Catch me if you can: How to recapture lumpfish using light as an attractant

The use of lumpfish in salmon farming allows the removal of sea lice all year round, without the use of chemicals or mechanical treatments. In Norway alone, around 31 million lumpfish are currently put into sea pens whereas no efficient method to re-catch these fish once they no longer are efficient salmon lice grazers (from 300 g) exists. At present, collecting lumpfish in sea-cages is a labour- and time-consuming process and, if these fish are to be harvested, an efficient method for collecting lumpfish is urgently needed. In this study, we tested coloured light as an attractant to lure lumpfish into passive traps (pods). Three small-scale pilot experiments both demonstrated the highest re-capture rate when a blue light-source was used, whereas red and yellow light gave the lowest re-capture rate. A subsequent large-scale trial failed to demonstrate significant re-catch of lumpfish. It is concluded that although blue light clearly attracted lumpfish in laboratory trials, further studies are needed in order to exploit this attribute commercially.     

Assessment of artificial substrates for lumpfish: effect of material thickness and water current speed

This study assessed the use of different types of substrates (450 g PVC, 130 g plastic) and water speed (5.0, 10 and 20 cm s^?1) on growth and substrate selection in lumpfish. There were no differences between the percentages of fish attached to both types of substrates as they grew for each of the three different water speeds. Substrate adherence was similar on both substrate types and for all water current speed as the study progressed and was between 25 to 30% in all groups at termination of the trial. Results from the present study show that increasing water speed did not affect attachment preferences in lumpfish as they grew. Larger specimens were observed attaching to both thin and thicker substrates equally. Water speed did not affect growth performance as there were no differences in growth observed at the end of the study period between the three groups of lumpfish. However, further studies are required to determine if higher water speeds affect both growth and attachment preference of lumpfish as they grow.     

Feeding behaviour and growth of lumpfish (Cyclopterus lumpus L.) fed with feed blocks

The aim of this project was to investigate if lumpfish can be fed using specially designed feed blocks instead of regular fish feed pellets. Two studies were performed. In Part I different designs of feed blocks were introduced and fish observed with underwater cameras to record feeding behaviour. Results indicate that lumpfish require feed blocks with grooves in order to graze from them and that the acclimation period is relatively short (2–4 hr) before the fish will use them as a feed source. In the second part of the project two duplicate groups of lumpfish with an initial mean (±SD) weight of 125.4 ± 45.7 g were individually weighed and randomly distributed into six 3.5 m³ circular flow‐through tanks with 45 fish in each tank. Fish in three tanks were fed using feed blocks with grooves and fish in three tanks were fed using a regular commercially available lumpfish extruded feed. Both groups received a daily feeding rate of 2% body/weight. From day 14 onwards, fish fed with marine pelleted feed had a significantly higher mean weight compared to fish fed with feed blocks. Although not significant, the condition factor was higher in the feed block group during the study period. Results from this study show that lumpfish will readily graze from feed blocks if they are presented in a way that allows them to do. In addition, the acclimation period required before the fish will utilize them appears to be short thus potentially allowing for their use in commercial salmon cages.     

Host preference of adult Caligus elongatus Nordmann in the laboratory and its implications for Atlantic cod aquaculture

The sea louse Caligus elongatus utilizes a range of marine fish species as hosts, and it has been suggested that fish farms are infected with adult C. elongatus from wild fish hosts. We assessed experimentally whether dislodged lice return to their original host species. Adult lice from wild lumpfish and saithe were presented to lumpfish, sea trout, Atlantic cod, saithe and European plaice. All fish species became infected. Lumpfish and cod were strongly preferred, followed by saithe, trout and plaice. Lice from wild saithe showed a preference for saithe and lumpfish, followed by cod, sea trout and plaice. The mtCO1 gene was used to determine the genotypes of the lice. Lice from lumpfish were genotype 1. Lice from saithe were mainly genotype 2. The two genotypes of C. elongatus differed slightly in their host preferences: lice from saithe were less discriminating. The data support the hypothesis that adult C. elongatus may transfer between different host species. Cod is an attractive host for lice from both lumpfish and saithe, which suggests that C. elongatus may become a serious pest of farmed cod.     

Outbreak of viral haemorrhagic septicaemia (VHS) in lumpfish (Cyclopterus lumpus) in Iceland caused by VHS virus genotype IV

A novel viral haemorrhagic septicaemia virus (VHSV) of genotype IV was isolated from wild lumpfish (Cyclopterus lumpus), brought to a land‐based farm in Iceland, to serve as broodfish. Two groups of lumpfish juveniles, kept in tanks in the same facility, got infected. The virus isolated was identified as VHSV by ELISA and real‐time RT‐PCR. Phylogenetic analysis, based on the glycoprotein (G) gene sequences, may indicate a novel subgroup of VHSV genotype IV. In controlled laboratory exposure studies with this new isolate, there was 3% survival in the I.P. injection challenged group while there was 90% survival in the immersion group. VHSV was not re‐isolated from fish challenged by immersion. In a cohabitation trial, lumpfish infected I.P. (shedders) were placed in tanks with naïve lumpfish as well as naïve Atlantic salmon (Salmo salar L.). 10% of the lumpfish shedders and 43%–50% of the cohabiting lumpfish survived after 4 weeks. 80%–92% of the Atlantic salmon survived, but no viral RNA was detected by real‐time RT‐PCR nor VHSV was isolated from Atlantic salmon. This is the first isolation of a notifiable virus in Iceland and the first report of VHSV of genotype IV in European waters.     

Calanus oil as a natural source for flesh pigmentation in Atlantic salmon (Salmo salar L.)

The present study was to understand how efficiently the astaxanthin in Calanus oil is utilized for flesh colouration in Atlantic salmon ( Salmo salar ). Postsmolts of the fish (309 g) were held at 7.9 °C and they were fed diets containing 20 or 60 mg astaxanthin per kilogram feed derived from a synthetic source or from Calanus oil for 181 days. Besides growth and feed intake assessments, at day 81 and 181, fish flesh were subjected to colour analysis and astaxanthin determination. Growth and feed performance did not vary between the groups. There were significant differences in the amount of astaxanthin in muscle between almost all groups both at day 81 ( P  < 0.05) and at day 181 ( P  < 0.001). However, a notable similarity between fish receiving 20 mg astaxanthin from the synthetic source and those receiving 60 mg astaxanthin from Calanus oil ( P  > 0.05) at day 181 indicated that comparable amounts were deposited only with the greater level of the natural source. Tristimuli colorimeter a* values support the analytical results at day 181. Although Calanus oil did serve as a natural dietary pigment source for farmed salmon, its inclusion level should provide more than 60 mg astaxanthin per kilogram feed to achieve colouration preferred by the market.     

Determining spatial feed distribution in sea cage aquaculture using an aerial camera platform

Within this paper we describe an unmanned aerial vehicle (UAV) based method to estimate the spatial feed pellet distribution in salmon fish-cages and exploit it within a case study to determine the radial pellet distribution for different rotor spreaders and blower configurations. Compared to previously used methods, capturing pellets thrown from a rotary feed spreader in rows of Styrofoam boxes, the UAV based method is simpler and faster to setup and allows to cover a larger portion of the sea cage surface area. We compare results obtained with the Styrofoam box method with results we obtained by an automatic analysis of aerial videos taken by the UAV during feeding experiments. The employed method helps to gain insight into the spatial feed pellet distribution in full-scale salmon fish-cages where the feeding pipe and actual fixation of the spreader may influence the dynamic behaviour of the feeding system. This can also be seen as a step towards a continuous measuring of the feed pellet distribution, particularly in view of possible future feeding systems that may allow to adapt the feed pellet distribution to the actual fish distribution.     

A Methodology for Evaluation of Dietary Feeding Stimulants for the Pacific White Shrimp, Litopenaeus vannamei

A simple and practical method for quantification of feeding stimulation of shrimp Litopenaeus vannamei was developed using feed preference as an index of comparison. Feed preference was defined as the percentage of shrimp observed in each feeding tray. Preliminary trials were undertaken with two commercial feeds (45% protein with 5% squid meal and 40% protein without squid meal). Results indicated the following criteria were suitable for use as methodology for evaluating feeding stimulation in 5-m diameter static flow tanks: shrimp density (2.5 shrimp/m2); observational period (1 or 2 h post-addition of feed to trays), feed rate (2%), and between-trial feed rate (2%). A further investigation was undertaken to evaluate the influence of protein level and source on feed preference using a basal diet consisting of wheat flour, casein, carboxymethyl cellulose binder, and limestone, with or without krill meal as a feeding stimulant. A significant difference was shown in feeding preference for the 16% protein/4% krill meal vs. one without krill meal; however, this relationship was not shown in 45% protein feed comparisons. A second trial comparing 0, 16,30, and 45 % protein/casein-based feeds showed similar results. From these findings, it was postulated that casein, itself, also serves as a feeding stimulant at high dietary inclusion levels. A third trial comparing 16% protein/casein or wheat gluten-based feeds Indicated a delay of at least 2 h in maximum feeding preference response in feeds in which 4% krill meal was added as a feeding stimulant. It was postulated that chemical stimulants from krill meal were more slowly released in wheat gluten-based feeds. Our methodology appears suitable for evaluation of potential feeding stimulants when incorporated into low-protein casein-based or wheat-gluten-based feeds.     

Comparison of diet composition,feeding, growth and health of lumpfish (Cyclopterus lumpus L.) fed either feed blocks or pelleted commercial feed

Two duplicate groups of individually tagged lumpfish (mean initial weight: 21.5 ± 3.2 g) were fed either a commercially available lumpfish feed or feed blocks for a period of 123 days. The aim was to evaluate and compare the effects of these feed types on growth, cataract development and histopathology in lumpfish. There were significant differences in growth rates between the groups with fish fed pelleted feed having the highest growth rates. The development of cataracts was significantly different with fish fed pelleted feed having a cataract prevalence of 87% at the end of the study period whilst fish fed with feed blocks had 10% prevalence. The results of the histological examination undertaken in this study showed overall small differences between the two dietary treatments. In some individuals in groups receiving both diets, there was mild to moderate expansion of the lamina propria with tissue most likely to represent fibrous tissue with scattered leucocytes. Overall, the findings of the present study show that lumpfish will readily graze from feed blocks and although growth is lower the prevalence of cataract is greatly reduced using feed blocks.     

SUBSTITUTABILITY OF FISHMEAL AND FISH OIL IN DIETS FOR SALMON AND TROUT: A META-ANALYSIS

Intensive aquaculture, especially the production of carnivorous species requires artificial feeding. Marine proteins are preferred to vegetable proteins, since fishmeal and oil provide the essential nutrients required by farmed fish. Given the stagnant production of industrial species and the rapid increase in aquaculture production, fishmeal availability would pose a biological constraint on aquaculture contribution to world fish supplies in the future, unless alternative feed sources can be incorporated in diets. In this paper, the technical substitutability between fish and vegetable-based feeds for salmon and trout are assessed through the estimation of Morishima elasticities of substitution. These are derived from a meta-analysis production function based on a large number of published feed trials. The results suggest that vegetable oil may be a potential substitute for fish oil, particularly in salmon aquaculture, but fishmeal is likely to remain a necessary component of feed unless some new feed source can be developed.     

Influence of high content of dietary soybean oil on quality of large fresh,smoked and frozen Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)

Atlantic salmon (Salmo salar) was grown in sea cages from 700 g to a market size of 3.2 kg on diets containing either 29% Peruvian high polyunsaturated fatty acids (PUFA) fish oil (FO) or 29% soybean oil (SO) as oil source. Chemical analyses and a triangular consumer test were performed on fresh muscle, while colour, texture and liquid holding capacity (LHC) analyses were performed on both fresh muscle, frozen muscle (stored for 3 months) and smoked salmon. The growth and chemical composition of flesh was not affected by the dietary treatment. The muscle fatty acid (FA) profile was reflected by the dietary oil source, and the amount of malondialdehyde (MDA) was threefold higher in the salmon fed FO than SO. Muscle pigment concentration was significantly different (p < 0.01) with 7.9 mg kg^–1 for FO and 5.6 mg kg^–1 for SO fed salmon, respectively. This result was also significantly (p < 0.05) reflected in the difference between the instrumentally measured colour of fresh, frozen and smoked muscle, and visual impressions of fresh and frozen muscle. Gaping, texture and liquid holding capacity was not affected by the dietary treatment, and the consumer panel did not detect any differences between the dietary groups. SO can be used as a dietary oil source in the grow-out phase of salmon production without sacrificing product quality in terms of texture, liquid holding capacity and consumer preference. However, a total substitution of high PUFA fish oil by SO in diets for salmon grown to market size, affects muscle colour and the FA profile significantly. (p < 0.05).     

Feed discrimination and selection in self-fed European sea bass Dicentrarchus labrax L.

Abstract This study was conducted to evaluate feed discrimination and preference of European sea bass Dicentrarchus labrax L., taking into account the effects of feed location, previous feeding experience and light conditions. Fish (63 g) were held in tanks and exposed to a 12L:12D photoperiod and ambient temperature. The following feeding practices were applied in triplicate: three‐choice feeding (self‐ feeding with feeds formulated for carnivorous, herbivorous and omnivorous fish rotated on a weekly basis) and monofeeding (self‐feeding with one of these feeds). After 9 weeks (phase I), fish previously held in monofeeding, were subjected to three‐choice feeding for 2 weeks (phase II). In phase I, fish discriminated between feeds after their rotational displacements and preferred the feed formulated for carnivorous species. This also supported the best growth. Fish used in phase II preferred the same feed. There was no preference for any location within tanks. Feeding was generally diurnal, although in some tests with the feeds for herbivores and omnivores, diurnal and nocturnal feed demands were similar and fewer in number than with the feed formulated for carnivores.     

Pattern of feed intake in four species of fish under commercial farming conditions: implications for feeding management

Meal duration and feed ingestion rate were measured in sea cage-reared Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, yellowtail Seriola quinqueradiata and red sea bream Pagrus major fed dry extruded feed in discrete meals. At the population level, satiation times in yellowtail, salmon and trout were typically about 15–25 min, but time to satiation was longer (60–90 min) in red sea bream. In all species, feed ingestion rate declined progressively during the course of the meal as the fish became satiated. Initial feed ingestion rates in salmon were ≈ 0.3–0.5 kg feed tonne fish^–1 min^–1 and in trout 0.5–0.9 kg feed tonne fish^–1 min^–1, although the capacity to deliver feed may have restricted ingestion. Water temperature had little effect on ingestion rates, possibly because the number of meals per day (1–3) was varied with water temperature, and this may have standardized hunger level at the start of meals. Yellowtail ingested feed at ≈ 3.5 kg feed tonne fish^–1 min^–1 at water temperatures of 18 °C and 28 °C, whereas red sea bream ingested feed at initial rates of 0.6 and 1.4 kg feed tonne fish^–1 min^–1at 26.5 °C and 18 °C respectively. The findings are discussed in relation to feeding strategies to minimize interfish competition for feed and to improve the ability of fish farmers to detect the point at which fish are satiated.     

Quality of wild-captured saithe (Pollachius virens L.) fed formulated diets for 8 months

Fish farms may attract wild fish that feed on waste feed from the cages. Saithe, Pollachius virens L., are particularly numerous around salmon cages in northern Europe and may obtain a significant proportion of their diet from waste feed. It has been claimed that these fish are of inferior quality to saithe that feed on natural diets; differences are said to include soft muscle tissue and a different taste. In order to document such changes in quality we performed a feeding experiment. Young wild saithe were collected and fed either a lipid-rich salmon diet or a lean cod diet for 8 months. All fish were individually tagged and growth was monitored throughout the experiment. Parameters related to flesh quality were measured. Diet clearly influenced the growth rate of the fish, and many fish reached a very high hepatosomatic index when fed on a salmon diet. However, many fish had a low feed intake and thus a low rate of growth. There were some differences in skin and muscle colour, pH and in sensory parameters between wild-caught and artificially fed saithe at the end of the experiment. Those fed the cod diet were more similar to wild saithe than those fed the salmon diet.     

Risk factor analysis for sea lice, Caligus rogercresseyi, levels in farmed salmonids in southern Chile

Sea lice, Caligus rogercresseyi, are ectoparasitic copepods, which severely affect the salmon farming industry in southern Chile, reducing the health status of fish and producing both direct and indirect economic losses. Local farmers have reported increasing infestation levels since 2004, reaching a peak in 2007. In response to this situation, the Chilean Fisheries Service (Sernapesca) developed a surveillance programme; the first step of which consisted of a general survey of salmon farms. This survey included documenting counts of parasite burdens on fish and measurements of several husbandry and environmental factors providing an evaluation of risk factors for the observed infestation levels. The information collected was analysed using a linear mixed model technique, which takes into account the clustered structure of data, decomposing the unexplained variation and assigning it to different aggregation levels of the productive system. Geographical zones, fish species, treatment against sea lice performed 1 month before sampling, stocking density, fish weight and water salinity were the variables significantly associated with sea lice burdens. In contrast, treatments performed 2-3 months before sampling, use of photoperiod in sea cages and water temperature, were not significant. There was significant unexplained variation at all aggregation levels, i.e. sub-zone, fish farm and cage level, with the fish farm level showing the greatest variation.     

An epidemiological study of cataracts in wild and farmed lumpfish (Cyclopterus lumpus L.) and the relation to nutrition

Twelve groups of farmed lumpfish and one of wild lumpfish were screened for cataract and sampled for fish muscle tissue, whole heart and both eye lenses to investigate possible relations between cataract and tissue free amino acid concentrations. Cataract prevalence ranged from 20% to 100%, with the highest average score of 7.3 (max 8) and incidences of severe cataract (>5) in all groups. Cataract could not be explained by suboptimal histidine concentrations in the feed. Neither muscle nor cardiac tissues had concentrations of free histidine compounds. The lumpfish lens contained N‐acetylhistidine (NAH), of which low concentrations were strongly related to cataract severity. However, no correlation between lens NAH and cataract severity was found in the present sample set. Wild lumpfish had higher levels compared to farmed lumpfish, suggesting that the farmed lumpfish may have been deficient in histidine or have a higher utilization of NAH due to osmotic problems. Thus, cataract in farmed lumpfish may be related to primary or secondary disturbed nutrient metabolism or malnutrition, shown by the high levels of specific amino acids in different tissues, which may cause osmotic imbalance and cataract development. This nutritional or environmental‐related welfare problem deserves further research.     

Effects of stocking density on growth performance and welfare‐related physiological parameters of Atlantic salmon Salmo salar L. in recirculating aquaculture system

Stocking density, representing a potential source of long‐term stress, is widely recognized as a critical factor in aquaculture husbandry. Atlantic salmon were reared at low‐density (LSD, ~9.80–18.41 kg m^?3, initial to final density), medium‐density (MSD, ~19.62–36.96 kg m^?3) and high‐density (HSD, ~28.79–53.54 kg m^?3) stocking levels for 66 days to investigate the stress‐induced changes in fish growth and welfare. At the end of the trial, the salmon in HSD group showed significant lower final weight and higher ration level than those in MSD and LSD groups (P < 0.05). The salmon farmed in LSD group had higher special growth rate (SGR) and lower feed conversion ratio (FCR) (P < 0.05). However, stocking density could not affect the mortality, condition factor and coefficient of variation of salmon. The pectoral fin index of salmon in LSD group was significantly higher than that in HSD group (P < 0.05). Fifteen haematological and serum parameters were detected to assess the stress and welfare levels of salmon. The salmon farmed in HSD group had higher glucose (GLU) level and lower Cl^?, haemoglobin (HGB) and red blood cell (RBC) concentrations (P < 0.05). Contrast to the pattern of superoxide dismutase (SOD) activity, the cortisol, maleic dialdehyde (MDA) and alkaline phosphatase (ALP) levels of HSD group were higher than those in other two groups (P < 0.05). All these findings will provide a reference for selecting suitable stocking density in Atlantic salmon farming industry.     

Formation of periphyton biofilm and subsequent biofouling on different substrates in nutrient enriched brackishwater shrimp ponds

Periphyton grown on substrates is known to improve water quality in aquaculture ponds. Five different substrates, (i) bamboo pipe (ii) plastic sheet (iii) polyvinylchloride (PVC) pipe (iv) fibrous scrubber, and, (v) ceramic tile were evaluated for the formation of biofilm in this experiment. The substrates were suspended 25 cm below the water surface. Each type of substrate was collected fortnightly to analyze the abundance and biomass of different periphytic algae and of the biofouling organism. The study was terminated after 60 days due to severe fouling by polychaete. Results showed that pond water nutrients were high on day 60 with mean total ammonia-N, nitrite-N and soluble reactive phosphorus concentrations of 309.6 ± 8.6 μg L^− 1, 26.0 ± 2.7 μg L^− 1 and 87.2 ± 7.1 μg L^− 1 respectively. During the first two weeks the substrates were colonized by 19 periphytic algae. The most abundant family was Bacillariophyta (8 genera) followed by Chlorophyta (7 genera) and Cyanophyta (4 genera). Periphyton colonization on bamboo pipe showed the highest (p < 0.05) biomass in terms of chlorophyll a amongst all the substrates used. The biomass varied from 179 to 1137 μg m^− 2 with mean values of 1137.2 ± 0.6, 929.6 ± 0.6, 684.2 ± 1.2, 179.1 ± 0.6 and 657.0 ± 0.6 μg m^− 2 on bamboo pipe, PVC pipe, plastic sheet, fibrous scrubber and ceramic tile respectively for the first 15 days. From 3rd week, polychaetes began to form tubes on the substrate. By day 60, the whole surface of all substrates was covered with tightly packed polychaete tubes with mean densities of 168.0 ± 15.4, 121.0 ± 13.5, 72.8 ± 9.8, 72.4 ± 7.4 and 56.0 ± 6.8 polychaete tubes cm^− 2 for bamboo, PVC, plastic, fibrous scrubber and ceramic tile respectively. This study illustrated the invasive nature of attached polychaete thus hampering the formation of periphyton biofilm on substrates which could have been used for improving water quality in enriched brackishwater shrimp ponds.     

Diurnal stream habitat use of juvenile Atlantic salmon, brown trout and rainbow trout in winter

Abstract  The diurnal winter habitat of three species of juvenile salmonids was examined in a tributary of Skaneateles Lake, NY to compare habitat differences among species and to determine if species/age classes were selecting specific habitats. A total of 792 observations were made on the depth, velocity, substrate and cover (amount and type) used by sympatric subyearling Atlantic salmon, subyearling brown trout and subyearling and yearling rainbow trout. Subyearling Atlantic salmon occurred in shallower areas with faster velocities and less cover than the other salmonid groups. Subyearling salmon was also the only group associated with substrate of a size larger than the average size substrate in the study reach during both winters. Subyearling brown trout exhibited a preference for vegetative cover. Compared with available habitat, yearling rainbow trout were the most selective in their habitat use. All salmonid groups were associated with more substrate cover in 2002 under high flow conditions. Differences in the winter habitat use of these salmonid groups have important management implications in terms of both habitat protection and habitat enhancement.