Impact of Aeration on the Growth Performance of Silver Barb,Puntius gonionotus,during Fingerling Rearing

Impact of aeration on growth of silver barb, Puntius gonionotus during fingerling rearing was studied through a 100‐d rearing experiment conducted in 18 concrete tanks of 50 m² (10 × 5 × 1.2 m) size. Fry (0.74 ± 0.27 g, 35 ± 6 mm) were stocked in the experimental tanks at three stocking densities (25, 50, and 75 fry/m²) and were evaluated with and without provision of 6 h (2400–0600 h) of night time aeration. Aeration resulted in higher pH and dissolved oxygen regime and increased fingerling length and weight. The results suggest a rearing density of 75/m² to be ideal for rearing fry to fingerling of this species when aeration is provided, whereas, under non‐aerated condition, rearing the fry to fingerling stage at 50/m² was found advantageous over those at 25 and 75/m².     

The impact of light intensity and algal-induced turbidity on first-feeding Seriola lalandi larvae

Feeding performance (intensity and incidence) of first‐feeding yellowtail kingfish larvae was evaluated under a range of light intensities and algal‐induced turbidities. Larvae were fed with varying degrees of success under all light intensities tested (0–17 μmol s^?1 m^?2), in both clearwater and greenwater (8 × 10⁴ cells mL^?1). There was a consistent trend for feeding performance to increase with larval age and light intensity in both clearwater and greenwater conditions, demonstrating that visual proficiency increases with larval age. Feeding intensity remained low over the first 3 days of first feeding across all light intensities tested. Days 6 and 7 post‐hatch larvae showed considerably higher feeding intensities particularly at 8 and 17 μmol s^?1 m^?2. This improvement indicates an ontogenetic shift in sensory or locomotor competence. First‐feeding larvae performed equally well in both clearwater and greenwater (8 × 10⁴ cells mL^?1) conditions, although at the lowest light intensity tested (0.1 μmol s^?1 m^?2) feeding performance was noticeably reduced. Feeding performance was severely diminished across all larval ages at an algal cell density of 32 × 10⁴ cells mL^?1, demonstrating that for this species algal‐induced turbidities >16 × 10⁴ cells mL^?1 adversely affect the ability to capture free‐swimming prey during the first‐feeding window.     

Culture of Macrobrachium rosenbergii (De Man 1879) in experimental cages in a freshwater eutrophic lake at different stocking densities

Macrobrachium rosenbergii (de Man 1879) juveniles (0.4 g) were cultured in experimental cages (L × W × H: 2.5 × 1 × 1 m) in Laguna de Bay, the largest lake in the Philippines. The following stocking densities at four replicates each were used: 15, 30, 60 and 90 prawns m⁻² of cage bottom. The mean sizes at harvest after 5 months of culture ranged from 14.3 g for the highest stocking density to 26.3 g for the lowest. The mean size at harvest, daily growth rate and size class distribution were significantly influenced by stocking density, with those at the lowest stocking density showing significantly better growth and overall proportion of larger prawns. Heterogeneous individual growth (HIG) was fairly evident in all treatments. The percentage of blue‐clawed males was not influenced by treatment but the mean weight was significantly higher in the lower stocking densities. Both the percentage and mean weight of berried females were significantly higher in the lowest stocking density. Survival was the highest in the lower stocking densities (55.3%, 54.0%, 52.7% and 36.9% for 15, 30, 60 and 90 prawns m⁻² respectively). Feed conversion ratio (FCR) improved with decreasing stocking density, ranging from 2.1 to 3. As expected, yield per cropping increased with stocking density and ranged from 450 to 1089 g m⁻² yr⁻¹ of actual cage area. Production values obtained in the cage cultured M. rosenbergii were comparable to or even higher than those reported from pond culture, given that the stocking densities used in this study were generally higher than in ponds. The results show that the farming of M. rosenbergii in cages in lakes is a viable alternative to pond culture and has the potential of improve aquaculture production in lakeshore fish farming communities.     

Detection of migratory herring in a shallow channel using 12- and 100-kHz sidescan sonars

A hydroacoustic monitoring program for migratory herring was conducted in Drogden Channel, near Copenhagen, Denmark, beginning in June, 1996. Using installations of 100-kHz sidescan sonar oriented across the channel, herring schools were observed at ranges up to 500 m in water depths of 10–14 m. In October 1997, this effort was supplemented with a 12-kHz sidescan mounted on a motorized tripod allowing azimuthal sector scanning. This 12-kHz sidescan was able to detect herring schools up to a 1 200-m range. Two examples are examined to assess the limits of herring school detectability and the feasibility of abundance estimation. In both cases, herring schools are detectable by their transience and up to 20 dB signal excess relative to the nominally stationary background reverberation, dominated by seabed backscattering. Attempts are made to extract quantitative abundance estimates using methods based on school size and density, and through quantitative echo-integration. Acoustic ray tracing was found to be useful in interpreting the results, and in particular modeling boundary-reflection focusing as a potential source of positive bias in herring abundance estimates.     

Observations from moorings in the Aleutian Passes: temperature,salinity and transport

Between May 2001 and September 2003, a series of moorings were deployed in four of the Aleutian Passes – Tanaga Pass (12 months of data), Akutan Pass and Seguam Pass (18 months), and Amukta Pass (36 months). Instruments on each mooring measured temperature, salinity and current velocity. Tidal currents dominated the flow in each pass, including a strong fortnightly component in the three deeper passes (Tanaga, Seguam, and Amukta). Net transport in each of the passes was northward, varying from 0.1 × 10⁶ m³ s^?1 in Akutan Pass and 0.4 × 10⁶ m³ s^?1 in Seguam to >4.0 × 10⁶ m³ s^?1 in Amukta Pass. The transport in Amukta Pass, calculated from current meters, was approximately five times as large as previously estimated from hydrographic surveys. At monthly and longer periods, the variability in transport in Amukta Pass was related to the position and strength of the Alaskan Stream southeast of the pass. Vertical mixing was examined in Akutan and Seguam Passes. Strong tidal currents mix the water column top‐to‐bottom over the shallow sills in the passes, a depth of 80 m in Akutan and 140 m in Seguam Pass, providing a critical source of nutrients to the Bering Sea ecosystem.     

Optimizing stocking density and microalgae ration improves the growth potential of tropical black‐lip oyster,Saccostrea echinata,larvae

The combined effects of stocking density and microalgae ration on survival and size of Saccostrea echinata larvae were studied in two‐factor experiments for the major developmental stages: D‐veliger (1‐day posthatch [dph], Experiment 1), umbonate (12 dph, Experiment 2), and eyed (19 dph, Experiment 3) larvae. Larvae were stocked into replicate sets of four 10‐L aquaria with ambient 1‐μm filtered sea water (28 ± 1.5°C and 36 ppt) and cultured for four days at densities of 0.5, 2, 5, 7, or 10 larvae/mL and provided with microalgae rations at each of five densities (cells larvae^?1 day^?1); 0, 1, 3, 5, or 8 × 10³ (D‐veliger larvae, Experiment 1); 0, 5, 12, 18, or 25 × 10³ (umbonate larvae, Experiment 2); and 0, 15, 30, 40, or 60 × 10³ (eyed larvae, Experiment 3). Microalgae rations for each larval life stage were selected on the basis of increasing food requirement with larval size and comprised a 2:1:1 mixture of Chaetoceros calcitrans, Tisochrysis lutea, and Pavlova spp., calculated on an equal dry‐weight basis. Contour plots were generated from larval survival and larval size (dorso‐ventral measurement [DVM]) data to determine optimal culture conditions. Larvae showed high survival (54–100%) over a wide range of both treatment parameters across all life stages, confirming broad tolerance limits for this species. The interaction effects of larval stocking density and microalgae ration on larval size were significant (p < 0.001) across all life stages. Results indicate that maximum larval size (DVM) is achieved when S. echinata are cultured at: 6–8 larvae/mL and fed 5–6 × 10³ cells larvae^?1 day^?1 for D‐veligers (mean DVM >80 μm), at 2–8 larvae/mL and fed 11–25 × 10³ cells larvae^?1 day^?1 for umbonate larvae (mean DVM > 190 μm), and at 1–4 larvae/mL and fed 15–40 × 10³ cells larvae^?1 day^?1 for eyed larvae (mean DVM >230 μm). Results will help refine current hatchery methods for S. echinata supporting further development toward commercial aquaculture production of this species.     

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.     

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.     

Spawning performance and seed production from hybridization between Oreochromis spilurus and the GIFT strain of the Nile tilapia Oreochromis niloticus

This study compared the spawning performance of four crosses between the salt‐tolerant tilapia Oreochromis spilurus and the fast‐growing genetically improved farmed tilapia (GIFT) strain of the Nile tilapia Oreochromis niloticus: (1) O. spilurus♀×O. spilurus♂ (SS); (2) Nile ♀× Nile ♂ (NN); (3) Nile ♀×O. spilurus♂ (NS) and (4) O. spilurus♀× Nile ♂ (SN). In each cross, males and females having mean weights of 157 and 115 g, respectively were stocked in 0.43 m³ tanks at a male to female ratio of 1:3. Seeds (unhatched eggs, yolk‐sac fry and free swimming fry) were harvested biweekly for 127 days. Viable spawns resulted from all crosses. The NN cross produced the highest total seeds tank^?1 (2890), seeds (kg female)^?1 day^?1 (48.3), seeds m^?2 day^?1 (23.3) and seeds female^?1 day^?1 (7.9), followed by the SS and SN crosses. The NS cross had the lowest fecundity. Lower spawning parameters in the NS and SN crosses may be attributed to the lower social compatibility between the males and females compared with that of the pure parents. The survival and growth of the offspring from the four crosses will be compared in seawater (37–40 g L^?1) to assess whether hybrid vigor was produced.     

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 hatchery-reared juvenile spotted babylon Babylonia areolata Link 1807 cultured to marketable size in intensive flowthrough and semi-closed recirculating water systems

Hatchery‐reared juvenile spotted babylon Babylonia areolata (mean initial shell length 12.8 mm) were cultured intensively to marketable size in three 3.0 × 2.5 × 0.7 m indoor canvas rectangular tanks. The duplicate treatments of flowthrough and semi‐closed recirculating sea‐water systems were compared at an initial stocking density of 300 individuals m^?2 (2250 juveniles per tank). The animals were fed ad libitum with fresh carangid fish Selaroides leptolepis once daily. During 240 culture days, average growth rates in shell length and body weight were 3.86 mm month^?1 and 1.47 g month^?1 for the flowthrough system and 3.21 mm month^?1 and 1.10 g month^?1 for those in the semi‐closed recirculating system. Survival in the flowthrough system (95.77%) was significantly higher than that in the semi‐closed recirculating system (79.28%). Feed conversion ratios were 1.68 and 1.96 for flowthrough and semi‐closed recirculating systems respectively.     

Preliminary assessment of large‐scale co‐culture of sandfish (Holothuria scabra) with the Babylon snail (Babylonia areolata) in earthen ponds and in raceways

Holothuria scabra (sandfish) and Babylonia areolata were trialed in two large‐scale co‐culture experiments. Experiment 1 assessed co‐culture in 4 × 400 m² earthen ponds where Babylonia were cultured in a central pen at a density of 400 individuals/m² with sandfish occupying the remaining pond space at 1.1 individuals/m². Sandfish grew from 18.20 ± 6.67 g to 119.03 ± 17.74 g in 92 days and Babylonia (fed trash fish in both experiments) grew from 0.90 ± 0.38 g to 4.93 ± 1.44 g, but Babylonia growth was not increased in co‐culture compared to monoculture. Water and sediment quality varied between co‐culture and monoculture ponds. Neither showed clear improvement due to sandfish culture. Experiment 2 compared non‐segregated sandfish‐Babylonia co‐culture with Babylonia monoculture in 20 m² concrete raceways. Sandfish were cultured at 2 individuals/m² and Babylonia at 300 individuals/m². Sandfish grew up to 1.91 g.day^?1 with 100% survival. Babylonia weight gain was significantly greater in co‐culture raceways (3.35 ± 0.64 g over 61 days), which was double that of Babylonia in monoculture. Substrate total N was reduced by 20% in co‐culture compared with monoculture (p = .032). This provisional study of commercial scale sandfish‐Babylonia co‐culture demonstrates culture compatibility, providing a basis for further system development.     

长江湖口段四大家鱼卵资源及其产卵场分布

为了解长江湖口段四大家鱼卵的资源现状和产卵场位置与产卵规模,本研究于2019年4月19日至8月5日利用浮游生物网对湖口江段设置的4个采样断面进行逐日调查.调查结果显示:采集到家鱼卵93粒,其中以鲢为绝对优势,占家鱼卵总数的80.65％.本次研究采集到的受精卵瞬时发育时期共9期,主要是尾芽出现期、囊胚期和原肠早期,分别占...     

Influence of feeding regime on intraspecific competition, fin damage and growth in 1+ Atlantic salmon parr (Salmo salar L.) held in freshwater production cages

The feeding behaviour, growth and feed conversion ratio (FCR) of cage‐held Atlantic salmon parr (Salmo salar L.) were studied when in 576 m³ (12 m × 12 m × 4 m) commercial freshwater cages under ambient water temperature (8.84±3.53°C) and photoperiod (11.02±2.05 h) for 205 days. The effect of feeding regime on fin damage was also investigated. Six groups (n=31 234±2051 fish group⁻¹, initial stocking density 1.25±0.14 kg m⁻³) were fed to satiation using either (a) an imposed regime involving scheduled, fixed ration feeding every 10 min from dawn till dusk or (b) on demand from dawn till dusk using commercial interactive feedback systems. During feeding, there were no significant differences in aggression although swimming speeds and turning angles were significantly higher in fish under the imposed regime. On‐demand feeding significantly reduced the incidence of dorsal fin damage. There was no clear relationship between fish size, feed regime and the incidence of fin damage until 1 week before the fish were transferred to marine cages, when the smallest fish under each feeding regime had the highest incidence of fin damage. Interestingly, growth did not differ between regimes, but fish under the imposed regime were significantly overfed and achieved higher FCRs.     

Design and development of a portable and streamlined nutrient film technique (NFT) aquaponic system

One pilot-scale portable Nutrient Film Technique (NFT) aquaponic system has been designed, developed, and tested at ICAR-CIFA, Bhubaneswar for a period of 90 days (October to December 2018) to study the efficiency of the new design. The experimental setup has three separate units, each consisting of four major components, such as Fibreglass Reinforced Plastic (FRP) round fish culture tank (ø2.15 × 0.9 m) with operational capacity 2800 L, biofilter unit made up of Polypropylene (PP) of 100 L capacity, FRP rectangular hydroponics tank (4 × 0.9 × 0.35 m) having 2.64 m² plantation area and High-density Polyethylene (HDPE) sump (ø0.6 × 0.7 m) of 200 L capacity. Implementation of custom designed and calibrated automatic water recirculation system gives an average flow rate of 94.7 L/h for continuous flow of nutrients from fish culture tank to hydroponics tank. The designed system harnesses gravity flow in 75 % of the cycle. For performance assessment, the system was initially stocked with 54 numbers of fish fry/m³ (153.7 g/m³) of pangas (Pangasius hypophthalmus) in culture tank and 27 marigold (Tagetes erecta) plants/m² in hydroponics tank. Length and weight gain of fish were by 77.04 % and 397.2 % from initial, respectively, and marigold plant harvested 107 number of flowers/m². The Total Ammoniacal Nitrogen (TAN) reduction in biofilter was found to be 61.97 %.     

Bonga shad (Ethmalosa fimbriata) spawning tactics in an upwelling environment

Successful recruitment in small pelagic fish populations inhabiting upwelling zones is subject to variation in fecundity and is driven by spatial and temporal fluctuations in environmental conditions, that is, mainly sea surface temperature, salinity and food availability. These fluctuations in abiotic factors have stimulated small pelagic fish populations to exhibit specifically adapted spawning tactics. To better understand to what extent a short‐lived exploited fish species such as bonga shad Ethmalosa fimbriata has adapted to an upwelling environment, we have investigated the interrelationship between upwelling intensity as a proxy for productivity and population fecundity by means of a virtual population analysis. We found that females of intermediate size contributed significantly more eggs to the population's fecundity than smaller or larger ones. Our model results further indicate that E. fimbriata exhibits a spawning preference at water temperatures of around 25°C and upwelling intensities of around 2.5 m³ s^?1 m^?1. Hence, we hypothesize that climate change‐driven increases in sea temperatures and modifications of upwelling‐favourable winds could significantly impact the species’ reproductive biology. To understand how climate change might impact fisheries, spawning tactics of small pelagic fishes are important to assess as well as their recruitment success. Such information is particularly relevant in countries where the fishery is critical at socio‐economic level, to better implement fisheries management addressing multiple stressors.     

Growth and Feed Utilization of Captive Wild Black Sea Bass Centropristis striata at Four Different Densities in a Recirculating Tank System

A study to determine the effects of four stocking densities on growth and feed utilization of wild‐caught black sea bass Centropristis striata was conducted in a pilot‐scale recirculating tank system. The outdoor system consisted of 12 insulated fiberglass tanks (dia. = 1.85 m; vol. = 2.17 m³) supported by biological filters, UV sterilizers, and heat pumps. Subadults (N= 525; ×± SD = 249 ± 16.8 g) were stocked at densities of 4.6 fish/m³ (1.18 kg/m³), 16 fish/ m³ (3.91 kg/m³), 25.3 fish/m³ (6.83 kg/m³), and 36 fish/m³ (7.95 kg1m³), with three replicate tanks per treatment. Fish were grown under 35 ppt salinity, 21‐25 C, and under ambient photoperiod conditions. A commercial flounder diet containing 50% protein and 12% lipid was hand‐fed twice daily to satiation for 201 d. Mean (range) total ammonia‐nitrogen, 0.61 (0‐2.1) mg/L, nitrite‐nitrogen, 0.77 (0.04‐3.6) mg/L, and nitrate‐nitrogen 40.1 (0‐306) mg/L were significantly higher (P < 0.0001) in the 25.3 and 36 fish/m³ treatments than in the 4.6 and 16 fish/m³ treatments [0.19 (0.05‐0.5), 0.1 (0.24‐0.63), and 11.9 (1.3‐82.2) mg/L, respectively]. However, there were no significant differences (P > 0.05) in growth (RGR = 196.8‐243.1%; DWG = 2.55‐2.83 g/d; and SGR = 0.55‐0.61%/d), coefficient of variation of body weight (C_wtV., = 0.24‐0.25), condition factor (K = 2.2‐2.4), feed consumption (FC = 1.45‐1.65%/d), and feed conversion ratio (FCR = 1.45‐1.52) among stocking densities. Final biomass densities on day 201 reached 3.48, 12.0, 21.1, and 27.2 kg/m³ at stocking densities of 4.6, 16, 25.3, and 36 fish/m³, respectively. Survival (83.8‐99.1%) did not differ among treatments. Apparent net protein retention (ANPR) was significantly higher (P < 0.005) for fish stocked at the lower densities of 4.6 and 16 fish/m3 (22.5‐23.7%) than for those stocked at 25.3 and 36 fish/m³ (21‐20.1%). There were no significant differences (P > 0.05) in apparent net energy retention (ANER = 55.9‐59.1 %) among stocking densities. Final whole body protein (15.3‐16.3%) and lipid (23.1‐26.4%) levels did not differ significantly (P > 0.05) among treatments. The results demonstrated that growth, survival, and feed utilization were not impaired under stocking densities ranging from 4.6‐36 fish/m³ (3.48‐27.2 kg/m3), despite a slight reduction in water quality at the higher densities. In addition, growth variation and final whole body protein and lipid levels were not influenced by these densities. The results suggest that black sea bass are tolerant of crowding and moderate variations in water quality during intensive culture in recirculating tank systems and that higher stocking densities are possible.     

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.