Cod Farming Research Articles

The First Report of Cod Gill Poxvirus in Gills of Atlantic Cod (Gadus morhua L.) Suffering From Cardiorespiratory Disease.

Atlantic cod farming experiences renewed growth in Norway, and increased awareness is essential to address emerging diseases in this species. There are few reports on gill diseases in cod, and to date, no viral gill infections of cod have been documented. In this study, we collected samples from three sequential time points in summer 2023 from farmed cod suffering from cardiorespiratory disease. We document severe heart and gill pathology, and a novel double-strand DNA virus was discovered in the gills. Through comprehensive genetic characterisation and comparative sequence analysis, this virus was classified as a new species in the genus Poxvirus, designated cod gill poxvirus (CGPV). We demonstrate disease causality with severe gill lesions as shown by histopathology and RNA scope insitu hybridisation, and poxvirus particles were identified in gill epithelial cells by transmission electron microscopy. Further, another gill pathogen not previously described in cod, Candidatus. Branchiomonas cysticola, was identified by pcr and insitu hybridisation. Our findings provide strong evidence for poxvirus in Atlantic cod and underscore the imminent threat posed to Atlantic cod farm industry.

Climate change with increasing seawater temperature will challenge the health of farmed Atlantic Cod (Gadus morhua L.)

Aquaculture is one of the fastest growing food production sectors in the world and further expansion is expected throughout the 21st century. However, climate change is threatening the development of the sector and action is needed to prepare the industry for the coming challenges. Using downscaled temperature projections based on the Intergovernmental Panel on Climate Change (IPCC) climate projection (Shared Socioeconomic Pathway, SSP2-4.5), we analysed potential future temperatures at a selected Atlantic cod (Gadus morhua L.) farm site in Northern Norway. Results showed that the farming area may experience increased temperatures the next 10–15 years, including more days with temperatures above 17°C. Based on the predicted future conditions, we designed a study with Atlantic cod (Gadus morhua L.) to evaluate effects from high temperature alone and in combination with Fransicella noatunensis infection. Fish were kept at 12°C and 17°C for eight weeks and samples of skin and spleen collected at different timepoints were analysed with transcriptomics, histology, scanning electron microscopy and immunohistochemistry. Results showed that high temperature had a stronger effect on the barrier functions of skin than the infection. Increased temperature induced gene expression changes in skin and spleen, heat shock protein 47 and cold inducible RNA binding protein were identified as potential gene markers for thermal stress. The effect of bacterial challenge was small at 12°C. At high temperature, the development of severe pathology in spleen coincided with a significant decrease of immunoglobulins transcripts, which contrasted with the activation of multiple immune genes. In addition, we used an in vitro model of skin biopsies and scale explants exposed to hydrogen peroxide (H2O2) to assess the effects of thermal and oxidative stress. High temperature and H2O2 reduced proliferation and migration of keratocytes, and increased expression of stress markers, and compounding effects were observed with combined stressors. Results suggest that the projected increased seawater temperature will pose a significant threat to Norwegian cod farming, affecting various biological processes and making fish more vulnerable to stressors and pathogens. Cod farming needs high attention to temperature changes, and special precautions should be taken if the temperature increases beyond cods’ thermal optimum.

Intergenerational effects of early life-stage temperature modulation on gene expression and DNA methylation in Atlantic cod (Gadus morhua)

ABSTRACT After suffering several collapses, the cod farming industry is now in the process of trying to re-establish itself. We have used material from Norway’s National Cod Breeding Program to study how different early life-stage temperature regimes affect DNA methylation and gene expression. Long-term effects were detected by sampling fish several weeks after the end of differential treatments, and offspring from the different exposure groups was also sampled. Many overlapping genes were found between the different exposure groups and generations, coupled with genes associated with differential CpG methylation levels. Genes involved in muscle fibre development, general metabolic processes and formation of deformities were significantly affected, and genes relevant for intergenerational transfer of epigenetic marks were also detected. We believe the use of environmental cues can be a useful strategy for improving the production of Atlantic cod.

Short and Long-Term Effects of Early and Late Weaning on Atlantic Cod, Gadus morhua

Studies have shown negative short-term effects of early weaning (EW) in finfish larvae but information on long-term effects of EW on growth and subsequent economic loss is lacking. We evaluated the short- and long-term effects of EW and late weaning (LW) on Atlantic cod. Cod larvae were fed with enriched rotifers from 2 to 35 days post-hatch (dph) and weaning carried out from 21 to 35 dph (EW) or with enriched rotifers from 2 to 29 dph followed by enriched Artemia nauplii from 25 to 56 dph and weaning carried out from 45 to 56 dph (LW). At 190 dph, 50 fish from each tank were tagged with an electronic tag and were transferred to sea cages at 10 months old. At the end of 30 months post-hatch, the weight of the fish was recorded. Our results showed a significant short-term effect of the weaning method on the growth of Atlantic cod at 65 dph, but no significant difference at 90 and 190 dph. However, fish from LW showed a significantly higher body weight compared to fish from EW at 30 months post-hatch. A cost analysis indicated substantial benefit for commercial cod farming by using LW and we recommend using LW to gain sizable financial benefit.

CAPOT: A flexible rapid assessment model to estimate local deposition of fish cage farm wastes

The Cage Aquaculture Particulate Output and Transport (CAPOT) model is an easy to use and flexible farm-scale model that can rapidly estimate particulate waste deposition from fish cage production. This paper describes and tests the model and demonstrates its use for Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua). The spreadsheet-based model gives outputs for waste distribution in a variety of spatial modelling software formats, used for further analysis. The model was tested at a commercial Atlantic cod farm and commercial Atlantic salmon farm under full production conditions. Sediment trap data showed predictions, using actual recorded feed and biomass data, to be 96% (±36%) similar for Atlantic cod beyond 5 m from the cage edge, giving a satisfactory estimate of local benthic impact in the vicinity of the farm. For Atlantic salmon, using estimated production biomass and FCR (Feed Conversion Ratio) to calculate feed input, the model overestimated wastes directly beneath the cages (120% ± 148%) and underestimated beyond 5 m from the cage edge, being 48% (±42%) similar to sediment trap data. CAPOT is a suitable initial, rapid assessment model to give an overview of potential impact of particulate waste from new or expanded fish cage farms, with little operator expertise by a wide range of stakeholders.

Development of cod farming in Norway: Past and current biological and market status and future prospects and directions

AbstractAtlantic cod is a historically abundant species in the North Atlantic region and has contributed to the prosperity of many nations. But a decline in stocks in the last century has prompted to initiate commercial farming of cod in captive conditions. Several approaches have been employed ranging from stock enhancement, capture‐based aquaculture and intensive cod farming. However, except for the enhancement efforts which were carried out for almost a century, efforts on other methods were intermittent coinciding with lower quotas. Intensive farming was attempted in Norway, Scotland, Ireland, Canada, Iceland and Faroe Islands in the 2000s. But it was carried out hastily to cash in the demand for cod in the market even though there were many biological knowledge gaps that are required for a successful aquaculture venture. The reasons for the failure of commercial farming in Norway during the 2000s were not only because of limited knowledge of the biology of cod but also the economic meltdown in Europe in 2008. Cod farming came to a halt; however, the Norwegian National Cod Breeding Program (NCBP) initiated in 2003 continued to operate and produced a fifth generation of a domesticated cod in 2019. Efforts to fill the gaps and the selective breeding for better growth and disease resistance within NCBP have improved the quality of the juveniles produced. We will discuss the past efforts and reasons for failure in farming of cod, how the current situation looks and the future direction in terms of cod biology, political atmosphere and market.

Wild fish as reservoirs of parasites on Australian Murray cod farms

Controlling pathogens within the aquaculture systems is important to prevent their impact on both human health and wild native populations. It is not uncommon for aquaculture ponds to contain undesirable species of fish which can compete for food or space with the farmed fish or play a role as a reservoir of diseases. The aims of this study were to determine the occurrence of parasites in undesirable species of fish commonly found in Australian Murray cod farms in New South Wales to determine if they can act as a reservoir for important parasites. In the present study, a total of 106 Australian smelt (Retropinna semoni), and 144 gudgeons (Hypseleotris spp.) were sampled from Murray cod ponds for parasitic infections. These fish are among the most common undesirable fish found on Murray cod farms in the region. No metazoan parasites were found in Australian smelt. One hundred and nine gudgeons were used for parasitology and 35 for histology. Parasites were examined morphologically followed by analyses of their DNA sequence data. Seven percent of infected gudgeons (out of total 109 examined) had externally visible signs of parasitic infection. The gudgeons had high parasitic burdens with 89.9% containing encysted metacercaria, identified as Apatemon hypseleotris, belonging to the family Strigeidae, 41.3% non-encysted metacercaria identified as Clinostomum sp., belonging to the family Clinostomidae, 6.4% (larval) cestodes identified as the metacestode of the genus Parvitaenia, belonging to the family Gryporhynchidae and a single Camallanus larval nematode (0.9%), all known to be of low host specificity and potentially transmissible to Murray cod. Histopathology results showed the presence of an additional parasite, a monogenean parasite in the gill. Some of the parasites found in the present study can be pathogenic for infected fish. This study provides critical baseline information on the occurrence of parasites in wild reservoir fish on Murray cod farms. Further research is needed to understand the potential risks to Murray cod populations in farm systems as well as to other fish in natural water resources where Murray cod are released.

Temporal changes in the gut microbiota in farmed Atlantic cod (Gadus morhua) outweigh the response to diet supplementation with macroalgae

BackgroundAquaculture successfully meets global food demands for many fish species. However, aquaculture production of Atlantic cod (Gadus morhua) is just 2.5% of total market production. For cod farming to be a viable economic venture specific challenges on how to increase growth, health and farming productivity need to be addressed. Feed ingredients play a key role here. Macroalgae (seaweeds) have been suggested as a functional feed supplement with both health and economic benefits for terrestrial farmed animals and fish. The impact of such dietary supplements to cod gut integrity and microbiota, which contribute to overall fish robustness is unknown. The objective of this study was to supplement the diet of juvenile Atlantic cod with macroalgae and determine the impacts on fish condition and growth, gut morphology and hindgut microbiota composition (16S rRNA amplicon sequencing). Fish were fed one of three diets: control (no macroalgal inclusion), 10% inclusion of either egg wrack (Ascophyllum nodosum) or sea lettuce (Ulva rigida) macroalgae in a 12-week trial.ResultsThe results demonstrated there was no significant difference in fish condition, gut morphology or hindgut microbiota between the U. rigida supplemented fish group and the control group at any time-point. This trend was not observed with the A. nodosum treatment. Fish within this group were further categorised as either ‘Normal’ or ‘Lower Growth’. ‘Lower Growth’ individuals found the diet unpalatable resulting in reduced weight and condition factor combined with an altered gut morphology and microbiome relative to the other treatments. Excluding this group, our results show that the hindgut microbiota was largely driven by temporal pressures with the microbial communities becoming more similar over time irrespective of dietary treatment. The core microbiome at the final time-point consisted of the orders Vibrionales (Vibrio and Photobacterium), Bacteroidales (Bacteroidetes and Macellibacteroides) and Clostridiales (Lachnoclostridium).ConclusionsOur study indicates that U. rigida macroalgae can be supplemented at 10% inclusion levels in the diet of juvenile farmed Atlantic cod without any impact on fish condition or hindgut microbial community structure. We also conclude that 10% dietary inclusion of A. nodosum is not a suitable feed supplement in a farmed cod diet.

Tracking escaped Atlantic cod (Gadus morhua L.) aggregated around Norwegian farms: Considerations for management strategies

AbstractTo examine site fidelity and potential for ecosystem impacts, 20 escapee cod (Gadus morhua L.) from fjord‐based cod farms were tagged with acoustic transmitters, released in the vicinity of the same farm, and their subsequent behaviour and survival monitored using a fixed array of acoustic receivers. Most individuals demonstrated high fidelity to their farm where tagged, and this increased during the polar night. Only five individuals (25%) were occasionally detected at another farm (4 km distance), and only three cod (15%) migrated out of the fjord during the 6‐month study period. Vertical movements were consistently greater in the hours around noon than at night, a behaviour inconsistent with that observed for wild fish. A high mortality rate (40%) was observed during the first 4 months post‐release, and actual mortality may have been even higher, limiting the potential for negative ecosystem effects from cod escapees. Findings from this study are used to discuss the development of recapture strategies for minimising potential impacts from cod escapees to ensure sustainable farming activity.

Performance of triploid Atlantic cod (Gadus morhua L.) in commercial aquaculture

The use of triploid fish can potentially reduce two of the major obstacles in Atlantic cod aquaculture; early sexual maturation that causes reduced profitability, and avoiding introgression between farmed cod and native populations, by preventing spawning in the netpens or that escapees reproduce.Cod eggs were pressure treated to produce triploid fish. However, we observed that the pressure treatment produced a mixture of triploid and diploid individuals. The diploid and triploid fish were reared together; in a seawater pond during their larval and juvenile period, and in a commercial cod farm from juveniles to slaughter. Two experiments were performed on two separate year-classes of cod: in the first experiment, fish were reared under artificial continuous light, while in the second experiment the fish were reared under ambient light conditions.Triploid cod had lower gonadosomatic index at all measurements compared to the diploids. However, from a production point of view, triploidisation alone only slightly reduced the gonadosomatic index and had to be combined with traditionally employed artificial light in order to be effective. Triploid fish were generally lighter than the diploids, but this difference disappeared towards time-of-harvest in the year-class without artificial light, possibly because of the lower maturation rate among the triploids. The triploid fish had a higher incidence of skeletal deformities compared to the diploids. Statement of RelevanceThe use of sterile fish by means of triploidisation is a promising method to reduce sexual maturation and the same time eliminate potential interbreeding of escaped cod with wild cod. In this paper we compare growth, maturation and deformities between triploid and diploid cod reared in common garden under commercial condition.

Quality and Shelf Life of Liver of Farmed Cod (Gadus morhua)

ABSTRACTLivers of Atlantic cod (Gadus morhua) are traditionally used in cod liver oil production or consumed cooked or canned. The farming of cod is a relatively new industry in Norway. The aim of this study was to determine quality and shelf life of fresh liver from farmed cod during chilled storage on ice by hydrolysis and oxidation state and sensory quality and the influence on canned liver. In two experiments, livers from farmed cod were stored chilled and sampled from Days 0 to 13, respectively. Quality, measured as hydrolytic and oxidation degradation, was reduced after 7 days of storage, while sensory quality was reduced after 4 days. Free fatty acids increased from Day 7 in both experiments, while peroxide value and anisidine value showed no change when the livers were single wrapped. Rancid odor was the first sign of oxidation and was registered after three to four days of storage. Canning within 2 days of storage prevented leakage of oil from the canned livers. Sensory analyses of oxidation are recommended as a sensitive and rapid method to detect oxidation of chilled cod liver.

Benthic artificial reefs as a means to reduce the environmental effects of cod mariculture in Skutulsfjörður, Iceland

Artificial reefs (AR) have been deployed below commercial fish farms in tropical, subtropical and temperate marine locations in an effort to reduce some of the negative effects of aquaculture, and this study describes an AR deployment at a boreal site. This study examined the development and succession of two benthic communities on artificial reefs in the Icelandic fjord, Skutulsfjorður. Two plastic, triangle-shaped, porous artificial reefs were moored on the seafloor: a) below a cod farm and b) at a nearby reference site, and were monitored for 4 months, on a bi-weekly basis by SCUBA divers. Monitoring included both visual observations, mainly of the motile biota, and subsampling of the fouling community by removing pieces of plastic mesh that were attached to the reefs for this purpose. Diverse biological communities developed on the artificial reefs at both fish farm and reference sites; however, overall species richness, abundance and sessile species cover were consistently greater at the farm site. Although the biota recorded were typical boreal species, many of the same taxa observed in warmer waters, in similar studies, were found on these reefs. Artificial reefs are one of many options that may be considered to enhance the sustainability of coastal aquaculture, and we suggest that: a) ARs should be studied over the course of a year or more, and b) efforts should be made to consider how we may harvest the biota associated with the ARs for commercial use.

1H NMR metabolic profiling of cod (Gadus morhua) larvae: potential effects of temperature and diet composition during early developmental stages.

ABSTRACTMarine aquaculture offers a great source of protein for the increasing human population, and farming of, for example, Atlantic salmon is a global industry. Atlantic cod farming however, is an example of a promising industry where the potential is not yet realized. Research has revealed that a major bottleneck to successful farming of cod is poor quality of the larvae and juveniles. A large research program was designed to increase our understanding of how environmental factors such as temperature and nutrition affects cod larvae development. Data on larvae growth and development were used together with nuclear magnetic resonance. The NMR data indicated that the temperature influenced the metabolome of the larvae; differences were related to osmolytes such as betaine/TMAO, the amino acid taurine, and creatine and lactate which reflect muscle activity. The larvae were fed Artemia from stage 2, and this was probably reflected in a high taurine content of older larvae. Larvae fed with copepods in the nutrition experiment also displayed a high taurine content, together with higher creatine and betaine/TMAO content. Data on the cod larvae metabolome should be coupled to data on gene expression, in order to identify events which are regulated on the genetic level versus regulation resulting from temperature or nutrition during development, to fully understand how the environment affects larval development.

Path dependency, institutionalization and co-evolution: The missing diffusion of the blue revolution in Norwegian aquaculture

Scholars taking the evolutionary perspective argue that technologies, competence and institutions of successful paths may spill over to related industry initiatives and subsequent industry paths. The notion of co-evolution has been introduced as an analytical category for such interconnectivity. In this article, we investigate the development of salmon farming in Norway as a successful industry path and its linkages with cod farming, a subsequent emerging industry path. In the public debate, there has been an expectation that knowledge and solutions from salmon farming will diffuse to aquaculture for other species. However, this diffusion appears to be missing. Cod farming is an area that should capitalize on the success of salmon aquaculture, and we investigate why cod farmers appear to be unable to utilize the experience and knowledge of salmon farmers and copy their solutions. We found that the development of a specialized institutional arrangement for salmon farming makes these models incompatible with the needs of farming of other species, resulting in limited co-evolution between subsequent aquaculture industry paths. Thus, a situation characterized by strong co-evolution within an industry path, facilitating the development of an institutional arrangement tailor-made for the firms of the industry, reduce the possibilities for co-evolution between related industry paths.

An improved multiple-locus variable-number of tandem repeat analysis (MLVA) for the fish pathogen Francisella noatunensis using capillary electrophoresis

BackgroundFrancisellosis, caused by the bacterium Francisella noatunensis subsp. noatunensis, remains a serious threat to Atlantic cod (Gadhus morhua) farming in Norway and potentially in other countries. As outbreak strains appear clonal in population structure, access to highly discriminatory typing tools is critical for understanding the epidemiology of francisellosis infections in aquaculture. In this study, a simplified multiple-locus variable-number of tandem repeat analysis (MLVA) targeting five highly polymorphic variable number of tandem repeat (VNTR) loci in a single multiplex PCR was developed to rapidly discriminate between outbreak strains.ResultsThe assay resulted in identification of at least 13 different allelic profiles or subpopulations among 91 F. noatunensis isolates from farmed cod in Norway. The VNTR loci appear relatively stable, with isolates originating from individual outbreaks showing identical MLVA profiles following repeated passage. MLVA displayed greater discriminatory power than pulse-field gel electrophoresis (PFGE). Both MLVA and PFGE show good epidemiological concordance by their abilities to separate outbreak strains from epidemiologically unrelated isolates.ConclusionsThe MLVA method presented here is robust, easy to perform and provides a good alternative to other typing systems for F. noatunensis subsp. noatunensis and epidemiological study of francisellosis in cod.

Genetic marking of farmed Atlantic cod (Gadus morhua l.) and detection of escapes from a commercial cod farm

Abstract A genetically marked Atlantic cod (Gadus morhua L.) strain was used to identify escapes from commercial cod farms, and to investigate the potential interbreeding between farmed and wild cod. This farmed cod was homozygote for a rare allele (30) in the GPI-1 locus expressed in white muscle tissue. Juveniles were produced from this strain in 2007 and 2008, and 500 000 individuals of each year class were transported to a cod farm in western Norway, where they were raised under commercial conditions. A monitoring fishing program was established from spring 2007 to detect escapees during the farming period. The first farmed cod escapees, identified to the 2007 year class through the genetic mark, age and body size, were detected during the fishing survey in November 2008. The second escape of the same year class was detected during the natural spawning season in early April 2009. A third escape was detected in November 2009, and this time the farmed cod were identified to the 2008 year class. The escapees were spreading through the whole fjord system, including local spawning sites for wild cod. Detailed examination of the escaped cod revealed a substantial degree of sexual maturation, and nearly 1000 cod larvae and early juveniles were therefore collected through spring 2009. The genetic analyses identified eight of these as genetically marked, demonstrating successful reproduction either in the cage or after escape. Interbreeding between escaped and wild cod may also have occurred, but cannot be proven from our material. In all years after the three identified escapes, genetically marked cod were found in the fjord area. In addition, several specimens were observed in adjacent fjord systems, demonstrating long-term survival in the local spawning areas as well as substantial spread over larger distances.

Towards cod without spawning: artificial continuous light in submerged sea-cages maintains growth and delays sexual maturation for farmed Atlantic cod Gadus morhua

Sexual maturation and spawning in sea-cages is a major production and environ- mental challenge for the Atlantic cod farming industry. Altered photoperiod has arrested sexual maturation in cod kept in indoor or covered experimental tanks, but only delayed or caused asyn- chronous maturation in cod kept in sea-cages. To arrest the onset of puberty more efficiently, we reduced the relative differences in light intensity between night and day by lowering 4 sub- mersible sea-cages, each stocked with 400 juvenile cod, to 20 m depth for 14 mo. Two cages were continuously illuminated (LL), and 2 cages served as controls with natural light (NL) conditions. Cod grew well in both treatments and showed very low mortality. Final weights did not differ, although the pattern of growth differed through time. Continuous light did not arrest maturation, but delayed it by 3 to 6 mo; gonadosomatic indices reached 21.2% for NL females during spawn- ing in February to April, but reached only 10.2% for the LL females over a protracted spawning period from May to September. The liver index for NL fish decreased during spawning by 6% (females) and 15% (males). In contrast, the liver index in the LL fish decreased relatively little (females = 5%, males = 3%), suggesting these fish invested less energy in maturation. Submer- gence combined with sufficient artificial lighting will both delay and reduce the extent of matura- tion, which can improve production strategies through better feed conversion ratios and reduce the risks associated with 'escape through spawning'. Deeper submergence, combined with shading and stronger lighting, may even arrest maturation.

Differentially expressed proteins in the skin mucus of Atlantic cod (Gadus morhua) upon natural infection with Vibrio anguillarum

BackgroundVibriosis caused by V. anguillarum is a commonly encountered disease in Atlantic cod farms and several studies indicate that the initiation of infection occurs after the attachment of the pathogen to the mucosal surfaces (gut, skin and gills) of fish. Therefore it is necessary to investigate the role of different mucosal components in fish upon V. anguillarum infection. The present study has two parts; in the first part we analyzed the differential expression of skin mucus proteins from Atlantic cod naturally infected with V. anguillarum using two dimensional gel electrophoresis coupled with mass spectrometry. In the second part, a separate bath challenge experiment with V. anguillarum was conducted to assess the mRNA levels of the genes in skin tissue, corresponding to the selected proteins identified in the first part.ResultsComparative proteome analysis of skin mucus of cod upon natural infection with V. anguillarum revealed key immune relevant proteins like calpain small subunit 1, glutathione-S-transferase omega 1, proteasome 26S subunit, 14-kDa apolipoprotein, beta 2-tubulin, cold inducible RNA binding protein, malate dehydrogenase 2 (mitochondrial) and type II keratin that exhibited significant differential expression. Additionally a number of protein spots which showed large variability amongst individual fish were also identified. Some of the proteins identified were mapped to the immunologically relevant JNK (c-Jun N-terminal kinases) signalling pathway that is connected to cellular events associated with pathogenesis. A bath challenge experiment with V. anguillarum showed differential expression of beta 2-tubulin, calpain small subunit 1, cold inducible RNA binding protein, flotillin1, and glutathione S-transferase omega 1 transcripts in the skin tissue of cod during early stages of infection.ConclusionsDifferentially expressed proteins identified in the cod skin mucus point towards their possible involvement in V. anguillarum pathogenesis. The role of some of these proteins in vibriosis in cod described in this paper can be considered unconventional with respect to their established functions in higher vertebrates. Based on the differential expression of these proteins they are possibly important components of fish defence against bacteria and innate immunity at large. The feasibility of utilizing these proteins/genes as markers of bacterial infection or stress in cod needs to be explored further.

Cortisol treatment of prespawning female cod affects cytogenesis related factors in eggs and embryos

A stable supply of viable eggs and embryos is crucial for successful farming of Atlantic cod. Stress during broodstock rearing can have negative effects on offspring, but little is known about the molecular mechanisms that cause abnormal development. Maternally transferred mRNAs have been shown to be essential for normal development, and stress may therefore influence their expression and the subsequent embryonic development. We investigated if mimicked stress in cod females affects mRNA concentrations in eggs/embryos, and if this can be linked to viability of embryos. Three weeks before peak spawning, 20 fish were intraperitoneally implanted with either cortisol-containing or cortisol-free (sham) osmotic pumps. At peak spawning all individuals were stripped and eggs were fertilized and incubated until hatching. Samples were collected from unfertilized eggs and embryos for analysis of gene expression (microarray), viability, steroids and vitellogenin. Plasma concentration of cortisol (ng/ml) in treated females was significantly higher at spawning (127.1±20.9) than that of sham control (11.3±6.7). This difference was also reflected in eggs and embryos. Percent fertilization, asymmetric cell division and hatching were not affected. However, numerous genes were differentially expressed in eggs and embryos in response to elevated cortisol, especially in maternal (oocyte and blastula) stages. Among these differentially expressed genes, some were found to be linked to cytogenesis (stxbp6, fbxw2, capn12, thbs4, sytl2, coro1c, sel1l3), induction of mesodermal fate (fgfrl1) and import of the glucocorticoid receptor to the cell nucleus (ipo7). Gene ontology overrepresentation analysis on the whole set of differentially expressed genes at maternal stages (539 genes) revealed enriched activity in membrane associated regions, which largely corresponds to cytogenesis related processes. These results suggest that despite no visible phenotypic effects in early embryos, broodstock stress affects the egg/embryonic transcriptome, especially in relation to cytogenesis. Furthermore, effects related to egg/embryo phenotypes are difficult to measure at early stages of development, and instead might become apparent at later life stages.

Extent and ecological importance of escape through spawning in sea-cages for Atlantic cod

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 3:33-49 (2012) - DOI: https://doi.org/10.3354/aei00049 Extent and ecological importance of escape through spawning in sea-cages for Atlantic cod Ingebrigt Uglem1,*, Øyvind Knutsen2, Olav Sigurd Kjesbu3, Øyvind J. Hansen4, Jarle Mork5, Pål Arne Bjørn3,4, Rebekka Varne5, Rune Nilsen3,4, Ingrid Ellingsen2, Tim Dempster6,7 1Norwegian Institute of Nature Research, Tungasletta 2, 7485 Trondheim, Norway 2SINTEF Fisheries and Aquaculture, PO Box 4762 Sluppen, 7465 Trondheim, Norway 3Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway 4NOFIMA Marin, Muninbakken 9-13, PO Box 6122, 9291 Tromsø, Norway 5Trondheim Biological Station, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway 6Sustainable Aquaculture Laboratory − Temperate and Tropical (SALTT), Department of Zoology, University of Melbourne, 3010 Victoria, Australia 7Centre for Research-based Innovation in Aquaculture Technology (CREATE), SINTEF Fisheries and Aquaculture, PO Box 4762 Sluppen, 7465 Trondheim, Norway *Email: ingebrigt.uglem@nina.no ABSTRACT: The culture of certain fish species to sizes at which they can reproduce has led to the escape of fertilised eggs or ‘escape through spawning’. To investigate the extent and ecological importance of spawning in sea-cages for Atlantic cod Gadus morhua (L.), we (1) evaluated the extent, frequency and timing of spawning in cod culture; (2) analysed the quality of eggs released from farms in terms of variation in fatty acids; (3) modelled the distribution of eggs and larvae from a commercial cod culture site; and (4) predicted the post-escape survival of eggs through summarizing existing knowledge on survival rates of different life stages. Collectively, our results indicate that cod farming has the potential to produce large amounts of eggs and larvae through spawning in cages, with numbers of eggs spawned being 4 to 5 times higher in the second than in the first year. Our scenarios suggest that a typical sea-cage with 60000 fish may produce 1.4 to 21 tons of 3 yr old first generation farmed cod through spawning in sea-cages. The quality of escaped eggs and larvae is likely to be sufficient for larvae to survive until the first feeding, while survival until adulthood, though difficult to predict, may be high under favourable conditions. Simulations indicate that eggs and larvae from farms may mix with those of wild fish during the spawning season, and thus experience comparable larval environments. However, several implementable management measures exist that will diminish the extent of egg escape in future cod farming. KEY WORDS: Atlantic cod · Gadus morhua · Aquaculture · Escape · Spawning in farms Full text in pdf format PreviousNextCite this article as: Uglem I, Knutsen Ø, Kjesbu OS, Hansen ØJ and others (2012) Extent and ecological importance of escape through spawning in sea-cages for Atlantic cod. Aquacult Environ Interact 3:33-49. https://doi.org/10.3354/aei00049 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 3, No. 1. Online publication date: November 14, 2012 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2012 Inter-Research.