Altered behaviour and reduced survival of juvenile olive flounder, Paralichthys olivaceus, infected by an invasive monogenean, Neoheterobothrium hirame

Full-length transcriptome sequencing from multiple immune-related tissues of Paralichthys olivaceus

Olive flounder (Paralichthys olivaceus) is an important economical flatfish in Japan, Korea and China, but its production has been greatly threatened by various of diseases. Although RNA-seq has provided valuable insights into the host-pathogen interaction, there are still some disadvantages, such as a short sequencing length, the incomplete or inaccurate splicing. Therefore, we generated a full-length transcriptome using mixed immune-related tissues of P. olivaceus with PacBio Sequel platform. In this study, 379,671 full-length non-chimeric (flnc) reads were generated with average length of 2482 bp, which is longer than any previously reported in P. olivaceus. A total of 66,420 isoforms of transcript were identified, 46,850 of which were novel isoforms of known genes accounting for 70.54%. In addition, 7720 novel genes, 12,540 alternative splicing (AS) events, 9296 alternative polyadenylation (APA) events, 2298 transcription factors (TFs), 10,270 lncRNAs and 5400 fusion transcripts were identified. Furthermore, functional annotation showed that most of the full-length transcripts were enriched in immune-related signaling pathways. Otherwise, the mRNA-miRNA interacting networks confirmed that 28.5% of mRNAs were predicted to be targeted by more than one miRNA. These results facilitate the understanding of gene structure, post-transcriptional regulatory networks, and subsequently proteomic diversity. In conclusion, our study provides the full-length transcriptome from multiple immune-related tissues of P. olivaceus, which is valuable for exploring its immune responses.

Spatial ecology of coastal Atlantic cod Gadus morhua associated with parasite load

Acoustic tags and receivers were used to investigate the spatial ecology of coastal Atlantic cod Gadus morhua (n = 32, mean fork length: 50 cm, range: 33-80 cm) on the Norwegian Skagerrak coast in 2012. Monthly home ranges (HR), swimming activity and depth use varied considerably among individuals and through the months of June, July and August. HR sizes for the period ranged from 0.25 to 5.20 km2 (mean = 2.30 km2. Two thirds of the tagged G. morhua were infected with black spot disease Cryptocotyle lingua parasites; these fish had larger HRs and occupied deeper water compared with non-infected fish. The infected fish also tended to be more active in terms of horizontal swimming. From an ecological and evolutionary perspective, any environmental change that modifies G. morhua behaviour may therefore also alter the parasite load of the population, and its conservation and fishery status.

Rapid fluctuation in infection levels of Neoheterobothrium hirame (Monogenea) in Japanese flounder Paralichthys olivaceus in the Joban area, Japan

Neoheterobothrium hirame a haematophagous monogenean parasite on Japanese flounder Paralichthys olivaceus occurred at high prevalences (> 70%) from 1999 to 2002 but thereafter declined and remained low (< 20%) from 2003 to 2005 in the Joban area, Japan. In 2006, N. hirame became abundant again reaching a prevalence of 63%. Generalized linear models explained these rapid fluctuations in infection in relation to inshore water temperature, which affected the reproductive success of the parasite, and also the encounter rate between host and parasite through changes in their respective population densities. Severely anaemic fish were few, 2.4% even in 1999-2002 and 2006, suggesting that the effect of N. hirame infection on the P. olivaceus population was small in this area.