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Distribution and abundance of common parasitic nematodes in marine fishes is not well documented in many geographic regions. Understanding the influence of large-scale environmental changes on infection rates of fish by nematodes requires quantitative assessments of parasite abundance for multiple host species. We collected samples of two species of cod and eight species of rockfish (total of 232 specimens) from waters near Kodiak Island, Alaska, USA during Spring and Summer of 2015, and dissected and recorded all internal nematode parasites. We quantified the prevalence and intensity of nematode parasites in the ten host species, and tested for differences in prevalence among host species. We found three species of nematode: Anisakis simplex, sensu lato (Van Thiel), Pseudoterranova decipiens, sensu lato (Krabbe), and Hysterothylacium sp. (Ward and Magath). Eighty-two percent of the examined fish were infected with at least one parasitic nematode. The overall prevalence of P. decipiens, A. simplex, and Hysterothylacium sp. was 56%, 62%, and 2%, respectively. Anisakis simplex and P. decipiens were abundant and present in all ten species of host fish examined, whereas Hysterothylacium sp. was rare and found in only five of the host fish species. Prevalence and mean intensity of P. decipiens and A. simplex varied across the ten host species, and the number of parasites varied substantially among individual hosts within host species. The mean intensity of P. terranova and A. simplex in our study was substantially higher than the mean intensity for these same species from multiple other locations in a recent meta-analysis. This study provides a baseline of nematode parasite abundance in long-lived fish in waters near Kodiak Island, AK, and fills an important gap in our quantitative understanding of patterns of occurrence and abundance of these common and widespread parasites of marine fish.

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Jelly and confectionery products are high in sugar and calories. Xylitol and stevioside are natural low-calorie sweeteners and they can be used as an alternative; however, their effects on fish gelatin are unknown. The gelatin was extracted from cod skins and added to xylitol or stevioside (0, 2, 6, 10, 14, and 20% (w/v)) to form gel products. This paper investigated how xylitol and stevioside affected the physical and rheological behaviors of fish gelatin, such as color, gel strength, texture profile analysis, storage modulus (G′), loss modulus (G″), and viscosity. Results showed that the change of color and viscosity in gel products were similar when various concentrations of xylitol or stevioside were added to the fish gelatin. But the effects of xylitol/stevioside on texture profile analysis and G′, G″ were different, which might due to the structure variation in xylitol and stevioside. The linear structure of xylitol resulted in ionic interaction, hydrogen bonding, van der Waals forces, and hydrophobic association between xylitol and fish gelatin. Therefore, xylitol is a promising sweetener substitute, which was probably related to its greater solubility and number of –OH groups. [ABSTRACT FROM AUTHOR]

The population structure of Pacific cod Gadus macrocephalus in the southern part of the range and adjacent regions is studied on the basis of the results of microsatellite analyses. Collected data indicate heterogeneity of this species population within the studied area. According to the obtained FST values, Pacific cod from the waters of the Republic of Korea (Yellow Sea side) and northwestern part of the Sea of Okhotsk significantly differ from all other studied regions (Table 4). Significant differentiation was also revealed between samples from the waters of the Tatar Strait and all other regions except for South Kurils Pacific cod (both Sea of Okhotsk and Pacific Ocean sides). These two latter sample collections were similar to each other as well. A low level of differentiation was also shown for the Peter the Great Bay and the East Sea/Sea of Japan waters of the Republic of Korea. [ABSTRACT FROM AUTHOR]

Summary: Two cod stocks (western Baltic cod, WBC, and eastern Baltic cod, EBC) are managed in the Baltic Sea which is characterized by different main spawning areas and different main spawning periods. In this study we analyse the spatial and temporal occurrence of spawning individuals of both cod stocks in the main spawning grounds of the Baltic Sea based on eight microsatellite loci. Our results suggest that EBC (Gadus morhua callarias) has formed currently temporally stable, substantially homogeneous population not only in the Bornholm Sea (ICES SD: 25) but also in the Arkona Sea (ICES SD: 24). The presented analyses proved that EBC (G. m. callarias) can temporarily also spawn in the Belt Sea. [ABSTRACT FROM AUTHOR]

Differences in zooplankton populations in relation to climate have been explored extensively on the southeastern Bering Sea shelf, specifically in relation to recruitment of the commercially important species walleye pollock (Gadus chalcogrammus). We addressed two research questions in this study: (i) Does the relative abundance of individual copepod species life history stages differ across warm and cold periods and (ii) Do estimated secondary production rates for copepods differ across warm and cold periods? For most copepod species, warmer conditions resulted in increased abundances in May, the opposite was observed in colder conditions. Abundances of smaller-sized copepod species did not differ significantly between the warm and cold periods, whereas abundances of larger-sized Calanus spp. increased during the cold period during July and September. Estimated secondary production rates in the warm period were highest in May for smaller-sized copepods; production in the cold period was dominated by the larger-sized Calanus spp. in July and September. We hypothesize that these observed patterns are a function of temperature-driven changes in phenology combined with shifts in size-based trophic relationships with primary producers. Based on this hypothesis, we present a conceptual model that builds upon the Oscillating Control Hypothesis to explain how variability in copepod production links to pollock variability. Specifically, fluctuations in spring sea-ice drive regime-dependent copepod production over the southeastern Bering Sea, but greatest impacts to upper trophic levels are driven by cascading July/September differences in copepod production. [ABSTRACT FROM AUTHOR]

This paper describes a methodology that combines meta-population theory and stock assessment models to gain insights about spatial heterogeneity of the meta-population in an operational time frame. The methodology was tested with stochastic simulations for different degrees of connectivity between sub-populations and applied to two case studies, North Sea cod (Gadus morua) and Northeast Atlantic sardine (Sardina pilchardus). Considering that the biological components of a population can be partitioned into discrete spatial units, we extended this idea into a property of additivity of sub-population abundances. If the additivity results hold true for putative sub-populations, then assessment results based on sub-populations will provide information to develop and monitor the implementation of finer scale/local management. The simulation study confirmed that when sub-populations are independent and not too heterogeneous with regards to productivity, the sum of stock assessment model estimates of sub-populations’ SSB is similar to the SSB estimates of the meta-population. It also showed that a strong diffusion process can be detected and that the stronger the connection between SSB and recruitment, the better the diffusion process will be detected. On the other hand it showed that weak to moderate diffusion processes are not easy to identify and large differences between sub-populations productivities may be confounded with weak diffusion processes. The application to North Sea cod and Atlantic sardine exemplified how much insight can be gained. In both cases the results obtained were sufficiently robust to support the regional analysis. [ABSTRACT FROM AUTHOR]

In the current study activity and latency to explore, as well as the correlation of these traits, were examined in individually marked juvenile Gadus morhua at 7, 10 and 13° C. It was concluded that individual rank order of both traits was maintained across temperature but that the level of change differed between individuals. [ABSTRACT FROM AUTHOR]

Fishery-independent surveys are useful for estimating abundance of fish populations and their spatial distribution. It is necessary in the case of semipelagic species to perform acoustic-trawl (AT) and bottom-trawl (BT) surveys to ensure that sampling encompasses both midwater and demersal components of the population. Abundance estimates from both survey types are negatively biased because of the blind zones associated with fish vertical distribution. These biases can vary spatially and temporally, resulting in confounded trends and additional variation in abundance estimates. To improve abundance estimates for semipelagic species we propose a new method for combining BT and AT survey data using environmental variables to predict the vertical overlap. Using walleye pollock ( Gadus chalcogrammus) AT and BT surveys in the eastern Bering Sea as an example, we show that combined estimates provide more reliable whole water column and spatial distribution estimates than either survey can by itself. Although the combined estimates are still relative, they account for the uncertainty in the bias ratio between the two survey methods and the uncertainty associated with the extent of the water column sampled by both surveys. Our method of combining BT and AT data can be extended to other semipelagic species. [ABSTRACT FROM AUTHOR]

According to the results of analysis of genetic differentiation and Bayesian hierarchical cluster analysis of polymorphism in microsatellite loci, it was demonstrated that the development of marginal groups represented by subspecies level taxa (Greenland ( Gadus macrocephalus ogac) and White Sea ( Gadus morhua marisalbi) cod) occurred in the Late Holocene in a similar scenario, but in different regions and from different initial forms. The development of these reproductively independent cod groups was a result of physiological adaptations to arctic conditions in coastal northern water areas that developed under global cooling in the Subboreal. [ABSTRACT FROM AUTHOR]

This study investigates how product quality and shelf life of vacuum-packed cod loins are affected when surface bacteria are targeted in thermal processing regimes. A mathematical heat transfer model was used to generate two mild thermal processing regimes for temperature controlled water baths at 70 °C and 90 °C. The results show that shelf life assessment based on sensory evaluation is closely linked to microbial growth. This study shows that even if mild heat treatments do have a noticeable effect of inactivating bacteria on the surface of the fish muscle, such processes do not prolong shelf life considerably. This may be due to the overall limited effect of mild heat processing on bacterial inactivation, but may also be explained by the fact that for postrigor fish, the microbial contamination might be at a too advanced stage for the investigated mild processing to have significant effect. Practical applications For the consumer fresh fish is a superior product compared to frozen fish. Consequently, there is a higher demand and a higher market price for fresh seafood products. The aim of the present study was to evaluate in-pack surface pasteurization as a mean to increase shelf life for a prepackaged white fish product. Since the surface of the fish fillet is the entry point of microbial contamination as well as the main colonization area, targeting the surface seems the obvious choice to minimize the negative impact of extensive heat processing. We show that modeling the heat treatment is a valuable tool for limiting the detrimental effect of heat treatment. However, when microbial contamination is high, very mild heat processing does not prolong shelf life considerably. [ABSTRACT FROM AUTHOR]

In the nearshore Gulf of Maine, a combination of factors (overfishing, ecosystem change, and ocean warming) is thought to govern groundfish recovery. We analyzed feeding habits of demersal predatory fish from Midcoast Maine (abundant river herring) and Passamaquoddy Bay (low river herring) in eastern Maine, using stomach content and stable isotope analyses, to determine the prevalence of river herring (alewife, Alosa pseudoharengus, and blueback herring, A. aestivalis) in nearshore (<4.5 km) groundfish diets. Invertebrates dominated all predator diets at all sites. At Midcoast sites, catch-per-unit-effort (CPUE) of Atlantic cod was higher, and fish predators showed a strong seasonal pattern in river herring consumption compared to Passamaqouddy Bay. Cod, pollock ( Pollachius virens), and sculpins ( Myoxocephalus octodecimspinosus and M. scorpius) from Midcoast sites tended to be enriched in δN relative to Passamaquoddy Bay. Contrasting fast vs. slow turnover tissue (fin vs. muscle) indicated that focal species migrated or food availability changed seasonally and Atlantic mackerel ( Scomber scombrus) in Passamaquoddy Bay were assimilating into a trophically depleted food web. We posit that lack of forage fish in Passamaquoddy Bay contributed to conditions that encourage an invertebrate based diet. River herring are also an order of magnitude less abundant in Passamaquoddy Bay than at Midcoast sites, limiting the availability of this seasonal food source. River restoration may contribute to recovery of groundfish stocks nearshore by increasing the availability of high lipid, seasonally available prey. [ABSTRACT FROM AUTHOR]

Coastal seine surveys contain some of the only direct measures of age-0 abundance for Atlantic cod ( Gadus morhua) and Pacific cod ( Gadus macrocephalus), yet their utility in forecasting future year-class strength has not been evaluated among regions. We analyzed coastal time series from the Gulf of Alaska, Newfoundland, and Norway to test the hypothesis that recruitment signals are stronger when assessed under thermal conditions that provide high juvenile growth potential. Weaker recruitment signals were associated with low growth potential from cold winters (Newfoundland) and recent warmer summers (Norway). We conclude that temperature-dependent growth strongly influences the utility of coastal surveys in recruitment forecasting among regions. Temporal changes in growth potential (e.g., via climate change) will likely affect recruitment signals by way of changes in juvenile mortality or spatial shifts to more favorable thermal habitats. [ABSTRACT FROM AUTHOR]

The study was designed to investigate the effect of four cycles of 5 weeks starvation followed by 10-week refeeding compared with daily feeding under either natural photoperiod or continuous light ( LL) regime on body composition and flesh quality in Atlantic cod in sea cages, northern Norway. The fish were sampled for body composition and flesh quality parameters at the start of the trial, twice at the end of a 10-week feeding period and twice at the end of a 5-week starvation period. There was effect of both feeding and light regime on growth, the two starving groups losing weight during starvation and regaining weight during refeeding, and the group under LL being heavier. But, the mean overall growth did not vary between groups. Starvation/refeeding regime resulted in higher slaughter yield, but no overall effect was seen on hepatosomatic index, water content, water holding capacity ( WHC), muscle pH, hardness or flesh colour compared with control groups. Continuous light increased gutted weight and slaughter yield, lowered WHC and depressed maturation compared with fish under natural light regime. Increased growth rate resulted in softer fillets and lower muscle pH. [ABSTRACT FROM AUTHOR]

This study evaluated the survival, growth performance and hematological changes of juvenile Pacific cod Gadus macrocephalus in land-based culture tanks with different water temperatures using deep sea water. Experimental water temperatures were set at 6, 10, and 14 °C by mixing surface sea water and deep sea water. One hundred juveniles (120.3 ± 26.3 g, 22.0 ± 1.2 cm) were placed in each experimental tank (2 m in diameter × 0.65 m water depth). Fish were fed twice daily with extruded pellets to satiation for the 55-day experiment. Growth performance and blood chemistry were analyzed at the end of the experiment. Pacific cod were not tolerant of long-term exposure to a water temperature of 14 °C, while their feeding activity and metabolism were still active. Hematological changes suggested that Pacific cod were stressed at both the lowest and highest temperatures examined in this study. In summary, the results in this study suggest that a water temperature of 8.5 °C may be the most favorable temperature for optimal growth performance and physiological activities of Pacific cod with a size range of 120-180 g. [ABSTRACT FROM AUTHOR]

The present study evaluated the effects of chilled storage and cryopreservation on sperm motion characteristics, antioxidant enzyme activities, and lipid peroxidation in the Pacific cod Gadus macrocephalus. Sperm motility and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (Gr), and lipid peroxidation (measured via malondialdehyde (MDA) content) were determined after the milt was stored at 4°C for 12 h, cryopreserved without cryoprotectant in 12% propylene glycol (PG), cryopreserved in 12% PG+0.1 mol/L trehalose, or cryopreserved in 12% PG spermatozoa but centrifuged to decant the supernatant prior to cryopreservation (only sperm cells were cryopreserved). After chilled storage or cryopreservation, the SOD, CAT and GPx activities were reduced in sperm cells and increased in seminal plasma in almost all treatments; sperm motility parameters were also decreased. However, the addition of trehalose into the cryoprotectant could significantly improve the postthaw sperm quality as revealed by the sperm average path velocity. This improvement might be attributed to the function of trehalose in scavenging reactive oxygen species. Chilled storage and cryopreservation had significant effects on sperm motion characteristics, antioxidant enzyme activities, and lipid peroxidation in the Pacific cod. [ABSTRACT FROM AUTHOR]

We employed common-garden experiments to test for genetic variation in responses of larval life-history traits to temperature between two populations of Atlantic cod ( Gadus morhua L., 1758) that naturally experience contrasting thermal environments during early life due to spatial and temporal differences in spawning. Southern Gulf of St. Lawrence cod larvae experienced faster growth in warmer water and low, uniform survival across all experimental temperatures (3, 7, 11 °C), consistent with previous studies on this spring-spawning population. In contrast, larvae from fall-spawning Southwestern Scotian Shelf cod collected near Sambro, Nova Scotia, lacked plasticity for growth but experienced much lower survival at higher temperatures. Phenotypes that are positively associated with fitness were observed at temperatures closest to those experienced in the wild, consistent with the hypothesis that these populations are adapted to local thermal regimes. The lack of growth plasticity observed in Sambro cod might be due to costly maintenance of plasticity in stable environments or energy savings at cold temperatures. However, additional experiments need to be conducted on Sambro cod and other fall-spawning marine fishes to determine to what extent responses to projected changes in climate will differ among populations. [ABSTRACT FROM AUTHOR]

A basic challenge to successful management and conflict resolution is to correctly identify the spatial scale at which strategies for harvesting are developed. For commercially exploited marine fish, distributional boundaries of many stocks are based on the premise that productivity is similar at spatial scales that represent a small fraction of an individual's potential migration distance. Within such confined geographic regions, differences among individual life history traits--primary determinants of population productivity--are assumed to be negligible. The empirical basis for these assumptions bears re-examination for some widely distributed species, such as Atlantic cod (Gadusmorhua L.), for which there is evidence that life history structuring is evident at much finer scales than previously thought. Here, we focus on a unique system in the Norwegian Skagerrak, divided into inner and outer fjord habitats between which cod movement across distances of a few kilometres is limited and populations show signals of genetic differentiation. Based on back-calculated length-at-age data, cod in the inner fjord are systematically smaller at young ages (1-5 years) and are characterized by shorter asymptotic body lengths than cod in the outer fjord. Our work on growth and life history supports genetic analyses which indicate that productivity and resilience of widely distributed marine fish are likely to differ at considerably smaller spatial scales than those delineated by traditional stock management boundaries. [ABSTRACT FROM AUTHOR]

The spatio-temporal variation in sea-spawning whitefish (Coregonus lavaretus s. l.) larval densities and their sizes was analysed with the aim to suggest a useful sampling dimensioning in terms of number of replicates and to find an optimum time for sampling to minimize the sampling variance. We also investigated the potential to predict optimal sampling in advance based on air temperature. The larval data used in the study were collected in the northernmost part of the Baltic Sea during 1979-2011. The analyses of the optimum time for sampling showed a sharp peak associated with a huge variation in density for larvae sizes15 mm length. Larvae sizes in the range 20-30 mm had intermediate densities with relatively low variance, while the densities of larger larvae declined with an increase in the relative precision. The 20-30 mm range was identified as a reliable size window for sampling, and the best predictor of larvae size was the temperature sum, using offshore air temperatures starting at 26 April. The between-year variance of the larvae mean sizes in the size range 20-30 mm was on the average 64% higher for fixed date sampling compared with fixed temperature sum sampling. The optimum sampling time was identified to the date when reaching 270 °Cd for the southern, and 335 °C d for the northern locations. These temperature sums were generally reached in the first 2 weeks of June, but some years as late as the last week in June. Confidence intervals from a negative binomial distribution should be used rather than intervals based on the normal distribution due to the skewed sampling distributions. Bootstrap analyses showed that 10-30 replicates may give sufficient precision to detect significant changes in sea-spawning whitefish larval densities. Revisiting the same areas during the larval growth season (time window) did not improve the precision significantly. [ABSTRACT FROM AUTHOR]

The protection of spawning fish from anthropogenic impacts requires information on the location, timing, and interannual persistence of spawning aggregations. In this study, generalized additive models were used to predict the spawning habitat of North Sea cod, based on the abundance of spawning fish within three population subareas and nine environmental layers. The length of spawning cod differed among population subareas, consistent with published evidence of maturation differences. In the northeast North Sea (Viking), the peak in the spawning season was estimated to occur after the survey which made the prediction of spawning grounds for this area less certain. Cod were found to prefer areas with temperatures around 5-78C for spawning and there was a general preference for high salinity waters. Persistence of cod spawning grounds over the study period was related to interannual stability in temperature, with high variability in the use of Southern Bight spawning grounds. As such, cod appear to minimize interannual variability in the initial environmental conditions affecting offspring survival by selecting suitable cold spawning grounds. Seabed conditions also affected spawning distribution with cod selecting coarse sand and avoiding areas of very high tidal flow. The model prediction was compared with the distribution of cod aggregations during the spawning season reported by fishing boats. Seventy per cent of the aggregations was located in areas classified as occasional or recurrent spawning grounds. The predicted distribution confirmed the widespread occurrence of spawning in the North Sea and showed good agreement with recent and past studies of cod egg distribution, suggesting that nearly all major historical areas of spawning still appear in use today. However, the study also found that the recent recovery of spawning-stock biomass was not uniform across the stock, being centred in the northwest subarea [ABSTRACT FROM AUTHOR]

The effects of starvation at the first feeding stage on the survival and growth of walleye pollock Gadus chalcogrammus larvae were examined in rearing experiments performed in the laboratory. Newly hatched larvae grown at 2 °C, 5 °C, and 8 °C that commenced feeding at 3, 2, and 1 days post-hatching (dph) exhibited yolk exhaustion at 8, 8, and 5 dph and reached the point-of-no-return (PNR) at 15, 14, and 10 dph, respectively. Larvae kept at 5 °C were starved for 2-16 dph and then reared to examine the effect of delayed initial feeding on growth and survival. The larvae that were fed earlier grew better and showed higher survival rates. The time thresholds after which delayed feeding would prevent the larvae from growing and surviving were 2-3 and 0-1 days, respectively, before the PNR. Walleye pollock larvae have a long mixed endogenous and exogenous feeding period and relatively high starvation tolerance, as is typically observed in cold water fishes. Delayed initial feeding affects their survival and growth, even during the mixed feeding period. The availability of prey at the first feeding stage would have a critical effect on the stock size of this species. [ABSTRACT FROM AUTHOR]

The thermophysical properties (thermal conductivity, thermal diffusivity, and specific heat) of big-eyed tuna and pacific cod were measured at various temperatures (5–50°C) by the modified version of current probe method. The optimal prediction models for these thermophysical properties were determined. The random model was applied to predict the thermal conductivity of seafood in a wide range of temperature and it provided the accurate predictions for the samples. The thermal diffusivities of the samples could be predicted by Martens’s equation. An additive relationship exists between the specific heat of the sample, the composition, and the specific heat of each component. [ABSTRACT FROM AUTHOR]

Background. The Gotland Basin spawning ground is one of three main spawning areas of Baltic cod, Gadus morhua Linnaeus, 1758. The threshold water parameters for cod development are the salinity exceeding ll%o and the oxygen level above 2 mL ⋅ L-1. Such conditions are only present when the ll‰ isohaline is above the 2 mL ⋅ L-1 isooxygen. In such situation the water volume between the isolines is called the "suitable reproduction volume". When the position of the isolines is reversed, the salinity and the oxygen level of the water layer demarcated by them are below the required thresholds and as such the water is unsuitable for the cod development. We refer to it as the "unsuitable reproduction volume". The main aim of the presently reported study was to examine whether variations in suitable and unsuitable reproduction habitat estimates could explain the fluctuations in cod recruitment. Material and methods. The suitable and unsuitable reproduction volumes in the Gotland Basin were estimated based on single point observations at three oceanographic monitoring stations using the contouring software Bal-thypsograph. To test the spatial hydrological heterogeneity in the Gotland Basin we used 15 observations during 1969-1995 on four stations in each of two transects. The oceanographic monitoring and demersal trawl research survey data from 1974-2012 have been used in analyses. Results. The sufficient reproduction conditions in the southern Gotland Basin persisted only until 1981. In later decades the reproduction potential of the Gotland Basin has decreased. The latest major North Sea water inflows in 1993 and 2003 in the Central Gotland Basin formed the suitable reproduction volume below the layers where cod eggs are floating. A significant relation between the recruit abundance and suitable and the unsuitable reproduction volumes was found only for the Southern Gotland Basin (P < 0.03). Conclusions. We demonstrated that single-point estimates sufficiently quantify the reproduction conditions in the Gotland Basin and thus can be used for estimation of the reproduction volumes. The unsuitable reproduction volume concept can be used as an ecological indicator for egg survival probability in the Gotland Basin. However, it is too premature to re-define the concept of the suitable reproduction volume because it is applicable only to the Gotland spawning ground. [ABSTRACT FROM AUTHOR]

Ocean acidification impacts fish and other marine species through increased seawater P CO 2 levels (hypercapnia). Knowledge of the physiological mechanisms mediating effects in various tissues of fish is incomplete. Here we tested the effects of extracellular hypercapnia and acidosis on energy metabolism of gill and liver cells of Atlantic cod. Exposure media mimicked blood conditions in vivo , either during normo- or hypercapnia and at control or acidic extracellular pH (pH e ). We determined metabolic rate and energy expenditure for protein biosynthesis, Na + /K + -ATPase and H + -ATPase and considered nutrition status by measurements of metabolic rate and protein biosynthesis in media with and without free amino acids (FAA). Addition of FAA stimulated hepatic but not branchial oxygen consumption. Normo- and hypercapnic acidosis as well as hypercapnia at control pH e depressed metabolic stimulation of hepatocytes. In gill cells, acidosis depressed respiration independent of P CO 2 and FAA levels. For both cell types, depressed respiration was not correlated with the same reduction in energy allocated to protein biosynthesis or Na + /K + -ATPase. Hepatic energy expenditure for protein synthesis and Na + /K + -ATPase was even elevated at acidic compared to control pH e suggesting increased costs for ion regulation and cellular reorganization. Hypercapnia at control pH e strongly reduced oxygen demand of branchial Na + /K + -ATPase with a similar trend for H + -ATPase. We conclude that extracellular acidosis triggers metabolic depression in gill and metabolically stimulated liver cells. Additionally, hypercapnia itself seems to limit capacities for metabolic usage of amino acids in liver cells while it decreases the use and costs of ion regulatory ATPases in gill cells. [ABSTRACT FROM AUTHOR]

The performance of midwater trawls used during acoustic surveys for walleye pollock ( Gadus chalcogrammus ) was estimated using a novel method of combining acoustic and catch information. Direct comparisons of acoustic and catch derived density showed a poor correlation between the two ( r 2 = 0.07), suggesting this discrepancy might be in part due to trawl performance. Trawl efficiency and selectivity were determined by comparing acoustically derived fish density within the trawling volume with catch-based density in a modeling framework. Additional factors thought to potentially influence trawl performance, consisting of environmental conditions including water temperature, bottom and fishing depth, variables relating to survey methodology including survey vessel, codend liner, and the time of day when trawling occured, and fish population characteristics including spawning state and condition factor were evaluated in the models. Incorporating efficiency and selectivity parameters resulted in improved model fits, as did the addition of explanatory variables. Efficiency was found to be associated with the proportion of spawning fish in the catch, water temperature, and the time of day, while selectivity appeared to be influenced by condition factor and the survey vessel used. The acoustic-catch modeling approach confers advantages of making available large historic datasets where acoustic data was collected during trawling and providing sufficient contrasts in parameters of interest not easily achieved with direct trawl performance experiments. [ABSTRACT FROM AUTHOR]

The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high-resolution radio-acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 ( G. morhua) and 14·4 days ( G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions ( KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length ( LT) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 LT s−1, respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species. [ABSTRACT FROM AUTHOR]

The feeding habits of co-occurring gadid species Atlantic cod ( Gadus morhua) and Greenland cod ( Gadus ogac) in coastal Newfoundland waters, examined using stable isotope ( δC and δN) and stomach content analysis, indicated little dietary niche overlap and interspecific competition for food resources despite similar trophic levels. Both species consumed a variety of invertebrates and fish but showed a preference for different prey items. Polychaetes, fish and small crustaceans dominated G. ogac stomach contents while small crustaceans, in particular hyperiid amphipods and fish, dominated those of G. morhua. In general, G. morhua consumed more pelagic prey and had a significantly more pelagic (more negative) δC signature while G. ogac consumed primarily benthic prey and had a more benthic (more positive) δC signature. δN levels were similar in these species suggesting similar trophic positions, with levels increasing with fish length in both species. Dietary overlap was not significant in both stomach and stable isotope analyses. We conclude that interspecific competition for food is low between G. ogac and G. morhua and is unlikely to be a factor in the slow rebuilding of Atlantic cod in this region. [ABSTRACT FROM AUTHOR]

Highlights: [•] Distribution of thermal habitats of the US Northeast Continental Shelf have changed. [•] Thermal habitat area relates to the distributional abundance of zooplankton species. [•] Zooplankton taxa Pseudocalanus spp. has declined in key areas for Atlantic cod. [•] Observations are consistent with reduced reproductive output of cod. [Copyright &y& Elsevier]

The gastro-intestinal tract serves as the route of infection of most bacterial pathogens in fish, and the immune response genes in the gut produce substances that provide an initial defense during pathogen invasion. The expression of some genes involved in antibacterial defense, cell-mediated immunity and inflammation in the distal intestine of Atlantic cod, Gadus morhua L., was investigated following intraperitoneal vaccination with heat-killed Vibrio anguillarum. Tissue samples of the distal intestine were collected at 0, 1, 3, 7 and 10 days post-vaccination (dpv) and processed for semi-quantitative RT-PCR analyses. Expression of the bactericidal/permeability-increasing protein/lipopolysaccharide-binding protein (BPI/LBP), g-type lysozyme, non-specific cytotoxic cell receptor protein-1 (NCCRP-1) and interleukin-8 (IL-8) significantly increased during the early stages post-vaccination, that is, 1-3 dpv, followed by a decrease in their expression returning to their initial levels. Transferrin and apolipoprotein A-I, although weakly expressed in the distal intestine, also increased in the vaccinated fish. Interleukin-1β (IL-1β) was significantly decreased in its expression level relative to the PBS-injected fish at 3 and 7 dpv. The expression of these immune-related genes in the distal intestine as a result of vaccination provides valuable information on the mechanisms of gut immunity in the fish against pathogenic bacteria, particularly during the early stages of infection. [ABSTRACT FROM AUTHOR]

Atlantic cod Gadus morhua L. were fed high plant protein diets added to either shrimp-shell meal or crab-shell meal. The aims were to investigate if diluting dietary energy would reduce the liver index ( HSI) and if marine ash would add value to plant protein-based diets. Two control diets were used: a high plant protein control diet ( PP) with no marine ash addition, and a fishmeal-based diet ( FM) with no marine ash addition. All diets were evaluated in small cod (initial weight 79 ± 15g) and in market-size cod (initial weight 1579 ± 20 g). Addition of crab-shell meal up to 20% and shrimp-shell meal up to 10% did not influence liver size in either small or market-size cod. An addition of up to 20% crab-shell meal and 10% shrimp-shell meal improved growth compared to the PP control diet, and stimulated increased feed intake. However, 10% shrimp-shell meal and 20% crab-shell meal diets resulted in a similar intake of energy and protein as the control groups. Increasing shrimp-shell meal to 20% resulted in reductions in feed intake, fat digestibility and growth, and in altered gut histology. All diets, except the 20% shrimp added diet, resulted in normal ranges of plasma nutrients and blood hematological values, showing good fish health with or without the marine ash addition. [ABSTRACT FROM AUTHOR]

Hernandez, K. M., Risch, D., Cholewiak, D. M., Dean, M. J., Hatch, L. T., Hoffman, W. S., Rice, A. N., Zemeckis, D., and Van Parijs, S. M. 2013. Acoustic monitoring of Atlantic cod (Gadus morhua) in Massachusetts Bay: implications for management and conservation. – ICES Journal of Marine Science, 70: 628–635.Atlantic cod (Gadus morhua) stocks in northeastern US waters are depleted and stock recovery has been slow; research into the spawning behaviour of this species can help inform conservation and management measures. Male cod produce low-frequency grunts during courtship and spawning. Passive acoustic monitoring (PAM) offers a different perspective from which to investigate the occurrence, spatial extent and duration of spawning cod aggregations. A marine autonomous recording unit was deployed in the “Spring Cod Conservation Zone” (SCCZ) located in Massachusetts Bay, western Atlantic, to record cod grunts from April–June 2011. Cod grunts were present on 98.67% of the recording days (n = 75 days). They occurred across all 24 h, although significantly more grunts were found during the day than night-time (p = 0.0065). Grunt durations ranged from 57–360 ms, and the fundamental frequency and second harmonic had mean peak frequencies of 49.7 ± 5.6 and 102.9 Hz ± 10.9 sd, respectively. Cod grunt rates were low compared with those reported for other spawning fish, and may be indicative of diel movement patterns. Next steps will focus on expanding PAM coverage within the SCCZ, alongside prospecting for unknown spawning grounds within existing archival data. [ABSTRACT FROM PUBLISHER]

Baltic cod, like other species, is susceptible to inter-annual fluctuations in sexual maturation, depending on the length, age, sex, extent of the habitat area, and stock abundance of the cod population. Maturity is one of the biological indicators used to detect changes in a stock that can be caused by fishing. To address these issues specifically for the eastern Baltic cod stock, long-term data (1990-2006) from Polish research vessels in the southern Baltic were examined. To date, the ICES has used the same maturity ogives over extended periods and assumed invariant sex ratios for the assessment of eastern Baltic cod. The combined maturity ogives calculated in the present study were markedly lower, particularly for age groups 2-4 (5), in all periods, than those used in the ICES assessment. Moreover, the proportion of females increased with length and age, suggesting that annual verification of the sex ratio is needed. The present study also revealed that the total length (L50%) and the age (mean age-at-maturity; MAM50%) at which 50% achieved first sexual maturity were higher for females than for males in the study period. The long-term mean L50% and MAM50% for females were 43.9 cm and 4.3 years, respectively, and for males 34.8 cm and 3.4 years. There was also a spatial difference between calculated maturity ogives, with slightly lower L50% (range: 1.4-8.6 cm) in the Gdańsk Basin than in the Bornholm Basin. The increasing trend in fishing mortality observed in 1993-2004 ( ICES data) did not translate into a temporal trend in calculated maturity ogives. However, changes in L50% and MAM50% reflected recruitment variations ( ICES data). The significance of these findings is discussed in the context of the environment and recruits abundance. [ABSTRACT FROM AUTHOR]

Previous studies have found strong evidences for Atlantic cod ( Gadus morhua) egg retention in fjords, which are caused by the combination of vertical salinity structure, estuarine circulation, and egg specific gravity, supporting small-scaled geographical differentiations of local populations. Here, we assess the variability in egg specific gravity for selected local populations of this species, that is, two fjord-spawning populations and one coastal-spawning population from Northern Norway (66-71°N/10-25°E). Eggs were naturally spawned by raised broodstocks (March to April 2009), and egg specific gravity was measured by a density-gradient column. The phenotype of egg specific gravity was similar among the three local populations. However, the associated variability was greater at the individual level than at the population level. The noted gradual decrease in specific gravity from gastrulation to hatching with an increase just before hatching could be a generic pattern in pelagic marine fish eggs. This study provides needed input to adequately understand and model fish egg dispersal. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Hurst, T. P., Moss, J. H., and Miller, J. A. 2012. Distributional patterns of 0-group Pacific cod (Gadus macrocephalus) in the eastern Bering Sea under variable recruitment and thermal conditions. – ICES Journal of Marine Science, 69: 163–174.Despite the importance of Pacific cod in Bering Sea fisheries and foodwebs, little is known about the habitat use and the distribution of early life stages. We analysed 6 years of catch data for 0-group Pacific cod in fishery-independent surveys of the Bering Sea shelf. Juvenile cod were most commonly captured on the middle shelf over depths of 50–80 m and were rarely captured north of 58°N. Consistently high catches were observed east of the Pribilof Islands and north of Port Moller along the Alaska Peninsula. There was evidence of density-dependent habitat selection at the local scale as the frequency of occurrence increased with regional catch per unit effort. At the basin scale, the southerly distribution of the weak 2009 cohort suggested the possibility of a range contraction for small cohorts. There was no consistent shift in the distribution of juvenile Pacific cod in response to interannual climate variability. These results for Pacific cod contrast with those observed for walleye pollock, which appears to exhibit greater variance in distribution, but are similar to patterns observed for juvenile Atlantic cod. Future work should focus on distribution in nearshore habitats and examine the patterns of dispersal and the connectivity of the Bering Sea and Gulf of Alaska populations. [ABSTRACT FROM PUBLISHER]

Summary An Atlantic cod, Gadus morhua L., with unique golden pigmentation was caught during a commercial trawl on the Svalbard Bank. Stomach content analysis excluded the possibility of golden pigmentation resulting from diet. Skin morphology, mitochondrial and molecular species markers and also the concentration of melatonin (MEL) were examined. Skin samples from five areas below and above the lateral line contained correctly developed melanophores, but their distribution was different from those observed in the skin samples of standard coloured cod. Only the difference between the numbers of melanophores below the lateral line was statistically significant (8 vs 19.8 in standard coloured cod). DNA analyses allowed exclusion of the possibility of interspecies hybridisation with haddock Melanogrammus aeglefinus. MEL concentrations in the skin sample of the golden cod compared to the control sample of standard coloured cod were similar and with no statistically significant differences. Some abnormalities observed in the detailed morphology and melanophore distribution suggest a genetic or hormonal nature in the golden pigmentation of the cod. Some of these, e.g. mutations of TYR (tyrosinase) genes or of the MSH (melanophore-stimulating hormone) level can be tested in further analyses. [ABSTRACT FROM AUTHOR]

Abstract: Cortisol is released into the bloodstream of fish in response to exogenous stimuli referred to as stressors, and long-term or repetitive exposure to stressors can lead to poor growth and disease susceptibility in aquaculture-reared fish. Thus, as has been shown for other fish species (e.g. rainbow trout), the identification of fish with an attenuated cortisol response to stress may be beneficial to the emerging cod aquaculture industry. In this study, we: 1) examined if differences in the magnitude of the cortisol response to a standardized stressor (30s handling) could be consistently detected within a multi-family population of cod; 2) determined if these differences were related to growth, and independent of stressor type; and 3) assessed whether single nucleotide polymorphisms (SNPs) identified by the Atlantic Cod Genomics and Broodstock Development Project (CGP) were correlated significantly with the magnitude of cortisol response. In this study, we were able to consistently separate fish with a high (HR) cortisol response from those with a low cortisol response (LR) to handling and heat stress. We showed that the percentage of HR and LR responders differed dramatically among the 10 cod families (with some families having no LR or HR individuals), and that significant negative correlations existed between cortisol responsiveness (total Z score) and wet mass, specific growth rate and condition factor; LR fish were approx. 55% heavier at the end of the year long study. Finally, we identified four polymorphic SNPs (QTLs) that were significantly associated with the magnitude of cortisol response to handling stress. This research suggests that there is a genetic component to this phenotype (HR vs. LR) in Atlantic cod, and that responsiveness to stress at the juvenile stage may be an important trait to consider in broodstock selection. [Copyright &y& Elsevier]

Abstract: Electrical stunning of farmed Atlantic cod is a method used to render the fish unconscious before further processing. However, evaluations of the stunning method at plants have shown that the electrical parameters need to be optimized to achieve instant stunning and prolonged duration of unconsciousness. One aim of the present study was to establish suitable stunning conditions for cod to comply with future fish welfare regulations. AQUI-S™ is an anaesthetic capable of producing rested fish at slaughter. In the current study, we wanted to assess some welfare aspects of using this agent. In addition, the two stunning methods were compared in terms of the magnitude of the stress response, and the resulting effect on product quality. The data show it was possible to stun cod instantly (0.5s) at 107 Vrms, 0.5+0.2 Arms. However, it was necessary to expose the fish for a longer period (e.g. 15s) to the same voltage to prolong the period of unconsciousness to facilitate killing without recovery. AQUI-S™ (68mgL−1) rendered the fish unconscious without recovery. No noticeable avoidance behaviour or distress was observed during stunning. Blood pH, lactate levels, and blood drainage, as determined after recovery, were similar for both stunning methods. The ability of the white muscle to twitch was not affected by treatment although electrical stunning caused a drop in initial white muscle pH. Hence, a tendency for a more rapid onset of rigor mortis was observed. No detrimental effects on product quality (Quality Index scores, tendency for gaping, ultimate pH, and fillet texture) were observed for either stunning method. Moreover, no blood spots and discolourations of fillets, or spinal fractures were observed. To comply with both good fish welfare protocols, and at the same time ensuring good product quality, we have fundamentally shown that this is indeed possible when cod are stunned with either of the methods described here. [Copyright &y& Elsevier]

The article discusses a study on species of Exophiala, opportunistic fungal pathogens that may infect warm- and cold-blooded animals, including salomonids and Atlantic cod. Abnormal swimming behavior, skin pigmentation and increased mortality were observed in cod kept in an indoor tank. The study found that the chronic multifocal inflammation in internal organs of cod leading to disease and mortality was caused by Exophilia angulospora, based on the morphology and sequence analysis. Further studies should reportedly include challenge experiments of Exophiala angulospora on cod and salmonids.

Wright, P. J., Millar, C. P., and Gibb, F. M. 2011. Intrastock differences in maturation schedules of Atlantic cod, Gadus morhua. – ICES Journal of Marine Science, 68: 1918–1927.Differences in maturation schedules from three subpopulations of North Sea cod (Gadus morhua) were examined using the demographic probabilistic maturation reaction norm (PMRN) approach. Declines in maturation probability with size and age were evident within the North Sea cod stock, but the magnitude of decline differed among subpopulations. The difference in the rate of decline led to significant spatial differences in recent times. Changes in maturation probability could not be explained by colonization from adjacent regions indicating a local response to conditions. The greatest decline in maturation probability followed the near collapse of regional spawning biomass during the 1980s and 1990s. A new methodology was developed to integrate the effects of temperature and competitive biomass into the estimation of the PMRN. Temperature had a positive effect on maturation probability, but could only partially explain the decreasing trend in PMRN midpoints. Consequently, regional selection for early maturing genotypes provides the most parsimonious explanation for the declines in maturation probability observed. The difference in maturation probability among North Sea cod subpopulations, and the additive contribution of temperature to the estimation of change, underscores the need to account for population structuring and to incorporate temperature as a covariate in future applications of the PMRN. [ABSTRACT FROM PUBLISHER]

The article discusses findings of a study which presented a detailed state-dependent optimality model of larval cod Gadus morhua in a water column with environmental gradients and circadian light cycles. Several factors that influence larval feeding rates and predation risk include ambient light, body size, swimming activity and depth position. In developing the model, the objective is to explain the observed patterns in larval fish growth and survival. For the main source of fish mortality, one factor with strong implication is prey distribution.

Trends in interannual variation in maturation and spawning terms of various age cohorts in the Eastern Baltic cod population in 1997-2009 were studied. Specific features in the age structure of the mature population part that were established by the end of the first decade of the 21st century were clarified. The role of cod age cohorts in the current population reproduction was considered taking into account the data on cod recruitment and fecundity. [ABSTRACT FROM AUTHOR]

The past decades of monitoring discharges from oil and gas industry have revealed that although there are indications of adverse effects in tissues of aquatic organisms, little is known about their temporal development. Furthermore, observations in wild-caught individuals have not been clearly reproduced in laboratory studies or caging studies, and vice versa, and the results are therefore not easily interpretable. There is clearly a need for exposure studies designed for monitoring the development of effect markers in individual fish over chronic periods to low contaminant levels. Through repetitive nondestructive sampling, the progression of effects may be monitored in individuals, significantly reducing the number of fish needed in exposure studies. A laboratory exposure study was designed to be able to monitor selected parameters in individual Atlantic cod (Gadus morhua). Passive integrated transponders in combination with visible implant elastomers were used to study individual fish during the exposure period (44 wk). Fish were measured (weight and length) and a blood sample was taken for analysis of hematocrit, DNA damage (micronucleus), and oxidative stress (total oxyradical scavenging capacity) at up to seven time points. There were no apparent adverse effects of treatments on the health of experimental fish, frequency of micronucleated erythrocytes, or oxidative stress in whole blood. It is possible that the time scale was not sufficient for development and detection of parameters included here or that red blood cells may not be a suitable matrix for the selected analyses. Future studies need to include other parameters in blood to investigate their sensitivity to low-concentration exposures. [ABSTRACT FROM AUTHOR]

Produced water (PW) discharged from offshore oil industry activities contains substances that are known to contribute to a range of mechanisms of toxicity. In the present study selected reproductive biomarkers were studied in prespawning Atlantic cod (Gadus morhua) exposed to PW. The fish were exposed for 12 wk within a continuous flow-through system at realistic environmental near-field concentrations. Concentrations of polyaromatic hydrocarbon (PAH) and alkylphenol (AP) compounds were analyzed by gas chromatography with mass spectrometric detection measurement, as were PAH and AP metabolites in fish bile for verification of exposure conditions and presence of compounds in PW. A suite of reproductive biomarkers (vitellogenin, zona radiata protein, and plasma steroid concentrations) and histological alterations of the gonads were determined. Results showed that exposure to sufficiently high levels of PW produced an increase in vitellogenin levels in female fish compared to the control. Impaired oocyte development and reduced estrogen levels were also observed in PW-exposed female fish. In male fish testicular development was altered, showing a rise in amount of spermatogonia and primary spermatocytes and a reduction in quantity of mature sperm in the PW-exposed fish compared to control. Data indicate that sufficiently high levels of PW have the potential to adversely affect the reproductive fitness of cod. [ABSTRACT FROM AUTHOR]

The aims of this study were to investigate effects of dietary mineral supplementation on chemical and sensory quality parameters of fresh farmed cod fillets and on the quality of salt-cured farmed cod. Farmed cod were fed three experimental diets with different levels of mineral supplements (no supplementation, supplementation without zinc and copper, full supplementation) for approximately 2 yr. After slaughter, one-third of the experimental fish were subjected to chemical and physical analysis, another third were used for sensory analysis and the remaining fish were salt cured. Potassium, copper, and muscle protein were higher in muscle tissue of cod fed full supplementation than cod fed without supplementation. Instrumental color analysis showed that the cut side of fresh fillets of cod fed full supplementation were slightly more green and yellow than fillets of cod fed without extra supplements. A sensory panel could, however, not detect any differences between heated fresh cod given feed with or without mineral supplements. However, the quality of salt ripened cod which had received a complete mineral supplement in the diet was reduced because of increased yellowness, probably caused by the increased level of copper in the muscle. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article discusses research done on the life history characteristics of fjord cod Gadus morhua in Skagerrak, Norway. Life history changes are considered as stress indicators in harvested populations. The study procedure included the measurement of the fork length of the fish and the identification of the maturity state from the visual inspection of the gonads. The data gathered indicated the shift of age and length distributions towards larger and older fish, contrary to expectations with the historic sample.

Climate change and overfishing may lead to ecosystem instability and may benefit nonexploited organisms such as jellyfish. In the Irish Sea, an increase in jellyfish abundance was evident ( r=0.29, P=0.03) in a 16-year time-series (1994-2009) collected during juvenile fish surveys. Jellyfish abundance correlated positively with sea surface temperature (SST) over the preceding 18 months ( r=0.65, p<0.001) and copepod biomass in the previous year ( r=0.56, p=0.03) and negatively with spring (February-May) precipitation ( r=−0.57, p=0.02). Principal components regression indicated that climatic indices explained 68% of the interannual variability in jellyfish abundance ( P=0.003), where the components were based on the North Atlantic Oscillation Index, SST and precipitation. The frequency of cnidarian material present in Continuous Plankton Recorder (CPR) samples has also increased since 1970, with a period of frequent outbreaks between 1982 and 1991. Before this period, the herring stock in the northern Irish Sea declined rapidly to a low level, potentially stimulating structural change in the ecosystem. In 1985, there was a step decrease in CPR copepod biomass and in 1989, a step increase in the phytoplankton colour index, suggesting a cascading regime shift during the 1980s. Subsequent overexploitation of gadids, coupled with warm temperatures and the poor recruitment of cod, led to the rapid decline in cod biomass from 1990. While the biomass of sprat has decreased in the last decade, the herring stock has recovered partially. Reductions in demersal fishing pressure since 2000, intended to stimulate cod recovery, appear to have facilitated further rises in haddock biomass. Since the 1980s regime shift, sea temperatures have increased, the fish community has altered and jellyfish abundance has risen such that jellyfish and haddock may now play an increasingly important role in the ecosystem. [ABSTRACT FROM AUTHOR]

The article discusses a study which measured the thermal experience of several adult Atlantic cod from different stocks in the northeast Atlantic using electronic tags. Data from the study showed that cod is an adaptable and tolerant species capable of surviving and growing in a wide range of temperate marine climates. It was demonstrated that the total thermal niche of the species ranged from -1.5 to 19 degrees centigrade, which was narrower during the spawning period. It also concluded that their growth rates increased with temperature.