Thor Hangstad - Academia.edu (original) (raw)

Papers by Thor Hangstad

DESCRIPTION Forsøk på å redusere antall av lakselus i merder har vært et hovedmål helt siden 1970... more DESCRIPTION Forsøk på å redusere antall av lakselus i merder har vært et hovedmål helt siden 1970-tallet, ikke bare som en økonomisk bekymring, men også i form av dyrevelferd og potensielle påvirkninger på økosystemet. I dag blir lusemengden i hovedsak regulert ved hjelp av kjemoterapeutiske midler,men økende resistens mot lusemidler er et økende problem. I dag, representerer rensefisk det eneste miljøvennlige alternativ til kjemisk avlusning av laksefisk. Men de artene rensefisk som for tiden er i bruk for biologisk avlusning f.eks. Berggylt, Labrus bergylta og bergnebb, rupestris Ctenolabrus L. er temperaturfølsomme, noe som gjør dem uegnet til bruk ved lave (<6 0 C) temperaturer. Rognkjeks, Cyclopterus lumpus L. har blitt foreslått som en art man kan bruke ved lave temperaturer. Inntil nå er svært lite som har blitt publisert om oppførselen til rognkjeks. Et begrenset antall studier har blitt utført med villfanget rognkjeks, dette inkluderer beskrivelse av larver, yngel og vok...

Aquaculture, 2014

Growth and performance of Atlantic salmon in the presence of lumpfish were assessed in two studie... more Growth and performance of Atlantic salmon in the presence of lumpfish were assessed in two studies. In the first study, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean (±SD) weight of 619 (±49) g and reared for 159 days. Control cages were without lumpfish, while two of the cages were stocked with 12 lumpfish (10% density), and two with 18 lumpfish (15% density) with a mean (±SD) weight of 54.0 (±7.2) g. The lumpfish were removed from the cages after 56 days, but feed consumption and growth of the salmon were monitored for another 12 weeks until 17 November 2012 to investigate possible long term effect from the presence of lumpfish on growth performance of the salmon. In the second study, six sea cages (5 × 5 × 5 m) were each stocked with 80 Atlantic salmon with a mean (±SD) weight of 2400 (±220) g and reared for 60 days. Two of the cages were further stocked with 4 lumpfish (5% density), and two with 8 lumpfish (10% density) with a mean (±SD) weight of 360 (±30) g. Two cages without lumpfish acted as controls. In both studies sea lice infestation levels were recorded every other week. In the study with small salmon and lumpfish, the presence of lumpfish did not have any negative short-or long-term effects on feed conversion ratio (FCR) or specific growth rate (SGR) in salmon. However, when large salmon were reared together with large lumpfish, FCR was lower and SGR higher in the control cages compared to the two lumpfish treatments. Significantly lower sea lice infection levels were seen on Atlantic salmon when reared together with small lumpfish compared to the control group without lumpfish, whereas this trend was not as clear when reared with larger lumpfish.

Journal of Ethology, 2014

Your article is protected by copyright and all rights are held exclusively by Japan Ethological S... more Your article is protected by copyright and all rights are held exclusively by Japan Ethological Society and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Aquaculture, 2014

The salmon louse is an ectoparasitic copepod that causes major economic losses in the Atlantic sa... more The salmon louse is an ectoparasitic copepod that causes major economic losses in the Atlantic salmon aquaculture industry. To assess the efficacy of lumpfish grazing on attached sea lice on Atlantic salmon, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean ± SD weight of 619 ± 49 g. Two of the cages were further stocked with 12 lumpfish (10% density) and two with 18 lumpfish (15% density) with a mean ± SD weight of 54.0 ± 7.2 g. Two cages without lumpfish acted as controls. Sea lice infestation levels were recorded every other week for 54 days. To determine the diet preferences of lumpfish in the cages, gastric lavage was performed every 2 weeks. No differences in salmon or lumpfish growth between test groups and controls were observed. There were clear signs of lumpfish grazing on sea lice, with significantly lower average numbers of pre-adult, mature males and females stages of Lepeophtheirus salmonis per salmon. Lumpfish reduced the mature female stage of L. salmonis to levels equal to or lower than the counts recorded prior to the start of the study. There were no significant differences between the treatments (10% and 15% densities) in grazing efficacy. There was clear evidence of grazing from the results of gastric lavage, with 28% of all lumpfish found to have ingested sea lice on the last sampling day. Overall, the present results indicate that lumpfish is a suitable cold-water option for biological delousing of Atlantic salmon.

Aquatic Toxicology, 2012

Due to a northward shift in oil and gas activities, there is an increasing need to understand the... more Due to a northward shift in oil and gas activities, there is an increasing need to understand the potential anthropogenic impacts of oil-related compounds on sub-Arctic and Arctic organisms, particularly those in coastal habitats. Capelin (Mallotus villosus), a key fish species in the Barents Sea ecosystem, undertakes aggregated spawning at both intertidal and subtidal coastal localities in northern Norway. To investigate the sensitivity of capelin embryos to oil compounds, newly fertilized capelin eggs were collected from a spawning beach and exposed until hatch (32 days) to either the water soluble fraction of crude oil or the single PAH compound, pyrene. Threshold levels for egg mortality, development and hatching success were determined. Concentrations of 40 g/L crude oil ( 26 PAHs) and 55 g/L pyrene significantly increased embryonic mortality rates and decreased hatching success, compared with controls, indicating that a potential oil spill in the vicinity of capelin spawning grounds may cause significant impacts. No significant incidence of adverse effects such as yolk sac oedema, pericardia oedema, haemorrhages, craniofacial abnormalities, premature hatch or inhibited growth was observed. Histological studies of hatched larvae did not reveal specific sublethal effects in tissues and organs. Developmental delays and subsequent embryo death were noticed at the period of eye pigmentation in affected groups. Early life-history stages of capelin are sensitive indicators of PAH impacts, but the mechanisms responsible for the toxic effects require further investigation.

DESCRIPTION Forsøk på å redusere antall av lakselus i merder har vært et hovedmål helt siden 1970... more DESCRIPTION Forsøk på å redusere antall av lakselus i merder har vært et hovedmål helt siden 1970-tallet, ikke bare som en økonomisk bekymring, men også i form av dyrevelferd og potensielle påvirkninger på økosystemet. I dag blir lusemengden i hovedsak regulert ved hjelp av kjemoterapeutiske midler,men økende resistens mot lusemidler er et økende problem. I dag, representerer rensefisk det eneste miljøvennlige alternativ til kjemisk avlusning av laksefisk. Men de artene rensefisk som for tiden er i bruk for biologisk avlusning f.eks. Berggylt, Labrus bergylta og bergnebb, rupestris Ctenolabrus L. er temperaturfølsomme, noe som gjør dem uegnet til bruk ved lave (<6 0 C) temperaturer. Rognkjeks, Cyclopterus lumpus L. har blitt foreslått som en art man kan bruke ved lave temperaturer. Inntil nå er svært lite som har blitt publisert om oppførselen til rognkjeks. Et begrenset antall studier har blitt utført med villfanget rognkjeks, dette inkluderer beskrivelse av larver, yngel og vok...

Aquaculture, 2014

Growth and performance of Atlantic salmon in the presence of lumpfish were assessed in two studie... more Growth and performance of Atlantic salmon in the presence of lumpfish were assessed in two studies. In the first study, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean (±SD) weight of 619 (±49) g and reared for 159 days. Control cages were without lumpfish, while two of the cages were stocked with 12 lumpfish (10% density), and two with 18 lumpfish (15% density) with a mean (±SD) weight of 54.0 (±7.2) g. The lumpfish were removed from the cages after 56 days, but feed consumption and growth of the salmon were monitored for another 12 weeks until 17 November 2012 to investigate possible long term effect from the presence of lumpfish on growth performance of the salmon. In the second study, six sea cages (5 × 5 × 5 m) were each stocked with 80 Atlantic salmon with a mean (±SD) weight of 2400 (±220) g and reared for 60 days. Two of the cages were further stocked with 4 lumpfish (5% density), and two with 8 lumpfish (10% density) with a mean (±SD) weight of 360 (±30) g. Two cages without lumpfish acted as controls. In both studies sea lice infestation levels were recorded every other week. In the study with small salmon and lumpfish, the presence of lumpfish did not have any negative short-or long-term effects on feed conversion ratio (FCR) or specific growth rate (SGR) in salmon. However, when large salmon were reared together with large lumpfish, FCR was lower and SGR higher in the control cages compared to the two lumpfish treatments. Significantly lower sea lice infection levels were seen on Atlantic salmon when reared together with small lumpfish compared to the control group without lumpfish, whereas this trend was not as clear when reared with larger lumpfish.

Journal of Ethology, 2014

Your article is protected by copyright and all rights are held exclusively by Japan Ethological S... more Your article is protected by copyright and all rights are held exclusively by Japan Ethological Society and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Aquaculture, 2014

The salmon louse is an ectoparasitic copepod that causes major economic losses in the Atlantic sa... more The salmon louse is an ectoparasitic copepod that causes major economic losses in the Atlantic salmon aquaculture industry. To assess the efficacy of lumpfish grazing on attached sea lice on Atlantic salmon, six sea cages (5 × 5 × 5 m) were each stocked with 120 Atlantic salmon with a mean ± SD weight of 619 ± 49 g. Two of the cages were further stocked with 12 lumpfish (10% density) and two with 18 lumpfish (15% density) with a mean ± SD weight of 54.0 ± 7.2 g. Two cages without lumpfish acted as controls. Sea lice infestation levels were recorded every other week for 54 days. To determine the diet preferences of lumpfish in the cages, gastric lavage was performed every 2 weeks. No differences in salmon or lumpfish growth between test groups and controls were observed. There were clear signs of lumpfish grazing on sea lice, with significantly lower average numbers of pre-adult, mature males and females stages of Lepeophtheirus salmonis per salmon. Lumpfish reduced the mature female stage of L. salmonis to levels equal to or lower than the counts recorded prior to the start of the study. There were no significant differences between the treatments (10% and 15% densities) in grazing efficacy. There was clear evidence of grazing from the results of gastric lavage, with 28% of all lumpfish found to have ingested sea lice on the last sampling day. Overall, the present results indicate that lumpfish is a suitable cold-water option for biological delousing of Atlantic salmon.

Aquatic Toxicology, 2012

Due to a northward shift in oil and gas activities, there is an increasing need to understand the... more Due to a northward shift in oil and gas activities, there is an increasing need to understand the potential anthropogenic impacts of oil-related compounds on sub-Arctic and Arctic organisms, particularly those in coastal habitats. Capelin (Mallotus villosus), a key fish species in the Barents Sea ecosystem, undertakes aggregated spawning at both intertidal and subtidal coastal localities in northern Norway. To investigate the sensitivity of capelin embryos to oil compounds, newly fertilized capelin eggs were collected from a spawning beach and exposed until hatch (32 days) to either the water soluble fraction of crude oil or the single PAH compound, pyrene. Threshold levels for egg mortality, development and hatching success were determined. Concentrations of 40 g/L crude oil ( 26 PAHs) and 55 g/L pyrene significantly increased embryonic mortality rates and decreased hatching success, compared with controls, indicating that a potential oil spill in the vicinity of capelin spawning grounds may cause significant impacts. No significant incidence of adverse effects such as yolk sac oedema, pericardia oedema, haemorrhages, craniofacial abnormalities, premature hatch or inhibited growth was observed. Histological studies of hatched larvae did not reveal specific sublethal effects in tissues and organs. Developmental delays and subsequent embryo death were noticed at the period of eye pigmentation in affected groups. Early life-history stages of capelin are sensitive indicators of PAH impacts, but the mechanisms responsible for the toxic effects require further investigation.