Search

Master's thesis in Biological chemistry Baking av torsk i kokeskap er vanlig praksis både i matindustrien og på storkjøkken. Kokken velger passende program på grunnlag av erfaring, mens i matindustrien er holdbarhet ofte en viktig tilleggsfaktor. I sistnevnte er det større behov for en kraftigere varmebehandling, enn hva som er nødvendig om fisken skal serveres umiddelbart etter varmebehandling. Det er viktig å optimalisere varmebehandling for å tilfredsstille god sikkerhet og kvalitet. Uheldig varmebehandling kan resultere i krymping og en fisk som er tørr og trevlete. Den systematiske undersøkelsen i denne oppgaven kan kombineres med kokkens erfaring for å optimalisere tilberedningen av torsk. I denne oppgaven ble Atlantisk torsk (Gadus morhua) undersøkt for varme- og saltinduserte kvalitetsendringer, både før og etter at muskelvevet ble utsatt for ulike varmebelastninger. Kvalitetsendringer i form av rest-entalpi under denaturering, mikrostruktur, vannbindingsevne, tekstur, farge og reologi ble undersøkt. Torsken ble behandlet i lake med 0, 1,5 og 4,5 % salt og inneholdt deretter tilnærmet lik fiskens biologiske saltinnhold (P > 0,05), samt ~ 1 og 3 % salt. Dataene skal senere brukes direkte eller indirekte til å lage en modell i COMSOL Multiphysics for å finne varmebehandlinger som er trygge og samtidig opprettholder god kvalitet på torsk. På denne måten kan matindustrien redusere væsketapet og sammen med storkjøkken tilby saftigere fisk med en tekstur tilpasset brukernes ønsker. Når proteiner denaturerer, delvis som følger av salt, men i større grad som følger av varme endres kvaliteten i muskelvevet. Myosin og aktin, to av de viktigste muskelproteinene ble destabilisert ved tilsetting av salt, som resulterte i at lavere temperatur og mengde energi måtte til for å denaturere proteinene. Mikrostrukturen i muskelvevet ble til en viss grad påvirket av saltinnhold. Størst hulrom mellom cellene ble observert for prøver behandlet i ferskvann. Hulrommet ble noe redusert ved økende saltkonsentrasjon. Hulrommet mellom muskelceller viste en tendens til økning ved økt varmebelastning. Saltet torsk hadde signifikant høyere vannbindingsevne etter sentrifugering, sammenlignet med usaltet torsk. Dette ble observert både for rå og varmebehandlede prøver opptil 70 °C. Saltkonsentrasjonen var av større betydning for vannbindingsevnen ved lavere temperaturer (< 50 °C), men ved 50 °C og over ble det ikke lenger observert signifikante forskjeller mellom prøver behandlet i 1,5 og 4,5 % salt. Koketapet var generelt lavt ved alle behandlinger, og såpass nært deteksjonsgrensen at resultatet var noe usikkert. Overordnet trend viste størst koketap for prøver behandlet i ferskvann, som økte med økende temperatur. Prøver behandlet i ulik saltkonsentrasjon viste ikke signifikant forskjellig koketap for noen av temperaturene. Tekstur målt som hardhet viste mykest muskelvev ved lave temperaturer, som holdt seg relativt stabil frem til 40 °C. Temperaturer over dette resulterte i et hardere muskelvev, med signifikante forskjeller mellom 40 og 80 °C. Prøver behandlet i lake med ulik saltkonsentrasjon viste imidlertid ikke signifikant forskjellig resultat. Reologianalysen viste samme trend, med en generelt økende elastisitet som følger av økt temperatur etter at myosin var denaturert. Før dette ble muskelvevet mer viskøst ved økende temperatur. Fargeanalyse viste at varmebehandling hadde størst effekt på lysheten i torsken som var signifikant høyere ved 80 °C, sammenlignet med 30 °C for alle saltkonsentrasjoner. Prøver behandlet i lake med 4,5 % salt var signifikant mørkere i fargen enn prøver behandlet i ferskvann etter varmebehandling fra 30 – 80 °C. Ved hvilken temperatur torsk bør varmebehandles avhenger av bruksområde og ønsket holdbarhet. Det anbefales å tilberede torsk med litt salt ettersom muskelvevet holder bedre på vann, som gir en saftigere tekstur under varmebehandling. Om fisken inneholdt 1 eller 3 % salt spilte liten rolle for vannbindingsevnen når temperaturen kom opp i 50 – 70 °C, som er vanlig ved tilberedning av torsk. Derfor anbefales førstnevnte for å redusere inntaket av salt. I tillegg anbefales bruk av dampovn for å redusere uttørking og skorpedannelse ved høye temperaturer.

The timing and success of spawning in marine fish are of fundamental importance to population persistence and distribution and, for commercial species, sustainability. Their physiological processes of reproduction are regulated, in part, by water temperature, and therefore changes in marine climate may have dramatic effects on spawning performance. Using adult Atlantic cod ( Gadus morhua ) as a case study, we examined the links between water temperature, body size, vitellogenesis, and spawning time by conducting extensive laboratory and field studies. Our experiments documented that vitellogenesis generally starts at autumnal equinox and that oocyte growth and investment are greater in cod held at warmer temperatures. Furthermore, spawning occurred earlier when oocyte growth was more rapid. Large females spawned earlier than smaller females at warmer temperatures, but this effect vanished at colder temperatures. The experimental results were confirmed by measurements of oocyte growth collected from wild-caught cod in northern (Barents Sea) and southern (Irish Sea and North Sea) populations. The established, general model of oocyte maturation was consistent with published egg production curves of cod from these waters, considering relevant in situ temperatures recorded by individual data-storage tags on cod. These findings have considerable relevance for future studies of fish recruitment in relation to climate change.

Tagging-recovery studies have been used successfully on many occasions, and the data analysed in a variety of ways with respect to fish movement. Here we provide a synoptic account of useful statistical techniques for delimiting area utilization and movement patterns of a population of individuals. We focus specifically on kernel smoothing for population utilization distribution and gen- eralized additive models for temporal movement patterns. Furthermore, we use these 2 techniques to re-analyse data from tagging studies on coastal Atlantic cod Gadus morhua, shedding new light on one of the underlying mechanisms determining the population structure of the coastal cod along the Norwegian Skagerrak coast. Cod were found to use small areas. On average 25% of a population used areas smaller than 10 km 2 , while 95% of a population used areas smaller than 160 km 2 . The movements displayed were fjord-limited and predominantly within the bounds of the population's home range. By re-analysing existing data on neutral genetic markers, we show that the cross- distance of the area utilized was smaller than the distance over which pair-wise genetic differences appear.

Coastal marine species with pelagic egg and larval stages, such as the Atlantic cod Gadus morhua, can be structured into genetically distinct local populations on a surprisingly small geographic scale considering their dispersal potential. Mechanisms responsible for such small-scale genetic structure may involve homing of adults to their natal spawning grounds, but also local reten- tion of pelagic eggs and larvae. For example, spawning within sheltered fjord habitats is expected to favour local retention of early life stages. Here, we studied the distribution of cod eggs along inshore- offshore transects in 20 Norwegian fjords. The general pattern exhibited across all fjords was a higher concentration of cod eggs inside the fjords than further offshore. In particular, fjords with shal- low sills (model threshold 37 m) show an abrupt reduction in egg density over the sill. This study pro- vides empirical support for an offspring retention hypothesis, which may help to explain the mainte- nance of local population structure in pelagic marine systems.

Increasing use of the chitin synthesis inhibitor diflubenzuron against the ectoparasitic salmon louse Lepeophtheirus salmonis in marine aquaculture has raised concerns over its environmental impacts. This study evaluated how diflubenzuron affects Atlantic cod Gadus morhua, a fish species often found near Atlantic salmon Salmo salar farms, focusing on uptake kinetics and hepatic transcriptional responses. Two experiments were conducted, one time-series trial in which the fish were given a daily dose (3 mg kg–1 fish) of diflubenzuron for 14 d followed by a 3 wk depuration period, and one dose-response trial with increasing concentrations (3, 10 and 50 mg kg–1 fish). The highest diflubenzuron concentrations were found in the liver at Day 15. No detectable levels of diflubenzuron were found in liver or muscle 3 wk after the end of the treatment. At the molecular level, small effects of diflubenzuron treatment on gene transcription were observed. In the time-series experiment, the strongest effects were seen at Day 8, with 2 transcripts being upregulated (bclx2 and cpt1a) and 8 transcripts being downregulated (gstp1, gstm1, gstt1, ugt1a, nat2, cat, p53 and slc16a9a). Five transcripts (cyp3a, cpt1a, ptgs2, elovl5 and mapk1) responded significantly to diflubenzuron exposure in the dose-response experiment. This study shows that diflubenzuron can be taken up by Atlantic cod, that it is rapidly cleared from the body and that when present this pharmaceutical causes only small effects on the expression of genes involved in detoxification pathways. Taken together, our data suggest that accumulated diflubenzuron at the levels studied would have a relatively small effect on wild Atlantic cod. 2018-07-09

Fish stocks experiencing high fishing mortality show a tendency to mature earlier and at a smaller size, which may have a genetic component and therefore long-lasting economic and biological effects. To date, the economic effects of such ecoevolutionary dynamics have not been empirically investigated. Using 70 y of data, we develop a bioeconomic model for Northeast Arctic cod to compare the economic yield in a model in which life-history traits can vary only through phenotypic plasticity with a model in which, in addition, genetic changes can occur. We find that evolutionary changes toward faster growth and earlier maturation occur consistently even if a stock is optimally managed. However, if a stock is managed optimally, the evolutionary changes actually increase economic yield because faster growth and earlier maturation raise the stock’s productivity. The optimal fishing mortality is almost identical for the evolutionary and nonevolutionary model and substantially lower than what it has been historically. Therefore, the costs of ignoring evolution under optimal management regimes are negligible. However, if fishing mortality is as high as it has been historically, evolutionary changes may result in economic losses, but only if the fishery is selecting for medium-sized individuals. Because evolution facilitates growth, the fish are younger and still immature when they are susceptible to getting caught, which outweighs the increase in productivity due to fish spawning at an earlier age.

A total of 30 isolates of Francisella noatunensis subsp. noatunensis isolated from Atlantic cod Gadus morhua L. were tested for susceptibility, in the form of minimal inhibitory concentration (MIC) values, against the following antibacterial agents: flumequine, oxolinic acid, ciprofloxacin, florfenicol, oxytetracycline, erythromycin, streptomycin sulphate, trimetoprim/ sulphadiazine and rifampin. All the isolates had a low susceptibility to oxytetracycline, trimetoprim/ sulphadiazine (Tribrissen®), erythromycin, ciprofloxacin and streptomycin with MIC values of 64, 64 to 128, 16, 8 and 32 to 128 μg ml−1, respectively. The strains were, on the other hand, susceptible to florfenicol, oxolinic acid, flumequine and rifampin with MIC values of 0.5, 0.25, 0.25 and 0.25 to 1 μg ml−1, respectively. 2017-02-17

Life history changes serve as stress indicators in harvested populations. Data from recent decades show that many species of marine fish are now maturing at younger ages and smaller sizes, associated with a general increase in harvest intensity. However, data from earlier times are generally sparse or lacking. In this study we compare present life history characteristics of fjord cod Gadus morhua in the Skagerrak, southern Norway, to century-old (1905) scientific data. Contrary to our expectations, age and length distributions were shifted towards older and larger fish in the most recent data set compared to the historic sample. Also, fish in the historic sample tended to be smaller at age and reached 50% maturity at a smaller size and younger age compared to the present sample. These results are in contrast to most other studies on life history changes in harvested fish. 2016-03-01

The genome of the Atlantic cod has been sequenced, and genomic analysis reveals an immune system that differs significantly from that in other vertebrates. The major histocompatibility complex (MHC) II has been lost, as have some other genes that are essential for MHC II function. But there is an expansion in the number of MHC I genes and a unique composition for its toll-like receptor family. These compensatory changes in both adaptive and innate immunity mean that cod is no more susceptible to disease than most other vertebrates. These findings challenge current models of vertebrate immune evolution, and may facilitate the development of targeted vaccines for disease management in aquaculture. Atlantic cod (Gadus morhua) is a large, cold-adapted teleost that sustains long-standing commercial fisheries and incipient aquaculture1,2. Here we present the genome sequence of Atlantic cod, showing evidence for complex thermal adaptations in its haemoglobin gene cluster and an unusual immune architecture compared to other sequenced vertebrates. The genome assembly was obtained exclusively by 454 sequencing of shotgun and paired-end libraries, and automated annotation identified 22,154 genes. The major histocompatibility complex (MHC) II is a conserved feature of the adaptive immune system of jawed vertebrates3,4, but we show that Atlantic cod has lost the genes for MHC II, CD4 and invariant chain (Ii) that are essential for the function of this pathway. Nevertheless, Atlantic cod is not exceptionally susceptible to disease under natural conditions5. We find a highly expanded number of MHC I genes and a unique composition of its Toll-like receptor (TLR) families. This indicates how the Atlantic cod immune system has evolved compensatory mechanisms in both adaptive and innate immunity in the absence of MHC II. These observations affect fundamental assumptions about the evolution of the adaptive immune system and its components in vertebrates.

In order to provide better fisheries management and conservation decisions, there is a need to discern the underlying relationship between the spawning stock and recruitment of marine fishes, a relationship which is influenced by the environmental conditions. Here, we demonstrate how the environmental conditions (temperature and the food availability for fish larvae) influence the stock–recruitment relationship and indeed what kind of stock–recruitment relationship we might see under different environmental conditions. Using unique zooplankton data from the Continuous Plankton Recorder, we find that food availability (i.e. zooplankton) in essence determines which model applies for the once large North Sea cod ( Gadus morhua ) stock. Further, we show that recruitment is strengthened during cold years and weakened during warm years. Our combined model explained 45 per cent of the total variance in cod recruitment, while the traditional Ricker and Beverton–Holt models only explained about 10 per cent. Specifically, our approach predicts that a full recovery of the North Sea cod stock might not be expected until the environment becomes more favourable.

e17456 Background Fisheries exploitation, habitat destruction, and climate are important drivers of variability in recruitment success. Understanding variability in recruitment can reveal mechanisms behind widespread decline in the abundance of key species in marine and terrestrial ecosystems. For fish populations, the match-mismatch theory hypothesizes that successful recruitment is a function of the timing and duration of larval fish abundance and prey availability. However, the underlying mechanisms of match-mismatch dynamics and the factors driving spatial differences between high and low recruitment remain poorly understood. Methodology/Principal Findings We used empirical observations of larval fish abundance, a mechanistic individual-based model, and a reanalysis of ocean temperature data from 1960 to 2002 to estimate the survival of larval cod (Gadus morhua). From the model, we quantified how survival rates changed during the warmest and coldest years at four important cod spawning sites in the North Atlantic. The modeled difference in survival probability was not large for any given month between cold or warm years. However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively. We also found that the importance of match-mismatch dynamics generally increased with latitude. Conclusions/Significance Our analyses indicate that a key factor for enhancing survival is the duration of the overlap between larval and prey abundance and not the actual timing of the peak abundance. During warm years, the duration of the overlap between larval fish and their prey is prolonged due to an early onset of the spring bloom. This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment.

Journal homepage: http://www.esajournals.org/loi/ecol Until the last decade it was assumed that most marine species have pronounced gene flow over vast areas, largely because of their potential for dispersal during early life stages. However, recent genetic, modeling, and field studies have shown that marine populations may be structured at scales that are inconsistent with extensive dispersal of eggs and larvae. Such findings have stimulated the birth of new studies explaining the mechanisms that promote population structure and isolation in the oceans, in the face of high potential for dispersal. Here we study the vertical and horizontal distribution of cod (Gadus morhua) eggs in relation to small-scale circulation and water column hydrography in a coastal location of southern Norway. Previous studies conducted in this region have shown that cod populations inhabiting fjord locations, which are on average 30 km apart, are genetically differentiated, a remarkable outcome considering that Atlantic cod have pelagic egg stages and long pelagic larval duration. We document that cod eggs are found in greater abundance in shallow water layers, which on average are flowing up the fjord (away from the open ocean), and in the inner portion of the fjord, which is subject to lower current speeds compared to the outer or mouth of the fjord. Eggs were found to be neutrally buoyant at shallow depths, a trait that also favors local retention, given the local circulation. The same patterns held during two environmentally contrasting years. These results strongly suggest that population structure of Atlantic cod is favored and maintained by a balance between water circulation and egg characteristics.

Background The vertebrate globin genes encoding the α- and β-subunits of the tetrameric hemoglobins are clustered at two unlinked loci. The highly conserved linear order of the genes flanking the hemoglobins provides a strong anchor for inferring common ancestry of the globin clusters. In fish, the number of α-β-linked globin genes varies considerably between different sublineages and seems to be related to prevailing physico-chemical conditions. Draft sequences of the Atlantic cod genome enabled us to determine the genomic organization of the globin repertoire in this marine species that copes with fluctuating environments of the temperate and Arctic regions. Results The Atlantic cod genome was shown to contain 14 globin genes, including nine hemoglobin genes organized in two unlinked clusters designated β5-α1-β1-α4 and β3-β4-α2-α3-β2. The diverged cod hemoglobin genes displayed different expression levels in adult fish, and tetrameric hemoglobins with or without a Root effect were predicted. The novel finding of maternally inherited hemoglobin mRNAs is consistent with a potential role played by fish hemoglobins in the non-specific immune response. In silico analysis of the six teleost genomes available showed that the two α-β globin clusters are flanked by paralogs of five duplicated genes, in agreement with the proposed teleost-specific duplication of the ancestral vertebrate globin cluster. Screening the genome of extant urochordate and cephalochordate species for conserved globin-flanking genes revealed linkage of RHBDF1, MPG and ARHGAP17 to globin genes in the tunicate Ciona intestinalis, while these genes together with LCMT are closely positioned in amphioxus (Branchiostoma floridae), but seem to be unlinked to the multiple globin genes identified in this species. Conclusion The plasticity of Atlantic cod to variable environmental conditions probably involves the expression of multiple globins with potentially different properties. The interspecific difference in number of fish hemoglobin genes contrasts with the highly conserved synteny of the flanking genes. The proximity of globin-flanking genes in the tunicate and amphioxus genomes resembles the RHBDF1-MPG-α-globin-ARHGAP17-LCMT linked genes in man and chicken. We hypothesize that the fusion of the three chordate linkage groups 3, 15 and 17 more than 800 MYA led to the ancestral vertebrate globin cluster during a geological period of increased atmospheric oxygen content.

Journal homepage: http://www.elsevier.com/wps/find/journaldescription.cws_home/503309/description#description In this paper we report on the fate of vitellogenic follicles (VF) as either alpha atretic follicles (αF) or post-ovulatory follicles (POFs) using histology and captive Atlantic cod (Gadus morhua) in three experiments. In Experiment 1 the production and persistence of αF was determined by taking repeated biopsy samples from tagged females held in temperature regimes (mean ± SD) controlled at 4.5 (0.3) and 8.1 (0.3) °C. The αF lasted (mean ± 2 SE, n) 5.3 days (2.5, 8) and 9.7 days (4.9, 8) in the warmer and cooler water respectively and the combined average was 7.5 days (2.9, 16). In Experiment 2 we took biopsy samples at intervals and monitored egg production from individual females accompanied by a male and used the stage of egg development to age POFs found in the biopsy samples. The females, some immature, were killed at intervals, up to 45 days post-spawning, and then the biopsy and ovary samples were stained by periodic acid Schiffs’ reagent to prepare descriptions of POFs aged from 11 h to 45 days old. Spent female ovaries contained POFs, and a thicker ovarian wall (tunica) exceeding 0.34 mm whilst immature fish lacked POFs and their ovary tunica was thinner (less than 0.15 mm). In Experiment 3 the persistence of POFs was monitored in a simulated North Sea (10–16.1 °C) and Barents Sea (7.5–11.2 °C) regime using ovary sections stained by periodic acid Schiffs’ reagent. In both regimes the POFs regressed at a temperature sensitive rate during the experiment lasting 104 days. Some αF from large VF persisted longer than expected (more than 4 months after spawning) and were called cysts based on their appearance and greater expected lifetime. These histological characteristics were successfully applied to assess maturity of wild cod caught on surveys in the North and Barents Seas after an assumed 150 and 310 days, respectively, after the spawning season. Taken together this article presents reliable figures on the lifetime of atretic and post-ovulatory follicles as well as variation in ovarian thickness with spawning experience, which will be most useful input in the further work to assess reproductive potential.

Journal homepage: http://www.elsevier.com/wps/find/journaldescription.cws_home/503309/description#description Some fish species have wide distribution areas that span very different habitats. In this investigation we have studied Atlantic cod (Gadus morhua), which is an example of such a species, to demonstrate how this may have caused adaptations to key features such as fecundity, growth and age and size at first spawning. We have studied cod from the Barents Sea, Icelandic waters, North Sea and Irish Sea. The ovary sampling was undertaken over several years, however, not always sequentially, in order to assess whether the relationships between fecundity and other key features were constant or variable. Also, we compared historical maturity ogives and growth from the different regions. There was a clear pattern with fish maturing at a greater age and size in the north compared to the south. For three of the four cod stocks we demonstrated a significant reduction in relative potential fecundity as maturity progressed towards spawning, i.e., as the mean diameter of vitellogenic follicles increased. To be able to compare potential fecundity in a standardised way both in time and space, we constructed models that included mean diameter as one of the independent variables. Our potential fecundity comparisons clearly indicated a north-south gradient with increasing size-specific fecundity towards the south. The higher fecundity of the fish in the south could only partly be explained by the higher condition and temperature that was observed in these waters.

Journal homepage: http://www.elsevier.com/wps/find/journaldescription.cws_home/503302/description#description A bite–and–pull demand–feeding system was introduced to groups of cultured cod (Gadus morhua). For half of the groups trigger actuations were rewarded with food, while actuations were unrewarded in the other groups. Initially, cod responded with frequent triggering, irrespective of whether triggering was rewarded with food or not. The high initial curiosity–driven triggering rate declined rapidly, and was almost perfectly described by an exponential decay model with a decay rate of 7% min-1. After 3 hours, the triggering frequency of the rewarded fish diverged from that of unrewarded fish, and it remained higher throughout the 9 days of the experiment. The initial curiosity–driven triggering allowed the cod to establish the relationship between action and reward in a short time. It is inferred that the time trajectory of action frequency of rewarded fish is the result of several factors and that operant learning can only be verified by comparing action frequencies of rewarded and unrewarded fish, and not by the temporal development in action frequency of rewarded fish alone.

Recent studies in the marine environment have suggested that the limited phenotypic plasticity of cold-adapted species like Atlantic cod (Gadus morhua L.) will cause distributions to shift toward the poles in response to rising sea temperatures. Some cod stocks are predicted to collapse, but this remains speculative because almost no information is available on the thermal tolerance of cod in its natural environment. We used electronic tags to measure the thermal experience of 384 adult Atlantic cod from eight different stocks found in the NE Atlantic. Over 100,000 days of data were collected in total. The data demonstrate that cod is an adaptable and tolerant species capable of surviving and growing in a wide range of temperate marine climates. Total thermal niche ranged from -1.5°C to 19°C; this range was narrower (1°C to 8°C) during the spawning season. Cod in each of the stocks studied had a thermal niche of approximately 12°C, but latitudinal differences in water temperature meant that cod in the warmer, southern regions experienced three times the degree days (~4000 DD year-1) than individuals from northern regions (~1200 DD year-1). Growth rates increased with temperature, reaching a maximum in those cod with a mean thermal history of between 8°C and 10°C. Our direct observations of habitat occupation suggest that adult cod will be able to tolerate warming seas but that cod populations may still be affected because the effects of marine climate change will impact cod at earlier life-history stages or via indirect effects on prey species.

Rapid development of fish mariculture and efforts to restock depleted populations have raised concerns about the effects on wild populations and the risk of genetic introgression from hybridisation. Reproduction of many marine fish species involves substantial vertical movements, but nothing is known of the vertical dynamics of farmed fish in spawning shoals. We combined laboratory observations and field biotelemetry to examine the depth-related reproductive behaviour and vertical dynamics of individual farmed and wild Atlantic cod Gadus morhua (L). We first tested the prediction that the depth distributions of male and female wild cod differ both in the laboratory and in the field. We then tested the prediction that farmed cod have a shallower depth distribution than wild cod and thus lack the sex-based vertical dynamics of wild cod. In both the laboratory and field, male farmed and wild fish tended to be located deeper than females, and wild fish were deeper than farmed fish. In the field, wild males were near the seafloor, considerably deeper than wild females and farmed fish. Residency on the spawning ground was longer for wild fish, but a substantial proportion (61%) of farmed fish remained for more than 3 d. Our study reinforces the idea that vertical dynamics play a key role in reproduction of an important fisheries species, and demonstrates clear differences in vertical distribution between farmed and wild fish on a spawning ground. The results suggest that escaped farmed cod, and in particular, farmed females, are likely to hybridise with wild cod. 2014-09-04

Open access article Worldwide depletion of fish stocks has led fisheries managers to become increasingly concerned about rebuilding and recovery planning. To succeed, factors affecting recovery dynamics need to be understood, including the role of fisheries-induced evolution. Here we investigate a stock’s response to fishing followed by a harvest moratorium by analyzing an individual-based evolutionary model parameterized for Atlantic cod Gadus morhua from its northern range, representative of long-lived, late-maturing species. The model allows evolution of life-history processes including maturation, reproduction, and growth. It also incorporates environmental variability, phenotypic plasticity, and density-dependent feedbacks. Fisheries-induced evolution affects recovery in several ways. The first decades of recovery were dominated by demographic and density-dependent processes. Biomass rebuilding was only lightly influenced by fisheries-induced evolution, whereas other stock characteristics such as maturation age, spawning stock biomass, and recruitment were substantially affected, recovering to new demographic equilibria below their preharvest levels. This is because genetic traits took thousands of years to evolve back to preharvest levels, indicating that natural selection driving recovery of these traits is weaker than fisheries-induced selection was. Our results strengthen the case for proactive management of fisheries-induced evolution, as the restoration of genetic traits altered by fishing is slow and may even be impractical.

Article published in Animal Genetics, 41 (5): 515-522 OCT 2010 This study presents a molecular genetic characterization of Atlantic cod reared in commercial marine farms. Samples consisted of approximately 47 fish collected from nine cages located on four farms throughout Norway. In addition, 28 farmed escapees were recaptured in the sea (443 fish in total). Nine microsatellite loci and the Pan I gene were analysed, revealing a total of 181 alleles. Each sample contained 43–63% of total allelic variation. Comparing variation with published data for wild cod indicates that lower genetic variation exists within single cages than in wild populations. Significant linkage disequilibrium was observed amongst pairs of loci in all samples, suggesting a low number of contributing parental fish. Global FST was 0.049, and the highest pairwise FST value (pooled loci) was 0.085. For single loci, the Pan I gene was the most diagnostic, displaying a global FST of 0.203. Simulations amongst the samples collected on farms revealed an overall correct self-assignment percentage of 75%, demonstrating a high probability of identifying individuals to their farm of origin. Identification of the 28 escapees revealed a single cage as the most likely source of origin for half of the escapees, whilst the remaining fish were assigned to a mixture of samples, suggesting more than one source of escapees.

Viral encephalopathy and retinopathy (VER) was diagnosed in 5 to 24 g sized farmed Atlantic cod Gadus morhua kept in sea cages at Parisvatn, Hordaland county, on the west coast of Norway. Moderate mortality (10 to 15%) was observed, along with anorexia and abnormal swimming behaviour, such as looping or spiral swimming and reduced coordination. Nodavirus was detected by 2 different real-time RT-PCR assays, and this was later confirmed by immunohistochemistry. This is the first report of an outbreak of VER in farmed cod in Norway, and the first report that VER affect cod exceeding 5 g in size. Published version

Presented at SETAC Europe 17th Annual Meeting, 20-24 May 2007, Porto, Portugal Two long term studies to assess the effects of produced water (0.01-1 %) on the early life stages of cod were performed. Experiment 1 examined the egg to early fry stage (90 days), and experiment 2 examined the early fry stage to juvenile (78 days). Following exposure, the fish were transferred to clean seawater and monitored for two years till sexual maturation. One group of fish from each exposure regimen was used in spawning experiments No effects on hatching success, growth, survival or sexual differentiation were detected for cod (eggs, larvae and fry) exposed to low concentrations of produced water (dilution 1:1000 or 1:10000). Yolk sack larvae were found to be the most sensitive to produced water exposure. Larvae exposed to 1 % produced water showed an inability to start feed, resulting in 100 % mortality. At the fry stage a significant up-regulation of VTG was shown in groups exposed to 1% produced water and estradiol. CYP1A were significantly up-regulated in fry exposed to 1% produced water, and down-regulated after exposure to 10 ppb estradiol. Exposure to 10 ppb estradiol resulted in severe abnormalities of male testis development and many different morphological signs of intersex were observed. Norwegian Research Council Norsk Hydro

We estimated the spatial scale of genetically distinguishable populations of coastal Atlantic cod Gadus morhua using microsatellite DNA markers. Significant overall heterogeneity in allele frequencies was found among 5 cod samples (n = 493) along a 79 km segment of the Norwe- gian Skagerrak coast (FST = 0.0013; p = 0.021). Most (3 out of 4) samples separated by less than 30 km were genetically highly similar (FST < 0), whereas more distantly separated samples were typically genetically different. This genetic differentiation pattern indicates a patchy population structure with local coastal cod populations being limited in geographic extent to approx. 30 km or less. The spatial structure is thus on the scale of local fjords, suggesting a role for local topography in shaping popu- lation structure. The population structuring of coastal cod is more fine-scaled than hitherto reported, but is consistent with mark-recapture studies and data on egg distributions, and emphasises the need to focus on local populations in the management of marine fishes.

Bottom trawling activities resuspend large amounts of sediment and may be the main agent of sediment transportation in some areas. During periods of intensive fishing by large trawler fleets the high-turbidity environmental conditions they create may become semi-permanent. Little is known about the potential effects of this resuspended sediment on the survival and physiology of marine fish. We carried out a worst-case-scenario simulation whereby groups of cod Gadus morhua were exposed to the highest reported mud concentration behind trawls (550 mg l -1 ) for periods of 24 h, 5 d and 10 d. No mortality was observed in any of the experimental groups. Histological analy- ses of gill lamellae of fish exposed to mud suspension for 24 h showed acute pathological changes in the form of multifocal degenerative lesions. After 5 d exposure, adaptive changes to cope with the turbid environment were observed. These comprised hypertrophy and hyperplasia of the gill epithe- lium and became more marked and widespread after 10 d exposure. The gill lesions observed were similar to those reported in other species exposed to a turbid environment and were in those cases reversible. Analyses of blood plasma cortisol levels showed higher values for fish in the 5 d exposure group than for fish in the 1 d exposure group. No other between-group differences were significant. The within-group variation was high in all groups but especially in the 10 d exposure group.

The recruitment of Atlantic cod stocks shows different responses to temperature changes. Cod stocks inhabiting the lower temperature range show generally an increase in recruitment with increasing temperature, while cod stocks inhabiting the uppermost part of the temperature range show a decrease in recruitment with increasing temperature. In the present paper possible functional relationships between temperature and cod recruitment mechanisms are analysed. Temperature influences the recruitment processes in a large number of ways; partly directly on vital rates in cod, and partly indirectly through trophic transfer. The copepod Calanus finmarchicus is the dominant prey species for the early stages of cod. It proposed that the recruitment-temperature relation of Atlantic cod is a proxy for the food abundance during the early stages, and that advection of C. finmarchicus from the core production regions in the central parts of the North Atlantic Subpolar Gyre to the fringes where the cod stocks have their habitats explains the particular recruitment response to temperature.

The relationship between spawning stock biomass and recruitment in Atlantic cod stocks is investigated by ranking the SSB values according to size and applying a moving average of ten points. The resulting averages are plotted against the average recruitment produced by the respective SSBs. The plot in most cases resembles a Beverton and Holt or Ricker type of relationship, showing substantial reduction in mean recruitment at low levels of SSB even though the relationship is not forced towards the origin. Applying a moving average of ten years to the time series of data shows how SSB and recruitment relationships have developed. For some stocks the apparent relationship might be explained by medium- or long-term variation in the recruitment caused by environmental conditions. Considering all the available data, there is nevertheless substantial evidence of reduced recruitment at low levels of SSB for the cod.

Introduction: Despite numerous investigations the nature and origin of x -cells remain unknown. These ovoid, pale-staining cells with a large, round nucleus and prominent nucleolus are known to occur in the form of lesions, termed x -cell tumours. X -cells may produce large aggregations that resemble true neoplasms. They can be found in quite different organs as skin, pseudobranch, gills, ultimobranchial body, kidney, gonad and spleen (Peters et al. 1978; Dawe, 1981; Diamant & McVicar, 1987). X-celllesions are mainly described in marine species from cold or temperate zones, but a recent publication reported on x -cell tumours in a freshwater species living in warmwater (Diamant et al. 1994).

The investigation was carried out in a marine pond in western Norway during spring and summer 1990. Two genetic defined strains of Atlantic cod (Gadus morhua L.) were used as broodstocks. A total of 11.1 x 10^6 cod larvae and eggs were released in the pond from 16 to 22 March. Approximately 80 % of the specimens were homozygous for the rare 30-allele at the PGI-1 locus (Strain-A), and the remaining were offspring from a farmed cod stock (Strain-B). Hydrographical parameters and feeding conditions of larval and juvenile cod were monitored. Gel electrophoresis of samples collected from the pond, revealed significant variation in the Strain-A/Strain-B frequencies with increasing age. The percentage of Strain-A dropped pronounced from the larval to the juvenile stage, and Strain-A had lower larval and juvenile growth rates than Strain-B, indicating size-dependent mortality during the pre-recruit period.