Showing papers on "Atlantic cod published in 2008"
TL;DR: The impact of hypoxia on MS is similar, when expressed as a proportion of MS in normoxia, in cod, European sea bass, the common sole, and turbot (Psetta maxima).
159 citations
TL;DR: A bioenergetics model was devised to investigate the evolution of migration distance and its dependence on individual states and found optimal energy allocation and migration strategies were found using state-dependent optimization.
Abstract: Individuals migrate to exploit heterogeneities between spatially separated environments to modulate growth, survival, or reproduction. We devised a bioenergetics model to investigate the evolution of migration distance and its dependence on individual states. Atlantic cod Gadus morhua ranges from sedentary populations to stocks that migrate several thousand kilometers annually. We focused on the Northeast Arctic cod stock, which migrates south to spawn. A linear relationship between migration distance and the expected survival of offspring was assumed, here understood as the prospects for future survival and development that a fertilized egg faces at a particular spawning location. Reasons for why it may increase southward include warmer water that increases development rates, and thereby survival, along the pelagic drift trajectory. In the model, ingested energy can either be allocated to growth or stored for migration and reproduction. When migrating, individuals forgo foraging opportunities and expend energy. Optimal energy allocation and migration strategies were found using state-dependent optimization, with body length, age, condition, and current food availability as individual states. For both a historical and contemporary fishing regime we modeled two behaviors: (1) homing cod returning to the same spawning site each year and (2) roaming cod with no such constraints. The model predicted distinct regions of locally high spawning stock biomass. Large individuals in good condition migrated farthest, and these also tended to mature later in life. The roaming cod spread farther south as they grew larger and older. Homing cod did not have this freedom, and spawning was generally concentrated along a narrower stretch of the coastline. Under contemporary fishing, individuals matured earlier at a smaller size, had shorter migrations, spawned over a contracted geographical range, and tended to be in poorer condition. The effects were most pronounced for the homing behavior.
158 citations
TL;DR: It is suggested that it is necessary to develop enrichment techniques to produce rotifers with sufficient amounts of all micronutrients, with reference to the requirements given for larger fish (NRC 1993), where only thiamine, vitamin A, manganese, selenium and perhaps copper, appear too low in the rotifer cultured without extra micronsutrient supplementation.
Abstract: The current best practice intensive culture of larval Atlantic cod includes feeding rotifers from onset of exogenous feeding until 25–30 days after hatching. These larvae grow considerably slower and develop higher frequencies of deformities than larvae reared in semi-extensive systems, using copepods as feed. The present study compares the micronutrient concentrations in rotifers with those of copepods, with the aim of identifying nutrients that may be limiting for normal growth and development of cod larvae. An additional criterion used is the nutrient requirements given for fish in general, by NRC (1993), as nutrient requirements of cod remains to be determined. Rotifers were fed on four different diets, consisting of baker’s yeast with cod liver oil (3.3 : 1 dry weight (DW)/v), baker’s yeast with Algamac 2000 TM (3.5 : 1 DW), baker’s yeast with live algae Chlorella (4.1 : 1 DW), and Culture Selco 3000 TM (CS). CS was a complete commercial diet for rotifers while the other diets are considered as based on raw ingredients. Compared with copepod nutrient levels, rotifers grown on yeast-based diets supplemented with either cod liver oil, Algamac 2000 or Chlorella were apparently sufficient for covering the requirements in cod larvae for all the B-vitamins, except thiamine. Rotifers cultured on the CS diet also had sufficient amounts of thiamine. Of the minerals, only calcium and magnesium were sufficient, using this criterion while iron was on the borderline. However, with reference to the requirements given for larger fish (NRC 1993), only thiamine, vitamin A, manganese, selenium and perhaps copper, appear too low in the rotifers cultured without extra micronutrient supplementation. The other nutrients were present at levels intermediate between copepod and fish requirement levels. This study suggests that it is necessary to develop enrichment techniques to produce rotifers with sufficient amounts of all micronutrients. Such techniques will also be important tools for determining which nutrients are present at levels below the actual requirements in cod larvae.
149 citations
TL;DR: Characteristics of temperature-dependent metabolic adaptation, as well as their impli- cations for climate-dependent energy budgets, biogeography and fitness are reviewed and analysed for populations of Atlantic cod Gadus morhua in relation to findings in other fish species from north and southern hemispheres.
Abstract: Characteristics of temperature-dependent metabolic adaptation, as well as their impli- cations for climate-dependent energy budgets, biogeography and fitness are reviewed and analysed for populations of Atlantic cod Gadus morhua in relation to findings in other fish species from north- ern and southern hemispheres, especially various species of eelpout (Zoarcidae). The analysis builds on the recently posited concept of oxygen- and capacity-dependent thermal tolerance in aquatic ectotherms. Mechanistic physiological studies are used to explain both functional differences between populations and current observations (such as the northward movement of cod, or the changes in seasonal abundance of eelpout due to global warming). Available data support the hypothesis that natural selection favours individuals that maximize growth and energy efficiency at the expense of ranges of thermal tolerance. The levels of energy turnover are subject to the con- straints of resource availability and temperature variability. Temperature variability in the cold, such as in the sub-Arctic, causes a rise in maintenance costs at the expense of growth, but possibly in favour of motility, and thus of foraging capacity. These different trends are mirrored in higher capac- ities for gene expression of key enzymes involved in aerobic metabolism (during cold acclimation) in northern as compared to southern cod populations of the East Atlantic. However, detailed patterns, as well as many of the underlying mechanisms, remain underexplored, especially with respect to the suggested hierarchy of energy allocation to energy budget components.
144 citations
TL;DR: The SNP markers presented here are powerful tools for future genetics work related to management and aquaculture, and some SNPs exhibiting high levels of population divergence have potential to significantly enhance studies on the population structure of Atlantic cod.
Abstract: The Atlantic cod (Gadus morhua) is a groundfish of great economic value in fisheries and an emerging species in aquaculture. Genetic markers are needed to identify wild stocks in order to ensure sustainable management, and for marker-assisted selection and pedigree determination in aquaculture. Here, we report on the development and evaluation of a large number of Single Nucleotide Polymorphism (SNP) markers from the alignment of Expressed Sequence Tag (EST) sequences in Atlantic cod. We also present basic population parameters of the SNPs in samples of North-East Arctic cod and Norwegian coastal cod obtained from three different localities, and test for SNPs that may have been targeted by natural selection. A total of 17,056 EST sequences were used to find 724 putative SNPs, from which 318 segregating SNPs were isolated. The SNPs were tested on Atlantic cod from four different sites, comprising both North-East Arctic cod (NEAC) and Norwegian coastal cod (NCC). The average heterozygosity of the SNPs was 0.25 and the average minor allele frequency was 0.18. F
ST
values were highly variable, with the majority of SNPs displaying very little differentiation while others had F
ST
values as high as 0.83. The F
ST
values of 29 SNPs were found to be larger than expected under a strictly neutral model, suggesting that these loci are, or have been, influenced by natural selection. For the majority of these outlier SNPs, allele frequencies in a northern sample of NCC were intermediate between allele frequencies in a southern sample of NCC and a sample of NEAC, indicating a cline in allele frequencies similar to that found at the Pantophysin I locus. The SNP markers presented here are powerful tools for future genetics work related to management and aquaculture. In particular, some SNPs exhibiting high levels of population divergence have potential to significantly enhance studies on the population structure of Atlantic cod.
143 citations
TL;DR: Cod within the North Sea are currently managed as a single stock, and yet mounting empirical evidence supports the existence of a metapopulation of regionally variable, genetically distinct, sub-stocks, which results in the overfishing and likely collapse of the weaker components.
Abstract: The plight of the marine fisheries is attracting increasing attention as unsustainably high exploitation levels, exacerbated by more extreme climatic conditions, are driving stocks to the point of collapse. The North Atlantic cod (Gadus morhua), a species which until recently formed a major component of the demersal fisheries, has undergone significant declines across its range. The North Sea stock is typical of many, with a spawning stock biomass that has remained below the safe biological limit since 2000 and recruitment levels near the lowest on record. Cod within the North Sea are currently managed as a single stock, and yet mounting empirical evidence supports the existence of a metapopulation of regionally variable, genetically distinct, sub-stocks. Applying the same management strategies to multiple stocks that differ in their resilience to exploitation inevitably results in the overfishing and likely collapse of the weaker components. Indeed, recent studies have identified two North Sea spawning stocks that have undergone disproportionally large collapses with very substantial reductions in egg production. Similarly affected cod stocks in the northwest Atlantic have shown little evidence of recovery, despite fishery closures. The possible implications of ignoring sub-structuring within management units for biocomplexity, local adaptation and ecosystem stability are considered.
136 citations
TL;DR: Inputs of effluents from offshore oil and gas production platforms (produced water) in the Norwegian sector have been monitored through an integrated chemical and biological effects programme since 2001, and results indicated that exposure levels were low and caused minor environmental impact at the deployment locations.
127 citations
TL;DR: In this paper, the authors examined the potential impacts of future climate change on the distribution and production of Atlantic cod (Gadus morhua) on the northeastern USA's continental shelf.
Abstract: We examined the potential impacts of future climate change on the distribution and production of Atlantic cod (Gadus morhua) on the northeastern USA’s continental shelf. We began by examining the response of cod to bottom water temperature changes observed over the past four decades using fishery-independent resource survey data. After accounting for the overall decline in cod during this period, we show that the probability of catching cod at specified locations decreased markedly with increasing bottom temperature. Our analysis of future changes in water temperature was based on output from three coupled atmosphere–ocean general circulation models under high and low CO2 emissions. An increase of 3.5°C in the Mid-Atlantic Bight. Under these conditions, cod appear vulnerable to a loss of thermal habitat on Georges Bank, with a substantial loss of thermal habitat farther south. We also examined temperature effects on cod recruitment and growth in one stock area, the Gulf of Maine, to explore potential implications for yield and resilience to fishing. Cod survival during the early life stages declined with increasing water temperatures, offsetting potential increases in growth with warmer temperatures and resulting in a predicted loss in yield and increased vulnerability to high fishing mortality rates. Substantial differential impacts under the low versus high emission scenarios are evident for cod off the northeastern USA.
125 citations
TL;DR: This work examines the glacial persistence of Atlantic cod populations using two ecological-niche-models (ENM) and the first broad synthesis of multi-locus gene sequence data for this species, and suggests that the Greenland G. morhua population post-dates the LGM.
Abstract: Scant scientific attention has been given to the abundance and distribution of marine biota in the face of the lower sea level, and steeper latitudinal gradient in climate, during the ice-age conditions that have dominated the past million years. Here we examine the glacial persistence of Atlantic cod (Gadus morhua) populations using two ecological-niche-models (ENM) and the first broad synthesis of multi-locus gene sequence data for this species. One ENM uses a maximum entropy approach (MAXENT); the other is a new ENM for Atlantic cod, using ecophysiological parameters based on observed reproductive events rather than adult distribution. Both the ENMs were tested for present-day conditions, then used to hindcast ranges at the last glacial maximum (LGM) ca 21 kyr ago, employing climate model data. Although the LGM range of Atlantic cod was much smaller, and fragmented, both the ENMs agreed that populations should have been able to persist in suitable habitat on both sides of the Atlantic. The genetic results showed a degree of trans-Atlantic divergence consistent with genealogically continuous populations on both sides of the North Atlantic since long before the LGM, confirming the ENM results. In contrast, both the ENMs and the genetic data suggest that the Greenland G. morhua population post-dates the LGM.
122 citations
McDonald Institute for Archaeological Research1, University of York2, Royal Belgian Institute of Natural Sciences3, Nicolaus Copernicus University in Toruń4, University of Kiel5, University of Bergen6, University of Copenhagen7, The Graduate Center, CUNY8, Norwegian College of Fishery Science9, University of Bradford10, York Archaeological Trust11, Suffolk University12, American Museum of Natural History13, Max Planck Society14
TL;DR: This article used stable isotope analysis to identify the approximate region of catch of cod by analysing bones from medieval settlements in northern and western Europe, finding that geographical structuring is indeed evident, making it possible to identify bones from cod caught in distant waters.
113 citations
TL;DR: The spatial and temporal changes in the bacterial communities associated with the Atlantic cod Gadus morhua were investigated using terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S recombinant DNA (rDNA).
Abstract: The spatial and temporal changes in the bacterial communities associated with the Atlantic cod Gadus morhua were investigated using terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S recombinant DNA (rDNA) Epidermal mucous was sampled from 366 cod caught in three harvest locations (Baltic, Icelandic, and North Seas) over three seasons (spring 2002, autumn 2002, and spring 2003), and an automated method for the high-throughput processing of environmental samples was developed using a Qiagen BioRobot The analysis revealed that a diverse consortium of bacteria were found on fish; γ-proteobacteria and Cytophaga–Flavobacter–Bacteroides (CFB) species were dominant T-RFLP peak profiles suggested that operational taxonomic units (OTUs) related to Photobacterium sp, Psychrobacter sp, and Bacteroides sp were common to all sites in all three seasons, but there were intersite variations in community composition Cod caught from different seas had distinct reproducible bacterial assemblages Whereas communities from fish caught in the Baltic and Icelandic Seas were relatively stable over the three seasons, those from fish from the North Sea changed significantly over time
TL;DR: The culture-independent approach employed in this study generated a dynamic description of bacterial colonization of cod larvae and live feed and revealed the existence of previously undescribed bacterial associations with eggs and rotifers which would almost certainly have gone undetected using conventional culture based methods.
TL;DR: Based on these projections, at its current level of productivity, this population is certain to be extirpated within 40 years in the absence of fishing and in 20 years with fishery removals at the level of the total allowable catch in 2007 and 2008.
Abstract: Atlantic cod (Gadus morhua) was the dominant demersal fish and most important predator in the southern Gulf of St. Lawrence ecosystem as recently as the 1980s. However, productivity of southern Gul...
TL;DR: Despite its importance in North Atlantic fisheries and potential use in aquaculture, relatively few gene expression examination exists for this species, and systematic evaluations of reference gene stability in quantitative real-time RT-PCR (qRT-PCRs) studies are lacking.
Abstract: Extensive sequencing efforts have been taking place for the Atlantic cod (Gadus morhua) in recent years, the number of ESTs in the Genbank has reached more than 140.000. Despite its importance in North Atlantic fisheries and potential use in aquaculture, relatively few gene expression examination exists for this species, and systematic evaluations of reference gene stability in quantitative real-time RT-PCR (qRT-PCR) studies are lacking. The stability of 10 potential reference genes was examined in six tissues of Atlantic cod obtained from four populations, to determine the most suitable genes to be used in qRT-PCR analyses. Relative transcription levels of genes encoding β-actin (ACTB), elongation factor 1A (EF1A), actin-related protein-2 (ARP-2), glyceraldehyde-3P-dehydrogenase (GAPDH), ubiquitin (Ubi), acidic ribosomal protein (ARP), ribosomal protein S9 (S9), ribosomal protein L4 (RPL4), RPL22 and RPL37 were quantified in gills, brain, liver, head kidney, muscle and middle intestine in six juvenile fish from three wild populations and from farmed Atlantic cod. Reference gene stability was investigated using the geNorm and NormFinder tools. Based on calculations performed with the geNorm, which determines the most stable genes from a set of tested genes in a given cDNA sample, ARP, Ubi, S9 and RPL37 were among the most stable genes in all tissues. When the same calculations were done with NormFinder, the same genes plus RPL4 and EF1A were ranked as the preferable genes. Overall, this work suggests that the Ubi and ARP can be useful as reference genes in qRT-PCR examination of gene expression studying wild populations of Atlantic cod.
TL;DR: In this article, the sperm motility was induced in a one-step procedure by adding 4.5 mL seawater before applying the coverglass and sperm swimming activity was recorded twice for each male and stored on MiniDV tapes.
Abstract: Sperm competition is recognized as an important selective force in reproductive biology (Birkhead & M ller 1998) and it occurs when sperm from more than one male compete for fertilization of the ova (Parker 1970). Sperm competition has led to the evolution of adaptive sperm traits (Andersson 1994; Birkhead & M ller 1998), and several studies on ¢sh species have shown a strong positive correlation between fertilization or hatching rate and sperm motility (Kime,Van Look, Mcallister, Huyskens, Rurangwa & Ollevier 2001; Kupriyanova & Havenhand 2002; Gage, Macfarlane, Yeates, Ward, Searle & Parker 2004; Schulte-Hostedde & Burness 2005; Casselman, Schulte-Hostedde & Montgomerie 2006). However, in species with sperm competition, males not only need to be able to fertilize the eggs, but in addition, do better than the competing males to achieve fertilization. Although sperm competition is widespread among ¢sh species (Stockley, Gage, Parker & M ller 1997; Taborsky1998), few studies have examined the in£uence of diierent sperm traits on relative paternity when males compete for fertilization. The Atlantic cod (Gadus morhua L.) aggregate annually at spawning areas in spring, and spawning pairs are often joined by several satellite males that shed their sperm among the newly released eggs (Brawn 1961). In addition, multiple paternities per spawning bout are found in captivity (Hutchings, Bishop & Mcgregor-Shaw 1999; Rakitin, Ferguson & Trippel 1999). Thus, it seems likely that the Atlantic cod is naturally adapted to sperm competition. Wild-caught sexually mature adult Atlantic cod were trawl captured in the basin of Balsfjord (69119 0N, 19121 0E), Northern Norway, in April 2005. Four ripe males and ¢ve ripe females were randomly selected for the breeding experiment, and their gametes were collected by gently applying pressure to their abdomen after drying the ¢sh surface to avoid contaminating the samples. As each female produces millions of small eggs that are externally fertilized, we were able to conduct controlled in vitro fertilization while concurrently measuring sperm traits. Sperm from fourmales weremixed and shed over unfertilized eggs from ¢ve diierent females in an aqueous environment to which Atlantic cod is naturally adapted, in order to examinewhat sperm traits determine relative paternity. An aliquot (o0.12 mL) of undiluted milt placed on a cooled (approximately 5 1C) microscope slide with an 80-mm-deep chamber was used for spermmotility analyses. Sperm motility was induced in a one-step procedure by adding 4.5 mL seawater before applying the coverglass. A video camera (Sony XC-ST50CE, Sony, Tokyo, Japan) mounted on a negative phasecontrast microscope (Olympus CH30, Olympus, Tokyo, Japan) ( 10 objective) was used to record sperm activity from each male. Sperm swimming activity was recorded twice for eachmale and stored on MiniDV tapes. Computer-assisted spermanalysis was used to examine sperm motility in ¢sh, and a total of 2548 sperm cell trajectories were analysed using an HTM-CEROS sperm tracker (CEROS version 12; Hamilton Thorne Research, Beverly, MA, USA). The sperm analyser was set as follows: frame rate 50Hz; number of frames 25; minimumcontrast 9; andminimum cell size 8 pixels. Four qualitatively diierent Aquaculture Research, 2008, 39, 212^216 doi:10.1111/j.1365-2109.2007.01863.x
TL;DR: In conclusion, food deprived cod are less resistant to stress than fed cod, but the effects are persistent (including tissue damage indicators and oxidative stress) and may have negative long term consequences.
TL;DR: It is shown that M O2 and plasma cortisol, but not plasma glucose or gill hsp 70 levels, are sensitive indicators of thermal stress in Atlantic cod and support previous reports that the upper critical temperature for this species is 16° C.
Abstract: Survival, oxygen consumption ( M O2 ), total plasma cortisol and glucose levels and gill heat-shock protein 70 (hsp70) expression were measured in 10 and 50 g juvenile Atlantic cod Gadus morhua during an acute temperature increase (2° C h −1 ) to their critical thermal maximum. Ninety three per cent of the fish in both size classes survived to 24° C; however, mortality was 100% within 15 min of reaching this temperature. The M O2 for both size classes increased significantly with temperature, reaching peak values at 22° C that were c. 2·8-fold those of control (10° C) fish. Resting plasma cortisol and glucose levels were lower in 10 g as compared to 50 g fish. Plasma glucose levels were highly variable in both size classes, and significant increases were only seen at >22° C for the 10 g fish. In contrast, plasma cortisol showed an exponential increase with temperature starting at 16° C in both size classes, and reached maximum levels at 22° C that were 19-fold (10 g fish) and 35-fold (50 g fish) higher than their respective control groups. Both the constitutive (73 kDa) and inducible (72 kDa) isoforms of hsp70 were detected in both size classes using the widely utilized mouse monoclonal antibody. Expression of these isoforms, however, did not change when Atlantic cod were exposed to elevated temperature, and the 72 kDa isoform was not detected using salmonid-specific antibodies. These results indicate that juvenile Atlantic cod are very sensitive to acute increases in water temperature. In addition, they (1) show that M O2 and plasma cortisol, but not plasma glucose or gill hsp 70 levels, are sensitive indicators of thermal stress in Atlantic cod and (2) support previous reports that the upper critical temperature for this species is 16° C.
TL;DR: Analysis of the pantophysin locus (Pan I) of the same individuals revealed that individuals carrying the Pan IAA genotype are likely to display a shallow water feeding migrations while individuals carryingThe Pan IBB genotype preferred deeper waters and forage near thermal fronts, and the heterozygote exhibited both type of behaviours.
Abstract: Throughout their geographic distribution, marine fish species often form subpopulations with limited connectivity, among which individuals display a variety of migratory behaviours Fish behaviour experiments using Data Storage Tags (DSTs) have been useful to define the natural movement of individuals In Icelandic waters, such experiments have indicated the presence of two distinct behaviour types of the Atlantic cod Gadus morhua, related to vertical migrations and habitat choice in feeding migrations Some individuals have been shown to stay most of the time in shallow waters characterised by the seasonal trend in temperature for the shelf waters, while other migrate to deeper and colder waters where most of them forage in temperature fronts characterized by highly variable temperatures The analysis of the pantophysin locus (Pan I) of the same individuals revealed that individuals carrying the Pan IAA genotype are likely to display a shallow water feeding migrations while individuals carrying the Pan IBB genotype preferred deeper waters and forage near thermal fronts The heterozygote exhibited both type of behaviours This study therefore suggests that further research need to be done on the pantophysin locus and its potential effects on cod phenotypes to assess the potential relationship between this locus and the behavioural types described
01 Jan 2008
TL;DR: Low-field (LF) (1)H NMR T 2 relaxation measurements were used to study changes in water distribution in lean (Atlantic cod) and fatty (Atlantic salmon) fish during salting in 15% NaCl and 25%NaCl brines, revealing changes in the water properties.
Abstract: Water distribution in brine salted cod (Gadus morhua) and salmon (Salmo salar): : A low-Field 1H NMR study.
TL;DR: The parentage of 300 Atlantic cod fry from eggs collected on a single day in a commercial mass spawning breeding tank was analysed by DNA profiling and suggested a mechanism for multiple paternity of egg batches.
TL;DR: This article examined the spatial dynamics of Atlantic cod, Gadus morhua, through its life history on the northeast and southeast coasts of Newfoundland in order to delineate dispersal and critical habitat requirements as potential determinants of appropriate spatial scales for management.
TL;DR: The results showed that there is a considerable potential for ecosystem effects caused by escaped farmed cod, and mitigating actions such as an efficient recapture fishery for escapees may be possible.
Abstract: Commercial farming of Atlantic cod (Gadus morhua L) is now being developed in several countries The ecological consequences of cod culture are poorly understood, but recent research suggests that Atlantic cod are more prone to escape from net pens than Atlantic salmon Here, we describe the movements and the spatiotemporal distribution of farmed cod after escape relative to wild cod, both during and outside the natural spawning season The experimental design included simulating escape incidents of farmed cod tagged with acoustic transmitters and using an array of automatic listening stations to monitor their dispersal and distribution For comparison, local wild cod were monitored using the same array of receivers The farmed cod dispersed rapidly after a simulated escape, they randomly distributed over large areas and their distribution overlapped with local wild cod Moreover, escaped farmed fish were found at local cod spawning areas during the spawning season The study also indicated that the recapture rate of escaped farmed cod was high compared with that of escaped farmed salmon Thus, while our results showed that there is a considerable potential for ecosystem effects caused by escaped farmed cod, mitigating actions such as an efficient recapture fishery for escapees may be possible
TL;DR: A pilot experiment performed in Heimarkspollen in Austevoll demonstrated for the first time that farmed cod are capable of producing viable cod larvae that mix with larvae from wild cod.
Abstract: Escapes of farmed fish from aquaculture installations, as well as large scale stock enhancement and sea ranching activities, are regarded as risk factors for negative genetic impacts on native gene pools. These aspects have been discussed for several decades, and a number of recent experiments on Atlantic salmon have clearly demonstrated dramatically reduced overall fitness of farmed offspring compared with offspring of wild origin. The Atlantic cod (Gadus morhua L.) is now the most promising new marine species for large scale farming in Norway, and more than 500 commercial farming licenses have been issued, corresponding to a maximum annual production capacity of about 300,000 tonnes. In comparison with the environmental problems caused by escapes from the salmon farming industry, cod farming presents new challenges. As a marine species, cod are able to spawn in the net pens during the ongrowing period and thus release genetic material into the environment. Coastal cod stocks in Norwegian waters are depl...
TL;DR: Cod sperm quality is modified during the spawning period, the highest-quality samples being collected during the medium part of this season.
Abstract: The biology of cod reproduction is well described in the scientific literature. However, sperm biology and spermatozoa management are poorly studied in this species. Because of its recent farming expansion, a better knowledge of cod gametes is becoming especially useful. This work aimed at establishing tools to study sperm biology in cod, and also investigated the existence of changes in cod sperm quality during the spawning period. We showed that sperm concentration could be assessed using spectrophotometry at 260 nm. Sperm motility significantly decreased after a 168-h storage at 4 degrees C. A 1:9 dilution of sperm in a non-activating medium (1/3 seawater and 2/3 freshwater, osmotic pressure: 360 mOsm kg(-1)) improved sperm storage. Sperm concentration, sperm velocity and storage capacity at 4 degrees C peaked during the medium period of the spawning season and then decreased to values close to those observed at the beginning of the reproductive period. The measured values of osmotic pressure, pH, protein, Na+, Cl- and Ca2+ concentrations of the seminal fluid were modified along the spawning period. Cell damage was noted at the end of the spawning period: local blebs were observed on the flagellum but also loops at its distal part. On the other hand, spermatocrit did not vary with the sampling date. In conclusion, cod sperm quality is modified during the spawning period, the highest-quality samples being collected during the medium part of this season.
TL;DR: Observations are consistent with the hypotheses that some form of intrasexual competition or mate choice is a constituent of the mating system of this species and that the ratio of effective to census population size in broadcast-spawning marine fishes is very small.
Abstract: We tested the hypothesis that reproductive success is randomly distributed within spawning aggregations of Atlantic cod Gadus morhua, a broadcast-spawning marine fish for which no parental care is provided. Based on microsatellite DNA-parentage assignment of 8913 offspring from 4 large (n = 52 to 93) experimental spawning aggregations, we quantified individual variation in male reproductive success and evaluated the degree to which this variation could be explained by aspects of morphology, condition, and spawning behaviour. Reproductive success was highly skewed, with more than 80% of the offspring within each group sired by 2 to 7 individuals. Body size and agonistic interactions initiated were positively associated with male reproductive success within each group. The lengths of fins prominent during courtship and mating were also correlated with reproductive success within one of the spawning groups for which data were available. Our observa- tions are consistent with the hypotheses that some form of intrasexual competition or mate choice is a constituent of the mating system of this species and that the ratio of effective to census population size in broadcast-spawning marine fishes is very small.
TL;DR: The changes in the expression of some stress and immune genes as well as the profiles of plasma cortisol were examined using Atlantic cod as a model for the stress response in gadoid fish to have implications with respect to fish welfare and assessment of the health status of the farmed fish.
Abstract: Using Atlantic cod, Gadus morhua, as a model for the stress response in gadoid fish, the changes in the expression of some stress and immune genes as well as the profiles of plasma cortisol were examined. Adult fish were kept at a density of ca. 100 kg m−3 by lowering the water level in the rearing tank for 1 h and this short-term crowding stress was repeated thrice over a 12-h interval period. Blood samples were collected before exposure and at 2, 24 and 72 h post crowding. Plasma cortisol level significantly increased at 2 h post crowding but returned to pre-crowding levels 24 h after exposure. The relative expression of the stress response genes, glucose transporter-3 and a putative heat shock protein 70 significantly increased at 2 and 24 h post crowding respectively. Significant up-regulation of the pro-inflammatory cytokines, interleukin (IL)-1β and IL-8, as well as anti-bacterial genes, g-type lysozyme and bactericidal permeability-increasing protein/lipopolysaccharide-binding protein (BPI/LBP) was also observed at 2 h and the levels were maintained until 72 h post exposure, except for BPI/LBP which had maximum up-regulation at 24 h. The present observations have implications with respect to fish welfare and assessment of the health status of the farmed fish.
01 Jan 2008
TL;DR: Among-stock comparisons illustrate that fishing has played a dominant role in the dynamics of all cod stocks, but variability in climate has contributed to variability in recruitment, individual growth, and natural mortality.
Abstract: Many stocks of Atlantic cod (Gadus morhua) on both sides of the North Atlantic are currently at much reduced levels of biomass, but this situation is not in all instances the result of long, continuous decline. Most Northwest Atlantic stocks declined to low levels during the 1970s, but increased during the 1980s before declining even more severely during the late 1980s and early 1990s. Several of these stocks have shown little recovery despite severe restrictions on directed fishing. Many stocks in the Northeast Atlantic have experienced sustained increases and sustained decreases, but generally not in concert. Among-stock comparisons illustrate that fishing has played a dominant role in the dynamics of all cod stocks, but variability in climate has contributed to variability in recruitment, individual growth, and natural mortality. A cooling event during the last three decades of the twentieth century contributed to the rapid decline of several stocks in the Northwest Atlantic, and changes in life-history traits (growth rate, age and size at maturity) and in the biotic environment (predators and prey) may be contributing to recovery being slow.
TL;DR: The results indicate that it should be possible to manipulate the fatty acid compositions of cod tissues in desired directions by introducing mixtures of different feed oils at various points in the production cycle.
TL;DR: Examination of large samples of cod from six geographical areas of the North East Atlantic yielded abundant baseline data on parasite distribution and abundance which reveals relatively rich regional parasite faunas in cod from the NorthEast Atlantic which are dominated by generalist parasites with Arcto-Boreal distribution.
Abstract: Although numerous studies on parasites of the Atlantic cod, Gadus morhua L. have been conducted in the North Atlantic, comparative analyses on local cod parasite faunas are virtually lacking. The present study is based on examination of large samples of cod from six geographical areas of the North East Atlantic which yielded abundant baseline data on parasite distribution and abundance. A total of 826 fish was sampled in the Baltic, Celtic, Irish and North seas, Icelandic waters and Trondheimsfjord (Norway) in 2002 (spring and autumn) and 2003 (spring). The gills and internal organs (oesophagus, stomach, intestine, pyloric caeca, liver, heart, spleen, gall bladder and gonads) were examined for macroparasites following a standardised protocol. The taxonomic consistency of the identification was ensured thorough the entire study. We discuss some problems in parasite identification, outline the composition of the parasite faunas in cod in the six North East Atlantic regions, provide novel data on parasite prevalence and abundance and a comparative assessment of the structure of the regional parasite faunas with respect to the higher-level taxonomic groupings, host specificity and zoogeographical distribution of the parasites. Altogether 57 different parasite forms were found including seven new host records (Diclidophora merlangi, Rhipidocotyle sp., Fellodistomum sp., Steringotrema sp., Cucullanus sp., Spinitectus sp., and Chondracanthus ornatus). The predominant groups of cod parasites were trematodes (19 species) and nematodes (13 species) including larval anisakids which comprised 58.2% of the total number of individuals. Our study reveals relatively rich regional parasite faunas in cod from the North East Atlantic which are dominated by generalist parasites with Arcto-Boreal distribution. Further, it provides more detailed data on the distribution in the North East Atlantic of the majority of cod parasites which may serve as baselines for future studies on the effect of climate change. Based on the faunal comparisons, predictions can be made in relation to the structure and diversity of the parasite communities in the North East Atlantic regions studied.