ABSTRACT.One of the main problems facing Atlantic halibut hatcheries is the high mortality in the early stages of larval development. Several factors could be involved, for example: water quality, diseases or abnormalities, such as deformities occurring in the yolk sac larvae prior to exogenous feeding. The aim of this study was to identify differences in bacterial flora associated with yolk sac larvae with oral deformity. We also aimed to establish whether there is any relationship between bacterial strains and the "gaping jaws" syndrome. During our study, 74 bacterial isolates were obtained using three different nutrient media: Marine Agar, R2A and TCBS. Some of these bacteria were characterized using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) and 16S rRNA sequencing. The immune response in larvae exhibiting the "gaping jaws" condition was measured by real time PCR. Our results showed significant differences in bacterial flora between normal and gaping larvae. The gaping yolk sac larvae were predominantly colonized by members of the families Vibrionaceae and Flavobacteriaceae. Bacteria belonging to the Bacillus and Pseudoalteromonas genera were also present but less frequent. It was not possible to associate a type or group of bacteria directly related to "gaping". Strikingly, larvae with gaping jaws had an increase in the expression of two immune related genes, like hepcidin and chemokine (MIP-1ß). These results indicate activation of the immune response in larvae with "gaping jaws" syndrome and this response could be related to bacteria isolated from gaping condition. Keywords: Atlantic halibut, Hippoglossus hippoglossus, bacterial flora, "gaping jaws", immune genes.Caracterización de la flora cultivable y la respuesta inmune en larvas con saco vitelino del halibut del Atlántico (Hippoglossus hippoglossus L.) con el síndrome de "gaping jaws" RESUMEN. Uno de los mayores problemas que enfrentan los criaderos de halibut del Atlántico es la alta mortalidad en estados tempranos del desarrollo larval. Distintos factores pueden estar involucrados, e.g., calidad del agua, enfermedades o anormalidades tales como deformidades que ocurren en las larvas en estado de saco vitelino antes de la alimentación exógena. El objetivo de este estudio fue identificar diferencias en la flora bacteriana asociada a larvas con saco vitelino con deformidad oral. Además se buscó establecer si existió relación entre alguna cepa bacteriana y el síndrome de "gaping jaws". Durante el estudio, 74 cepas bacterianas fueron aisladas usando diferentes medios de cultivo: agar marino, R2A y agar TCBS. Algunas de las bacterias fueron caracterizadas usando reacción en cadena de la polimerasa con análisis del polimorfismo de los fragmentos de restricción (PCR-RFLP) y secuenciación del gen ribosomal 16S. La respuesta inmune de larvas con el síndrome de "gaping jaws" fue medida por PCR en tiempo real. Los resultados evidenciaron diferencias significativas en la flora entre larvas normales y "gaping jaws". Las larvas c...
