Publications

Here you will find publications from DTU Aqua:

Recent publications

2018
 

Transgenerational effects of cyanobacterial toxins on a tropical micro-crustacean Daphnia lumholtzi across three generations

Year: 2018

Transgenerational effects of cyanobacterial toxins on a tropical micro-crustacean Daphnia lumholtzi across three generations

Dao, T-S., Vo, T-M-C., Wiegand, C., Bui, B-T. & Dinh, K. V. 2018 In : Environmental Pollution.

Publication: Research - peer-reviewJournal article – Annual report year: 2018

Original languageEnglish
JournalEnvironmental Pollution
ISSN0269-7491
DOIs
StateAccepted/In press - 2018

 

Experimental anal infection of rainbow trout with Flavobacterium psychrophilum : A novel challenge model

Year: 2018

Flavobacterium psychrophilum is a Gram‐negative psychrophilic bacterium causing rainbow trout fry syndrome (RTFS) in fry and bacterial coldwater disease (BCWD) in older fish. Both diseases challenge fish welfare and economy in hatcheries and in on‐growing facilities. The bacteria enter hosts through gills, skin, and the gastrointestinal tract, and transfer horizontally in contaminated water and vertically with sexual products of both male and female fish (Madetoja, Dalsgaard, & Wiklund, 2002; Madsen & Dalsgaard, 1999; Nematollahi, Decostere, Pasmans, & Haesebrouck, 2003). Protection afforded by experimental vaccination (injection or immersion) using bacterins (formalin‐killed whole cell) has been described (Hoare, Ngo, Bartie, & Adams, 2017; Madetoja et al., 2006), although no commercial vaccine is presently available for control of RTFS and BCWD. Further research on RTFS/BCWD vaccinology will benefit from an improved challenge method as current methods comprising intraperitoneal (i.p.) injection, bath, and bath exposure after treatment with stressors such as hydrogen peroxide (Henriksen, Kania, Buchmann, & Dalsgaard, 2015; Madsen & Dalsgaard, 1999) remain difficult to reproduce and rely on wounding the structural integrity of mucosal surfaces. The present study compares different infection methods and evaluates systems where the rainbow trout surface (skin, gills, and gut) is kept intact or injured. We compared six different challenge methods comprising anal intubation, i.p. injection, co‐habitation, and bath challenge exposing either nontreated intact fish, fish chemically damaged by exposure to hydrogen peroxide or fish mechanically damaged by needle insertion in the tail‐fin. Disease development was subsequently recorded for 4 weeks.
Original languageEnglish
JournalJournal of Fish Diseases
Number of pages3
ISSN0140-7775
DOIs
StateAccepted/In press - 2018

 

Summer distribution and demography of Antarctic krill Euphausia superba Dana, 1852 (Euphausiacea) at the South Orkney Islands, 2011–2015

Year: 2018

Summer distribution and demography of Antarctic krill Euphausia superba Dana, 1852 (Euphausiacea) at the South Orkney Islands, 2011–2015

Krafft, B. A., Krag, L. A., Knutsen, T., Skaret, G., Jensen, K. H. M., Krakstad, J. O., Larsen, S. H., Melle, W., Iversen, S. A. & Godø, O. R. 2018 In : Journal of Crustacean Biology.

Publication: Research - peer-reviewJournal article – Annual report year: 2018

We carried out a survey of Antarctic krill (Euphausia superba Dana, 1850) from 2011 to 2015 to establish a long-term, time-series dataset of distribution, abundance, and demography for this species in the South Orkney Islands sector of the Southern Ocean. This species is abundant in this region and is subjected to high-intensity fishing, but previous assessments of density and population dynamics are few and outdated. Our data for Antarctic krill was collected from
trawl stations along survey line transects covering the South Orkney plateau and shelf region during the summers of five consecutive years. We used concurrent data on hydrography, bathymetry, and proxies for algal biomass to describe potential spatial patterns of demography and abundance of E. superba. Comparative analysis of the demographic composition showed that 2012 differed from the other years by having a higher proportion of juveniles; otherwise a consistent pattern was found among years and within the study area. The highest
biomass during the study period occurred along the northern shelf edge of the South Orkney Islands. Results of the linear mixed-effect model used to evaluate a diverse range of variables revealed that the only predictors for this hotspot were the short distance from land and great bottom depth. No clear differences in demographic composition for the study area were detected, which indicates that the area is highly dynamic and dominated by flux and advection of krill, both to, from, and within the area. Despite this finding, the results demonstrate that the shelf break on the northwest South Orkney Islands is predictable over time as a krill concentration and retention hotspot during the summer season
Original languageEnglish
JournalJournal of Crustacean Biology
ISSN0278-0372
DOIs
StateAccepted/In press - 2018

 

Effects of oil spills on Arctic pelagic ecosystems - Winter exposure and variations in sensitivity

Year: 2018

In a world where climate is changing faster than ever previously recorded, the Arctic is in the front line experiencing substantial environmental changes at accelerating speed. One of these changes, the declining sea ice cover, encourages exploration of the regions abundant offshore fossil fuel reserves. This has raised international concerns about emergency preparedness and
oil spill prevention, because the time scale of ecosystem impact and recovery could be extensive in Arctic regions. The vulnerability of Arctic marine ecosystems to oil spills is influenced by a strong seasonal biological production and a number of unique species adaptations that result in variations in sensitivity over the annual cycle. A particular challenge for risk assessment of oil activities is that biological background data from the winter period often is insufficient. This thesis outlines my work on effects of oil spills on Arctic pelagic ecosystems, where I have focused on winter exposure and variations in sensitivity of the lower trophic levels – the microbial and copepod communities. These communities are fundamental to the function of the marine ecosystem because their interactions generate the high-energy lipids that upper trophic levels rely on for coping with strong seasonal variations in food availability. The
thesis is based on four papers addressing two main questions; Firstly, how does a surface oil spill impact ice-associated plankton communities during the ice-covered period, and how is vulnerability affected by available oil spill response methods (paper I and II)? And secondly, how does an oil spill on deep water impact overwintering zooplankton communities, and how is species vulnerability affected by differences in reproduction strategy (paper III and IV)? Based on mesocosm studies, we first show that a surface oil spill in sea ice in winter can lead to alterations in the structure and function of ice-associated plankton communities in spring, and potentially cause indirect cascading ecosystem effects through trophic interactions in the Arctic marine food web. During the ice-covered period, these plankton communities are less vulnerable to an oil spill treated with in situ burning, and more vulnerable when chemical
dispersant is used. Then, based on laboratory studies, we further show that an oil spill on deep water in winter can severely impact the two most important zooplankton species in Arctic ecosystems, which are important ecosystem components responsible for energy transfer to upper trophic levels of the marine food web. Both lipid content and reproduction strategy play an important role for determining the vulnerability to oil exposure during their overwintering.
The findings of this thesis provides novel insights to the seasonal vulnerability of Arctic pelagic ecosystems to oil spills, which is important for improving risk assessment of oil activities in the Arctic
Original languageEnglish
PublisherNational Institute of Aquatic Resources, Technical University of Denmark
Number of pages107
StatePublished - 2018

 

European eel larval ontogeny and physiology Insights at morphological and molecular level

Year: 2018

The research conducted within this PhD project contributes to filling gaps in knowledge about the enigmatic life cycle of European eel (Anguilla anguilla) by addressing biotic and abiotic factors influencing early larval stages. This involves experimental studies and utilization of state-of-the-art molecular tools elucidating links between morphology and molecular mechanisms in the quest to identify suitable rearing and feeding conditions for larviculture. As such, this thesis comprises six studies within three main topics: i) temperature,
ii) salinity and iii) nutrition, influencing larval development and survival.
The first three studies address the influence of temperature on early larval ontogeny. Here, Study 1 determined the thermal tolerance limits and identified an intermediate thermal environment for future larval culture with efficient growth and low frequency of deformities associated with high expression of growth hormone (improved growth) and low expression of heat shock proteins (decreased stress). Moreover, Study 2 revealed that expression of genes encoding thyroid hormone receptors and deiodinases, associated with the
mediation of thyroid hormone action, show sensitivity to temperature and are involved in and during early larval development. Additionally, Study 3 shed light on the molecular ontogeny of the larval immune system under different thermal scenarios and identified an immune-compromised phase during which mortality is high and larvae are more vulnerable to pathogen infection. This will have important implications on rearing conditions and disease prevention protocols in eel hatcheries but also improve our understanding of ocean warming impacts on fish recruitment. Thereafter, experimental work focused on the salinity tolerance of these marine larvae. Here, Study 4 clearly demonstrated that culture regimes reducing salinity towards isoosmotic conditions facilitated enhanced European eel pre-leptocephalus development and survival revealing the existence of underlying, highly sensitive and regulated osmoregulation processes in the early larval stage. This novel insight gained by morphologically and molecularly defined physiological thermal and osmoregulatory tolerance limits and preferences gradually led to improved protocols for pre-leptocephalus larval culture and resulted in significantly increased numbers of healthier and stronger larvae reaching the first-feeding stages. Previous to these culture condition improvements, a pilot nutritional trial was performed.
Here, Study 5 for the first time explored several diets, tested attractants and described behavioral feeding patterns of European eel larvae. Finally, with much enhanced numbers of larvae and using the previously identified benchmark diet as well as enhanced temperature condition, Study 6 revealed that initiation of
exogenous feeding in European eel occurs concurrently with the onset of the genetically pre-programmed underlying hormonal control of ingestion and the enzymatic regulation of digestion, known to regulate physiological functions of feeding. The here gained knowledge, improved the understanding of an
undisclosed phase of the European eel life cycle, which is the transition from yolk-sac pre-leptocephalus larvae to the exogenous feeding leptocephalus stage and constitutes essential information in order to develop efficient feeding strategies for future larviculture of this species. In conclusion, the conducted research elucidated molecular aspects of important biological processes in order
to more closely understand the complexity of regulations involved in early European eel ontogeny and physiology. The gained knowledge contributes to our understanding of unknown mysterious aspects of the European eel life cycle and most importantly provides promising steps for eel aquaculture towards
completing the life cycle in captivity of this socially and economically important as well as critically endangered fish species
Original languageEnglish
PublisherDTU aqua. National Institute of Aquatic Resources
Number of pages156
StatePublished - 2018