Morphological characterization and transcriptome analysis of opercular deformity in golden pompano (Trachinotus ovatus)

Skeletal deformity is one of the major threats to aquaculture because of its negative effects in important economic losses. Recently, a high rate of opercular deformities was observed in farmed golden pompano (Trachinotus ovatus), which is a key species for marine cage culture in the South China Sea. In the present study, a structural, histological, and biochemical analysis of the deformed opercular complex in T. ovatus was carried out using micro-CT, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), paraffin section, and staining. A 3D reconstruction of the deformed and normal opercle complex has revealed an inward folding of both opercle and subopercle, and frequently affected branchiostegal rays being coated by the deformed opercle and subopercle. In addition, an increased Ca, P, and Mg content was identified in the deformed opercle. The Hematoxylin-eosin (HE) and tartrate resistant acid phosphatase (TRAP) staining of the deformed opercle have shown a higher osteoclast activity and increased bone resorption area. Further analyses on the difference of gene expression between the deformed and normal opercle have been performed using Illumina sequencing platform. As a result, a total of 1220 DEGs (including 508 up-regulated and 712 down-regulated genes) were identified. DEGs related to osteoblast and osteoclast differentiation revealed an important role of bone metabolism in opercular deformity. Moreover, GO and KEGG analysis of these DEGs showed that they were significantly enriched in functions and pathways related to muscle form, development and contraction. Additionally affected pathways including ion homeostasis suggested that functions of gills such as breathing and osmoregulation might be affected by the deformed opercle.