Characterization of culturable bacterial flora and immune response in yolk-sac larvae of Atlantic halibut (Hippoglossus hippoglossus L.) with "Jawgaping" Syndrome

Abstract

ABSTRACT. One of the main problems facing Atlantic halibut hatcheries is 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 aimed also to establish whether there is any relationship between bacterial strains and the “jaw gaping syndrome”. During our study, 74 bacterial strains were isolated using three different nutrient media: Marine Agar, R2A and TCBS. Some of these bacteria were characterized using PCR-RFLP and 16S rRNA sequencing. The immune response in larvae exhibiting the jaw gaping condition was measured by qPCR. 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 Vibrionaceae and Flavobacteriaceae family. Bacteria belong of the Bacillus and Pseudoalteromonas families were also present but less frequent. It was not possible identified a type or group of bacteria related directly to “gaping”; however strikingly that the immune response of larvae was increase the expression of two immune related genes like hepcidin and MIP-1beta in larvae with gaping jaws. These results indicate the activation of immune response in larvae with gaping jaws syndrome and this response could be related to pathogenic bacteria.