Stocking density for the intensive rearing of juvenile crayfish, <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> (Astacidae), using <Emphasis Type="Italic">Artemia</Emphasis> nauplii to supplement a dry diet from the onset of exogenous feeding

Recent advances in intensive rearing of astacid juvenile crayfish have greatly improved the results. This challenges the current application possibilities of the studies performed previously, and new research on density is required. A 100-day experiment was carried out under controlled conditions to evaluate density effects on survival and growth rates of juvenile crayfish in optimal conditions of feeding. Juvenile stage 2 Pacifastacus leniusculus were stocked in fibreglass tanks (1 m², 200 l water) at 20 ± 1°C and fed a dry diet for salmonids supplemented with restricted amounts of Artemia nauplii. Stocking densities were 100, 300, 600 and 1,000 crayfish m⁻². Mean survival rate was reduced significantly with increased stocking density, ranging from 86.33% (100 m⁻²) to 39.13% (1,000 m⁻²). All checks showed that at the lowest initial density (100 m⁻²) animals grew significantly faster those at higher densities, recording a final carapace length of 15.28 mm and weight of 1.08 g. Among the treatments of 300, 600 and 1,000 m⁻² no differences were found either in carapace length or in weight throughout the experimental period, with a final mean growth of 14 mm carapace length and 0.72 g weight. The final proportion of animals with chelae autotomy rose significantly with increasing stocking density, ranging from 14.44% (100 m⁻²) to 41.45% (1,000 m⁻²). This study shows that diet is a decisive factor for stocking successfully high densities under controlled conditions and provides useful information to set adequate densities in accordance with the production objectives.     

Does space matter? Optimizing stocking density of Holothuria arguinensis and Holothuria mammata

Stocking density is an important factor affecting growth in aquaculture. The main objectives of this study are to evaluate the effects of different stocking densities on Holothuria arguinensis and Holothuria mammata's growth and determine the optimal density. Four different stocking densities were selected for H. arguinensis (1, 3, 5 and 7 ind/0.2 m²) and three for H. mammata (6, 10 and 12 ind/0.5 m²). Growth (specific growth rate (SGR) and growth rate (GR)), weight change, coefficient of variation and productivity were estimated, additionally the feeding rate on H. mammata. Growth on H. arguinensis decreased as the stocking density increased, showing the higher growth at the stocking density of 1 ind/0.2 m² (SGR: 1.24%/day ± 0.16 and GR: 0.94 g/day ± 0.05), with a 104.65% (±9.98) of weight change. The best H. mammata growth was registered at 10 ind/m² (SGR: 0.56% ± 0.04%/day and GR: 0.48 ± 0.04 g/day) and 25.48% (±1.52) of weight change. H. mammata feeding rate decreased as stocking density increased. Crowding stress could be considered the main factor affecting the sea cucumbers growth and performance on our study. The optimal stocking density for H. arguinensis and H. mammata under tank‐based conditions were established as 1 ind/0.2 m² and 5 ind/0.5 m² respectively. The critic biomass for H. arguinensis (471.65 g/m²) and for H. mammata (988.11 g/m²) were reached during the experiment at the fourth and fifth weeks respectively. Therefore, to ensure and increase growth of these species under tank, their biomass should be maintained under those thresholds.     

Effects of photoperiod and stocking density on survival,growth and physiological responses of narrow clawed crayfish (Astacus leptodactylus)

Photoperiod and stocking density are critical factors influencing the performance of decapod crustaceans in culture, however, their influence on growth; survival and biochemical physiology of crayfish broodstock have rarely been considered. Analysis of biochemical physiology in crayfish broodstock during the non‐breeding season provides information on the energy storage requirements of broodstock for increased survival and reproductive output. Growth rate, moulting frequency, survival and biochemical physiology were measured in Astacus leptodactylus broodstock that were cultured at three different photoperiods (18L:6D; 12L:12D; and 6L:18D) and three stocking densities (10, 20 and 40 individuals m^?2) during non‐breeding season. Survival of crayfish was highest at 18L:6D photophase and 10 m^?2 (100%) than other treatments. Survival in the high stocking density was high when combined with 18L:6D photophase, but weight gain (WG) and specific growth rate (SGR) were higher at shorter photophase and lower stocking density. Longer photophase (18L:6D) increased stress responses, characterized by increased haemolymph lactate and glucose levels. Stocking density did not affect proximate composition of crayfish; however, individuals cultured at 18L:6D photophase had higher lipid content than other photoperiod treatments. The study demonstrated that culturing A. leptodactylus at 18L:6D photophase and 10 m^?2 is critical for increased survival of broodstock.     

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.     

Growth performance of pengba,Osteobrama belangeri (Valenciennes, 1844) and water quality changes during fingerling rearing with varied stocking density in large outdoor concrete tanks

Fingerling rearing of pengba, Osteobrama belangeri, was conducted at varied densities for 90 days in 12 outdoor concrete tanks (10 m × 5 m × 1 m). The tanks, grouped into four triplicated treatments, were stocked with fry at 20, 30, 40 and 50 fry m^‐3; and designated as control, T‐1, T‐2 and T‐3 respectively. Tanks were filled up to 90 cm depth. Evaporation loss compensated fortnightly. Fish sampling and monitoring of water quality parameters done at fortnight intervals. Survival varied between 71.5% and 84.0% in treatments. Both survival and total length significantly reduced with increasing densities from control to T‐2 (p < .05), while no differences were observed between T‐2 and T‐3 (p > .05). Similarly, significant reductions in final body weight and specific growth rate were observed with increased densities and these values further reduced in T‐3 than T‐2 (p < .05). Such results corroborated the inverse relationship between stocking density and growth. Gross biomass yields in two higher densities (T‐2 and T‐3), despite their lower survivals, were significantly higher than the two lower densities. The numbers of fingerlings harvested were 35, 74 and 112% higher than the control in T‐1, T‐2 and T‐3 respectively. The lowest size obtained even at the highest density (T‐3) was of 7.0 ± 1.0 cm and 3.99 ± 0.17 g, which can be considered as ideal grow‐out stocking size of pengba. Therefore, the study showed feasibility of stocking up to 50 fry m^‐3 for rearing from fry to fingerling stage. However, the other lower densities may be used in case of requirement of larger fingerlings.     

Effects of stocking density on the survival,growth and physical injury of Marsupenaeus japonicus juveniles in a flowing water aquaculture system

Stocking density is a biotic factor affecting the production of cultivated animals in aquaculture. Herein, a rearing trial was conducted to investigate the impact of stocking density on the survival, growth performance and physical injury of Marsupenaeus japonicus juveniles in a flowing water aquaculture system. Five stocking densities were examined in this study, that is, 10, 20, 40, 80 and 160 individuals/m². Throughout the experiment, ammonia nitrogen and nitrite concentrations ranged from 0.02 ± 0.006 mg/L to 0.08 ± 0.035 mg/L and 0.002 ± 0.001 mg/L to 0.076 ± 0.021 mg/L respectively. The survival rate, specific growth rate (SGR), weight gain (WG), absolute growth rate (AGR) and coefficient of variation for weight (CV) across the stocking densities ranged from 90.38 ± 3.20% to 94.33 ± 4.73%, 1.42 ± 0.16%/day to 1.53 ± 0.05%/day, 1.09 ± 0.19 g to 1.15 ± 0.16 g, 0.018 ± 0.003 g/day to 0.019 ± 0.004 g/day and 16.21 ± 5.78% to 35.09 ± 10.68% respectively. Within the investigated densities, the survival rate and the abovementioned growth parameters were not significantly (p > .05) affected by the stocking density, consequently, a higher stocking density resulted in a significantly (p < .05) greater final biomass. The results regarding physical injury showed that the antennal breakage rate displayed a tendency of a positive correlation with the stocking density. Overall, the current study provides basic data for establishing a viable intensive farming system for M. japonicus and a promising indicator for easily assessing the crowding stress status of M. japonicus.     

Enhanced growth and immuno‐physiological response of Genetically Improved Farmed Tilapia in indoor biofloc units at different stocking densities

An experimental trial was conducted for 90 days to evaluate the growth performance, immunophysiological response of GIFT strain of Tilapia in biofloc‐based rearing system and to assess the relative percentage survival in 3 days after challenging with the virulent strain of Aeromonas hydrophila. Fingerlings with an average body weight 0.98 ± 0.06 g were stocked in triplicate at different stocking densities of 200 (SD1), 250 (SD2), 300 (SD3) and 350 (SD4) m^?3 in biofloc‐based treatments and 150 (C) m^?3 in control (clear water). Biofloc‐based units (SD1 and SD2) obtained significantly better (P < 0.05) growth performances at the end of the experimental period. Mean body weight of fish in biofloc‐based units showed a decreasing trend with increase in stocking density with 100% survival in all units including control. The stress parameters were significantly lower in biofloc‐based rearing units especially in treatments SD1 and SD2 as compared to the control. The fish from the biofloc‐based units (SD1 and SD2) possessed significantly (P < 0.05) higher immune status as compared to control and other biofloc treatments in terms of respiratory burst, serum lysozyme and myeloperoxidase activity. Relative survival percentages were significantly better in biofloc treatments with highest in SD1 and SD2 (83.33%) after challenge study. GIFT strain of Tilapia at higher stocking densities 200–250 nos m^?3 can be taken as optimum stocking density whereas higher stocking densities up to 350 nos m^?3 can be reared in the biofloc systems without compromising the growth and immunity.     

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.     

Stocking density and date decisions in semi‐intensive shrimp Litopenaeus vannamei (Boone, 1931) farming: a bioeconomic approach

This article analyses the optimal selection of stocking density and date in semi‐intensive culture of shrimp Litopenaeus vannamei (Boone, 1931). The empirical evaluation of productive and economic scenarios derived from the specific choice of these management variables is often unfeasible for decision makers. To overcome this limitation, the bioeconomic modelling is widely applicable in aquaculture systems. In the present study, profit maximization for a semi‐intensive shrimp farm is obtained through the development of a bioeconomic model to analyse the combination of stocking density (range: 6–30 postlarvae (PL) m^?2) and date (from March 1st to June 1st) as decision variables for a shrimp farm located in Sinaloa, Mexico. The results show that pond water temperatures prevailing during culture cycle when the stocking date is June 1st (temperature in 19‐weeks culture period: 30.76 ± 0.87°C) and the stocking density is 20–24 PL m^?2 produce a maximized Present Value Profit (PVπ) of  USThis article analyses the optimal selection of stocking density and date in semi‐intensive culture of shrimp Litopenaeus vannamei (Boone, 1931). The empirical evaluation of productive and economic scenarios derived from the specific choice of these management variables is often unfeasible for decision makers. To overcome this limitation, the bioeconomic modelling is widely applicable in aquaculture systems. In the present study, profit maximization for a semi‐intensive shrimp farm is obtained through the development of a bioeconomic model to analyse the combination of stocking density (range: 6–30 postlarvae (PL) m^?2) and date (from March 1st to June 1st) as decision variables for a shrimp farm located in Sinaloa, Mexico. The results show that pond water temperatures prevailing during culture cycle when the stocking date is June 1st (temperature in 19‐weeks culture period: 30.76 ± 0.87°C) and the stocking density is 20–24 PL m^?2 produce a maximized Present Value Profit (PVπ) of  US$^?ha 10 350 and PVπ US$^?ha 2526 for weekly mortality rates at low (2.1%) and medium (5.8%) levels respectively. The marginal change in the cost of feed (±1%) has the greatest effect on PVπ (?0.58% and 0.59% respectively). The discussion focuses on the combined effect of mortality rate, stocking density and especially, on the stocking date decision, for a given production planning framework, taking into account that the stocking date is the main management decision variable to cope with viral diseases outbreaks.     

Larval rearing of hilsa shad,Tenualosa ilisha (Hamilton 1822)

Hilsa, Tenualosa ilisha has received much attention for culture due to decline of the natural population. Lack of knowledge on larval rearing is the bottleneck for its culture. This study was aimed at developing larval rearing protocols for hilsa shad. Hilsa larvae (4 days old, 4.76 ± 0.06 mm/0.49 ± 0.01 mg) were stocked in fibreglass‐reinforced plastic tanks (1.7 m³ water volume) at 300, 600 and 1,200 nos/m³ in triplicates in three experimental systems viz., E‐I (circular, 0.567 m water depth), E‐II (circular, 0.962 m water depth) and E‐III (rectangular, 0.567 m water depth) and reared for 46 days. The larvae were supplied with Chlorella vulgaris, Brachionus calyciflorus, mixed phytoplankton and mixed zooplankton during 4–50, 6–25, 8–50 and 26–50 days of their age respectively. In each system, higher (p < 0.05) fry survival at 300 nos/m³ than in higher densities indicates density dependent stress. Circular tanks showed higher survival (13.3%–61.31%) than in rectangular tanks (6.88%–27.26%) in each stocking density, indicating the importance of tank shape for rearing. Water depth affected fry survival in circular tanks (E‐I and E‐II) at 300 nos/m³; at 0.962 m depth, survival was higher (61.31%, p < 0.05) than that of 0.567 m depth (49.93%). Good fry survival was achieved through feeding the larvae initially with Chlorella followed by co‐feeding with Brachionus, mixed phytoplankton and zooplankton and rearing in circular tanks at 300 nos/m³ densities at 1 m depth. This first‐ever larval rearing protocol is useful for mass production of fry to support hilsa aquaculture in future.     

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.     

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.     

Evaluation of practical diets containing various terrestrial protein sources on survival and growth parameters of redclaw crayfish Cherax quadricarinatus

Redclaw aquaculture has developed at a rapid pace during the past few years, yet no specialized diet for the species has been developed. The present study was designed to evaluate whether soybean‐based diets containing either fishmeal (FM), poultry by‐product meal (PBM), ground peameal (GPM) or distillers dried grains with solubles (DDGS) meal as a protein source are suitable for redclaw aquaculture. Juvenile redclaw crayfish Cherax quadricarinatus (0.125±0.025 g) were stocked into 20 rectangular tanks at a stocking density of 12.5 m^?2 for 8 weeks. Crayfish in four replicate tanks were maintained on one of five diets formulated to contain 35% crude protein and 7.1% lipids. Each 100 g of diet contained 25 g of protein from soybean meal (SBM) and 10 g of protein from the alternative protein sources mentioned above. A fifth treatment that did not receive feed was included to account for growth from natural productivity. There were no significant differences in survival (86–90%), growth (3.84–4.98 g animal^?1) or feed conversion ratio (2.10–2.79) of crayfish among the four treatments (P>0.05). Survival and growth of crayfish in the treatment that received no supplementary feed were significantly less than those in treatments offered experimental diets. Results of the present experiment suggest that SBM‐based diets with PBM, FM, DDGS or GPM have similar effects on growth performance and survival of juvenile redclaw, C. quadricarinatus.     

Stocking Density Effects on Production Characteristics and Body Composition of Market Size Cobia,Rachycentron canadum,Reared in Recirculating Aquaculture Systems

Culture density in excess of a critical threshold can result in a negative relationship between stocking density and fish production. This study was conducted to evaluate production characteristics of juvenile cobia, Rachycentron canadum, reared to market size in production‐scale recirculating aquaculture systems (RAS) at three different densities. Cobia (322 ± 69 g initial weight) were reared for 119 d at densities to attain a final in‐tank biomass of 10, 20, or 30 kg/m³. The specific objective was to determine the effects of in‐tank crowding resulting from higher biomass per unit rearing volume independent of system loading rates. Survival was ≥96% among all treatments. Mean final weight ranged from 2.13 to 2.15 kg with feed conversion efficiencies of 65–66%. No significant differences were detected in growth rate, survival, feed efficiency, or body composition. This study demonstrates that cobia can be reared to >2 kg final weight at densities ≤30 kg/m³ under suitable environmental conditions without detrimental effects on production.     

Growth,digestive enzymes activities,serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (Oreochromis niloticus) reared at different stocking densities in in‐pond raceway recirculating culture system

The feeding trial was conducted in 80 days to assess the effects of stoking densities on growth, digestive enzymes activities, serum biochemical parameters and antioxidant status of juvenile genetically improved farmed tilapia (GIFT, Oreochromis niloticus) reared in in‐pond raceway recirculating culture system (IPRS). Fish (initial body weight: 6.25 ± 0.32g ) were randomly allotted to six in‐pond raceways (22 × 5 × 2.5 m) stocked at three different stocking densities: low stocking density (LSD, 0.28 kg/m³), medium stocking density (MSD, 0.57kg /m³) and high stocking density (HSD, 0.85 kg /m³). The results indicated that no significant differences were observed in final body weight, weight gain and specific growth rate of GIFT reared at different stocking densities on day 20 (p > 0.05). Fish reared in the HSD group showed poor growth than those reared in the LSD and MSD groups on day 50, but fish reared in the MSD and HSD groups showed poor growth than those reared in the LSD group on day 80. There were no significant differences found in digestive enzyme activities, serum cortisol, lysozyme and superoxide dismutase (SOD) content, hepatic catalase (CAT), total SOD, total antioxidant capacity (T‐AOC) activities and malondialdehyde (MDA) content among fish reared at different densities treatments (p > 0.05). Fish reared in the HSD group exhibited significant higher red blood cell number, haematocrit and glucose (GLU) contents on day 80 (p < 0.05). In brief, under this trial conditions, high stocking densities (0.57 kg/m³) resulted in decrease in growth, and GIFT might have an adaptation capability to crowding stress without a change in antioxidant activity, some physiological and immune parameters.     

Performance of the seaweeds Gracilaria salicornia and Caulerpa lentillifera as biofilters in a hatchery scale recirculating aquaculture system for juvenile spotted babylons (Babylonia areolata)

This study was conducted to determine the feasibility of using seaweeds as biofilters in a hatchery scale recirculating aquaculture system for juvenile spotted babylons (Babylonia areolata). Two seaweeds Gracilaria salicornia and Caulerpa lentillifera were used with three initial biomass levels of each species (280, 560 and 840 g wet weight m⁻³). Spotted babylon with an average initial shell length of 1.32 ± 0.01 cm and body weight of 0.37 ± 0.01 g was used with a stocking density of 300 snails m⁻². The experiment was carried out in triplicate over a period of 120 days. Results showed that seawater quality (water temperature, conductivity, salinity, pH, dissolved oxygen and total suspended solids) gradually changed with no significant differences between treatments throughout the experimental period, except alkalinity, total ammonia nitrogen, nitrite–nitrogen, nitrate–nitrogen and phosphate. Growth rates in weight and shell length of the spotted babylon cultured in all seaweed treatments used were not significantly different between seaweeds and density treatments, but significant differences in final survival rate of the spotted babylon were found between seaweed and density treatments. Growth rate and biomass gain of C. lentillifera were significantly higher than those of G. salicornia for all stocking density treatments. This study shows that Gracilaria salicornia and Caulerpa lentillifera can be used as biofilters for regulating water quality in a recirculating culture system for spotted babylons.     

The effect of stocking density on yield,growth, and survival of Asian river catfish (<Emphasis Type="Italic">Pangasius</Emphasis><Emphasis Type="Italic">bocourti</Emphasis> Sauvage, 1880) cultured in cages

Asian river catfish (Pangasius bocourti Sauvage, 1880) were cultured at five different stocking densities in cages (submerged volume 1 m³) suspended in a dugout pond from August to November 2009. Pangasius bocourti fingerlings (mean weight 27.09 ± 0.54 g) were stocked at densities of 12, 25, 50, 100, and 200 fish m⁻³. At the end of 3 months, the harvest weights (gross yields) were, respectively, 2.05 ± 0.30, 5.20 ± 0.31, 10.60 ± 0.42, 19.98 ± 0.78, and 42.37 ± 0.41 kg m⁻³. The mean fish weights among the stocking densities of 25, 50, 100, and 200 fish m⁻³ were not significantly different, but were significantly higher than that of the 12 fish m⁻³ density. The specific growth rates among high stocking densities of 50, 100, and 200 fish m⁻³ were not significantly different; however, they were significantly higher than those of the low stocking densities of 12 and 25 fish m⁻³. Asian river catfish performed poorly at the lowest density. The results indicate an initial lower stocking threshold for Asian river catfish of above 5.20 kg m⁻³. The Asian river catfish cultured in small cages placed in a pond reached the desirable market size (>200 g) within a 90-day grow-out period. The results show that the maximum yield for Asian river catfish during a 3-month production cycle was not reached.     

Effect of stocking density on growth performance of juvenile sea cucumber Holothuria tubulosa (Gmelin, 1788)

Stock density is one among the most important factors in aquaculture that directly influences the growth of organisms; however, there is limited information about the effects of stocking density on growth performance of sea cucumber Holothuria tubulosa (Gmelin, 1788) that has a commercial potential and represents a new species for aquaculture. In this study, we investigated the effect of stocking densities on the growth performance of juvenile H. tubulosa (40.3 ± 3.34 g) in laboratory conditions. Stocking densities were selected as 6, 15 and 30 ind m^?2 with total biomass 253.3 ± 0.18, 601.2 ± 0.11 and 1201.4 ± 0.15 g m^?2 respectively. We monitored the growth by wet weights and calculated the growth performance through weight gain, growth rate, specific growth rate, relative weight gain, coefficients of variation and survival rate during 8 weeks of research period. We found that individual mean weight gain in 6 ind m^?2 group was approximately 29.53 g while it was 3.03 g and ?4.36 g for 15 ind and 30 ind m^?2 groups respectively. Results have shown that the specific growth rate tends to decrease as the number of individuals in unit area increases. The final mean weight, growth rate, specific growth rate, relative weight gain and coefficients of variation were significantly different among treatment groups. In conclusion, a density of 6 ind m^?2 is recommended for stocking juvenile H. tubulosa under rearing conditions. Stocking density of 15 ind m^?2 is not favourable for long term as the growth rate is negligible where 30 ind m^?2 should be avoided in tank‐based rearing units.     

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.     

Extension of nursery culture of Scylla serrata (Forsskål) juveniles in net cages and ponds

To address the preference of mud crab farmers for larger size Scylla serrata juveniles (5.0–10 g body weight or BW; 3.0–5.0 cm internal carapace width or ICW), a study was conducted to compare the growth and survival of crab juveniles (2.0–5.0 g BW; 1.0–3.0 cm ICW) produced a month after stocking of megalopae in net cages when reared further in net cages installed in earthen ponds or when stocked directly in earthen ponds. In a 3 × 2 factorial experiment, three stocking densities (1, 3 and 5 ind m⁻²), two types of rearing units (net cages or earthen pond) were used. Megalopae were grown to juvenile stage for 30 days in net cages set inside a 4000 m² brackishwater pond and fed brown mussel (Modiolus metcalfei). Crab juveniles were then transferred to either net cages (mesh size of 1.0 mm) or earthen ponds at three stocking densities. After 1 month, no interaction between stocking density and rearing unit was detected so data were pooled for each stocking density and rearing unit. There were no significant differences in the growth or survival rate of crab juveniles across stocking density treatments. Regardless of stocking density, survival in net cages was higher (77.11±6.62%) than in ponds (40.41±3.59%). Growth, however, was significantly higher for crab juveniles reared in earthen ponds. The range of mean BW of 10.5–16.0 g and an ICW of 3.78–4.33 cm obtained are within the size range preferred by mud crab operators for stocking grow‐out ponds.