Large females connect Atlantic cod spawning sites.

The Earth's ecosystems are increasingly deprived of large animals. Global simulations suggest that this downsizing of nature has serious consequences for biosphere functioning. However, the historical loss of large animals means that it is now often impossible to secure empirical data revealing their true ecological importance. We tracked 465 mature Atlantic cod (Gadus morhua) during their winter spawning season and show that large females (up to 114 centimeters in length), which are still found in mid-Norway, were characterized by more complex movement networks compared with smaller females. Large males were sparse but displayed similar movement patterns. Our finding implies that management programs promoting large fish will have positive impacts on population resilience by facilitating the continued use of a diversity of spawning habitats and the connectivity between them.

Acid and enzymatic extraction of collagen from Atlantic cod (Gadus Morhua) swim bladders envisaging health-related applications.

Atlantic cod is processed industrially for food purposes, with several by-products being directed to animal feed and other ends. Looking particularly into swim bladders, the extraction of collagen can be a valuable strategy for by-product valorization, explored in the present work for the first time. Collagen was extracted using acetic acid (ASCsb) and pepsin (PSCsb) with yields of 5.72% (w/w) and 11.14% (w/w), respectively. SDS-PAGE profile showed that the extracts were compatible with type I collagen. FTIR, CD and XRD results suggest that the PSCsb structure underwent partial denaturation, with microDSC showing a band at 54 °C probably corresponding to a melting process, while ASCsb structure remained intact, with preserved triple helix and a denaturation temperature of 29.6 °C. Amino acid composition indicates that the total content of proline-like amino acids was 148/1000 residues for ASCsb and 141/1000 residues for PSCsb, with a hydroxylation degree of about 37%. The extracts exhibited a typical shear thinning behavior, interesting property regarding their further processing toward the development of biomaterials. In this regard, assessment of metabolic activity of human fibroblast cells cultured in the presence of collagen extracts with concentrations up to 3 mg/mL revealed the absence of cytotoxic behavior. Collagen extracts obtained from Atlantic cod swim bladders shown attractive properties regarding their use in cosmetic or biomedical applications.

Effects of freezing on length and mass measurements of Atlantic cod Gadus morhua in the Baltic Sea.

An aggregated sample of 925 Atlantic cod Gadus morhua collected by four countries in different regions of the Baltic Sea during different seasons were measured (total length, LT = 161-890 mm and weighed (mass, M = 45-6900 g) both before freezing and after defrosting. The cod were found to decrease significantly in both LT and M following death and frozen storage. There was an average (±SD) change in LT of -2.91% (±0.05%) following freezing, independent of starting LT . Total M changed by -2.65% (±0.14%), independent of starting mass. Shrinkage of LT and M did not differ significantly between 1 and 4 months frozen storage, though LT shrinkage was significantly greater after 1 or 4 months in the freezer compared with after 5 days. There was significant variation in LT and M shrinkage between regions of capture. A significant negative relationship between condition of cod and LT or M change was also observed. Equations to back-calculate fresh LT and M from thawed LT , M and standard length (LS ), gutted LT , gutted LS and gutted M are provided.

Size-dependent social attraction and repulsion explains the decision of Atlantic cod Gadus morhua to enter baited pots.

The present study tested whether the presence of already retained fishes inside baited fish pots acted as a social attraction and affected the entrance probability of Atlantic cod Gadus morhua in a fjord in northern Norway. Video analysis revealed that the probability of an entrance initially increased with the presence of low numbers of fishes inside the pot, but subsequently decreased at a critical number of caught fishes. The critical number was dependent on the size of the G. morhua attempting to enter. This demonstrates that social attraction and repulsion play a role in G. morhua pot fishing and has important implications for the capture efficiency of fisheries executed with pots.

High rates of glucose utilization in the gas gland of Atlantic cod (Gadus morhua) are supported by GLUT1 and HK1b.

The gas gland of physoclistous fish utilizes glucose to generate lactic acid that leads to the off-loading of oxygen from haemoglobin. This study addresses characteristics of the first two steps in glucose utilization in the gas gland of Atlantic cod (Gadus morhua). Glucose metabolism by isolated gas gland cells was 12- and 170-fold higher, respectively, than that in heart and red blood cells (RBCs) as determined by the production of (3)H2O from [2-(3)H]glucose. In the gas gland, essentially all of the glucose consumed was converted to lactate. Glucose uptake in the gas gland shows a very high dependence upon facilitated transport as evidenced by saturation of uptake of 2-deoxyglucose at a low extracellular concentration and a requirement for high levels of cytochalasin B for uptake inhibition despite the high efficacy of this treatment in heart and RBCs. Glucose transport is via glucose transporter 1 (GLUT1), which is localized to the glandular cells. GLUT1 western blot analysis from whole-tissue lysates displayed a band with a relative molecular mass of 52 kDa, consistent with the deduced amino acid sequence. Levels of 52 kDa GLUT1 in the gas gland were 2.3- and 33-fold higher, respectively, than those in heart and RBCs, respectively. Glucose phosphorylation is catalysed by hexokinase Ib (HKIb), a paralogue that cannot bind to the outer mitochondrial membrane. Transcript levels of HKIb in the gas gland were 52- and 57-fold more abundant, respectively, than those in heart and RBCs. It appears that high levels of GLUT1 protein and an unusual isoform of HKI are both critical for the high rates of glycolysis in gas gland cells.

The effect of temperature and body size on metabolic scope of activity in juvenile Atlantic cod Gadus morhua L.

Changes in ambient temperature affect the physiology and metabolism and thus the distribution of fish. In this study we used intermittent flow respirometry to determine the effect of temperature (2, 5, 10, 15 and 20°C) and wet body mass (BM) (~30-460g) on standard metabolic rate (SMR, mgO2h(-1)), maximum metabolic rate (MMR, mgO2h(-1)) and metabolic scope (MS, mgO2h(-1)) of juvenile Atlantic cod. SMR increased with BM irrespectively of temperature, resulting in an average scaling exponent of 0.87 (0.82-0.92). Q10 values were 1.8-2.1 at temperatures between 5 and 15°C but higher (2.6-4.3) between 2 and 5°C and lower (1.6-1.4) between 15 and 20°C in 200 and 450g cod. MMR increased with temperature in the smallest cod (50g) but in the larger cod MMR plateaued between 10, 15 and 20°C. This resulted in a negative correlation between the optimal temperature for MS (Topt) and BM, Topt being respectively 14.5, 11.8 and 10.9°C in a 50, 200 and 450g cod. Irrespective of BM cold water temperatures resulted in a reduction (30-35%) of MS whereas the reduction of MS at warm temperatures was only evident for larger fish (200 and 450g), caused by plateauing of MMR at 10°C and above. Warm temperatures thus seem favourable for smaller (50g) juvenile cod, but not for larger conspecifics (200 and 450g).

To glue or not to glue? Reassembling broken otoliths for population discrimination.

Twenty-five Atlantic cod Gadus morhua otoliths were examined using eight shape measurements along with Fourier analysis of their outlines to test whether discrimination using otolith shape is affected by gluing broken otoliths. Small differences in seven of the eight shape measurements were found between unbroken otoliths and the same otoliths after breaking and subsequently gluing together; however, none of the Fourier descriptors differed. Cluster analyses indicated that resultant morphological differences will have no impact when applying discriminant analysis.

Direct and social genetic parameters for growth and fin damage traits in Atlantic cod (Gadus morhua).

BACKGROUND: The aim of the study was to estimate genetic parameters for direct and social genetic effects (SGE) for growth and welfare traits in farmed Atlantic cod (Gadus morhua). A SGE refers to the effect of an individual's genes on trait performance of its social partners. In total, 2100 individually tagged juveniles from 100 families at an average age of 222 days post-hatching were used. Each family was separated into three groups of seven fish, and were randomly assigned to 100 experimental tanks, together with fish from two other families. Body weight and length of the first, second and third dorsal fin and the caudal fin measured by digital image analysis were measured at the start of the experiment, after two weeks, and after six weeks. Fin erosion was scored subjectively after six weeks. Variance components estimated using a conventional animal model were compared to those of an animal model including a SGE. RESULTS: Heritabilities from the conventional animal model ranged from 0.24 to 0.34 for body weight and 0.05 to 0.80 for fin length. Heritabilities for fin erosion were highest for the first dorsal fin (0.83 ± 0.08, mean ± standard error) and lowest for the third dorsal fin (0.01 ± 0.04). No significant SGE were found for body weight, whereas SGE for fin lengths were significant after two and six weeks. Contributions to the total heritable variance were equal to 21.5% (6.1 ± 2.1) for the direct effect, 33.1% (9.4 ± 3.2) for the direct-social covariance, and 45.4% (12.9 ± 4.1) for the social variance for length of the first dorsal fin. For fin erosion, SGE were only significant for the second and third dorsal fin. CONCLUSIONS: Including SGE for fin length and fin erosion in the animal model increased the estimated heritable variation. However, estimates of total heritable variances were inaccurate and a larger experiment is needed to accurately quantify total heritable variance. Despite this, our results demonstrate that considering social breeding values for fin length or fin erosion when selecting fish will enable us to improve response to selection for welfare traits in Atlantic cod juveniles.

Ultrastructure of spermatozoa of the Atlantic cod Gadus morhua L. observed by scanning and transmission electron microscopy.

The present study on wild caught Atlantic cod Gadus morhua provides a detailed description of the spermatozoa ultrastructure. The spermatozoa of G. morhua are composed of a head (nucleus) with no acrosome, a midpiece and a single flagellum. The total length is 67.69±6.33µm with a lanceolate sperm head that is 2.34±0.26µm long and 1.32±0.26µm wide. The nucleus presents homogeneous condensation of chromatin with few lacunae of decondensed chromatin. The nuclear fossa penetrates over three third of the nuclear axis and is tubiform. The axoneme is composed of a typical 9+2 microtubular doublet structure and is enclosed by the plasma membrane. Central microtubules are absent from the proximal portion of the anterior end of nuclear notch and a distal centriole complex is perpendicular to the axoneme. A group of mitochondria and vesicles is present in the midpiece. The ultrastructure of the Gadidae G. morhua spermatozoon differs from the structures described earlier for other Gadiformes. The unique features may be synapomorphic for marine Gadidae, and may contribute to the study of phylogenetic relationships in teleost fishes, and be a reference for future studies on spermatozoon quality and morphology in fish.

Regional changes in vertebra morphology during ontogeny reflect the life history of Atlantic cod (Gadus morhua L.).

This study examined vertebra formation, morphology, regional characters, and bending properties of the vertebral column of Atlantic cod throughout its life cycle (0-6 years). The first structure to form was the foremost neural arch, 21 days post hatching (dph), and the first vertebra centrum to form - as a chordacentrum - was the 3rd centrum at 28 dph. Thereafter, the notochord centra developed in a regular sequence towards the head and caudal fin. All vertebrae were formed within 50 dph. The vertebral column consisted of 52 (± 2) vertebrae (V) and could be divided into four distinct regions: (i) the cervical region (neck) (V1 and V2), characterized by short vertebra centra, prominent neural spines and absence of articulations with ribs; (ii) the abdominal region (trunk) (V3-V19), characterized by vertebrae with wing-shaped transverse processes (parapophyses) that all articulate with a rib; (iii) the caudal region (tail) (V20-V40), where the vertebra centra have haemal arches with prominent haemal spines; (iv) the ural region (V41 to the last vertebra), characterized by broad neural and haemal spines, providing sites of origin for muscles inserting on the fin rays - lepidotrichs - of the tail fin. The number of vertebrae in the cervical, abdominal and caudal regions was found to be constant, whereas in the ural region, numbers varied from 12 to 15. Geometric modelling based on combination of vertebra lengths, diameters and intervertebral distances showed an even flexibility throughout the column, except in the ural region, where flexibility increased. Throughout ontogeny, the vertebra centra of the different regions followed distinct patterns of growth; the relative length of the vertebrae increased in the cervical and abdominal regions, and decreased in the caudal and ural regions with increasing age. This may reflect changes in swimming mode with age, and/or that the production of large volumes of gametes during sexual maturation requires a significant increase in abdominal cavity volume.

Identification of stock components using morphological markers.

This study investigated the development of a quantitative method for distinguishing stock components of Icelandic cod Gadus morhua based on visual examination of morphology. The stock is known to be structured into genetically distinct geographic components (north and south of Iceland) and behavioural types that spawn sympatrically. Differences in morphology were tested between locations, genotypes (a proxy for behaviour) and sexes. Results show morphological markers on the head, fins and body of G. morhua that are correlated with the sex, genotype of the fish at the pantophysin (pan-I) locus and the location at which the fish were caught. Females were found to have relatively deep bodies, and the pan-I(BB) genotype (associated with deep-water feeding behaviour) have greater gaps between their fins. Overall, morphology is more useful for distinguishing sympatric genotypes but less powerful at identifying genetically distinct geographic sub-populations, perhaps because counter-gradient evolution reduces phenotypic differences even with an underlying genetic cause.

Fishery discards: factors affecting their variability within a demersal trawl fishery.

Discards represent one of the most important issues within current commercial fishing. It occurs for a range of reasons and is influenced by an even more complex array of factors. We address this issue by examining the data collected within the Danish discard observer program and describe the factors that influence discarding within the Danish Kattegat demersal fleet over the period 1997 to 2008. Generalised additive models were used to assess how discards of the 3 main target species, Norway lobster, cod and plaice, and their subcomponents (under and over minimum landings size) are influenced by important factors and their potential relevance to management. Our results show that discards are influenced by a range of different factors that are different for each species and portion of discards. We argue that knowledge about the factors influential to discarding and their use in relation to potential mitigation measures are essential for future fisheries management strategies.

Gonadal development of triploid Atlantic Cod Gadus morhua.

During their third and fourth years of life, triploid Atlantic cod Gadus morhua females exhibited diminished ovarian development at both macroscopic and microscopic levels, with significantly lower gonado-somatic indices (I(G)) and higher carcass yields (Y(C)) than diploid females during spawning periods. In contrast, diploid and triploid testes were indistinguishable through macroscopic and histological assessment. No significant differences were found in male I(G) or Y(C) in relation to ploidy, with the exception of a higher Y(C) for triploids during the first of the two monitored spawning seasons. As a result of suppressed oogenesis, triploid female G. morhua, but not triploid males, can be used to eliminate sexual maturation in this species and advance the development of the G. morhua aquaculture industry.

Electron spin resonance (ESR) detection of irradiated fish containing bone (gilthead sea bream, cod, and swordfish).

Food irradiation is a preservation method that has been approved by the European Union for a limited number of foods or food products and within a limited range of doses. European Community legislation states that all foods or food ingredients treated in this manner and authorized for sale in the European Union must be clearly labeled, and that market-level inspections must be carried out to ensure compliance with this regulation. To improve detection of irradiated foods, we evaluated the efficacy of electron spin resonance (ESR) spectroscopy for the identification of seafood that had been subjected to irradiation. Three fish species were tested: gilthead sea bream, cod, and swordfish. For each species, 18 samples of flesh-containing bone were analyzed after either irradiation at 0.5, 1, or 3 kGy or no irradiation (control). Induced radicals in irradiated samples produced distinct ESR signals that allowed differentiation from non-irradiated samples. Within the dose range tested, a linear dose-response relationship was observed (R(2) > 0.94). The gilthead sea bream displayed the highest radiosensitivity. The analytical procedure was validated and successfully used for the routine monitoring of locally marketed seafood. The main aims of the study were to develop a reliable tool for the enforcement of the proper labeling of irradiated foods and to obtain preliminary data on compliance with current laws in the Italian market.

Seasonal variations in seminal plasma and sperm characteristics of wild-caught and cultivated Atlantic cod, Gadus morhua.

The objective was to investigate changes, throughout the spawning season, in body size attributes and quantitative semen characteristics of wild-caught and cultivated Atlantic cod, Gadus morhua L. Sperm velocity increased significantly throughout the spawning season of cod from both origins. Curvilinear velocity (VCL; 30 sec post-activation) increased from 78.9+/-6.5 to 128.2+/-6.5 microm/sec (mean+/-SEM) between the beginning and end of the spawning season, respectively, for wild-caught cod, whereas for cultivated fish, it increased from 26.6+/-2.4 to 48.9+/-3.1 microm/sec between January and March. Spermatocrit did not undergo a significant seasonal change in wild-caught cod but did thicken for cultivated cod (24.6+/-4.2% in January to 40.5+/-4.4% in April; P<0.01). Sperm head area, perimeter, length, and width declined significantly at the end of the spawning season of cod from both origins (all P values<0.01). Seminal plasma osmolality and Na(+) ion concentration followed a dome-shaped function through the spawning season for both wild-caught and cultivated cod (P<0.05). For cultivated cod, seminal plasma pH was significantly lower at the start of the spawning season (P<0.001), whereas Ca(2+) increased then decreased (P<0.05). Body size attributes, spermatocrit, and seminal plasma constituents had significant relationships with sperm activity variables. These relationships varied as a function of time post-activation, month, and fish origin. Our findings may be used to (i) assess spermiation stage without killing males; (ii) optimize semen collection for hatchery production; (iii) characterize the potential impact of farming on sperm quality; and (iv) improve success of sperm cryopreservation and short-term storage.

Determination of fish gender using fractal analysis of ultrasound images.

The gender of cod Gadus morhua can be determined by considering the complexity in their gonadal ultrasonographic appearance. The fractal dimension (D(B)) can be used to describe this feature in images. B-mode gonadal ultrasound images in 32 cod, where gender was known, were collected. Fractal analysis was performed on these images and D(B) was determined using the box counting method. A receiver-operating curve (ROC) was drawn for D(B) as a test for male fish. Using a range of D(B) values, the maximum accuracy for this test was calculated and compared with the accuracy for identifying male fish by subjective analysis alone. The mean (and standard deviation) of the fractal dimension D(B) for male fish was 1.554 (0.073) while for female fish it was 1.468 (0.061); the difference was statistically significant (P = 0.001). The area under the ROC curve was 0.84 indicating the value of fractal analysis in gender determination in cod. Maximum accuracy (0.84) for D(B) as a test for male fish was obtained using the threshold value D(B) = 1.5058 compared with an accuracy of 0.78 for subjective image evaluation. The use of two thresholds, D(B) < 1.4475 (females) and D(B) > 1.5054 (males) gives an 80% certainty in the classification result. Fractal analysis is useful for gender determination in cod. This or a similar form of analysis may have wide application in veterinary imaging as a tool for quantification of complexity in images.

Nine decades of decreasing phenotypic variability in Atlantic cod.

Changes in phenotypic variability in natural populations have received little attention in comparison with changes in mean trait values. This is unfortunate because trait diversity may influence adaptive evolutionary change and population stability. We combine two unique data sets to illuminate complex trait changes in Atlantic cod along the Norwegian Skagerrak coast: (i) an annual beach seine survey starting in 1919, monitoring juvenile body size and abundance and (ii) capture-mark-recapture data from which we estimated selection on juvenile body size and growth. We demonstrate that the variability of juvenile size has been steadily decreasing across nine decades, with no evidence for a similar trend in mean size. We also report that small, slow-growing fish as well as large, fast-growing fish are selected against. Together, these results suggest long-term stabilizing selection acting on Atlantic cod, and emphasize the need for further studies evaluating the full complexity of trait changes in wild populations.

Effects of egg size, parental origin and feeding conditions on growth of larval and juvenile cod Gadus morhua.

An experimental study was performed to disentangle parental and environmental effects on the growth of Atlantic cod Gadus morhua larvae and juveniles. Eggs were collected during the spawning season from spawning pairs (families) kept separately in specially designed spawning compartments. Newly hatched larvae were released simultaneously into two mesocosms of 2,500 and 4,400 m(3). Larval growth was monitored by sampling over a 10 week period, after which juveniles were transferred to on-growing tanks, where they were tagged and kept for up to 2 years. Maternal origin was determined by individual microsatellite genotyping of the larvae (n = 3949, 24 families) and juveniles (n = 600). The results showed significant positive correlations between egg size and larval size during the whole mesocosm period. Correlations, however, weakened with time and were no longer significant at the first tank-rearing sampling at an age of 9 months. Significant family-specific differences in growth were observed. The coefficient of variation (c.v.) was calculated in order to examine variation in standard length of larvae during the mesocosm period. Inter-family c.v. was on average 69% of intra-family c.v. Differences in zooplankton densities between the two mesocosms were reflected in larval growth, condition factor and c.v. Low food abundance appeared to reduce c.v. and favour growth of larvae that showed relatively slow growth at high food abundance. It is suggested that genetically determined variation in growth potential is maintained by environmental variability.

Are the dynamics of gastric evacuation of natural prey in a piscivorous flatfish different from what is going on in a gadoid?

Despite the fact that the stomach of turbot Psetta maxima is a curved tube that forms a half circle, it was demonstrated that gastric evacuation in this predatory flatfish fed natural prey closely followed the surface-dependent cylinder model developed from studies on gadoids with a straight stomach. Evacuation experiments were performed on two size groups of P. maxima fed sandeel Ammodytes tobianus as well as on P. maxima fed brown shrimp Crangon crangon at three different temperatures. This enabled the provision of a gastric evacuation model for studies on P. maxima, which takes into account the effects of the explanatory variables predator size, temperature, prey energy density and resistance of prey to the digestive processes in the stomach. Basically, the cylinder model predicts that a square-root function accurately describes gastric evacuation, which is inconsistent with the conclusion of a previous study on P. maxima that evacuation of A. tobianus is essentially linear with time. Use of the cylinder model to the values of the explanatory variables presented in the latter study, however, gave accurate predictions of the actually acquired evacuation data, which points to the generic value of the model.

Nanostructures of the aragonitic otolith of cod (Gadus morhua).

Topographical relationships between the mineral and organic components are important to understand the process involved in biomineralisation. We examined nanostructural features of cod (Gadus morhua) otoliths using atomic force microscope (AFM). Acicular aragonitic fibres that form primary increments observed in scanning electron or light microscopy were composed of lamellae, themselves being composite arrangements of round granules (diameter<50 nm) surrounded by an organic (?) cortex. The lamellae presented a banding pattern, which might correspond to a growth period of about 15 min. Cod otolith granules were similar in size, shape and arrangement to that previously reported for another fish species. The existence of smallest otolith organization units is suggested since granules are themselves composite. Finally, the intra-daily growth rhythm makes it possible to consider very high-resolution biological and environmental reconstructions in the future.