Premiers resultats de l'elevage en cages de Tilapia nilotica (L.) dans le Lac Kossou,Cote d'IvoirePreliminary results of cage rearing Tilapia nilotica (L.) in Lake Kossou,Ivory Coast

The experimental rearing of T. nilotica in 1-m³ cages floating in Lake Kossou, Ivory Coast, was performed between March 1974 and April 1975. The fish were fed water-stable pellets (24.7% protein), the daily ration generally varying between 6 and 3.4% of the ichthyomass present. Fingerlings (9–55 g each) were stocked at densities of 200–400 fish/m³. They reached commercial size (more than 200 g) within 4–6 months, depending on the biomass present in the cage (stocking density and average individual weight of fish), as well as on limological conditions. The average annual mortality was 5.9%. Annual production varied from 36 to 64 kg/m³. The feed conversion rate averaged 2.8. A reduction of the daily ration for fish larger than 40 g reduced this value.Fingerlings should average at least 20–30 g in weight at initial stocking of the cage. Two crops a year can then be easily realized. If only male fish are reared, three harvests per year appear to be possible, increasing the annual cage production of fish close to 200 kg/m³ with proper management.The possible development of T. nilotica cage culture is actually hampered due to the lack of adequate fish feed available commercially, and to the lack of sufficient quantities of calibrated fingerlings throughout the year.     

Growth, Survival, and Feed Conversion Rates of Hatchery-Reared Mutton Snapper Lutjanus analis Cultured in Floating Net Cages

Abstract.— The aquaculture performance of mutton snapper Lutjanus analis raised in floating net cages was assessed by measuring their growth, survival, and feed conversion rates during a growout trial conducted in a 3.2‐ha saltwater lake in the Florida Keys, Florida, USA. Approximately 10,500 hatchery‐reared finger‐lings were stocked in two circular, high‐density polyethylene (HDPE) net cages of 7‐m diameter × 7‐m deep (300 m²) and 10‐m diameter × 7‐m deep (600 m³) dimensions. Cages were stocked at 25 fish/m³ (3.2 kg/m³) and 5 fish/m³ (0.72 kg/m³), respectively. Fish grew from a mean of 16.5 g to 302.8 g (25.6 cm TL) in 246 days in the former cage and from a mean of 42.3 g to 245.6 g (23.8 cm TL) in 178 d in the latter cage. Growth rates in weight were best expressed by the following exponential equations: cage 1 (high stocking density): W = 20.716 e^0.0112x (r²= 0.83); cage 2 (low stocking density): W = 38.848 e^0.0118x (r²= 0.81). Length‐weight data indicate that hatcheryraised, cage‐cultured mutton snapper are heavier per unit length than their wild counterparts. There was no significant difference (P < 0.05) between the slopes of the two lines, indicating that fish in the two cages grew at the same rate. The length‐weight relationships for mutton snapper stocked in cages 1 and 2 are expressed, respectively, by the equations W = 0.000009 L ^3.11 (r²= 0.99) and W = 0.000005 L ^3.22 (r²= 0.97). Overall feed conversion rate for both cages combined was 1.4. Approximately 10% of the fish sampled exhibited some degree of deformity, particularly scoliosis. Overall survival rate was 70%. Results suggest that L. analis has potential for aquaculture development in net cage systems.     

Effect of Density at Harvest on the Growth Performance and Profitability of Hatchery‐reared Spotted Rose Snapper,Lutjanus guttatus,Cultured in Floating Net Cages

This study evaluated the effect of the density at harvest on the performance and profitability of hatchery‐reared spotted rose snapper cultured in cages. The fish were stocked at harvest densities of 15, 20, and 22 kg/m³ in cages of 222 and 286 m³. More than 39,000 snapper fingerlings with an initial weight of 14 g were stocked. The fish were fed an extruded diet and cultured over a 360 d period. The thermal growth coefficient ranged from 0.04 to 0.05 and survival was 95% for all treatments, with the highest final weight (436.8 g) observed for fish reared at a density of 20 kg/m³. The allometric value b indicated that hatchery‐raised, cage‐cultured snapper were heavier than their wild counterparts. The major costs were feed (ranging from 44.7–45.9%), labor (22.4–32.6%), and seed costs (20.2–26.1%). The total production cost ranged from US$ 6.5 to US$ 7.5/kg. The baseline scenario was not economically feasible. However, a 10% increase in the sales price resulted in increases in the internal rate of return (183%) and net present value (US$ 97,628.9). These results suggest that L. guttatus has the potential for commercial production in cages.     

Economic production of estuary grouper, Epinephelus salmoides Maxwell,reared in floating net cages

The factors affecting production of estuary grouper, Epinephelus salmoides, in floating net cages are discussed. The concept of economic production in cage culture is outlined. Economic production of estuary grouper could be achieved by providing a suitable culture site with good water quality; ensuring proper farm management and regular maintenance of cages; preventing disease and ensuring efficient treatment; providing optimum stocking density, a balanced diet, optimal feeding frequency; manipulating fish behaviour by providing artificial hides; and manipulating physiological characteristics, e.g. by the use of growth promoters.The paper futher describes environmental parameters, such as dissolved oxygen content, water temperature, salinity, water current, bacteria count, pH, and bottom sediments, as important factors in site selection. Their effects on the growth and production of fish are discussed and their optimal levels determined. The problems involving management and maintenance of the farm are also outlined. The main problem in cage culture is fouling which demands considerable labour and money for cage maintenance. Other problems such as predators, poaching, and cannibalism are discussed at length. It is suggested that by manipulation of stocking density, production could be increased. The optimal stocking rate was found to be 60 fish/m³ which gives a high yield of marketable fish. Stocking could be further intensified by providing artificial hides using used car tyres. The net production could be increased by 230% if hiding space of 251 cm³ per fish was provided and the stocking density increased to 156 fish/m³. Although formulated feeds enhanced growth by 27.1% over that of groupers fed on trash fish, the production cost was much higher, rendering the use of formulated feeds alone uneconomical for commercial fish culture. Growth promoters such as 17α-methyltestosterone and nitrovin have been found to promote growth of young estuary grouper by 43.4 and 62.8%, respectively.Using various combinations of culture techniques, it was shown that net production could be increased from 23.76 kg/m³ using conventional culture methods to 136.75 kg/m³ with a combination of hiding space, heavy stocking, appropriate feeding frequency and formulated feeds incorporating growth promoters. The production time was also shortened considerably from 6 months to 2.7 months.Cost-benefit analysis of the eight culture techniques tested indicated that the production cost could be reduced from US$2.00/kg with conventional methods to as low as US$1.28/kg using a sophisticated method. However, based on current market proces, the conventional culture technique was still economically feasible, as the net income over total capital costs was 33.3%. Improvements of the conventional culture technique will increase the ratio of net income over total capital costs by 1–3 times.     

墨瑞鳕大棚水泥池养殖技术试验

为调整上海郊区的水产养殖结构,开发水产新品种,提升养殖效益,2021年在上海市郊某合作社开展了墨瑞鳕(Maccullochella peelii)大棚水泥池养殖试验。试验采用2口大棚水泥池,投放经标粗培育的平均体质量为150 g/尾的墨瑞鳕大规格鱼种,放养密度为25尾/m²,全程投喂粗蛋白质质量分数43%的海水鱼膨化饲料。经过13个月养殖,共收获墨瑞鳕商品鱼9 576 kg(单位产量13.3 kg/m³,平均规格696.2 g/尾),饲料系数为1.58,单位产值为1 030元/m³。墨瑞鳕大棚水泥池养殖试验成功,对水产养殖结构调优具有一定的借鉴作用。     

Cage‐pond integration of African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) with carps

Cage‐pond integration system is a new model for enhancing productivity of pond aquaculture system. A field trial was conducted using African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) in cages and carps in earthen ponds. There were four treatments replicated five times: (1) carps in ponds without cage, (2) tilapia at 30 fish m^?3 in cage and carps in open pond, (3) catfish at 100 fish m^?3 in cage and carps in open pond, (4) tilapia and catfish at 30 and 100 fish m^?3, respectively, in separate cages and carps in open pond. The carps were stocked at 1 fish m^?2. The cage occupied about 3% of the pond area. The caged tilapia and catfish were fed and the control ponds were fertilized. Results showed that the combined extrapolated net yield was significantly higher (P < 0.05) in the catfish, tilapia and carps integration system (9.4 ± 1.6 t ha^?1 year^?1) than in the carp polyculture (3.3 ± 0.7 t ha^?1 year^?1). The net return from the tilapia and carps (6860 US$ ha^?1 year^?1) and catfish, tilapia and carps integration systems (6668 US$ ha^?1 year^?1) was significantly higher than in the carp polyculture (1709 US$ ha^?1 year^?1) (P < 0.05). This experiment demonstrated that the cage‐pond integration of African catfish and Nile tilapia with carps is the best technology to increase production; whereas integration of tilapia and carp for profitability.     

Evaluation of a Low‐head Recirculating Aquaculture System Used for Rearing Florida Pompano to Market Size

A low‐head recirculating aquaculture system (RAS) for the production of Florida pompano, Trachinotus carolinus, from juvenile to market size was evaluated. The 32.4‐m³ RAS consisted of three dual‐drain, 3‐m diameter culture tanks of 7.8‐m³ volume each, two 0.71‐m³ moving bed bioreactors filled with media (67% fill with K1 Kaldness media) for biofiltration, two degassing towers for CO₂ removal and aeration, a drum filter with a 40‐µm screen for solids removal, and a 1‐hp low‐head propeller pump for water circulation. Supplemental oxygenation was provided in each tank by ultrafine ceramic diffusers and system salinity was maintained at 7.0 g/L. Juvenile pompano (0.043 kg mean weight) were stocked into each of the three tanks at an initial density of 1.7 kg/m³ (300 fish/tank). After 306 d of culture, the mean weight of the fish harvested from each tank ranged from 0.589 to 0.655 kg with survival ranging from 57.7 to 81.7%. During the culture period, the average water use per kilogram of fish was 3.26 or 1.82 m³ per fish harvested. Energy consumption per kilogram of fish was 47.2 or 22.4 kwh per fish harvested. The mean volumetric total ammonia nitrogen (TAN) removal rate of the bioreactors was 127.6 ± 58.3 g TAN removed/m³ media‐d with an average of 33.0% removal per pass. Results of this evaluation suggest that system modifications are warranted to enhance production to commercial levels (>60 kg/m³).     

Growth and production of the Amazonian tambaqui in fixed cages under different feeding regimes

Experimental culture of the native Amazonian fish tambaqui, Colossoma macropomum, in fixed cages was carried out over a period of 8 months, in Lake Urubu (Rio Grande do Norte, Brazil), to assess the viability of fixed cage culture of tambaqui and to test the influence of diet on growth rates. Nine synthetic net cages (1 m³) were each stocked with 45-day-old fish (mean weight 3 g; mean total body length 51 mm) at a density of 34 fry m^–3. During the first 2 months of culture, fish were fed a balanced formulated feed on an as-fed basis at the rate of 5% body weight day^–1. During months 3–8 this continued for fish in treatment 1 while those in treatment 2 were fed tropical regional fruits, on a wet weight basis at the rate of 5% body wt day^–1. Fish in treatment 3 were given no supplementary feed. Monthly biometric measurements were made on all fish. Fixed cage fish culture was shown to be a viable and simple technique. Survival in all treatments was 100%. With balanced supplementary feed, production was 14.4 kg m^–3, compared with 4.9 kg m^–3 and 2.1 kg m^–3, respectively, in the treatments where fish were fed with fruits and were not given any supplementary feed.     

Preliminary study on the effects of exclusion of wild fauna from aquaculture cages in a shallow marine environment

Previous investigations into the environmental impacts at a shallow-water oligotrophic marine experimental cage aquaculture site in Western Australia have found no accumulation of organic material, and limited changes in macrofaunal communities. It was hypothesised that wild fish populations in the area consumed particulate wastes emanating from the cage, thus reducing the benthic impacts. An experiment was designed to quantify the accumulation of organic material on the seabed occurring in the presence and absence of wild fauna. Three treatments were arranged in duplicate, cages without exclusion nets (normal situation) (CAGE-FISH); cages surrounded by a 35-mm mesh exclusion net (preventing wild fish access to the sea bed and water column near the cage) (CAGE-FISH-EXCL); and empty cages surrounded by exclusion nets (to control for effects from the exclusion net) (CAGE-EXCL). In addition, four reference sites without cages (REF) were sampled. Following baseline sampling, rainbow trout (Oncorhynchus mykiss) were stocked into the CAGE-FISH and the CAGE-FISH-EXCL treatments at an initial stocking density of 2.4 kg m⁻³. The experiment was terminated after 62 days, at a final stock density of 5.6 kg m⁻³. Sampling found significantly greater accumulation of nutrients and fine sediments under the cages enclosed in the exclusion net than in other treatments and sites. Levels of organic carbon deposition at cages with exclusion nets was found to be 4.5±1.0 g C m⁻² day⁻¹ (mean±S.E.) compared to 0.7 to 1.1 g C m⁻² day⁻¹ at control and reference sites.The accumulation of nutrients at the CAGE-FISH-EXCL sites was correlated to distinct changes in macrofaunal community composition, with a sharp increase in overall macrofaunal abundance and a growing dominance of capitellid polychaetes. Based on a comparison between sedimentation rates within and outside excluded areas, the proportions of the total sedimenting nutrients consumed by wild fish were calculated to be 40% to 60%. It was concluded that in the natural coastal system of Western Australia or comparable environments, wild fish are potential important consumers of cage aquaculture waste materials. The fact that sediment C, N and P did not increase below cages with fish and no exclusion nets suggests that the benthic fauna, including surface grazing fish, at these sites were able to assimilate much of the remaining total sedimentary nutrients.     

Sea bream culture in Egypt; status, constraints and potential

Marine fish farming in Egypt began in 1976 with the culture of gilthead sea bream, (Sparus aurata) as this fish was notably adaptable to brackish and marine pond conditions. Today, marine fish and shrimp farms amount to about 19,000 ha, out of which 42% is already in production while the rest, i.e., 58% is still under construction. In 1997, cultured gilthead sea bream production of 2,250 tons made up 3% of the 75,000 tons total aquaculture catch. In polyculture, usually with the grey mullet and sea bass, gilthead sea bream contributed 440 kg ha^–1 to the total yield of 1,700 kg ha^–1 (26%) over a period of 16 months. For the same period, the yield of monoculture ponds averaged 100 kg ha^–1, while in marine cages, yields ranged from 4–10 kg m³. In 1996–1997, fry of 0.25–1 g and fingerlings 1–10 g with a total of 3 million, were collected from the wild and 1 million fry were produced in the three marine hatcheries out of the four existing ones. The development of sea bream culture in Egypt is now severely inhibited by the shortage of seeds and adequate feeds. Exports of both sea bream and sea bass, during 1994–1996 averaged 1,300 tons per year.     

The Influence of Stocking Density on the Swimming Behavior of Adult Atlantic Cod,Gadus morhua,in a Near Shore Net Pen

Cage design and stocking density are important aspects of aquaculture farm design, therefore understanding how fish behave at different stocking densities is critical information for farm managers. In this study, high resolution acoustic telemetry was used to investigate the swimming behavior of adult Atlantic cod, Gadus morhua, that were stocked at four densities (5, 10, 25, and 45 kg/m³). Acoustic tags were placed into the abdominal cavity of five fish per density treatment so their swimming behavior could be continuously monitored throughout the study. An array of hydrophones made it possible to calculate the position of each fish in three dimensions, at ～2–5 sec intervals, for 4–30 d. Three underwater cameras were used to obtain additional data about the distribution of fish in the cage during the daytime. At the lowest density, the cod spent the majority (64.3 ± 0.08%) of their time in the bottom third of the net pen. As density increased, the fish moved higher in the water column, and this behavior was most evident at night, at all densities. At no time throughout the entire study were there any obvious occurrences of schooling behavior, even at the highest density (45 kg/m³).     

Evaluation of brook trout production in a coldwater recycle aquaculture system

Brook trout (Salvelinus fontinalis) are a commercially important coldwater species reared in Wisconsin and the Midwestern United States. Brook trout are raised by private, tribal, state, and federal fish hatchery facilities in Wisconsin. Approximately 10% of private coldwater aquaculture operations are presently raising brook trout of various strains for stocking uses and a limited amount for food markets. Growing brook trout to a larger size, if they can be reared in a shorter time span, may present a potential new sector for the aquaculture market in the Midwestern US. The present study reports hatchery production attributes, i.e., growth, survival, fin condition, feed efficiency, water chemistry requirements and general husbandry of Lake Superior strain (Nipigon) brook trout reared in a recirculating aquaculture system (RAS), operated at an average temperature of 13 °C. The recycle system at NADF reared 1379 kg of brook trout over a 10-month period from fingerling (9 g) to market size (340–454 g). The trout grew faster (0.84 g/day and 0.64 mm/day) in the RAS than fish cultured in traditional flow-through tank culture utilizing ground water at 7.6 °C (0.14 g/day and 0.35 mm/day). Final average weight of RAS fish was 260 g, while the flow-through fish averaged 65 g. Final tank densities for the RAS averaged 40.4 kg/m³ while flow-through tanks averaged 31.2 kg/m³. Throughout the project, feed conversions in the RAS ranged from 0.9 to 1.3. Water quality variables such as TAN, nitrite, DO, temperature, TSS, CO₂, ph, etc. were within safe limits for brook trout and will be discussed. It does appear from this initial research project that market size brook trout can be raised successfully in a recycle system within a similar time frame as a rainbow trout produced in a Wisconsin typical flow-through facility.     

Productivity and Economics of Nile Tilapia Oreochromis niloticus Cage Culture in South-East Brazil

ABSTRACT

Fish cage culture is an intensive, continuous-flow fish farming system, allowing intensive exploitation of water bodies with relatively low capital investment. This study aimed to determine the production function of Nile tilapia, Oreochromis niloticus, in cages; the profit-maximizing biomass at 300–400 and 500–600 fish per m³ for cages of different volumes; and the influence of water body conditions in fish performance. Feed intake, survival rate, and water temperature were monitored daily; dissolved oxygen, pH, and transparency of water were monitored each 15 days. Caged tilapia were fed daily on commercial, floating pellets (32% crude protein) at 0900, 1300, and 1700, and feeding rate was adjusted based on weight gain and survival rate. Data were analyzed statistically by ANOVA (P = 0.05) and regression analysis; the Mitscherlich function was chosen to represent the production function. Carrying capacity of both stocking densities reached 200 kg/m³ and no differences were found (P > 0.05) regarding accumulated biomass and individual average weight over time. The larger stocking density yielded larger accumulated biomass and had better feeding efficiency and no differences between individual average weights of fish at both densities were observed (P > 0.05). Profit-maximizing biomass at 500–600 fish/m³ was 145 kg/m³ and at 300–400 fish/m³ was 121 kg/m³. Cage farming of Nile tilapia at 500–600 fish/m³, individual average weight 283 g, presented many advantages: optimization of space and production time, better feed efficiency, higher fish production per unit volume of cages, and increased profitability.     

Growout production of camouflage grouper, Epinephelus polyphekadion (Bleeker), in a tank culture system

Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m³-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m^?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m^?3, 540.2 ± 150.82 g at 15 fish m-^?3 and 513.3 ± 134.52 g at 45 fish m^?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish^?1 day^?1, with mean weights of 1.49 ± 0.74 g fish^?1 day^?1 at five fish m^?3 through 0.53 to 2.38 g fish^?1 day^?1, 1.32 ± 0.57 g fish^?1 day^?1 at 15 fish m^?3 to 0.48-3.32 g fish^?1 day^?1 and 1.31 g fish^?1 day^?1 at 45 fish m^?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m^?3. The yield in terms of kg fish produced m^?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m^?3. The yield averaged 17.3 ±0.53 kg m^?3 at a stocking density of 45 fish m^?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.     

New production strategy for silver perch (Bidyanus bidyanus); over‐wintering fingerlings in a tank‐based recirculating aquaculture system

Slow growth and losses to bird predation and infectious diseases in winter can compromise the profitability of silver perch farming. To evaluate over‐wintering silver perch (Bidyanus bidyanus) in a recirculating aquaculture system (RAS), fingerlings (38 g) were stocked in either cages in a pond at ambient temperatures (10–21 °C) or tanks in the RAS at elevated temperatures (19–25 °C) and cultured for 125 days. Mean survival (96%), final weight (146 g), specific growth rate (1.07% day^?1) and production rate (28.1 kg m^?3) of fish in the RAS were significantly higher than for fish over‐wintered in cages (77%, 73 g, 0.53% day^?1, 11.1 kg m^?3). Fish from both treatments were then reared in cages for a further 129 days. Final mean weight of fish originally over‐wintered in the RAS was 426 g, while fish over‐wintered in cages were only 273 g. To determine optimal stocking densities, fingerlings (11.8 g) were stocked at 500, 1000 or 1500 fish m^?3 in tanks in the RAS and cultured for 124 days. Survival was not affected, but growth was significantly slower and feed conversion ratio higher at 1500 fish m^?3 compared with 500 or 1000 fish m^?3. Results demonstrate that over‐wintering silver perch in an RAS can produce large fingerlings for grow‐out in early spring. This strategy could eliminate bird predation, reduce losses to diseases and shorten the overall culture period.     

Effects of stocking density of Labeo rohita on survival, growth and production in cages

Labeo rohita (139.92 ± 0.76 mm/24.33 ± 0.45 g) was reared for 92 days in floating square cages (10 m² area, 1.5 m height) in a pond (2 ha) at six stocking densities (5, 7.5, 10, 15, 20 and 25 fish m^?2) each with 3 replicates. Fish were fed daily once in the morning with rice polish and groundnut oil cake (1:1) in dough form at 3 % of the total body weight. Survival ranged from 96 to 100 % in different stocking densities. Final average body weight, average body weight gain, mean daily body weight gain and SGR decreased (P < 0.05) with increasing stocking density. Conversely, final biomass, biomass gain and FCR increased (P < 0.05) with increasing stocking density. The highest growth rate of fish could be achieved up to 60 days at 5 fish m^?2 and 92 days at other densities. The reduced growth rate at 10–25 fish m^?2 for 60 days of culture indicated that stress is related to size and density of the fish, suggesting that utmost care is required to reduce the stress at high densities. Maximum production and profit was observed at the highest stocking density. Non-lethal levels of water and soil qualities at different sites (cage premises, and 20 and 200 m away from cage area) suggested that cage aquaculture could be done safely covering 0.9 % of pond area. Production of advanced fingerlings in cages was found a viable alternative to their culture in pond.     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m^?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day^?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m^?3. The gross yield (4.5–20.55 kg cage^?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m^?3 cage for larger size fish demand in a short period and 200 fish m^?3 for higher gross production with supplementary feed.     

Moderate stocking density does not influence the behavioural and physiological responses of rainbow trout (Oncorhynchus mykiss) in organic aquaculture

Welfare in farmed fish got particular attention during the last decades from both governmental and public sides. In aquaculture context, welfare concerns are mainly related to handling procedures, water quality and stoking densities. In Europe, authorities had to clarify the threshold limits of stocking densities to maintain fish good welfare, including for organics aquaculture through the EC regulation 710/2009. However, effects of stocking density on fish welfare are complex and sometimes contradictory. Moreover, there is a lack of knowledge about the impact of density on fish welfare in organic aquaculture. Thus, the aim of the study is to asses welfare state of rainbow trout (Oncorhynchus mykiss) at two initial stocking densities (low density, LD: 12 kg/m³ and high density, HD: 17 kg/m³) fed using organic feed by combining the monitoring of growth performances, behaviour (swimming activity) and physiological indicators (i.e. cortisol, glucose, lactate, hematocrit, red blood cellule count and lysozyme). At the end of experiment, the stocking density reached 21 kg/m³ and 30 kg/m³ for the LD and HD respectively. Overall, growth performances, swimming activity and level of physiological indicators of stress and welfare were similar between HD and LD over the experiment duration. To conclude, we observed no alteration of fish welfare between the two stocking densities monitored. This study suggests that a final stocking density of 30 kg/m³ can be considered for organic aquaculture of rainbow trout respecting welfare.     

Economic analysis of cobia (<Emphasis Type="Italic">Rachycentron canadum</Emphasis>) cage culture in large- and small-scale production systems in Brazil

Economic feasibility studies regarding aquaculture systems are relatively scarce, but they are important to potential investors and for the allocation of resources for research and technological development. This study evaluated the economic viability of cobia cage culture from the actual investment and operational costs of a large-scale operation off Recife, northeastern Brazil (industrial system; IS), and a family-run farm located in a near-shore area of Rio de Janeiro (familiar system; FS). The IS had twenty-four 1607 m³ floating cages deployed at a depth of 24 m, while the FS had six 75 m³ wooden cages installed in a sheltered 6- to 7-m-deep area. Analyses of profitability (gross revenue, operational profit, cost price and break-even production) and investment (net present value—NPV; and payback time) were performed. An analysis of sensitivity was also carried out. The IS required an initial investment of approximately US$ 1.5 million dollars and was more sensitive to FCR, selling price and productivity fluctuations than the FS. The FS required a relatively small initial investment (US$ 16,000 dollars), which makes it more flexible to variations in production parameters and market fluctuations. The NPV was positive for both systems, and the payback times were estimated to be 3.88 years for the IS and 2.07 years for the FS. Therefore, given the assumptions of this study, cage culture of cobia in Brazil may be considered economically feasible in offshore production systems and in near-shore, FSs. Governmental support through decreased import taxes is recommended as a way to accelerate the early development of the cage culture of marine fish in Brazil.