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Hatchery produced silver pompano, Trachinotus blochii fingerlings were stocked in nine cages at three different stocking densities of 15 (SD15), 10 (SD10) and 5 individuals m−3 (SD5) in triplicate. The results indicated that the percent weight gain, specific growth rate, and average daily growth were decreased with the high stocking density (SD15), and better performance was also observed in the low stocking density (SD5) treatment. Better feed conversion ratio was observed in SD5. Among the stocking density treatments, SD15 showed a higher yield than the rest of the groups. Comparison of yield to SD5 as the control, yield for SD10, and SD15 was 141.9% and 180.8%, respectively. Though the observed growth performance of silver pompano was better at SD5, the yield was significantly (P <.05) higher at SD15. Thus, we conclude that silver pompano with a stocking density of 15 individuals m−3 is optimum for better production and yield. [ABSTRACT FROM AUTHOR]

Biofouling in marine aquaculture is a specific problem where both the target culture species and/or infrastructure are exposed to a diverse array of fouling organisms, with significant production impacts. In shellfish aquaculture the key impact is the direct fouling of stock causing physical damage, mechanical interference, biological competition and environmental modification, while infrastructure is also impacted. In contrast, the key impact in finfish aquaculture is the fouling of infrastructure which restricts water exchange, increases disease risk and causes deformation of cages and structures. Consequently, the economic costs associated with biofouling control are substantial. Conservative estimates are consistently between 5–10% of production costs (equivalent to US$ 1.5 to 3 billion yr−1), illustrating the need for effective mitigation methods and technologies. The control of biofouling in aquaculture is achieved through the avoidance of natural recruitment, physical removal and the use of antifoulants. However, the continued rise and expansion of the aquaculture industry and the increasingly stringent legislation for biocides in food production necessitates the development of innovative antifouling strategies. These must meet environmental, societal, and economic benchmarks while effectively preventing the settlement and growth of resilient multi-species consortia of biofouling organisms. [ABSTRACT FROM AUTHOR]

Abstract: Atlantic cod (Gadus morhua) bite at netting materials in sea-cages, which is known to weaken and destroy net materials, contribute to the formation of net holes and lead to escapes. We determined the lateral pulling forces applied to nets through biting by cod in a laboratory set-up. A sensor for automatic logging of the lateral pulling force was used to obtain data for over 1000 undisturbed, objectively collected biting events. Lateral pull force varied between cod of different size (180 and 610g) and different net types, ranging from 0.9 to 9.4N. Further, pull forces were on average 1.5–2.5 times stronger during lengthy biting events compared to single, brief bites. Maximum lateral pulling forces exerted by 610g cod were similar to their body weight in air, while 180g fish were able to pull with a force equivalent to twice their own weight in air. All recorded lateral pull strengths significantly exceeded the known force needed to break single nylon fibres of the netting material. Our results advance understanding of mechanisms and forces involved when cod interact with sea-cage nets and provide important baseline data for the design and production of more bite-resistant netting. [Copyright &y& Elsevier]

Abstract: Submersible sea-cages represent an alternative method to standard surface-based cages, and could help solve several production problems that exist in surface-based farming, such as heavy storms, algal and jellyfish blooms and attacks by predators. In this study, we investigated growth, haematological, biochemical and immunological parameters of European sea bass (Dicentrarchus labrax) farmed in surface and submersible cages, to compare the physiological status under different rearing conditions. In addition, we evaluated the use of erythrocyte HSP70 levels as a biomarker of fish welfare. The study was conducted in two submerged and two surface cages filled with D. labrax. No significant differences were observed in the growth rate and the relative condition factor between the two groups. Significantly higher levels of serum cortisol, haematocrit plasma glucose and total plasma proteins were measured in surface-based cages. Conversely, fish in submerged cages showed higher haemolytic activity and lysozyme levels in both mucus and kidney than surface reared sea bass. Results obtained in this study indicate that submergence could be a favorable condition for sea bass farming, suggesting mariculture in submerged net cages as a promising system that allows producers to minimize stress (included that from predation by fish-eating birds) and therefore favor animal welfare. [Copyright &y& Elsevier]

Pigmentation capability of red porgy ( Pagrus pagrus) skin reared under open sea-cage conditions and fed an astaxanthin-enriched diet was studied. Skin lipid peroxide levels and lipid composition were also evaluated to establish the antioxidant role of astaxanthin under these sunlight-exposure conditions. Fish placed either in an offshore sea cage system (SC) or in an inland tank facility (T) housed inside a ‘shade-house’ enclosure were fed a commercial diet supplemented with 22 mg kg−1 astaxanthin. No differences in growth or survival were found. Both groups displayed a red skin, but SC fish presented a darker pigmentation, which externally reflected the higher deposition of melanin, astaxanthin and tunaxanthin found in its skin. The lower level of lipid peroxides found in SC fish might be related with the higher level of astaxanthin mentioned above. Nevertheless, lipid and fatty acid profiles did not show significant differences between groups. Our results indicate that sustainable production of red porgy with a natural red hue is possible on the basis of proper adjustment of two factors illumination and dietary astaxanthin. [ABSTRACT FROM AUTHOR]

Abstract: Fish-farming structures are widespread in coastal waters and are highly attractive to wild fish. Several studies have estimated that tons to tens of tons of wild fish aggregate around fish farms. These estimates assumed that the majority of wild fish are concentrated immediately beneath farms, although this assumption has never been explicitly tested. We tested the hypothesis that abundances of wild fish would be greatest immediately beneath farms and progressively diminish with distance at 4 full-scale coastal salmon (Salmo salar) farms in Norway. At each farm, fish were counted with a video-camera system at 5 different distances from the cages (farm=0m, 25, 50, 100 and 200m) throughout the water column on three separate days. Combined across all locations and times, the total abundance of wild fish was 20 times greater at the farm than at the 200m sampling distance. Saithe (Pollachius virens) dominated assemblages at all 4 farms and were consistently significantly more abundant at the farm than at the 25–200m distances. This ‘tight aggregation’ around farms corresponds to the reliance of saithe on waste feed when they school near farms. In contrast, patterns of distribution of both cod (Gadus morhua) and poor cod (Trisopterus minutus) varied among farms, with either highest abundances at the farm or a more even distribution of abundance across all 5 distances sampled. No specific pattern of aggregation was evident for the bottom-dwelling haddock (Melanogrammus aeglefinus). Our results suggest that the present 100m no-fishing zone around salmon farms protects the greatest proportion of farm-aggregated saithe and cod from fishing during the daytime. However, whether this reduces their overall susceptibility to fishing requires further research regarding nighttime distribution and movements. [Copyright &y& Elsevier]

Abstract: In the search for alternative farming methods, we investigated whether large salmon submerged below 10m in winter conditions behaved normally and performed as well as control fish held in standard surface cages. On average, 2345 salmon of ~3.5kg were kept in each of six 2000m3 sea-cages for 6weeks; three of which were submerged to 10–24m depth and three acted as surface controls (0–14m). Behaviour during both day and night was studied with echo-sounders, and underwater video cameras fitted with infra-red lamps. A sub-sample of fish from each cage was weighed, measured and assessed for fin and snout condition prior to and after the experimental period. In addition, the vertebral column of 50 fish from the control and submerged treatments were dissected and X-rayed to assess vertebral deformities. The submerged salmon seemed unable to re-fill any gas into the swim bladder, as a linear decrease in echo reflection to <5% of pre-submergence levels after 22days of submergence indicated loss of almost all gas from the physostomous swim bladders and negatively buoyant fish. Around day 22, submerged salmon swam at night time with a distinct ‘tail-down, head-up’ tilt (26°) compared to the horizontal swimming position of control fish (−3°). Average swimming speed (body length per second) of submerged salmon were 1.3–1.4 times faster (day: 0.77±0.02; night: 0.46±0.02, (mean±SE)) than control fish (day: 0.54±0.01; night: 0.37±0.02) both during day and night. Almost no mortality was seen, and the submerged salmon maintained similar diurnal vertical migrations as the surface fish, indicating that deep submergence did not exhaust the fish. However, submerged fish fed less efficiently, resulting in lower growth and reduced feed utilization. Fins and snouts of the submerged fish had small, but significantly more erosion than the control fish. Vertebrae in the tail region were significantly compressed in the submerged fish compared to control fish. This could be an early symptom of development of vertebral deformities. The results suggest that continuous submergence below 10m for longer than 2weeks reduces the welfare and performance of Atlantic salmon. [Copyright &y& Elsevier]

The article examines one research which determines the extent to which wild fish from surrounding waters aggregate around salmon farms across the farming regions in Norway. Wild fishes collected at nine farms and nine control locations were counted on three separate days in June-August 2007. After counting, it was revealed that Gadoid fishes, specifically Pollachius virens, Gadus morhua and Melanogrammus aeglefinus, were dominating farm-associated assemblages. Factors such as a heightened potential for the transfer of pathogens from salmon farms to wildfish as well as the altered availability of wild fish to fisheries are cited as two main reasons behind substantial aggregations of wild fishes at farms.

The article presents a study that determines the farm abundance and spatio-temporal distribution of Pollachius virens in a fjord system with concentrated salmon cage aquaculture in Øksfjord, Northern Norway. It notes on the use of video counting to estimate the abundance of the saithe at various depths, of acoustic transmitters to study its movement in the farms, and of passive listening stations to monitor its spatio-temporal distribution. It reveals the abundance of the saithe in both farms during the release of tagged saithe and discloses its periodic movement from release farm to natural areas. It entails that understanding fish movements can minimise the outbreaks of disease in fish farms and in the populations of wild fish in adjacent areas.

Abstract: Submergence of Atlantic salmon (Salmo salar L.) in commercial scale sea-cages (1600–2000 m3) affected their behaviour, but did not alter growth rates, food conversion ratios, appetite, condition factor or fin condition in comparison with control cages held under similar environmental conditions. Four sea-cages each held 3300–4200 Atlantic salmon of 0.45 kg; two cages acted as controls, while two were submerged for 22 days with the roof held at 3 m depth. Salmon in the control cages mainly swam at similar depths to those maintained by submerged fish, resulting in both treatments experiencing similar temperature, light, salinity and dissolved oxygen levels. Submerged fish swam an average of 1.6 times faster (0.88 BL s− 1) and in more structured schools than control fish (0.55 BL s− 1). Specific growth rates (1.1–1.3% day− 1), appetite (0.8–1.2% body weight day− 1) and condition factor (1.10–1.15) were high, while food conversion ratios (0.6–1.0) and the incidence of fin damage were low in all cages, with no significant differences between the control and submerged treatments. Our results highlight the potential for submergence of salmon in sea-cages for short periods to avoid negative surface events. [Copyright &y& Elsevier]

Abstract: We constructed a Lagrangian (individual-based) model of the behaviour of Atlantic salmon in sea-cages. The behaviour of individual fish was affected by a set of environmental factors and the other individuals in the population. The model was based on behavioural parameters derived from literature and comparisons between model performance and published quantitative data sets. Simulations demonstrated that the model was able to predict the circular schooling patterns familiar to caged Atlantic salmon based on social interactions among the individuals and a motivation to keep a certain distance to the cage wall. The model accurately predicted the vertical distribution patterns of salmon over 24 h within a sea-cage when verified against three detailed observational data sets from autumn, implying that the model closely replicated behavioural responses toward the combined effects of temperature and light. Deviations seen in the comparisons were possibly due to unmodelled features in the feeding response. Potential uses of the model include: 1) increasing understanding of how environmental factors affect fish behaviour; 2) coupling with measurements in a model-based estimator structure to accurately estimate biomasses within sea-cages; and 3) predicting the welfare status of fish in sea-cages under specific environmental conditions. [Copyright &y& Elsevier]

Abstract: Short-term submergence of Atlantic salmon (Salmo salar) in full-scale (1000–1200 m3) sea-cages (10 m×10 m×15 m deep) affected swimming speeds, schooling behaviours and growth rates. Five hundred salmon of 1.7 kg average weight were placed in each of two surface control cages and two cages submerged so that the roof was at 5 m depth. One submerged cage was submerged and lifted repeatedly (2, 3 and 4 days) while the second cage was submerged continuously for 17 days. After the initial submergence periods, salmon were on-grown at the surface for 3 months to determine if differences in growth rates after submergence persisted. A lack of replication at the cage level precludes the drawing of firm conclusions, particularly with respect to differences in growth rates; repeated trials will alleviate this problem. Submerged salmon swam 1.5 times faster (0.83 BL s−1) than salmon in surface control cages (0.55 BL s−1). No evidence of acute buoyancy control problems was observed in the submerged fish and submergence did not affect feed intake. Specific growth rates (SGRs) were lower in the submerged cages (0.18–0.22) compared to the control cages (0.24–0.30) at the end of the submergence period, however, temperature differences between the control and submerged cages likely explained much of this difference. After 3 months of on-growing in surface cages following the end of the submergence period, no significant differences in SGRs (range 0.81–0.87) existed among the cages. Our results contrast with the strongly negative effects of submergence previously found by trials using small-scale enclosures. Salmon appear to tolerate submergence in commercial scale cages through swimming faster, possibly as a behavioural adaptation to generate hydrodynamic lift to counter negative buoyancy. [Copyright &y& Elsevier]

Abstract: Net deformations of sea-cages in two full-scale commercial Atlantic salmon (Salmo salar) farms (Varaldsøy, Norway, Hestur, Faroe Islands) were determined in relation to incoming currents of varying velocities. Ambient currents were measured with acoustic current meters, and net deformation behaviour and cage volume reductions were found by using depth sensors (pressure sensors) placed on strategic locations at the net cage. Cages deformed in current flow largely through lifting of the bottom netting and deformation of the front and back walls. Currents and therefore net volume reductions differed between the two farms: at Varaldsøy, the most critical current/deformation combination was 0.13ms−1 and an estimated 20% cage volume reduction, while at Hestur, current speeds of 0.35ms−1 caused a corresponding 40% cage volume reduction. Substantial net deformation and cage volume reductions may have significant implications for both fish production and welfare. Development of a real time net volume indicator could assist farmers in maintaining adequate cage volumes for optimal production and serve as an indicator of the optimal timing for net replacement if biofouling levels contribute significantly to deformation. [Copyright &y& Elsevier]

A test of the antifouling properties of Wattyl NetClear® was conducted on fish farms containing southern bluefin tuna ( Thunnus maccoyii ) during a 6-month period (February-July 2002). Wattyl NetClear® is a water-based synthetic latex-based coating where the active antifouling agent is a mixture of two isothiazolinones likely to affect both biochemical conditioning and bacterial colonisation. The development of fouling was monitored using underwater stereo-photogrammetry on 3 treated and 3 untreated net cages with the main factors treatment, depth and cage nested within treatment. A significant treatment and depth effect was found but variable through time and in some instances with significant cage effects. By the end of the study, the difference in fouling load between treated and untreated nets was 14.7%. In total 72% of all free-space data points were on treated nets. The dominating fouling organisms were Enteromorpha sp. and sponges with low settlement of blue mussel and paper oysters. Passive deposition of tuna faeces contributed significantly to the cover. The largest cover of fouling was observed in April-May with a dominance of sponges in June-July. Enteromorpha sp. dominated shallow depths while sponges dominated at deeper levels. Tuna faeces were distributed independent of depth but varied with time. The results showed that fouling of fish cages consisted of both active settlement and passive deposition, the latter independent on antifouling treatment. [ABSTRACT FROM AUTHOR]