crecimiento, mientras que aquellos del ATL mostraron un menor crecimiento y una mayor frecuencia de malformaciones vertebrales, presentado los del CAN un crecimiento intermedio y una menor frecuencia de dichas malformaciones. Las heredabilidades fueron estimadas a distintas edades (163 y 690 días). Los valores estimados a esta edad fueron 0,25±0,06 para peso y 0,22±0,07 para talla siendo la correlaciones genéticas entre ambos caracteres altas y positivas a las dos edades estudiadas. En cuanto a las malformaciones, las heredabilidades fueron 0,56[0,17-0,69] para malformaciones vertebrales y 0,46[0,20-0,90] para malformaciones operculares, estimadas mediante métodos bayesianos. Respecto a las correlaciones genéticas con crecimiento, inicialmente se observó una correlación genética positiva entre crecimiento y malformaciones vertebrales, (83% de probabilidad de ser positiva para la correlación peso-malformaciones vertebrales; 81% para talla-malformaciones vertebrales). Sin embargo, estas correlaciones fueron negativas a la edad de sacrificio (94,2% de probabilidad de ser negativa para peso-malformaciones vertebrales; 80,6% para talla-malformaciones vertebrales). Como continuación de trabajo anterior, se planteó el estudio de anomalías morfológicas internas, de nuevo a la edad de 163 días. Los juveniles del CAN presentaron una menor frecuencia de malformaciones vertebrales así como de vejigas natatorias no inflamadas. Las heredabilidades fueron importantes para lordosis (0,53[0,25-0,77]), alteraciones de opérculo (0,37[0,01-0,81]) y no inflamación de la vejiga natatoria (0,36[0,12-0,72]), existiendo una correlación genética positiva entre lordosis y la presencia de vejiga no inflamadas (0,48[0,07-0,97]). Finalmente, se analizaron caracteres de calidad tanto de canal como de carne a la edad de sacrificio. De nuevo se observó un efecto del origen, presentando los individuos del ATL un menor porcentaje de grasa visceral pero también un menor rendimiento y peso de la canal. Con respecto a la calidad de la carne, los individuos de CAN mostraron mayores valores de firmeza y parámetros texturales derivados. Todos los caracteres de calidad de la canal analizados presentaron heredabilidades medias (0,17-0,24) y fueron estimados con precisión (errores estándar de 0,05 a 0,07) excepto el rendimiento canal y filete. En cuanto a la calidad de la carne, se estimó también una heredabilidad media para grasa muscular (0,31±0,08), humedad (0,24±0,07) y firmeza (0,21±0,06). Teniendo en cuenta las correlaciones genéticas de caracteres de canal y carne con aquellos de crecimiento, seleccionar por peso aumentaría el factor de condición (0,47±0,21), la indeseable grasa visceral (0,42±0,20) y la grasa muscular (0,29±0,14) pero disminuiría del rendimiento filete (-0,58±0,09) y la firmeza (-0,34±0,14). La selección por talla aumentaría el peso de la canal (0,87±0,07) y del filete (0,84±0,09). Además el factor de condición se mostró como un criterio de selección alternativo al ser no invasivo, de fácil medida y por mejorar indirectamente el contenido de grasa visceral (-0,46±0,16). [ENG] Gilthead sea bream (Sparus aurata L.) is the most relevant marine species in Mediterranean aquaculture. As consequence of the growth and consolidation of the gilthead sea bream industry, there is an increasing interest for genetic improvement to maximize the efficiency of its production. However, efficient breeding programs for this species are scarce, partly due to the biology of this species, and very little it is known concerning their population structure. Moreover, growth rates and the overall quality of the end product can be affected by the use of different rearing systems as well as by the different genetic origin of the stocks. Taking into account these circumstances, the main goal of this thesis was to obtain relevant information for the establishment of successful breeding programs in aquaculture of this species. For this purpose, a population of farmed gilthead sea bream sourced from three broodstock of different origins, breeders number and sex combinations [Cantabrian Sea (CAN), n = 59, 2♂:1♀; the Atlantic Ocean (ATL), n =98, 1♂:1♀ and Mediterranean Sea (MED) n = 47; 1♂:1♀] was obtained. Fingerlings were individually tagged for individual identification with a Passive Integrated Transporter (PIT) and reared under the same intensive conditions until harvest size. This population was analysed to develop several specific objectives focused on study some aspects poorly studied or unknown in sea bream. Initially, we study the genetic variability and the genetic structure of this population using a microsatellite multiplex to genetically characterize these broodstock and their progeny. Parental assignments and contributions were also analysed. Results showed the high genetic variability of the three studied origins and their genetic differentiation. Moreover, due to breeder unequal contributions effective sample sizes were reduced in the progenies. A total of 201 full-sib families, 21 paternal half-sib families and 9 maternal half-sib families were represented. Given the genetic differences observed among the studied origins, the effect of the origin of the broodstock on economically important traits was analysed which provide relevant phenotypic information for the acquisition of a stock in sea bream. Genetic parameters (heritabilities and genetic correlations) as well as phenotypic correlations for these traits were estimated in order to determine possible selection criteria. Due to their economically importance, growth rate and the presence of external deformities were studied at different ages (163, 368 y 516 days) as well as the slaughter age (690 days). The origin had an effect on these traits. Fish from MED showed the fastest growth while those from ATL showed the slowest growth and the highest incidence of vertebral column deformities, showing those from CAN an intermediate growth and the lowest frequency of these deformities. Heritabilities were estimated at initial and final ages (163 and 690 days) showing medium values increased with age. Estimated heritabilities were 0.25±0.06 for weight and 0.22±0.07 for length, being the genetic correlations between these traits high and positive at both studied ages. Regarding malformations, the heritabilities were 0.56[0.17-0.69] for deformities in the vertebral column and 0.46[0.20-0.90] for deformities in the operculum, estimated under a Bayesian approach. At earlier age, positive genetic correlations between growth and deformities in the vertebral column were observed (83% probability of being positive for weight-vertebral column deformity; 81% for length-vertebral column deformity). However, these correlations were negative at slaughter (94.2% probability of being negative for weight-vertebral column; 80.6% for length-vertebral column). This initially positive correlation could be explained by an increased aggravation of deformities in fast growing individuals, resulting later in deformed fish with slower growing rates. Following the previous work, we decided to analyze internal abnormalities at 163 days from a radiographic analysis. In this case, juveniles from CAN showed the lowest frequency of skeletal deformities as well as the lowest frequency of uninflated swimbladder. Considerable heritabilities were estimated for lordosis (0.53[0.25-0.77]), lack of operculum (0.37[0.01-0.81]) and uninflated swimbladder (0.36[0.12-0.72]) with a positive genetic correlation between uninflated swimbladder and lordosis (0.48[0.07-0.97]). Finally, since fish consumers show an increasing interest in quality products, carcass and raw flesh quality traits were analyzed at the slaughter age. An effect of the origin of the broodstock was observed. In this regard, fish from ATL showed the lowest visceral fat percentage, but at the same time, the lowest dressing weight and percentage. Regarding flesh quality traits, the highest values for hardness and derived textural parameters were observed in fish from CAN. All studied carcass traits showed medium heritabilities (ranging from 0.17 to 0.24) estimated with accuracy (standard errors from 0.05 to 0.07), except dressing and fillet percentages. Regarding flesh quality traits, heritabilities were medium as well for muscular fat (0.31±0.08), moisture (0.24±0.07), and hardness (0.21±0.06). Due to the fact that growth is the most economically important objective in the majority of fish genetic selection programs, we studied its genetic correlations with carcass and flesh quality traits. According to their correlations, selection for harvest weight may lead to an increase in condition factor (0.47±0.21), the undesirable visceral fat (0.42±0.20) and in fillet fat percentage (0.29±0.14) and, at the same time, to a decrease in fillet yield (-0.58±0.09) and in the flesh hardness (-0.34±0.14). Selection on length could improve dressing (0.87±0.07) and fillet weight (0.84±0.09). Condition factor was shown as an interesting alternative selection criterion since it is easy to measure, allows a non-invasive measurement in living candidates and could lead to a decrease in the undesirable visceral fat due to their genetic correlation (0.46±0.16). The differences observed among the different studied origins on economically important traits proved the importance of the acquisition of a stock in sea bream. Heritability estimates for growth and for several deformities at different ages indicate the potential for improvement of these traits by selective breeding using a family-based selection program. In light of the results it can be recommended to eliminate deformed fish from a breeding nucleus and later, select on growth. Further studies in upcoming generations would clarify the evolution of other traits related to the quality of the carcass and the flesh.