Consumption of sea lice by lumpfish (Cyclopterus lumpus): qPCR quantification and use of a non-destructive sampling method

Under embargo until: 2020-11-03In the present study, it was attempted to quantify sea lice grazing in lumpfish by using a recently published qPCR assay. This method utilizes a small aliquot (10 μL) of the stomach fluid of the lumpfish which can be collected using a sterile, 85 mm long pipette tip. We tested if repetitive sampling of stomach fluid influenced growth and survival in the sampled fish. The test lumpfish were sampled for stomach fluid at 6–16 days intervals for 95 days. No mortalities were recorded during the test period and there were no significant differences in growth compared to the control group. Quantification using the qPCR method was tested by two approaches; one with lumpfish that had grazed on sea lice ad libitum and the other with lumpfish that had been intubated with sea lice. The sea lice-specific qPCR assay had an inversely related relationship with the number of eaten lice, especially from stomach samples of lumpfish that naturally fed on sea lice as opposed to intubated fish.acceptedVersio

Gastric cancer in Iceland

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Comparing Body Density of Lumpfish (Cyclopterus lumpus) to Different Operational Welfare Indicators

Farmed lumpfish (Cyclopterus lumpus) are commonly used as cleaner fish in the salmonid aquaculture industry, but a knowledge gap exists with regards to their body density. Filling this knowledge gap is of importance, as the lumpfish has no swim bladder and thus relies on alternative methods for buoyancy, i.e., the body density difference between the fish and its surroundings. The aims of this study were to measure the body density of lumpfish and investigate the correlation between body density and different operational welfare indicators. A total of 138 lumpfish were sampled at five different aquaculture sites situated in the Faroe Islands. Weight in water and air was measured, body density was calculated, and operational welfare was assessed. The average body density of the juvenile lumpfish was 1.030 g mL−1. Fulton’s K, stomach score, and length were negatively correlated to body density, while the hepatosomatic index was positively correlated to body density. Liver colour was correlated to body density, but the groupings were too broad for a final definitive conclusion. The knowledge gained from this study might help the industry improve their understanding of the operational welfare indicators used for lumpfish. Additionally, the knowledge might also help the aquaculture industry improve their husbandry and feeding practices.publishedVersio

Effect of Photoperiod and Transfer Time on Atlantic Salmon Smolt Quality and Growth in Freshwater and Seawater Aquaculture Systems

Smoltification is a key process in Atlantic salmon aquaculture, given it prepares the fish for a successful transit from fresh to seawater. However, industry players have not yet reached a consensus on the best protocols to produce high-quality smolts. In this study, we assessed how the combination of two photoperiod regimes in freshwater (continuous light or LL, and natural photoperiod or LDN) and four transfer times to seawater (February, March, April, and May) affected smolt development and their subsequent growth in seawater until slaughter during commercial production. The results demonstrated that smoltification and growth in freshwater were only slightly modulated by the photoperiod treatment and were instead much more affected by the limiting effect of the low water temperature during that period. In seawater, the growth rate was the highest in the same groups, which had, however, experienced a delay in growth when in freshwater, and consequently, no differences in the final body weight between the eight treatments were found. Such compensatory growth in the sea was probably enhanced by the increasing smolt quality, which could allow for better performance in seawater. A significant link between the weight at slaughter and weight at transfer was observed only in the groups with a lower smolt quality (LL-Feb, LDN-Feb and LDN-Mar), which suggests that larger individuals could cope better with a saline environment. In contrast, smaller smolts probably suffered greater osmotic stress that hindered their performance at sea. Afterwards, as smolt quality increased in the subsequent transfer groups, the relevance of this size effect decreased. This means that the industry may benefit from transferring larger smolts to seawater, especially if these are suspected of having developed suboptimal seawater tolerance. Those individuals are likely to cope better with saline conditions than smaller smolts. Future research should focus on the possible long-term effects of freshwater-rearing regimes on smolt performance in the seawater phase.publishedVersio

Acoustic Delicing of Atlantic Salmon (Salmo salar): Fish Welfare and Salmon Lice (Lepeophtheirus salmonis) Dynamics

Acoustic lice treatment (AcuLice) is a newly developed system, which uses a composite acoustic sound image with low-frequency sound to remove salmon lice (Lepeophtheirus salmonis) from Atlantic salmon (Salmo salar). This field study documents the stress effects on Atlantic salmon and the effect on salmon lice dynamics during large-scale use of the AcuLice system. The effect of the AcuLice treatment on salmon lice dynamics was measured by weekly salmon lice counting at the facilities from mid-summer 2019 to late-spring 2020. The number of salmon lice treatments in the same period was also compared to a reference group. In addition, the number of weeks until the first salmon lice treatment (mechanical treatment) was compared between the two groups. Apart from a slight increase in plasma glucose, no significant differences were observed in the primary, secondary, or tertiary stress responses measured. For the mature female salmon lice, a significantly lower number (mean ± SEM) was shown for the AcuLice group (0.24 ± 0.03) compared to the reference group (0.44 ± 0.04). In addition, a lower number (mean ± SEM) of salmon lice treatments and a longer production period before the first salmon lice treatment occurred was observed at the AcuLice facilities (33.2 ± 3 weeks) compared to the reference facilities (20.3 ± 2 weeks). These data suggest that the use of the AcuLice system reduces the need for traditional salmon lice treatments with no added stress to the fish.publishedVersio

Effect of rearing temperature on flesh quality in Arctic charr (Salvelinus alpinus)

Currently, no information is available on the effect of progressively decreasing temperatures on the sensory quality of Arctic charr. The objective of this study was to investigate if and how different and progressively changing rearing temperatures affect the sensory quality of cooked and raw fillets of Arctic charr. The effects of rearing temperature on the sensory quality of Arctic charr (weight range 622–888 g) were investigated. Rearing temperature was changed during the experimental period as the fish were reared at constant or decreased temperature during October to April and subsequently reared at two constant temperatures from April to August establishing six different rearing temperature combinations. Significant differences were seen in all four main sensory attributes groups, that is odour, appearance, flavour and texture. Freshness characteristics such as sweet odour and flavour, and metallic odour and flavour increased with decreasing rearing temperature, whereas musty odour and flavour decreased. Rearing temperature had a clear effect on the colour of the fillets. Lower rearing temperature increased colour intensity substantially. Softness, juiciness and tenderness increased with decreased rearing temperature. A trend was seen towards more effect from final rearing temperature than initial temperature on the sensory attributes studied. Spoilage characteristics, that is, sour and rancid odour and flavour, and off-odour and flavour were either very weak or not noticeable in all sample groups.acceptedVersio

Experimental design and statistical analyses of fish growth studies

Every year, numerous studies are published that compare the effects of different factors on the growth of aquaculture fish. However, comparatively little attention has been given to the experimental designs of these studies - in how many rearing units should each treatment be replicated, how many fish should be in each tank (n) and how should the data be analysed. The reliability of the results increases with increased replication and n. In reality, however, the experimental design must strike a balance between limited resources and the reliability of the statistical analysis. A survey of recent publications in Aquaculture suggests, that most (83%) aquaculture growth studies apply each treatment in triplicates with an average of 26 fish in each tank (range: 4 to 100). The minimum difference that can reliably be detected with statistical analyses is determined by the number of replications of each treatment, n, the variance of the data and the number of treatments applied. In the present study, we accumulated information on the variance of data in aquaculture growth studies on different species to estimate the minimum detectable difference and to assist researchers in designing experiments effectively. These results suggest that the variance is similar for different aquaculture species and, therefore, the same designs (level of replication and n) are suitable for studies on different species of fish. The minimum difference (MDD) in mean body-mass of different treatment groups that can be detected in a typical aquaculture study (triplicates, 25 fish in each tank and average variance) with 80% statistical power (less than 20% chance of Type II error) is around 26% of the grand mean. Increasing the n from 25 to 100 will reduce the MDD to 19% of the grand mean, while a further increase in n will have comparatively lesser effect. Increasing replication to quadruplicates or sextuplicates (with n as 100), will further reduce the MDD to 16% and 12% of the grand mean respectively. MDD under 10% of the grand mean is only possible when fish for the experiment are selected within a narrow size range to reduce variance. Simulations were performed, where samples (experiments) were repeatedly drawn from artificial populations with identical distribution and with the same experimental design as is commonly used in growth studies. Two of the populations had dose-dependent responses to treatment while one population showed no response to treatment. The resulting data was analysed with a mixed model ANOVA and by fitting either polynomials or asymptotic models to the data. Contrary to earlier suggestions, the critical treatment (minimum treatment to generate maximum response) estimated with the ANOVA approached more closely the population responses than did the critical treatments estimated with the non-linear modelsRitrýnt tímaritPeer reviewedPre prin

Stocking density and its influence on the productivity of red cusk eel, Genypterus chilensis (Guichenot, 1848), in shallow raceways

We compared the growth properties of red cusk eel Genypterus chilensis with initial mean weight ± standard error, 106.2 ± 6.1 g reared in shallow raceways at three different stocking densities (28.5, 46.1, and 60.7 kg m-3) in a 226-day long growth trial at a constant temperature of 17°C. There was a trend towards higher specific growth rates at the highest density. Final mean weights were 333 ± 12, 352 ± 12, and 354 ± 15 g, at the 30, 45, and 60 kg m-3 density, respectively. Overall, the growth rates were higher in the 60 kg m-3 density group than the two other density groups. The daily feeding intake (%) was higher in the medium (0.51), and high (0.55) density groups compared the low-density group (0.45). Feed conversion efficiency (FCE) did not differ between the density groups. A significant size rank correlation was maintained in all density groups throughout the study. Calculated productivity increased almost linearly with increasing stocking density and was found to be 32, 34, and 39 g m-2 d-1 at 30, 45, and 60 kg m-3, respectively. The results show that the optimum density conditions for farming juvenile red cusk eel, both concerning growth rate, feed conversion, and productivity is at densities equal to or higher than 60 kg m-3.publishedVersio

Cleaner Fish Do Not Impact the Pigmentation of Salmon Lice (Lepeophtheirus salmonis) in Commercial Aquaculture Cages

Salmon lice are one of the biggest challenges to sustainable salmonid aquaculture. The species display high evolutionary potential, which is evident by its development of resistance to numerous chemical compounds used for delousing. In response to this, salmon farms now use non-chemical delousing methods to minimize the damage done by salmon lice, including heavy reliance on cleaner fish. Anecdotal reports from farmers and fish health personnel in areas where cleaner fish are used have suggested that salmon lice are becoming less pigmented, potentially making them harder for cleaner fish to visually detect. This experiment investigated changes in the pigmentation of salmon lice in relation to the use of cleaner fish, louse stage and sex, temperature, preferred salmon swimming depth, daylength, and salinity. Salmon lice were sampled from snorkel cages on a commercial salmon farm where three cages were stocked with farmed lumpfish and ballan wrasse, and three cages were without cleaner fish. Water temperature, salinity, and depth were recorded using a conductivity, temperature, and depth recorder. Pigmentation was measured via photographic analysis of individual lice. Although louse pigmentation varied considerably throughout the experiment, using cleaner fish throughout a single production cycle did not reduce average louse pigmentation compared to control cages. On average, male lice were significantly darker pigmented than females, but otherwise there were no patterns in louse pigmentation in relation to life stage, salinity, temperature, or daylength. Salmon lice exhibit a high degree of evolvability and have become resistant to every chemical removal treatment developed thus far. The present data suggest that, with the densities and species of cleaner fish commonly used in commercial salmon production, there is not strong directional selection on louse pigmentation. Lice, at least with regard to visual appearance, are not likely to adapt in a way which reduces cleaner fish efficacy anytime soon.publishedVersio

The effect of alternate-day feeding on growth and feed conversion in Atlantic cod Gadus morhua

This study aimed to investigate the effect of alternating feeding (Alt) compared with control being fed every day (Con) in the on-growth face of Atlantic cod. Individually marked fish (198 and 98 in the Con and Alt groups, respectively) was sampled for weight and length on 6 occasions over a 15-month period, where mean weight increased from 628 and 758 g to 2635 and 3041 g, for the Con and Alt groups, respectively. Feeding alternate day resulted in 13 percentage more weight gain in the alternating feeding group (2283 vs. 2007 g) and improved feed conversion ratio (FCR, 1.07) compared with control (FCR 1.45). The Alt group consumed significantly less feed (27%) compared with control. The results demonstrate that feeding costs can be drastically reduced without compromising biomass growth by using feeding on alternate days during the on-growing period of Atlantic cod.publishedVersio