Glucocorticoid receptor (DlGR1) is expressed in pre-larval and larval stages of the teleost fish Dicentrarchus labrax

Glucocorticoid hormone receptors (GR), members of the nuclear hormone receptor superfamily, are ligand-dependent transcription factors expressed in various tissues by binding to specific DNA sequences. Since glucocorticoids have a role in maintaining the homeostatic status in fish, we previously cloned and sequenced a GR (DlGR1) of adult Dicentrarchus labrax; we also showed mRNA expression (in situ hybridization) and tissue immunohistochemical localization of DlGR1 in several organs. This work has now been extended to the examination of the expression, tissue distribution, and cytolocalization of DlGR1 in larval developmental stages by similar methods to those used for the adult organs. The riboprobe included the DlGR1 cDNA transcriptional activation domain (1.0–1,300 nucleotide sequence) showing no significant similarity with a known second GR cDNA sequence of sea bass. The antibody was specific for an opportunely selected peptide sequence of the DlGR1 transcriptional domain. In histological sections of brain, head kidney, gills, liver, anterior intestine, and spleen cells, the riboprobe was mainly located in the cell nucleus. The antibody identified DlGR1 in the head kidney, gills, liver, and anterior intestine, mainly located in the cytosol. These results are in agreement with the receptor location in adult tissues. The greater presence of both the transcript and protein of DlGR1 in the late developmental stages suggests an increasing expression of this receptor. The cytolocalization (nuclear-cytosolic) and presumptive roles of DlGR1-containing tissues are discussed

Effects of chronic bottom fishing on the benthic epifauna and diets of demersal fishes on northern Georges Bank

Feeding by demersal fishes on benthic invertebrates constitutes an important link between fishery resources and continental shelf habitats. However, concurrent sampling of demersal fish diets and benthic invertebrate prey fields has been limited, particularly in relation to chronic bottom fishing disturbance on continental shelves worldwide. Here, we quantified differences in the epibenthic invertebrate and fish communities between sites with contrasting levels of disturbance from mobile bottom fishing gear for 2 gravel regions of Georges Bank in the northwest Atlantic. The main objectives were to compare a suite of biological indices for epibenthic invertebrates, demersal fishes, and fish diets across year and level of fishing disturbance. The fishes selected for diet comparisons included winter skate Leucoraja ocellata, little skate L. erinacea, Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, winter flounder Pseudopleuronectes americanus, and longhorn sculpin Myoxocephalus octodecemspinosus. Three baseline benthic epifaunal indices, species richness, abundance (no. l-1), and biomass (g l -1), were lower in the heavily fished areas; however, evenness was higher in these areas. The lengths of haddock, Atlantic cod, and winter flounder tended to be larger at the undisturbed sites. Fish stomach contents differed significantly among habitats for 3 benthivores: haddock, winter flounder, and longhorn sculpin; diets were more highly correlated with the benthic fauna within than among sites, which indicated site-specific feeding. In several cases, prey that contributed to the diet dissimilarity between sites were benthic epifauna most sensitive to the impact of bottom fishing disturbance; thus, the availability of epibenthic prey was determined by this disturbance. © Inter-Research 2013

Change in fish community structure in the barents sea

Change in oceanographic conditions causes structural alterations in marine fish communities, but this effect may go undetected as most monitoring programs until recently mainly have focused on oceanography and commercial species rather than on whole ecosystems. In this paper, the objective is to describe the spatial and temporal changes in the Barents Sea fish community in the period 1992–2004 while taking into consideration the observed abundance and biodiversity patterns for all 82 observed fish species. We found that the spatial structure of the Barents Sea fish community was determined by abiotic factors such as temperature and depth. The observed species clustered into a deep assemblage, a warm water southern assemblage, both associated with Atlantic water, and a cold water north-eastern assemblage associated with mixed water. The latitude of the cold water NE and warm water S assemblages varied from year to year, but no obvious northward migration was observed over time. In the period 1996–1999 we observed a significant reduction in total fish biomass, abundance, mean fish weight, and a change in community structure including an increase in the pelagic/demersal ratio. This change in community structure is probably due to extremely cold conditions in 1996 impacting on a fish community exposed to historically high fishing rates. After 1999 the fish community variables such as biomass, abundance, mean weight, P/D ratio as well as community composition did not return to levels of the early 90s, although fishing pressure and climatic conditions returned to earlier levels.The data were collected during the former annual shrimp survey conducted by the Norwegian Institute of Fisheries and Aquaculture (NIFA) and the Institute of Marine Research (IMR) in the Barents Sea from 1992 until 2004, and were funded by the Norwegian Ministry of Fisheries and Coastal Affairs. The scientific work was also funded by the Norwegian Government through the above mentioned ministry and through the Ministry of Education and Research. Michael Greenacre’s research was partially funded by the BBVA Foundation in Madrid and a grant from the Spanish Ministry of Education MTM2012-37195. The funders had no role in study design, data collection and analysis, decision to publish or the preparation of the manuscript