Sea Cages Research Articles

Effect of sea cage aquaculture on the length, weight, and condition of wild Atlantic cod Gadus morhua

Wild fish have been shown to associate with sea cage aquaculture and consume waste feed; however, little is known about the effects of waste feed consumption on wild fish. We used Atlantic cod Gadus morhua collected in the direct vicinity of sea cages and reference Northwest Atlantic Fisheries Organization divisions, either outside the direct vicinity (‘local division’) or completely removed from aquaculture (‘outside divisions’), to compare length, weight, and condition for cod ages 2 to 4. Concentrations of vegetable oil-based fatty acids (linoleic acid and α-linolenic acid) were then used as biomarkers for waste feed consumption to determine their role in explaining differences in length, weight, and Fulton’s condition index among cage-associated cod. Age 2 cage-associated cod were in lower condition than age 2 cod from the local division and lighter than age 2 cod from all outside divisions. Age 3 cage-associated cod were comparable to age 3 cod from the local division but in lower condition than age 3 cod from all outside divisions. However, age 4 cage-associated cod were longer and heavier than age 4 cod from the local division, but in lower condition than age 4 cod from 2 of 3 outside divisions. Additionally, there were positive relationships between fatty acid concentrations and length and weight for age 2 cage-associated cod, but no significant relationships for age 3 or 4 cage-associated cod. Results suggest the effects of waste feed consumption are contradictory but not consistent enough to disrupt established growth and condition patterns among divisions.

Biogeochemical impacts of fish farming on coastal sediments: Insights into the functional role of cable bacteria.

Fish farming in sea cages is a growing component of the global food industry. A prominent ecosystem impact of this industry is the increase in the downward flux of organic matter, which stimulates anaerobic mineralization and sulfide production in underlying sediments. When free sulfide is released to the overlying water, this can have a toxic effect on local marine ecosystems. The microbially-mediated process of sulfide oxidation has the potential to be an important natural mitigation and prevention strategy that has not been studied in fish farm sediments. We examined the microbial community composition (DNA-based 16S rRNA gene) underneath two active fish farms on the Southwestern coast of Iceland and performed laboratory incubations of resident sediment. Field observations confirmed the strong geochemical impact of fish farming on the sediment (up to 150 m away from cages). Sulfide accumulation was evidenced under the cages congruent with a higher supply of degradable organic matter from the cages. Phylogenetically diverse microbes capable of sulfide detoxification were present in the field sediment as well as in lab incubations, including cable bacteria (Candidatus Electrothrix), which display a unique metabolism based on long-distance electron transport. Microsensor profiling revealed that the activity of cable bacteria did not exert a dominant impact on the geochemistry of fish farm sediment at the time of sampling. However, laboratory incubations that mimic the recovery process during fallowing, revealed successful enrichment of cable bacteria within weeks, with concomitant high sulfur-oxidizing activity. Overall our results give insight into the role of microbially-mediated sulfide detoxification in aquaculture impacted sediments.

Fatigue vulnerability of sea cage to storm wave loads

Fatigue vulnerability of sea cage to storm wave loads

The variation of intestinal autochthonous bacteria in cultured tiger pufferfish Takifugu rubripes.

Intestinal autochthonous bacteria play important roles in the maintenance of the physiological homeostasis of animals, especially contributing to the host immune system. In the present study, the variation of autochthonous bacterial community in the intestinal tract of 2-7 months-old tiger pufferfish Takifugu rubripes and bacterial communities in the seawater of recirculating aquaculture system (RAS) and the following offshore sea cage aquaculture system (OSCS) were analyzed during the aquaculture period from May to October 2021. Proteobacteria was found to be the most dominant phyla in both intestinal and seawater bacterial communities, which accounted for 68.82% and 65.65% of the total bacterial abundance, respectively. Arcobacter was the most core bacterial taxon in the intestinal bacterial community, with the most dominant abundance (42.89%) at the genus level and dominant positions in co-occurrence relationships with other bacterial taxa (node-betweenness value of 150). Enterococcaceae was specifically enriched in the intestinal bacterial community of pufferfishes from RAS, while Vibrionaceae was enriched in the intestinal bacterial community from OSCS. The F-values of beta diversity analysis between intestinal and seawater bacterial communities generally increased from May (6.69) to October (32.32), indicating the increasing differences between the intestinal and seawater bacterial communities along with the aquaculture process. Four bacterial taxa of Weissella sp., Akkermansia muciniphila, Dietzia sp. and Psychrobacter pacificensis had significant correlations with immune response parameters, and they were suggested to be the indicators for immune status and pathological process of pufferfish. The knowledge about the specific core bacteria, potentially pathogenic bacteria and the change of bacterial community in the intestinal tract of cultured pufferfish is of great scientific significance and will contribute to the understanding of intestinal bacterial homeostasis and biosecurity practice in pufferfish aquaculture.

Why vaccines fail against Piscirickettsiosis in farmed salmon and trout and how to avoid it: A review.

Piscirickettsiosis is the most severe, persistent, and damaging disease that has affected the Chilean salmon industry since its origins in the 1980s. As a preventive strategy for this disease, different vaccines have been developed and used over the last 30 years. However, vaccinated salmon and trout frequently die in the sea cages and the use of antibiotics is still high demonstrating the low efficiency of the available vaccines. The reasons why the vaccines fail so often are still debated, but it could involve different extrinsic and intrinsic factors. Among the extrinsic factors, mainly associated with chronic stress, we can distinguish: 1) biotic including coinfection with sea lice, sealions attacks or harmful algal blooms; 2) abiotic including low oxygen or high temperature; and 3) farm-management factors including overcrowding or chemical delousing treatments. Among the intrinsic factors, we can distinguish: 1) fish-related factors including host's genetic variability (species, population and individual), sex or age; 2) pathogen-related factors including their variability and ability to evade host immune responses; and 3) vaccine-related factors including low immunogenicity and poor matches with the circulating pathogen strain. Based on the available evidence, in order to improve the development and the efficacy of vaccines against P. salmonis we recommend: a) Do not perform efficacy evaluations by intraperitoneal injection of pathogens because they generate an artificial protective immune response, instead cohabitation or immersion challenges must be used; b) Evaluate the diversity of pathogen strains in the field and ensure a good antigenic match with the vaccines; c)Investigate whether host genetic diversity could be improved, e.g. through selection, in favor of better and longer responses to vaccination; d) To reduce the stressful effects at the cage level, controlling the co-infection of pathogens and avoiding fish overcrowding. To date, we do not know the immunological mechanisms by which the vaccines against P. salmonis may or may not generate protection. More studies are required to identify what type of response, cellular or molecular, is required to develop effective vaccines.

Salmon lice (Lepeophtheirus salmonis) in the stomach contents of lumpfish (Cyclopterus lumpus) sampled from Norwegian fish farms: Relationship between lice grazing and operational conditions

Cleaner fish are commonly used as a control measure against salmon lice infestations in salmonid farms. Lumpfish (Cyclopterus lumpus) is the most common cleaner fish species used in Norwegian farms. However, little is known about how different operational, including environmental, conditions affect the salmon lice grazing efficacy by lumpfish. In this paper, we analyse salmon lice (Lepeophtheirus salmonis) in the stomach contents of a large sample of more than 20,000 lumpfish from 80 different Norwegian farms. We investigate the proportion of lumpfish with salmon lice and the mean number of salmon lice in the stomach contents of the lumpfish. We further explore how the salmon lice contents vary with different factors like lumpfish weight, weight of salmonids, salmon lice abundance in the cage, cloud cover, and sea temperature. We find that 3.1% of the 24,693 lumpfish contained salmon lice. Most of the lumpfish with salmon lice in their stomach contents contained few (one or two) lice, while there were a few lumpfish which contained many salmon lice. We find more salmon lice in the stomach contents with increasing abundance of salmon lice in the sea cage, lower weight of the salmonids, and in clear weather. Interestingly, for the relationship between lumpfish weight and salmon lice in the stomach contents, we find increased salmon lice grazing from ca. 5 g up to an optimal weight of ca. 40 g, and then a decrease from 40 g. Surprisingly, we find no relationship between sea temperature and salmon lice per lumpfish. We find more salmon lice in the stomach contents of the lumpfish with comparatively high condition. By studying the factors associated with most efficient salmon lice grazing, our paper contributes to understanding how different operational factors affect salmon lice grazing by lumpfish. For controllable factors, the results thus contribute to guiding the best practice for use of lumpfish as a salmon lice control measure.

Lesions of the biliary system in Atlantic salmon (Salmo salar L.).

Lesions of the biliary system in Atlantic salmon (Salmo salar L.).

Influence of Supplemental Dietary Cholesterol on Growth Performance, Indices of Stress, Fillet Pigmentation, and Upper Thermal Tolerance of Female Triploid Atlantic Salmon (Salmo salar).

The salmon aquaculture industry must be proactive at developing mitigation tools/strategies to offset the potential negative impacts of climate change. Therefore, this study examined if additional dietary cholesterol could enhance salmon production at elevated temperatures. We hypothesized that supplemental cholesterol could aid in maintaining cell rigidity, reducing stress and the need to mobilize astaxanthin muscle stores, and improving salmon growth and survival at high rearing temperatures. Accordingly, postsmolt female triploid salmon were exposed to an incremental temperature challenge (+0.2°C day-1) to mimic conditions that they experience in sea cages in the summer, with temperature held at both 16 and 18°C for several weeks [i.e., 3 weeks at 16°C, followed by an increase at 0.2°C day-1 to 18°C (10 days), then 5 weeks at 18°C] to prolong their exposure to elevated temperatures. From 16°C onwards, the fish were fed either a control diet, or one of two nutritionally equivalent experimental diets containing supplemental cholesterol [+1.30%, experimental diet #1 (ED1); or +1.76%, experimental diet #2 (ED2)]. Adding cholesterol to the diet did not affect the salmon's incremental thermal maximum (ITMax), growth, plasma cortisol, or liver stress-related transcript expression. However, ED2 appeared to have a small negative impact on survival, and both ED1 and ED2 reduced fillet "bleaching" above 18°C as measured using SalmoFan™ scores. Although the current results suggest that supplementing salmon diets with cholesterol would have few/minimal benefits for the industry, ≤ 5% of the female triploid Atlantic salmon used in this study irrespective of diet died before temperature reached 22°C. These latter data suggest that it is possible to produce all female populations of reproductively sterile salmon that can withstand summer temperatures in Atlantic Canada.

Research Article: Development of the Control System for Artificial Reproduction of Fish Populations Based on a Complex of Neroendocrinological Research and Biotech Innovations

The participation of the hypothalamic-hypophysial neurosecretory system (HHNS) in fish reproduction using light, electron microscopy and immunocytochemistry was established by ecologo-histophysiological studies for the first time in the world literature. At the beginning of passing fish migrations a violation of the HHNS basic osmoregulative function, causing habitat change is revealed. Simultaneously the HHNS causes the neurotropic effect on the central nervous system (CNS) arousal in the form of a dominant state of "Migration impulse." At the beginning of spawning, HHNS also initiates spawning behavior and completes it by participating in the body's protective-adaptive reactions to natural physiological stress. The functional role of the HHNS in fish reproduction is to initiate energy-intensive (reproductive) processes of migratory and spawning behaviors and to complete spawning by suppressing the hyperactivity of target glands, which ensures the body's transition to energy-saving plastic exchange. The analysis of the key role of the HHNS in the integration of fish reproduction by the self-regulation principle has allowed the development of a constructive working scheme. New biotech methods of managing breeding time, rates of survival and growth of valuable fish species were developed on this basis. They are presented in the form of 10 inventions. To stimulate sex maturation, drugs of isolated anterior and posterior pituitary lobes were developed and introduced in sturgeon industry, increasing the extent of their fish-breeding use by 15% and saving the pituitary up to 40%. To delay puberty, a method of industrial fish breeders reservation in the critical salinity habitat of 4-8‰, both in seawater and in table salt solutions has been developed. On this basis, a full-system method of sturgeon and salmon fish populations reproduction, covering all stages of farm biotechnology has been developed. It is carried out by mass breeders reservation in sea cages, obtaining there offspring and, after the river fish-farm growing youngs to their readiness for migration, the final cultivation them in sea cages gardens till large life-resistant youngs. For the implementation of the proposed industrial biotechnology and year-round fish farming a new installation of recirculating aquaculture systems (RAS) hatcheries and farms was developed by means of the off-season underground conditioning of fish cultivation habitat and by the principle of natural-industrial engineering ecology. Due to the general aim ‒ increasing the efficiency biotechnology of reproduction and logical relationships, all developments are integrated into the system of biotech management of fish population reproduction.

Review Article: Systemic Lupus Erythematosus in Gynecology

The participation of the hypothalamic-hypophysial neurosecretory system (HHNS) in fish reproduction using light, electron microscopy and immunocytochemistry was established by ecologo-histophysiological studies for the first time in the world literature. At the beginning of passing fish migrations a violation of the HHNS basic osmoregulative function, causing habitat change is revealed. Simultaneously the HHNS causes the neurotropic effect on the central nervous system (CNS) arousal in the form of a dominant state of "Migration impulse." At the beginning of spawning, HHNS also initiates spawning behavior and completes it by participating in the body's protective-adaptive reactions to natural physiological stress. The functional role of the HHNS in fish reproduction is to initiate energy-intensive (reproductive) processes of migratory and spawning behaviors and to complete spawning by suppressing the hyperactivity of target glands, which ensures the body's transition to energy-saving plastic exchange. The analysis of the key role of the HHNS in the integration of fish reproduction by the self-regulation principle has allowed the development of a constructive working scheme. New biotech methods of managing breeding time, rates of survival and growth of valuable fish species were developed on this basis. They are presented in the form of 10 inventions. To stimulate sex maturation, drugs of isolated anterior and posterior pituitary lobes were developed and introduced in sturgeon industry, increasing the extent of their fish-breeding use by 15% and saving the pituitary up to 40%. To delay puberty, a method of industrial fish breeders reservation in the critical salinity habitat of 4-8‰, both in seawater and in table salt solutions has been developed. On this basis, a full-system method of sturgeon and salmon fish populations reproduction, covering all stages of farm biotechnology has been developed. It is carried out by mass breeders reservation in sea cages, obtaining there offspring and, after the river fish-farm growing youngs to their readiness for migration, the final cultivation them in sea cages gardens till large life-resistant youngs. For the implementation of the proposed industrial biotechnology and year-round fish farming a new installation of recirculating aquaculture systems (RAS) hatcheries and farms was developed by means of the off-season underground conditioning of fish cultivation habitat and by the principle of natural-industrial engineering ecology. Due to the general aim ‒ increasing the efficiency biotechnology of reproduction and logical relationships, all developments are integrated into the system of biotech management of fish population reproduction.

Real-time monitoring of cause-specific mortality- and losses in industrial salmon farming

Mortality represents a major challenge in farming of salmon in open sea cages. Production takes place in large cages with up to 200,000 fish and offers no other treatment of individual fish than euthanasia of moribund fish. Improvements need to take place as preventing future problems. The described project was initiated with the objective to develop a standardized system for classification of mortality and losses in aquaculture. The WHO's International Classification of Disease (ICD) has served as a model tool, with adaptation into an animal production system. The system is based on causality with the underlying cause of death as the principal variable to monitor. The system describes the fish-farmer as the primary user, and with additional opportunities for the supply industry, authorities, and research to utilize anonymized data. The classification system is organized with an alphanumeric code in a hierarchical structure with three levels: six main categories, causal subcategories at level 2, and in principle, unlimited underlying causes at level three. The hierarchy allow both registration and retraction of data at each of the three different levels. The proposed code is conceptuated to also allow classification of other losses than mortality, thus being able to monitor the effect of the underlying cause for all areas of losses, including quality downgrading, reduced growth, reduced feed conversions etc. A code covering all areas of losses will enable the fish farmer to monitor the total effect of underlying causes, both in biological and monetary terms. Through systematic monitoring it will be possible to target resources in the direction of losses with the highest impact and the interventions with the highest pay-back. By establishing a unique code, it will further be possible to standardize registrations between area of losses within a company, between companies and regions, and potentially also between countries.

Effect of replacement of fishmeal by soybean products with attractants supplementation on the growth performance, feed utilization, body composition, plasma physiological responses and hepatic antioxidant abilities of juvenile golden pompano Trachinotus ovatus

A feeding experiment was carried out to develop a practical diet with low fishmeal for juvenile golden pompano (Trachinotus ovatus) by substituting fishmeal protein with soybean products mixture. Six isocaloric (17.6 KJ g−1) diets were designed by replacing 0 (FM100), 5 (FM95), 10 (FM90), 15 (FM85), 20 (FM80), and 25% (FM75) of the fishmeal with soybean products mixture (SPM) (soybean meal and soybean protein concentrate). The experiment diets were supplemented with 1.5%, 3%, 4.5%, 6% and 7.5% squid paste as attractants or palatability enhancer. The experimental fish (6.9 g) were cultured in sea cages (1.0 m × 1.0 m × 1.5 m) with 25 fish in each cage. Fish were fed the corresponding experimental diets to satiation twice daily for 8 weeks. At the end of the feeding experiment, no differences were found in the final weight and weight gain (WG) of fish fed FM100, FM85, FM80, and FM75 diets (P > 0.05). The WG was significantly (P < 0.05) better in the fish-fed FM95 diet compared to FM100 and FM75 diets. FCR in diet FM95 and FM90 was significantly (P < 0.05) than that of FM80 and FM75, but these values were not significantly different from those in other treatments. Although the condition factor value in diets FM90, FM85, and FM80 was significantly (P < 0.05) higher than that of FM100, these values were not significantly different from the rest of the other groups. There was no statistical difference in SGR, FR, VSI, and survival rates among different dietary treatments. The plasma AST activity was significantly lower in fish fed FM90 diet compared to fish fed with control, FM85, FM80, and FM75 (P < 0.05). There was no significant difference in plasma AST among all dietary treatments except FM95 and FM90. In contrast, the plasma AKP activity showed the opposite trend. Compared with the control, the fish-fed FM80 and FM75 diets had significantly decreased plasma cholesterol, triglyceride total protein, albumin, and globulin level (P < 0.05) while significantly increasing plasma COR levels (P < 0.05). There was no significant difference in ALT, Urea and glucose values among all treatments. No statistical difference was observed among the FM100, FM80, and FM75 treatments for those of plasma LYZ activity, C3, and C4 levels. The hepatic T-AOC and SOD activities were significantly increased in fish fed the FM90 diet (P < 0.05) compared to those in fish fed with FM100 diet. According to the current experiment, it can be concluded that SPM supplemented with SP could partially substitute fishmeal (25%) for juvenile golden pompano without any adverse symptoms.

Effects of dietary methionine on growth and body composition, indicators of digestion, protein metabolism and immunity, and resistance to heat stress of abalone Haliotis discus hannai

The present study was conducted to investigate the effects of dietary methionine on growth performance, protein metabolism, immunity and resistance to heat stress of abalone Haliotis discus hannai. Seven isonitrogenous (about 32% of crude protein) and isolipidic (about 3% of crude lipid) diets were designed with graded levels of methionine (0.46%, 0.77%, 0.97%, 1.19%, 1.41%, 1.71% and 2.07%, respectively). The experimental diets were named as M1 (control), M2, M3, M4, M5, M6 and M7, respectively. An 84-day feeding trial was conducted in sea cages (40 cm × 35 cm × 70 cm) for abalones (initial body weight: 4.10 ± 0.01 g), which were fed once every two days. The results showed that the biomass gain (BG) of abalone significantly increased (from 560.20 g to 643.83 g) with the increasing dietary methionine levels from 0.46% to 1.19%, and then decreased (from 643.83 g to 484.29 g) (P < 0.05). Based on the broken-line regression analysis of BG, the requirement of dietary methionine for abalone was determined to be 0.99% (dry matter of diet). The highest trypsin activity (862.10 U/mg prot.) and α-Amylase activity (0.28 U/mg prot.) in the intestine of abalone were observed in the M4 and M5 group, respectively. In the digestive gland, the gene expression of mtor, s6k and eif4e showed a significant quadratic trend with the increasing dietary methionine levels, and all of them reached their highest values in the M4 group. The highest mRNA level of gcn2 was observed in the M1 group. The glutathione content and total anti-oxidative capacity in cell-free hemolymph (CFH) were significantly increased as dietary methionine levels increasing from 0.46% to 1.19%, and then decreased (P < 0.05). The lowest gene expression level of keap1, nf-κb and tnf-α, and the highest gene expression level of nrf2 and iκbα in the digestive gland were found in the M4 group. After the heat stress test at the end of feeding trial, the minimum falling rate (19.44%) and the highest gene expression level of hsp70 and hsp90 in the digestive gland of abalone were found in the group with 1.19% of dietary methionine. In conclusion, appropriate dietary methionine (0.97%–1.19%) could improve the growth, protein synthesis, immunity and resistance to heat stress of abalone.

Elemental Fingerprinting of Wild and Farmed Fish Muscle to Authenticate and Validate Production Method.

In the context of expanding fish production and complex distribution chains, traceability, provenance and food safety tools are becoming increasingly important. Here, we compare the elemental fingerprints of gilthead seabream (Sparus aurata) muscle from wild and different aquaculture productions (semi-intensive earth ponds and intensive sea cages from two locations) to confirm their origin and evaluate the concentrations of elements with regulatory thresholds (Cu, Hg, Pb and Zn). Using a chemometric approach based on multi-elemental signatures, the sample origin was determined with an overall accuracy of 90%. Furthermore, in a model built to replicate a real-case scenario where it would be necessary to trace the production method of S. aurata without reliable information about its harvesting location, 27 of the 30 samples were correctly allocated to their original production method (sea-cage aquaculture), despite being from another location. The concentrations of the regulated elements ranged as follows: Cu (0.140–1.139 mg/Kg), Hg (0–0.506 mg/Kg), Pb (0–2.703 mg/Kg) and Zn (6.502–18.807 mg/Kg), with only Pb presenting concentrations consistently above the recommended limit for human consumption. The present findings contribute to establishing elemental fingerprinting as a reliable tool to trace fish production methods and underpin seafood authentication.

Effect of cage size on oxygen levels in Atlantic salmon sea cages: A model study

The supply of dissolved oxygen (DO) to salmon in sea cages depends on many interacting factors including biomass density, temperature and current speed. With other factors being equal, hypoxic conditions are more likely to arise in large cages compared to small. In this work, a mathematical model of DO in sea cages is used to analyse the effect of horizontal cage size in particular. It is shown and quantified how the DO level at key locations in the cage depend on cage radius and current speed, and the fraction of the cage volume with hypoxic conditions is estimated as a function of cage radius, current speed and temperature.The results of this study give new insight into how oxygen conditions are affected when cage size is scaled up or down. Although conditions at actual aquaculture sites are highly variable and complex, the results can help forecast the effect of increasing cage size at existing sites, and can help guide the planning of new production sites with regard to oxygen supply.

Oxygenation effects on temperature and dissolved oxygen at a commercial Atlantic salmon farm

As climate change continues to warm oceans and exacerbate deoxygenation, coastal ecosystems and anthropogenic activities that occur there are left vulnerable. Fish cultured in ocean net pens are increasingly subjected to oxygen stress. Aeration and oxygenation have been utilized to improve oxygen conditions in pond aquaculture; however, their use in open ocean net pens is still in its infancy. In this study, liquid oxygen was distributed through the NetOx Net system within sea cages in a commercial Atlantic salmon (Salmo salar) farm located off Saddle Island, Nova Scotia (Canada). Real-time sensors were used to measure temperature and oxygen before oxygenation, between oxygenation and the onset of de-stratification due to mixing, and after mixing had resulted in full de-stratification. Oxygenation likely resulted in the upwelling of cold deep water, lowering the cage temperature by ∼4 ℃ which in turn increased oxygen solubility and decreased fish metabolism (though no significant change in growth was observed); these factors resulted in an overall increase in oxygen concentrations by ∼1.5 mgL−1. Following de-stratification, the effects of the oxygenation system were diluted, and mixing due to oceanographic processes dominated the system. As climate change increases hypoxia in coastal regions, where aquaculture practices continue to expand, oxygenation systems will become commonplace. Therefore, it is important to understand whether they will work in an environment that is open to other elements.

In lumpfish We Trust? The Efficacy of Lumpfish Cyclopterus lumpus to Control Lepeophtheirus salmonis Infestations on Farmed Atlantic Salmon: A Review

In this review, we have systematized current knowledge about the effect of stocking lumpfish (Cyclopterus lumpus) as cleaner fish to control Lepeophtheirus salmonis infestations on farmed Atlantic salmon (Salmo salar L.). The review was prompted by recent reports in which the usefulness of lumpfish has been doubted, and the urgent need to investigate whether common lumpfish can be used to reduce L. salmonis numbers on farmed Atlantic salmon by active grazing on this species. Available published data clearly indicate that lumpfish graze on L. salmonis, and can significantly lower the lice burden in Atlantic salmon farming. It is possible to enhance the lice grazing behavior of lumpfish with the assistance of live feed conditioning prior to sea pen transfer, and with selective breeding. Data indicate that lice grazing of lumpfish is size dependent, and grazing effect is low for lumpfish larger than 200–250 g. Observations from large-scale rearing of Atlantic salmon in open sea cages in Norway, Iceland, the Faroe Islands, and Scotland also indicate that lumpfish can be effective in lowering infestations of L. salmonis on salmon. Overall, this present review reveals that lumpfish can actively contribute to lower numbers of L. salmonis on farmed Atlantic salmon.

Influence of dietary fermented Folium mori on growing performance, lipometabolism and disease resistance of golden pompano Trachinotus ovatus

Folium mori, as a plant unconventional feedstuff, are comparatively available due to cost-effectiveness, whereas their usage as aquafeed in pure form is restricted owing to the great fibre and antinutritional factors (ANFs) levels. Thereof, several methods of processing are introduced to remove antinutrient factors from the plant products, leading to improvement of bioactivity and digestibility. The assay was completed to evaluate the method of fermentation and the role of dietary fermented Folium mori (FFM) in golden pompano. Each of 5 diets with FFM at contents of 0.0%, 2.0%, 4.0%, 6.0% and 8.0% (D0.0, D2.0, D4.0, D6.0 and D8.0) was fed to the fishes with original body weight of 9.02g in triplicate sea cages for 56 days. The outcomes revealed that FFM in D4.0 and D6.0 elevated the growing performance of the fishes and the growing performance of D4.0 was remarkably improved in contrast to D0.0 and D2.0(P < 0.05). Whole body lipidic levels were obviously elevated when the diet FFM contents were below 8.0% (P < 0.05), whereas the contents of muscular moisture were generally reduced. In addition, FFM significantly increased serum high density lipoprotein (HDL) and remarkably reduced overall triglyceride (TG) in D2.0 to D6.0(P < 0.05). Moreover, FFM remarkably elevated the activities of lipase of stomach and hepatopancreas in contrast to D0.0 (P < 0.05) as well as intestinal tryptic enzyme in the entire FFM groups (P < 0.05). Eventually, FFM remarkably ameliorated disease-resistant characters of golden pompano to Vibrio harveyi in D4.0 and D6.0 (P < 0.05) and the RPS in D4.0 was optimal. To sum up, the present research displayed favorable role of FFM in growing performance, digestion, lipometabolism and disease-resistant characters, and the recommendation as to the supplementation content of diet FFM in compound feed of juvenile golden pompano is 4.0% as per the experiment status herein.

Estimation of Bluefin Tuna (Thunnus thynnus) mean length in sea cages by acoustical means

This paper proposes an indirect method to estimate Bluefin Tuna (Thunnus thynnus) biomass in cages using acoustic techniques. Two Simrad EK60 echosounders working at 120 and 200 kHz and a stereo camera were used to obtain target strength (TS) to fork length (FL) relationships for both operating frequencies. The equipment was placed at the bottom of a floating cage, facing towards the surface to record the ventral aspect of fish. The acoustic and optical recordings were automatically analysed and the combination of acoustic and optical results provided unequivocal TS-FL assignments. Good relationships between TS and FL were obtained for both frequencies even without discriminating data from different fish tilts and without using beam directivity compensation. Stronger correlations were obtained for compensated TS at 200 kHz when reduced tuna swimming tilt was considered. TS measurements were compared to MFS numerical predictions for a Bluefin swimbladder model, with the simulation results showing good agreement with experimental measurements. The results allow the mean tuna length to be predicted in growing or fattening cages from acoustic data raising the possibility of improving production management and of providing a useful tool for catch control estimations made by international organisations (like ICCAT) and government bodies.

BOOSTING BIOMASS GAIN AND MEAT QUALITY OF RAINBOW TROUT Oncorhynchus mykiss (Walbaum, 1792) - AN APPROACH FOR FOSTERING ROMANIAN AQUACULTURE

Rainbow trout Oncorhynchus mykiss (Walbaum, 1792) is one of the most widely cultured fish species, with a high market value. Although in the Black Sea there is a well-established tradition of cage farming in Turkish waters, in Romania rainbow trout farming has been limited to inland mountain areas. Whereas there is an increasing interest of Romanian economic operators to engage in sea cage farming, this research aimed at testing the adaptation of rainbow trout to the Romanian Black Sea marine environment, determining its growth rate, establishing the optimal size for transfer to saltwater, and increasing meat quality. The research was performed for 7 months, during the cold season, and comprised two batches of O. mykiss individuals transferred to marine water from a mountain trout farm (with initial mean biomasses of approximately 300 g and 180 g, respectively). Upon completion of the experiment, growth parameters showed values much higher compared to freshwater culture, and the biomass gain was remarkable in both batches (reaching final biomasses of approximately 1,700 g and 1,600 g, respectively), the results indicating smaller fish as best fitted for transfer to marine water. The carotenoid-enriched feed provided to the fish resulted in a highly nutritious meat, with the much-appreciated pink colorization