Effect of water recirculation rate and initial stocking densities on competent larvae and survival of the Pacific oyster Crassostrea gigas in a recirculation aquaculture system

The present study evaluated the effect of initial stocking density and water recirculation rate on larval yield (percent of initially stocked larvae alive at the end of the experiment) and production of competent larvae (percent of initially stocked larvae alive at the end of the experiment retained on a sieve with mesh size 239 μm) of Crassostrea gigas in a recirculation aquaculture system (RAS). Different initial larval stocking densities (80, 160 and 320 larvae mL^?1) and water flow rates (100, 200 and 300 mL min^?1, totalling renewal rates of 60, 120 and 180 times day^?1 of water volume in culture tanks, respectively) were evaluated in 2.4-L tanks using a completely randomized design in a factorial scheme. The physicochemical parameters of the water (temperature, salinity, pH, dissolved oxygen and conductivity) were stable in all treatments during the experimental period. Our results demonstrated that the production of C. gigas larvae was feasible at the proposed densities. However, the water renewal rate affected both yield and competent larvae in the recirculation aquaculture system. Oyster cultures with densities of 160 larvae mL^?1 and flow of water of 300 mL min^?1 showed the best yield (89.34 ± 18.43%) and rate of competent larvae (84.09 ± 16.38%) and are therefore recommended with the aim of optimizing larvae cultivation.

     

Effects of water flow rate on growth rate,mortality and biomass return of abalone in slab tanks

The capital‐intensive nature of land‐based abalone farming demands that infrastructure be fully utilized. This study investigated whether the negative impact of high stocking density in shallow raceway tanks could be ameliorated by optimizing water flow. We quantified the effect of flow rate (87–246 L min^?1) on the performance of 2‐year‐old hybrid abalone (Haliotis laevigata and Haliotis rubra) held at two stocking densities (11400 and 7600 tank^?1). A 50% higher density yielded a 27% increase in biomass gain, despite a 10% growth reduction and 3% higher mortality. At the lower density, there was an optimal flow rate of approximately 200 L^?1, at which biomass gain was 474 kg and the feed conversion ratio (FCR) was 1.31. At the higher density, biomass gain (max = 658 kg) and FCR (min = 1.41) improved linearly with increasing flow, suggesting that an optimal flow rate exists at 246 L^?1 or beyond those tested. Increased oxygen availability with increasing flow is thought to have enhanced abalone performance, although flows greater than 200 L min^?1 may have reduced performance at low density due to feed washout and nutrient leaching. Overall, greater financial return per tank was favoured by the combination of high stocking density and high water flow.     

The effects of water temperature and stocking density on survival,feeding and growth of the juveniles of the hybrid yellow catfish from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂)

In this study, we aimed to investigate the effects of water temperature and stocking density on the survival, feeding and growth of the juveniles of the hybrid yellow catfish from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂) using the parameters as follows: survival rate (%), feeding rate (% day^?1), feed conversion ratio, specific growth rate (% day^?1), coefficient of variation (%), productivity (P, g m^?3 day^?1) and condition factor. We reared the juvenile fish (3.25 ± 0.21 g) at 12 water temperature levels and six stocking density levels (each level included three aquaria in two batches of experiments). The results showed that all groups survived at a temperature range of ≤35°C during a 46‐day experimental period, and they could achieve a high growth at a water temperature range of 26–32°C. The optimal temperature for growth was 29.8°C. Productivity peaked at a stocking density of 1.9 kg m^?3. Our results indicated that the hybrid is very suitable for commercial aquaculture.     

Growth and survival of the grouper Epinephelus coioides (Hamilton) at different loading rates in tanks

The effect of increasing fish loading (decreasing water exchange rate, while holding fish stocking density constant) on growth, survival and feed conversion ratio was determined for two size groups of the orange‐spotted grouper Epinephelus coioides (Hamilton). Fingerlings (124.3–145.8 g initial body weight) and subadults (990.6–1147.1 g initial body weight) were reared in 1‐m³ circular tanks for 14 weeks. For the fingerlings experiment, three loading rates of 0.5, 2 and 6 kg L^?1 min^?1 were used, while in the experiment with subadults, the loading rates were 1, 3 and 6 kg L^?1 min^?1. The mean growth rate of fingerlings ranged from 1.60 to 2.14 g fish^?1 day^?1, and survival was high (95–100%); however, there were no significant differences (P > 0.05) as a result of the different loading rates. Similar results were obtained in the subadults experiment, in which the growth rate (3.10–4.90 g fish^?1 day^?1) and survival (86.7–100%) were not significantly (P > 0.05) affected by the different loading rates. In both experiments, the feed conversion ratios were also not affected significantly by the loading rates. These results show that water exchange in aerated, flowthrough tanks can be reduced to as low as 6 kg L^?1 min^?1 without adversely affecting growth, survival and feed conversion of fingerling and subadult groupers.     

Stocking Density for Nursery Production of Redclaw Crayfish,Cherax quadricarinatus,in a Recirculating System

Redclaw crayfish, Cherax quadricarinatus, early juveniles were reared at different stocking densities in a closed recirculation system using 12-L plastic containers as rearing tanks. Initial stocking densities were 1.0, 1.5, 2.0, 2.5, and 3.0 per liter (66, 89, 111, 133, and 156 crayfish/m², respectively). Rearing period was 42 days. Each density was tested with five replicates. Shelter (0.112 m²) was added to double the surface area of rearing tanks. Animals were fed ad libitum twice a day with a commercial diet containing 35% crude protein. There were no significant differences (P < 0.05) in length and specific growth rate (SGR) among stocking densities. Final weight and daily weight gain, however, were significantly higher at the density of 66 per m² (1.0 per liter). Total biomass at harvest increased with density. Survival was affected by stocking density from day 28 onward, decreasing with density from 62.7 ± 7.6% obtained at 66 crayfish/m² to 44.85 ± 8.18% at 156 crayfish/m².     

Effects of size grading on growth, survival and cheliped injuries of signal crayfish (Pacifastacus leniusculus Dana) summerlings (age 0+)

Effects of size grading and stocking density on growth and survival of 3.5‐month‐old signal crayfish (Pacifastacus leniusculus Dana) juveniles were investigated in a 3 × 2 factorial design with size group (small, large and mixed) and stocking density (25 and 200 individuals m^?2) as factors for 90 days. Carapace length and wet weight growth of the juveniles were affected by the presence or absence of other size groups, stocking density and animal size. All factors had statistically significant interactions, which make the interpretation of the results more complicated. The smaller crayfish grew faster in the absence of large animals and larger animals benefited from the presence of smaller cospecies. Increasing density decreased the growth in length and weight. Survival (82–100%) was good in all groups. Subsequently, the within population dynamics was studied by selectively removing the largest individuals (selectively removing (SR) group). Effects on growth and survival of the remaining juveniles were evaluated on 6‐month‐old P. leniusculus juveniles reared in plastic tanks (100 juveniles m^?2) for 122 days. Size distribution manipulation was performed at days 34 and 70. Juveniles in SR group grew significantly faster in comparison with a control group (RR), from which juveniles were removed randomly. Also, the survival rate was significantly higher in the SR group than in the RR group. In conclusion, size grading of juvenile P. leniusculus either at the start of the experiment or repeatedly during the experiment increased growth performance of smaller animals in length and weight.     

Effects of stocking density on the nutrient budget and growth of the western king prawn (Penaeus latisulcatus Kishinouye) in a recirculating aquaculture system

Intensification in the commercial culture of prawns can have a significant impact on the water quality and hence on the survival, growth and the surrounding environment. The present study aims to evaluate the effects of stocking density on the water quality and performance of the western king prawns (Penaeus latisulcatus) and the nutrient budget of the culture environment. Four stocking densities of 4, 8, 16 and 32 prawns m^?2 were tested in 12 recirculating systems. Prawn weight and specific growth rate increased with decreasing stocking density, while the survival rate showed the reverse trend. The mean total ammonia nitrogen, nitrate nitrogen, total phosphorus and soluble reactive phosphorus were significantly higher (P<0.05) at the higher stocking density. The nutrient budget revealed that the prawns could assimilate only 9.34–20.13% nitrogen and 4.97–11.25% phosphorus of the total nutrient inputs. The drained water at harvest was the major sink of phosphorus and nitrogen at stocking densities of 4, 8 and 16, which accounted for 45.59–64.82% and 44.28–65.62% of the total inputs, respectively, while a significant proportion of nitrogen sunk into the sediment at 32 prawns m^?2. The study suggested that the stocking densities of western king prawns can be up to 16 prawns m^?2 in the recirculating water environment.     

The effect of stocking density on growth in the gilthead sea-bream, Sparus aurata (L.)

The effect of stocking density on growth and size variability in gilthead sea-bream, Sparus aurata (L.), was tested by growing juveniles at densities of 0.35 kgm^?3, 1.3 kg m^?3 and 3.2 kg m^?3. Fish in the highest density group grew 25% slower than fish in the lowest density group. The coefficient of variation of weight (standard deviation/mean) did not change during the experiment. The effect of size variability on growth rate was tested by creating groups with coefficients of variation of weights ranging from 0.11 to 0.32, and growing them at similar density (1.5 kg m^?3). No differences in growth rates between groups were found. Only the more heterogeneous group showed a large decrease in the coefficient of variation over time. It was concluded that growth in gilthead sea-bream, although negatively correlated to stocking density, did not seem to be related to intraspecific competition as assessed by changes in size variability.     

Nutrient removal efficiency of Hydropuntia cornea in an integrated closed recirculation system with pink shrimp Farfantepenaeus brasiliensis

In this study, we have tested the effect of seaweed stocking density in an experimental seaweed biofilter using the economically important red seaweed Hydropuntia cornea integrated with the cultivation of the pink shrimp Farfantepenaeus brasiliensis. Nutrient removal efficiency was evaluated in relation to seaweed stocking density (2.5, 4, 6 and 8 g fw L^?1). Total ammonia nitrogen (TAN) was the main nitrogen source excreted by F. brasiliensis, with concentrations ranging from 41.6 to 65 μM of NH₄⁺‐N. H. cornea specific growth rates ranged from 0.8 ± 0.2 to 1.4 ± 0.5% day^?1 with lowest growth rates at higher seaweed stocking density (8 g fw L^?1). Nutrient removal was positively correlated with the cultivation densities in the system. TAN removal efficiency increased from 61 to 88.5% with increasing seaweed stocking density. Changes in the chemical composition of the seaweed were analysed and correlated with nutrient enrichment from shrimp effluent. The red seaweed H. cornea can be cultured and used to remove nutrients from shrimp effluents in an integrated multi‐trophic aquaculture system applied to a closed recirculation system. Recirculation through seaweed biofilters in land‐based intensive aquaculture farms can also be a tool to increase recirculation practices and establish full recirculation aquaculture systems (RAS) with all their known associated benefits.     

Influence of Stocking Density on Growth and Physiological Responses of Beluga,Huso huso (Brandt, 1869), and Ship Sturgeon,Acipenser nudiventris (Lovetsky, 1828), Juveniles in a Flow‐through System

The influence of three different initial stocking densities (low stocking density [LSD] = 1.5 kg/m²; medium stocking density [MSD] = 3 kg/m²; and high stocking density [HSD] = 6 kg/m²) in flow‐through systems was evaluated on growth and welfare in beluga, Huso huso, and ship sturgeon, Acipenser nudiventris, juveniles for 2 mo. Fish were kept in 18 concrete square tanks (2.0 × 1.0 × 1.2 m³) at 22.3 ± 0.4 C and under a natural photoperiod. In both species, the growth performance in terms of final body weight, weight gain, specific growth rate, and feed intake significantly decreased with increasing stocking density (P < 0.05). In both species, the percent of neutrophils increased after 60 d of trial (P < 0.05). Moreover, hematocrit and white blood cell counts increased after 60 d of trial in ship sturgeon (P < 0.05). Plasma immunoglobulin significantly decreased with increasing stocking density in both species. Plasma insulin‐like growth factor I decreased with increasing stocking density in beluga; however, it was not affected in ship sturgeon. Overall, these results showed that the LSD group in both species demonstrated more homogeneous and higher growth rate than the MSD and HSD groups.     

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.     

A method for the quantification and optimization of hydrodynamics in culture tanks

A method was developed to quantify hydrodynamic mixing parameters, and to optimize the physical environmental conditions, in culture tanks. Improved mixing will result in better tank water quality, more efficient use of available volume by the culture animals (leading to optimal stocking densities and better feed management) and possibly reduced water pumping requirements. Experiments were conducted to determine the influence of a range of flow rates, residence times, water depths and stocking densities on hydrodynamics in juvenile turbot (Scophthalmus maximus (L.)) tanks. Decreases in water depth resulted in significant improvements in mixing and the efficiency with which the water was used, as indicated by reductions in dead volumes. A depth of less than 9.4 cm at a flow rate of 2 l min^–1 was expected to minimize dead volumes in the tank. This indicated that mixing was better in shallower tanks. Within the range 0–13 l min^–1, increased flow rate improved mixing at a constant depth of 9 cm (and water volume of 18.54 l) though increased flow rates greater than about 2.5 l min^–1 produced only small improvements in mixing. Within the range 0–50 fish per tank (equivalent to a mean stocking density of 0–1.84 kg m^–2), stocking density did not significantly influence mixing in tanks with a depth of 9 cm and flow rate of 2 l min^–1. Such depth reductions, for demersal species, may be a useful means to either decrease water use without reducing residence time, or alternatively to increase the flushing rate without increasing water use, at a given stocking density. The large changes in the efficiency with which the tanks were used, which were achieved with ease, indicates that attention to water mixing can give positive benefits to a wide range of land-based farm operators. Care must be taken when adjusting tank hydrodynamics, that water quality is maintained and that biological parameters such as stress levels, sunlight effects and feed management are optimal.     

Effects of dietary propolis and vitamin E on growth performance and antioxidant status in juvenile rainbow trout (Oncorhynchus mykiss) under different flow rate

The present study investigated the effects of propolis and vitamin E supplementation in diets of juvenile rainbow trout subjected to two different flow rates (0.9 and 2.1 L min^?1) on growth performance, and vitamin A, C and E concentrations in tissues as well as malondialdehyde (MDA) levels. Juvenile rainbow trout were fed with diets containing 10 and 30 g propolis kg^?1, 60 mg kg^?1 vitamin E (Rovimix E‐50 adsorbate; min.%50 dl‐α‐tokopherly acetate) and without supplemented basal diet for 12 weeks. Weight gain (WG) in the C group was significantly lower (P < 0.05) than P10, P30 and E60 groups at both flow rate treatments. At 2.1 L min^?1, specific growth rate (SGR) in the C group was significantly lower (P < 0.05) than other groups, but at 0.9 L min^?1, SGR of fish did not differ among the diets groups (P > 0.05). Survival rate (SUR) was higher in propolis and vitamin E supplemented diet groups (P < 0.05) than control diet group at 0.9 L min^?1. Fish fed on diet E60 had higher (P < 0.05) tissue vitamin E concentration than fishes fed on other diets groups. Vitamin C concentration in rainbow trout tissues was significantly affected by the 30 g propolis supplemented diet group (P < 0.05), followed by the 10 g propolis supplemented diet group (P < 0.05). MDA level of E60 group was found significantly decreased instead of different than other groups (P < 0.05). The results of Student's t‐test revealed that WG, SGR, SUR values, vitamin (A, C, E) concentrations and MDA levels of tissues were negatively affected by 0.9 L min^?1flow rate treatment in juvenile rainbow trout.     

Viability of a bottom‐set tray ocean nursery system for Holothuria scabra Jaeger 1833

Scaling up the hatchery production of juvenile sandfish Holothuria scabra is constrained by limited hatchery space and the associated high operational costs. To shorten the hatchery rearing phase, ocean nursery systems like floating hapa nets have been used with good prospects but with limitations during rough sea conditions. In this study, the potential of bottom‐set trays (0.14 m²) as an alternative ocean nursery system for early sandfish juveniles (0.5 ± 0.1 cm) was evaluated. The effects of stocking density and presence of artificial substrates (AS) on the growth and survival were determined in a 60‐day field experiment. Average length and growth rates at lower stocking density treatment (100 individuals tray^?1) were significantly higher (1.45 ± 0.22 cm; 0.03 ± 0.01 cm day^?1) than at higher stocking density treatments (400 and 500 individuals tray^?1) 0.95 ± 0.06 cm; 0.03 ± 0.004 cm day^?1) with or without AS (p < .05) respectively. The coefficient of variation in length (CV) at high stocking densities were significantly higher than at low densities (p < .05) and growth rate was strongly negatively correlated with density. Survival was significantly higher (55% ± 9%) in trays with AS across all stocking density treatments than in trays without AS (34% ± 2%). Results suggest that AS may have reduced intra‐ and interspecific interactions, resulting to significantly lower growth variations and higher survival. The bottom‐set tray with AS can be a practical alternative ocean nursery unit for rearing early sandfish juveniles particularly when the sea surface condition is rough. With improved design and density management, survival and growth may be further enhanced.     

Survival rates of tilapia, Oreochromis spilurus (Günther), fingerlings reared at high densities during winter using warm underground sea water

The study was conducted to determine the optimum stocking density for rearing tilapia. Oreochromis spilurus (Günther), fingerlings in tanks during winter using warm (21-26°C) underground sea water (37%o). Seawater-acclimated fingerlings with mean weight of 2 g were stocked in eighteen 400-1 fibreglass tanks at 750 and 1000 fish m^?3. Fish were fed at the rates of 2.5, 3.0 and 3.5% day^?1 of the fish biomass. After 83 days, the mean individual daily weight gain was significantly higher (P < 0.028) at stocking of 750 fish m^?3 than at 1000 fish m^?3. Feed conversion ratio was significantly higher at stocking of 1000 fish m^?3 than at 750 fish m^?3 and at feeding rate of 3.5% day¹ than at 2.5% day^?1. However, because no significant differences were observed on survival rates between the two stocking densities and among feeding rates, it is recommended that the stocking density of 1000 fish m^?3 and a feeding rate of 2.5% day^?1 be used for optimum production of tilapia fingerlings in tanks during winter using warm underground sea water.     

Effects of stocking density on haematological parameters,growth and fin erosion of great sturgeon (Huso huso) juveniles

The influence of stocking density (1, 2, 4, 6 and 8 kg m^?2) was investigated on haematological parameters, growth and fin erosion of great sturgeon (Huso huso) juveniles for a period of 8 weeks. The mean weight of fish at the start of trial was 93.13±1.04 g. After 8 weeks of rearing, the mean weight was 362.4, 319.7, 267, 242.1 and 211.1 in densities 1–8 kg m^?2 respectively. The results of this study showed that growth parameters, including condition factor, weight, weight gain, feed conversion ratio, specific growth rate and body weight increase, had a statistically significant difference among treatments (P<0.05). A significant difference (P<0.05) was observed in haematocrit, but the other haematological parameters, including red blood cells, white blood cells (WBC), haemoglobin concentration, mean corpuscular haemoglobin, mean corpuscular volume, mean corpuscular haemoglobin concentration and differential WBC count, showed no significant effect with stocking density (P>0.05). At the end of the experiment, stocking density had no significant effect on plasma cortisol and glucose concentration. The fin length (dorsal, anal, ventral, pectoral and caudal) of fish was measured to calculate the fin index. According to this index, dorsal, anal, ventral and pectoral fins showed no significant difference among treatments (P>0.05), but the erosion of the caudal fin was significantly different between fish held on 6 and 8 kg m^?2 (P<0.05). These results showed that rearing density has a major effect on the growth indices of H. huso. Unlike many other fish, great sturgeon exhibited lower stress responses to high stocking density. This indicates that they are more tolerable to rearing conditions in high stocking densities. With respect to the various effects that density causes on growth, fin erosion and physiological and haematological parameters, better understanding of these phenomena considering different levels of density could have a beneficial impact on many rearing steps of this species.     

Effects of stocking density and feeding duration in cage‐cum‐pond‐integrated system on growth performance,water quality and economic benefits of Labeo victorianus (Boulenger 1901) culture

We evaluated the effect of varying cage stocking density (60, 90 and 120 fish m^?3) and feeding duration (10, 30 and 60 min) in a cage‐cum‐pond‐integrated system on growth performance, water quality and economic benefits in Labeo victorianus culture. Interactions between stocking density and feeding duration significantly (P < 0.05) affected the fish growth performance and yields in the cages‐cum‐pond system. Stocking density of 60 fish m^?3 resulted in the highest growth in cages and in ponds regardless of the feeding duration, but produced lower yields than at stocking density 90 fish m^?3_. The lowest Apparent Food Conversion Ratio (AFCR) in cages occurred at stocking density of 60 fish m^?3 and feeding duration of 30 min. Growth performance in the open ponds declined with increased feeding duration of the caged fish. Survival in cages and in the open ponds decreased with increased cage density, but was not affected by feeding duration. Low dissolved oxygen were recorded, at stocking density of 120 fish m^?3, the lowest DO occurred when feeding of caged fish lasted 60 min. Growth performance, water quality and economic benefits in Labeo victorianus culture positively respond to interaction between stocking density and feeding durations.     

Effects of dietary Persian oak (Quercus brantii var. persica) fruit extract on survival,growth performance,haematological and immunological parameters in rainbow trout,Oncorhynchus mykiss,fingerlings

The aim of study was to evaluate the effects of jaft (internal layer of oak fruit) extract on growth, haematological and immunological parameters in rainbow trout fingerlings. A total of 360 fish (average weight 6.25 g, total length 7.75 cm) were randomly distributed in 12 fibreglass tanks (stocking density: 1.04 g L^?1) with flow rate of 8 L min^?1. The ethanolic extraction of jaft was taken, and, then, a basal diet was supplemented with 0 (control), 0.5, 1 and 2 g kg^?1 to formulate four experimental diets. After 8 weeks, blood sampling was performed for haematological and immunological parameters. While immunological parameters such as IgM and lysozyme showed their lowest level in control group, their highest amounts appeared in 2 g kg^?1 group. C3, C4 and alternative complement activity increased in fish fed 2 g kg^?1 extract compared to control (P ? 0.05). Haematological parameters such as white blood cell, red blood cell, haemoglobin and haematocrit were enhanced in experimental groups (P ? 0.05). Survival and growth indices did not show significant changes in experimental treatments (P ? 0.05). Results indicated feeding rainbow trout with Persian oak extract at 0.5, 1.0 and 2.0 g kg^?1 levels significantly enhance the immunological parameters.     

Suitability of cage culture for Pacific abalone Haliotis discus hannai Ino production in China

Pacific abalone (Haliotis discus hannai Ino) aquaculture is a thriving industry in China. This study describes a novel submerged cage culture system for abalone rearing in Fujian, South China. The cage consisted of five vertical slots that were oriented perpendicular to the flow of water. The slots were separated by six vertically connected plastic plates for abalone attachment and shelter at the bottom of the cage. Experiment 1 was designed to determine the appropriate stocking density at the start of the abalone sea‐based production cycle. Eight‐month‐old hatchery reared and size‐graded juveniles were transferred to the sea‐based culture system. For different stocking densities, shell length of juveniles obtained in this novel culture system on 2, 3.5 and 5 months, respectively, was compared with shell lengths obtained in a traditionally multi‐tier basket culture system. In Experiment 2, daily growth rates (DGRs) in shell length and biomass in terms of wet weight of 2‐year‐old abalones reared in cage and tiered basket culture systems were compared over a 6‐month period. Results of Experiment 1 showed that growth of abalone in the cage culture system is density‐dependent; the mean final shell length of juveniles obtained was 6.7–15.9% higher than in tiered baskets system even at the same initial stocking density. In Experiment 2, DGRs in shell length of 53.83–78.38 μm day^?1 obtained in cage system were significantly higher than that in tiered baskets (P < 0.01). And in terms of wet weight biomass, it was 1.48–3.01 times higher in the cage system compared with the traditional system. Abalone survival was more than 87.5% in both culture systems in both experiments. Advantages of the newly established cage culture system included better growth performance of the animals reared and potential improvement of rearing conditions, such as improved water flow velocity and dissolved oxygen.     

Production and yield of Penaeus semisulcatus (de Haan) cultured at different densities

Two trials were conducted with two sizes, grow‐out (80.0 mg b.w.) and fattening (5.0 g b.w.), of Penaeus semisulcatus to compare the production and yield of shrimp cultured at different stocking densities within an indoor running‐seawater system. In the first experiment, postlarvae were cultured at 50, 100, 150 and 200 m^?3 for 68 days, while in the second experiment, juveniles were cultured at 24, 50, 74 and 100 m^?3 for 126 days. The results of the two experiments showed significant decrease in weight of shrimp as the stocking density increased. During the grow‐out stage, no statistical differences were observed on survival rates among the shrimp stocked at different densities. Thus, as the primary factor to consider at this stage is the number of shrimp produced, it is recommended to use a density of 200 shrimp m^?3. During the fattening stage, the survival rate at the highest density was statistically lower than the other three densities. The mean yield was 437.02, 869.16, 1217.62 and 1446.78 g m^?3 for shrimp stocked at 24, 50, 74 and 100 m^?3 respectively. Although the average harvest size of juveniles at the lowest stocking density was statistically higher than those stocked at the highest stocking density, both sizes (18.12 and 16.67 g) will be classified as one size group in the market, i.e. medium. As the yield significantly increases as the stocking density is increased, it is therefore recommended that the stocking density for the fattening stage be 100 shrimp m^?3.