Drivers of growth for Atlantic cod (Gadus morhua L.) in Icelandic waters – A Bayesian approach to determine spatiotemporal variation and its causes

This study assesses spatiotemporal and sex-specific growth of Atlantic cod Gadus morhua in Icelandic waters. We use a Bayesian approach which lends itself to fitting and comparing nested models such as these. We then compare fitted parameters of these models to potential explanatory variables using a redundancy analysis (RDA) to look for drivers of growth in G. morhua. Results indicate that models that incorporate differences in growth among time, space and sex are the best-fitting models according to deviance information criterion (DIC). Results from RDA indicate that capelin Mallotus villosus recruitment and biomass is highly correlated with deviations in the von Bertalannfy growth parameter k and that L_∞ is correlated with G. morhua landings in the model that uses year to account for time-varying growth and estimated G. morhua recruitment in the model that uses cohort to account for time-varying growth.     

The abundance and patterns of the egg and larval spatial distribution of Eastern Baltic cod Gadus morhua callarias (Gadidae) in 1931–1996

According to ichthyoplankton surveys of AtlantNIRO and published sources, the data on abundance of eggs and larvae of eastern Baltic cod Gadus morhua callarias at different spawning grounds of the Baltic Sea in 1931–1938, 1949–1956, and 1991–1996 are considered. We show that a similar type of spatial distribution of eggs and larvae of cod with localization of the greatest amount of its early ontogenetic stages in the Bornholm Basin in the southwest of the sea was observed in the 1930s and 1990s. The extension of the area of distribution was accompanied by an increase in the numbers of eggs and larvae of cod in all areas of the sea, and its decline was followed by a decrease in numbers, in the first turn, at northeastern spawning grounds in the Gotland Basin. The period of high numbers of eggs in 1949–1956 coincided with the century maximum of salinity of the near-bottom water layer.     

Fishing through time: population dynamics of plaice (Pleuronectes platessa) in the Kattegat–Skagerrak over a century

Over the past century, advances in technology and historical events such as climate change have resulted in significant changes in the exploitation pattern, population sizes and the potential yield of fish stocks. These variations provide contrast in the data that improves our knowledge on population dynamics and our ability to develop management strategies for long-term sustainable exploitation. In this study, we use a standardized scientific trawl survey to obtain a historical time series (1901–2007) of relative abundance, recruitment and size structure for plaice in the Kattegat–Skagerrak. Our work extends the available time series by more than 80 years so that the evaluation of trends is more informative than is possible from the current assessment. We show that the current adult biomass is approximately 40% of the maximum observed at the beginning of the century and during the 1960s. The average maximum individual length has been reduced by 10 cm over the studied time period. An analysis of trends in mean length indicates that fishing mortality was variable during the first half of the century and has increased steadily over the past 20 years. Recruitment has been the highest on record during recent years, suggesting that the alleged link between coastal environmental degradation and juvenile survival is of low importance. The overall findings of our work will provide managers with a historical perspective on the population dynamics of the stock, which will support the long-term management of plaice in the Kattegat–Skagerrak.     

Probiotics–pathogen interactions elicit differential regulation of cutaneous immune responses in epidermal cells of Atlantic cod Gadus morhua

Little is known on the cutaneous immune responses during probiotics–pathogen interactions in fish. Thus, this study employed Atlantic cod primary epidermal (EP) cell cultures as a model to understand this interaction. The probiotics–pathogen interactions in the EP cell cultures were elucidated using Vibrio anguillarum 2133 (VA) as the pathogen and two host-derived bacteria (GP21 and GP12) as the probiotics. There was a regional size difference on the EP cells; i.e., EP cells from the dorsal region were significantly larger than the EP cells at the ventral side. VA significantly decreased viability of EP cells. In the presence of probiotics, this inhibition was mitigated. The probiotics reduced VA-induced cellular apoptosis and the probiotics–pathogen interactions influenced cellular myeloperoxidase activity during the latter stage of co-incubation. The probiotics–pathogen interactions triggered differential regulation of immune-related genes and the effects of the interaction were dependent on the region where the cells were isolated and the length of the co-incubation period. In most cases, the presence of probiotics alone showed no significant change on the mRNA level of immune genes in the EP cells but triggered immunostimulatory activity when incubated with VA. This study showed that the virulence of VA in EP cells could be modulated by host-derived probiotics and the immunomodulatory characteristics of the two candidate probionts advanced their immune-related probiotic potential.     

Characterization of cold-adapted Atlantic cod (Gadus morhua) trypsin I — Kinetic parameters,autolysis and thermal stability

Atlantic cod trypsin I is a highly active cold-adapted protease. This study aimed at further characterization of this enzyme with respect to kinetic parameters, sites of autolysis and stability. For that purpose, trypsin I was purified by anion exchange chromatography. Its purity and identity was verified by SDS-PAGE analysis and mass spectrometry. Concomitantly, another cod trypsin isozyme, trypsin X, previously only described from its cDNA sequence was detected in a separate peak from the ion exchange chromatogram. There was a stepwise increase in the catalytic efficiency (k_cat/K_m) of cod trypsin I obtained with substrates containing one to three amino acid residues. As expected, the activity of trypsin I was maintained for longer periods of time at 15 °C than at higher temperatures. The residues of the trypsin I molecule most sensitive to autolysis were identified using Edman degradation. Eleven autolytic cleavage sites were detected within the trypsin I molecule. Unfolding experiments demonstrated that autolysis is a contributing factor in the stability of trypsin I. In addition, the data shows that cod trypsin I is less stable towards thermal unfolding than its mesophilic bovine analogue.     

The isolation of Atlantic cod, Gadus morhua (Gadiformes), populations in Northern Meromictic lakes—A recurrent arctic phenomenon

Although it has previously been considered to be a rare phenomenon, this paper provides evidence of eight occurrences of Atlantic cod in northern coastal saline lakes in Arctic Canada, Greenland, Norway, and Russia. Historic and current habitat features that are necessary for Atlantic cod to colonize and persist in Arctic meromictic lakes are discussed. Data analyses confirm that the persistence of Atlantic cod in Arctic lakes is a recurrent phenomenon, and these populations represent an important component of intraspecific biodiversity. Published in Russian in Voprosy Ikhtiologii, 2008, Vol. 48, No. 2, pp. 179–190. The text was submitted by the authors in English.     

Novel microsatellites from the European plaice (Pleuronectes platessa)––identification by data mining and cross-species amplification in other flatfishes

The European plaice (Pleuronectes platessa; Pleuronectidae) is considered the most important flatfish for fisheries in Europe. Overall catches have been reduced drastically throughout the past decades, indicating a severe decline in the natural populations. However, a limited set of genetic tools are available to improve stock assessment and management for the species. Sequences of European plaice and its congener, the winter flounder (Pleuronectes americanus) deposited in the public database were searched for short tandem repeats. Out of 22 loci derived from database sequences, eight were amplified successfully and genotyping of 23 wild-caught individuals showed expected heterozygosities ranging from 0.18 to 0.84. The average allele number was 4.75 per locus (range 2–11). Successful cross-species amplification of the markers was demonstrated from two related flatfishes. All eight markers were successfully amplified from the European flounder (Platichthys flesus), a phylogenetically closely related species, whereas three of them worked in Achiroides melanorhynchus, an endemic species of Southeast Asia for which no microsatellites have been described to date.     

Does temperature preference relate to the anaerobic capacity of Atlantic cod (Gadus morhua L.) with different haemoglobin phenotype?

The effect of Hb-I* phenotype on white muscle lactate dehydrogenease (LDH, E. C. 1.1.1.27) activity and buffering capacity was studied in Atlantic cod (Gadus morhua), acclimated and measured at temperatures near their behavioral temperature preference. It was hypothesized that these conditions would optimize biochemical processes but no difference was found in LDH activity between the Hb-I* phenotype after 56 d of acclimation to 6 and 14°C. However, LDH activity was both mass- and temperature-dependent; mean activity was 162.2±5.0 and 275.9±6.4 IU g^-1 wet mass (mean±SEM) at 6 and 14°C respectively and larger fish had the highest rate of enzyme activity. White muscle buffer capacity was unaffected by Hb-I* phenotype but higher in cod held at 14°C.     

Effects of temperature on egg and larval survival of cod (Gadus morhua) and sprat (Sprattus sprattus) in the Baltic Sea – implications for stock development

Hydrobiologia - Stock development of cod and sprat, two major fish species in the Baltic Sea, is linked by trophic interactions. Depending on recruitment success the Baltic may be pushed towards...     

The occurrence of some metazoan parasites of Atlantic cod, Gadus morhua L., in relation to age and sex of the host in Balsfjord (70°N), North Norway

Age and sex differences in the occurrence of some metazoan parasites were investigated in 243 cod (Gadus morhua L.) from Balsfjord, a subarctic fjord in northern Norway. Thirteen species of parasite were studied, comprising seven nematodes, three parasitic copepods, one acanthocephalan, one cestode and one digenean. The nematode Anisakis simplex showed significant increases in both prevalence and mean abundance with host age, while the digenean Hemiurus levinseni showed a significant increase in mean abundance with age. The increases probably result from a long parasite life-span for A. simplex and changes in the feeding pattern of cod with age for H. levinseni. Prevalence of the nematode Contracaecum sp. and mean abundance of the acanthocephalan Echinorhynchus gadi were significantly higher in male than in female cod, whereas mean abundance of H. levinseni was significantly higher in female cod. These results suggest that there may be differences in feeding behaviour between male and female cod in Balsfjord. Accepted: 14 November 1999     

Genetic and morphological variation in Echinorhynchus gadi Zoega in Müller, 1776 (Acanthocephala: Echinorhynchidae) from Atlantic cod Gadus morhua L

Previous studies have shown considerable variability in morphological features and the existence of genetically distinct sibling species in the acanthocephalan Echinorhynchus gadi Zoega in Müller, 1776. The aim of the present study was to follow up and extend those earlier studies by using a combination of DNA analysis and morphometrics to investigate differences between samples of E. gadi from Atlantic cod Gadus morhua L. caught at five fishing grounds in the Baltic Sea and three in different parts of the North Atlantic. Twelve morphological features were measured in 431 specimens of E. gadi, 99 individuals were studied by polymerase chain reaction-restriction fragment length polymorphosm (PCR-RFLP), and selected PCR products were sequenced. The molecular analyses showed the nucleotide sequences of E. gadi rDNA from cod caught at all the sampling sites to be identical. The comparative morphological study, in contrast, revealed significant differences between samples of E. gadi from different sampling sites and showed the separation of E. gadi into two groups corresponding approximately to the systematic classification of cod into the two subspecies, Atlantic G. morhua morhua and Baltic G. morhua callarias. The E. gadi infrapopulation size had a significant effect on some of the morphological features. The results are discussed in relation to cod population biology, the hydrography of the study area and the history of the Baltic Sea formation.     

Assessment of the diets of cod Gadus morhua and whiting Merlangius merlangus juveniles in a frontal region close to the Norwegian Trench: co‐existence or competition?

Over 200 pelagic juvenile cod Gadus morhua and whiting Merlangius merlangus were sampled in spring 2001 at stations inside and outside a frontal region close to the Norwegian Trench, and their stomach contents analysed in the context of zooplankton samples taken at the same time and same locations. Merlangius merlangus juveniles appeared to feed on a diverse zooplankton community, whereas G. morhua juveniles appeared to preferentially select Pseudocalanus elongatus, even though these prey items were not the dominant component of the prey community. The results suggest that during the pelagic juvenile stage, M. merlangus and G. morhua are direct competitors for zooplanktonic prey. In addition, because M. merlangus are more opportunistic, they may be more tolerant to changes in the species composition of the prey community, and therefore out‐compete G. morhua juveniles at times of low preferred prey abundance or under changing environmental conditions.     

1H, 13C and 15N resonance assignments and second structure information of Gad m 1: a β-parvalbumin allergen from Atlantic cod (Gadus morhua)

Gad m 1 is the major allergen from Atlantic cod. It belongs to β-parvalbumin protein family and is characterized by the presence of two calcium-binding sites so called EF-hand motifs. β-Parvalbumins such as Gad m 1 are the most important fish allergens and their high cross-reactivity is the cause of the observed polysensitization to various fish species in allergic patients. Despite extensive efforts, the complete elucidation of β-parvalbumin-IgE complexes has not been achieved yet. Allergen structural studies are essential for the development of novel immunotherapy strategies, including vaccination with hypoallergenic derivatives and chimeric molecules. Here, we report for the first time the NMR study of a β-parvalbumin: Gad m 1. This report includes: ¹H, ¹³C and ¹⁵N resonance assignments of Gad m 1 as well as the second structure information based on the ¹³C chemical shifts.     

Is there a link between the type of habitat and the patterns of abundance of holothurians in shallow rocky reefs?

The presence of a mosaic of habitats, largely determined by sea urchin grazing, across shallow rocky reefs may potentially influence in differences in the distribution patterns of invertebrates. The aim of this paper was to assess, using a correlative approach, whether the type of habitat influences the abundance patterns of holothurians in the eastern Atlantic. We hypothesized that abundances of large (> 10 cm) holothurians varied among four types of habitat (3 vegetated habitats with low abundances of the sea urchin D. antillarum vs. ‘barrens’ with hyperabundances of sea urchins), and that these differences were consistent at a hierarchy of spatial scales, including two islands and several replicated sites within each type of habitat and island. Three species of large holothurians were found, accounting for a total of 300 specimens. We found remarkable differences in abundances of holothurians between the ‘barrens’ and the three vegetated habitats. This pattern was strongest for the numerically dominant species, Holothuria sanctorii. Total abundances of holothurians were between 5 and 46 times more abundant in ‘barrens’ compared with the vegetated habitats. Inter-habitat differences were species-specific with some inconsistent patterns from one island to the other. The total abundances of holothurians tended to increase with the abundance of sea urchins within ‘barrens’. Our study suggests that there may be a link, at least for the dominant species Holothuria sanctorii, between the distribution and abundances of large holothurians and the habitat across shallow-waters of the eastern Atlantic.