Family differences on triploid induction, sexual maturation and its contribution to sea cage performance of Atlantic cod, Gadus morhua

Early maturation has been one of the biological bottlenecks of commercializing Atlantic cod culture. To overcome the bottleneck, production of sterile fish through triploidy and other molecular techniques have been suggested and attempted. Although studies have been carried out on triploid performance of Atlantic cod, no studies have been conducted to see the performance of triploid fish at family level. We produced 29 triploid sibling families using standard hydrostatic pressure technique of newly fertilized eggs with parallel, untreated diploid families. Larvae were reared in separate tanks using standard rearing protocols until reaching 20 g and were PIT tagged. PIT tagged juveniles were transferred to sea cages in duplicate. At 34 months post-hatch, all the fish were sampled and body weight, liver weight and gonadal weight were recorded. Results showed that significant family differences exist between diploid and triploid families in gonadal development, especially for the females. Fish from triploid families had significantly smaller gonadosomatic index than fish from diploid families, but diploid families were heavier than the triploid families. Our result highlight the need for considering a parallel strategy for triploid family selection within the conventional diploid breeding program to exploit the existing variation in triploid performance.acceptedVersio

Broodstock exposure to warming and elevated pCO<inf>2</inf> impairs gamete quality and narrows the temperature window of fertilisation in Atlantic cod

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Optimizing intensive culture protocols for Atlantic cod (Gadus morhua) larvae

Larval cod require live prey as food, and prey concentration (PC) and feeding frequency (FF) often afect their growth and survival. Apart from this, water exchange rates/water fow (WER/WF) and water current (WC) also afect the prey resident time in the tank and larval/early juvenile behaviour, respectively. High water current is also known to induce stress in fnfsh larvae, and this stress response is believed to be dependent on larval developmental stage. Thus, we conducted a study to evaluate three larval rearing protocols varying in prey concentration, feeding frequency, and water current/exchange rate. Three protocols were used: low prey concentration (PC), low feeding frequency (FF), and low water fow (protocol 1); medium PC, medium FF, and medium WF (protocol 2); and high PC, high FF, and high WF (protocol 3) (see Table 1). Larvae were sampled periodically for growth and cortisol measurements. Cortisol extraction and radioimmunoassay (RIA) were conducted using methods previously validated for cod larvae. Larvae reared using protocols 2 and 3 were signifcantly bigger and heavier than larvae reared using protocol 1. Rearing protocol had a signifcant efect on the cortisol level in larval cod. Larvae showed a developmental stage-dependent stress response. Protocol 2 had signifcantly higher survival than protocols 1 and 3. Our results indicate that an intermediate PC, FF, and WF (protocol 2) is suitable during cod larval rearing

Northern cod species face spawning habitat losses if global warming exceeds 1.5°C

Source at: http://doi.org/10.1126/sciadv.aas8821 Rapid climate change in the Northeast Atlantic and Arctic poses a threat to some of the world’s largest fish populations. Impacts of warming and acidification may become accessible through mechanism-based risk assessments and projections of future habitat suitability. We show that ocean acidification causes a narrowing of embryonic thermal ranges, which identifies the suitability of spawning habitats as a critical life-history bottleneck for two abundant cod species. Embryonic tolerance ranges linked to climate simulations reveal that ever-increasing CO2 emissions [Representative Concentration Pathway (RCP) 8.5] will deteriorate suitability of present spawning habitat for both Atlantic cod (Gadus morhua) and Polar cod (Boreogadus saida) by 2100. Moderate warming (RCP4.5) may avert dangerous climate impacts on Atlantic cod but still leaves few spawning areas for the more vulnerable Polar cod, which also loses the benefits of an ice-covered ocean. Emissions following RCP2.6, however, support largely unchanged habitat suitability for both species, suggesting that risks are minimized if warming is held “below 2°C, if not 1.5°C,” as pledged by the Paris Agreement

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

Atlantic 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.publishedVersio

Ocean Acidification Effects on Atlantic Cod Larval Survival and Recruitment to the Fished Population

-How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks

Divergent responses of Atlantic cod to ocean acidification and food limitation

In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end-of-century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade-off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish

Impact of pulsed direct current on embryos, larvae, and young juveniles of Atlantic cod and its implications for electrotrawling of brown shrimp

The application of electrical pulses in fishing gear is considered a promising option to increase the sustainability of demersal trawl fisheries. In the electrotrawl fishery for brown shrimp Crangon crangon, an electrical field selectively induces a startle response in the shrimp. Other benthic organisms remain mainly on the seafloor and escape underneath a hovering trawl. Previous experiments have indicated that this pulse has no short-term major harmful effects on adult fish and invertebrates. However, the impact on young marine life stages is still unknown. Because brown shrimp are caught in shallow coastal zones and estuaries, which serve as important nurseries or spawning areas for a wide range of marine species, electrotrawling on these grounds could harm embryos, larvae, and juveniles. We carried out experiments with different developmental stages of Atlantic Cod Gadus morhua, which are considered vulnerable to electrical pulses. Three embryonic stages, four larval stages, and one juvenile stage of Atlantic Cod were exposed to a homogeneous electrical field of 150 V-peak/m for 5 s, mimicking a worst-case scenario. We detected no significant differences in embryo mortality rate between control and exposed groups. However, for the embryonic stage exposed at 18 d postfertilization, the initial hatching rate was lower. Larvae that were exposed at 2 and 26 d posthatch exhibited higher mortality rates than the corresponding nonexposed control groups. In the other larval and juvenile stages, no short-term impact of exposure on survival was observed. Morphometric analysis of larvae and juveniles revealed no differences in measurements or deformations of the yolk, notochord, eye, or head. Although exposure to a worst-case electrical field did not impact survival or development for six of the eight young life stages of Atlantic Cod, the observed delayed hatching rate and decreased survival for larvae might indicate an impact of electric pulses and warrant further research

Ultrasound as potential inhibitor of salmon louse infestation - a small-scale study

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Rapport/Report 31/2015 – English summary

-Lakselus er den største miljømessige utfordringen for lakseoppdrettsnæringen. Å utvikle effektive metoder for å bekjempe lakselus har derfor svært høy prioritet. Ultralyd er lansert som en potensiell metode for å bekjempe lakselus, og målet for rapporten har vært å frambringe kunnskap for å vurdere om det kan være en egnet metode. Rapporten beskriver dannelsen og egenskaper for ultralyd i vann, og hvilken effekt ultralyd har på forskjellige begroingsorganismer. Studiene som er gjort på påslag av rur peker i retning av at ultralyd muligens kan benyttes til å hindre påslag av lakseluskopepoditter på vertsfisken. Virkningen av ultralyd på lakselus kan imidlertid bare dokumenteres gjennom kontrollerte forsøk. Det er lite som tyder på at ultralyd vil ha negativ effekt på oppdrettslaks eller villfisk i området rundt oppdrettsanleggene, men også det må fastslås ved hjelp av kontrollerte forsøk. Sel og hval kan høre ultralyd og vil kanskje bli påvirket, men ikke skadet. Ultralyd i vann representerer ingen utfordringer av HMS-messig karakter.Infection with salmon lice is currently the most serious environmental problem in commercial salmon farming. Development of new and efficient mitigating methods is therefore highly prioritized. Ultrasound might be such a method as it has been shown to have an effect on different biofouling organisms. Studies on barnacles indicate that ultrasound may also be efficient against attachment of salmon louse copepodids on the host fish, but this would have to be experimentally confirmed. It seems that ultrasound has no negative effects on fish, but probably a deterrent effect on marine mammals. Under water ultrasound is not a threat to human health