Increasing Stocking Density Research Articles

Influence of stocking density and interaction variability on disease progression of white spot syndrome virus-infected shrimp under different risk scenarios

White spot syndrome virus (WSSV), the causative agent of white spot disease (WSD), is the most significant viral pathogen affecting farmed shrimp. As the culture model for whiteleg shrimp has evolved into a higher-intensity model, the need to study the influence of stocking density on disease progression in pond culture systems has been reinforced. Therefore, we assessed WSD progression by deriving a direct correlation between seasonal disease outbreak risk, stocking density, and viral shedding rate (WSSV genome copies/L/g) using three different stocking densities: high (210 shrimp/m2), medium (140 shrimp/m2), and low (70 shrimp/m2). In Experiment 1 (three stocking densities at 25 °C) and Experiment 2 (stocking density × temperature conditions), shrimp showed relatively high cumulative mortality within the temperature range of optimal WSSV replication (23–29 °C). Notably, the mortality trend, peak viral loads, and viral shedding of WSSV-infected shrimp occurred earlier under high-density conditions, regardless of temperature. Thereafter, this study established WSD risk scenarios based on water temperature conditions and confirmed a significant difference in mortality trends between vulnerable and less vulnerable water temperature scenarios under high- and low-density conditions. The vulnerable water temperature scenario included constant (25 °C), shifting-up (20 °C to 30 °C), and shifting-down (30 °C to 20 °C) conditions, whereas the less vulnerable water temperature scenario included constant 20 °C and 30 °C conditions. Based on mortality trends, the WSD risk scenarios revealed that the times to 50 % mortality for shrimp at high, medium, and low densities were 4, 5, and 6 days post-infection (dpi) in the vulnerable water temperature scenario, and 6, 7, and 9 dpi in the less vulnerable water temperature scenario. Viral shedding variability was evaluated based on the correlation between viral loads and viral shedding rate, and linear regression analysis revealed a significant positive correlation between viral shedding rates and viral loads in shrimp, regardless of WSD risk scenarios or stocking density conditions. Notably, a relatively enhanced viral shedding rate was observed at higher stocking densities (from low- to high-density conditions) and under vulnerable water temperature scenarios. This study suggests that increased stocking density and vulnerable water temperature scenarios could induce greater interactions among WSSV-infected shrimp. It also confirmed the potential role of risk scenarios, stocking density, and viral shedding in WSD progression, providing insights into the disease outbreak mechanisms on shrimp farms.

Effect of Stocking Density on Growth, Biochemical Composition, and Blood Parameters in the Pacific Shortfin Eel (Anguilla bicolor pacifica) Elvers

This study examined the effect of stocking density on growth, biochemical composition, and blood parameters of the Pacific shortfin eel Anguilla bicolor pacifica. Elvers (1.95 ± 0.14 g body weight) were randomly stocked in indoor tanks and reared over 186 d at three stocking densities (0.3, 0.6, and 0.9 kg m-3) set up in triplicates. Except for survival and biometric indices, elvers maintained at 0.3 and 0.6 kg m-3 densities exhibited higher growth and feed utilization than those held at 0.9 kg m-3. Yield increased with stocking density, which were significantly higher at 0.6 and 0.9 kg m-3. RNA/DNA ratio did not reflect growth rate, but trends in survival and RNA/DNA ratio with stocking density were positively related. In contrast to body proximate composition, increasing stocking density resulted in significantly higher erucic acid (22:1n-9) and total saturated fatty acid levels at 0.6 and 0.9 kg m-3 densities, respectively. Serum glutamic pyruvic transaminase activity was significantly elevated at 0.6 kg m-3, while total protein, glucose, and triglycerides slightly decreased with increasing stocking density. Results suggest that Pacific shortfin eel elvers can be reared in indoor tanks at a stocking density of 0.3 – 0.6 kg m-3 to achieve acceptable growth, feed performance, and health condition.

Effect of stocking density on gonadal development, pigmentation and survival of Carassius carassius (Crucian carp) in a biofloc system

The present study was carried out to investigate the optimum stocking density for gonadal development, pigmentation, and survival of Carassius carassius stocked at varying stocking densities under a biofloc-based system. C. carassius (25 ± 0.15 g) were randomly distributed in sixteen tanks, each with 250 L water at the stocking densities viz. 1 kg/m3, 2 kg/m3, 3 kg/m3, 4 kg/m3 (10, 20, 30 and 40 fish/250 L). The carbon‑nitrogen ratio of 15:1 was maintained using wheat flour as a carbon source. The best gonad performance in terms of absolute fecundity (4449.98 ± 115.636), relative fecundity (114.67 ± 2.770), GSI (5.62 ± 0.018 and 2.93 ± 0.014 for females & males respectively), and advanced maturation stages (vitellogenic oocytes and seminiferous tubules with spermatozoa) was observed in the density treatment having 20 fish/250 L. The skin carotenoid content showed an increasing trend with maximum content (8.11 ± 0.018 μg/g)) recorded for the fish stocked at 20/250 L. The scales of the fish from the same treatment presented a higher concentration of yellow orange pigments giving an overall golden hue to the scales while as the density and dispersion of melanophores increased with an increase in stocking density giving an overall darker coloration to the fish, indicating a stressful condition at higher stocking density. The survival rate of fish showed no significant difference (p≥0.05) between the various density groups. The results of this experiment elucidate that Carassius carassius could be cultured with better gonad performance, increased carotenoid content, and high survival at a stocking density of 2 kg/m3 in a biofloc system.

Effects of stocking density on water quality, survival, blood parameters and growth performance of juvenile matrinxã (Brycon amazonicus) in the biofloc system

Biofloc technology (BFT) may be a promising alternative for production of juvenile matrinxã (Brycon amazonicus) as it allows greater fish productivity compared to ponds and is considered an economic and environmentally sustainable system. This study evaluated the effects of different stocking densities on water quality, survival, blood parameters and growth performance of juvenile matrinxã in the biofloc system. Juveniles of 5.89 ± 0.11 g were randomly distributed in five stocking densities (50, 140, 230, 320 and 410 fish ∙ m−3), in triplicate, in a BFT system. Extruded commercial feed (36% crude protein) was offered until apparent satiety four times per day for 61 days. In general, the increase in stocking density resulted in a reduction in dissolved oxygen, pH and alkalinity. Although nitrogenous compounds, total suspended solids, settleable solids and turbidity were greater in higher stocking densities, the water quality parameters were within the recommended range for matrinxã in all treatments. The stocking density had a quadratic effect on the variables specific growth rate, daily weight gain and mean final body weight. For the final stocking density and feed conversion ratio, the effect of stocking density was positive and linear. Survival rates were over 90% at stocking densities >230 fish ∙ m−3. We found a lower concentration of erythrocytes in juvenile matrinxã at the lowest stocking density (50 fish ∙ m−3) and the lymphocyte concentration was higher in the fish kept at 140 fish ∙ m−3 compared to those kept at 410 fish ∙ m−3; however, there was no difference among the other treatments. In conclusion, juvenile matrinxã can be efficiently produced using BFT at stocking densities of 291–293 fish ∙ m−3 or 13.50–13.60 kg ∙ m−3. Although the increase in stocking density is favorable for increasing the biomass and survival of matrinxã, an intensive management of solids and nitrate, as well as alkalinity corrections, are necessary to ensure proper functioning of the production and to avoid mortality of fish due inadequate water quality.

Influence of stocking density on the growth, immune and physiological responses, and cultivation environment of white-leg shrimp (Litopenaeus vannamei) in biofloc systems

Biofloc (BF) stands out as a promising system for sustainable shrimp farming. Optimizing various culture conditions, such as stocking density, carbohydrate source, and feeding management, is crucial for the widespread adoption of the BF system. This study compares the growth performance of white-leg shrimp (Litopenaeus vannamei) in culture ponds at low density (LD) with 50 organisms/m2 and high density (HD) with 200 organisms/m2. Post-larvae of white-leg shrimp were stocked for 16 weeks in both LD and HD groups. The LD group exhibited a superior survival rate, growth rate, and feed consumption compared to the HD group. The BF from the LD system recorded a significantly higher protein content (16.63 ± 0.21%) than the HD group (15.21 ± 0.34%). Heterotrophic bacterial counts in water did not significantly differ with stocking density. However, Vibrio count in water samples was higher in the HD group (3.59 ± 0.35 log CFU/mL) compared to the LD group (2.45 ± 0.43 log CFU/mL). The whole shrimp body analysis revealed significantly higher protein and lipid content in the LD group. In contrast, the total aerobic bacterial count in shrimp from the HD group was high, with the identification of Salmonella enterica ssp. arizonae. Additionally, Vibrio counts in shrimp samples were significantly higher in the HD group (4.63 ± 0.32 log CFU/g) compared to the LD group (3.57 ± 0.22 log CFU/g). The expression levels of immune-associated genes, including prophenoloxidase, transglutaminase, penaiedin 3, superoxide dismutase, lysozyme, serine proteinase, and the growth-related gene ras-related protein (rap-2a), were significantly enhanced in the LD group. Conversely, stress-related gene expression increased significantly in the HD group. Hepatopancreases amylase, lipase, and protease were higher in the LD group, while trypsin activity did not differ significantly. Antioxidant enzyme activity (catalase, glutathione, glutathione peroxidase, and superoxide dismutase) significantly increased in the LD group. The histological structure of hepatopancreas, musculature, and female gonads remained similar in both densities. However, negative effects were observed in the gills' histology of the HD group. These results suggest that increasing stocking density is associated with significantly negative biological, microbial, and physiological effects on white-leg shrimp under the BF system.

Growth performance, health status and flesh quality of striped catfish (Pangasianodon hypophthalmus) reared in variable stocking densities in biofloc system

Optimization of ideal stocking density in intensive aquaculture system is a challenging appraisal. Higher stocking density is inducing chronic stress, impacting negatively on physiology and increasing disease associated risks in fish. Hence, the study was designed to evaluate the water quality, growth performance, health status and flesh quality of striped catfish (Pangasianodon hypophthalmus). The fish (2.61–2.64 ± 0.01 g initial body weight) were reared in randomly designed variable stocking densities (SDs) including five treatments (30, 40, 50, 60 and 70 fish m−3) in triplicates at C:N ratio 15:1 in jaggery supplemented biofloc system for 120 days in 1000 –L experimental fiber-reinforced plastic tanks. SD30 acted as control treatment having low stocking density. During the culture, pH, alkalinity and dissolved oxygen level decreased and BOD increased with increased stocking density. TDS and TSS level increased upto SD50 treatment and further decreased in higher stocking density treatments. Higher population of heterotrophic, ammonifying and nitrifying bacteria significantly (p < 0.05) reduced TAN, NH3-N, NO2-N, and elevated NO3-Nas well as rate and potential of ammonification and nitrification in SD50 treatment than other treatments. Bacillariophyceae and protozoa were most dominant group in the biofloc microbiome in all the treatments. Highly elevated biofloc volume, floc microbiome, good floc characteristics and floc quality might have enhanced fish survival rate, body weight gain, SGR through improving FCR in SD50 than other SDs. Moreover, higher population of gut microbiota (TPC and probiotic) and elevated digestive enzymes activity in fish reared in SD50 treatment significantly (p < 0.05) enhanced PER, ANPU, and somatic indices (GSI and HSI) as well as enhanced colour (lightness, yellowness/blueness and whiteness), flesh quality and hardness. Fish reared in SD50 treatment showed significantly (p < 0.05) higher haematological (TEC, TLC and Hb), immunological (TSP, albumin, RBA and lysozyme), antioxidant responses (higher SOD and CAT) and lower metabolic stress enzymes responses (ALT, AST and glucose). Moreover, fish reared in SD50 treatment showed improved villi surface area and height in intestine and slightly vacuolated hepatocytes in liver. Overall, significantly (p < 0.05) better water quality, fish performance, health status and flesh quality were observed in SD50. Collectively, the findings suggest that farmers can be benefitted by fetching higher production through suitable stocking density (50fish m−3) of P. hypophthalmus in biofloc with improved water quality, growth performance, health status and flesh quality.

The Effectiveness of Biofloc System Cultivation with the Addition of Supplements Ginger Flour through Feed on the Growth of Tilapia

Demand for tilapia consumption cannot be fulfilled due to limited availability. Intensive cultivation is carried out by increasing the stocking density to overcome this. An increase in stocking density can lead to a decrease in water quality which in turn can inhibit growth. To overcome this problem, biofloc system cultivation is carried out with herbal supplements through feed to maintain water quality and optimal fish growth. This study aims to determine the effectiveness of the ginger diet on the growth of tilapia reared for 60 days compared to the ginger and garlic diet for 90 days with biofloc system cultivation. The study was conducted by the experimental method using a completely randomized design, with 3 treatments, 1 control, and each was repeated 4 times for 60 days. The results showed that cultivating tilapia using the biofloc system with the ginger diet for 60 days significantly increased growth, while the garlic diet for 90 days was only significant for weight gain. A ginger diet for 60 days on tilapia and 90 days on gourami with a biofloc cultivation system has the same pattern and effectiveness on growth with an optimal dose of 5.63 g kg-1 feed. The cultivation of the biofloc system was more effective with the ginger diet for 60 days compared to the ginger and garlic diet for 90 days on fish growth. This shows that biofloc cultivation for 60 days with a ginger diet is recommended for fish farming.

Combined intestinal microbiota and transcriptomic analysis to investigate the effect of different stocking densities on the ability of Pacific white shrimp (Litopenaeus vannamei) to utilize Chlorella sorokiniana

Aiming to investigate the impact of different stocking densities on the ability of Pacific white shrimp (Litopenaeus vannamei) to utilize Chlorella sorokiniana (CHL), a 3 × 2 factorial design stocking experiment was used in this study. Specifically, shrimp was fed with two dietary protein sources (fishmeal [FM] and CHL) at low (LSD; 100 per m3), medium (MSD; 200 per m3) and high (HSD; 300 per m3) stocking densities for 8 weeks. The growth performance and resistance to Vibrio parahaemolyticus (1.0 × 107 CFU/mL) of shrimp decreased with the increase of stocking density, but dietary CHL improved this result. Differences between the CHL and FM groups for V. parahaemolyticus resistance were significant only under high-density conditions (P < 0.05). Significant interactions between stocking density and protein source were found on the activities of catalase (CAT), superoxide dismutase (SOD) and phenol oxidase (PO), and the contents of malondialdehyde (MDA) in the hepatopancreas and the activities of intestinal amylase, most of which were significantly different between CHL and FM groups only at high stocking density (P < 0.05). Analysis of 16S rDNA sequencing showed that dietary CHL increased the alpha diversity of intestinal microbiota, inhibited the colonization of pathogenic bacteria and enhanced the abundance of beneficial bacteria. Transcriptomic results showed that at high stocking densities, differentially expressed genes (DEGs) in the FM vs CHL group were mostly upregulated and primarily enriched in immune and metabolic related pathways including Toll, immune deficiency (Imd) and glycolysis–gluconeogenesis pathways. Pearson correlation analysis revealed significant correlation between the top ten intestinal bacteria at the genus level and markedly enriched DEGs, also more were detected under high density situations. In conclusion, CHL has great potential as a novel protein source in the intensive farming of shrimp.

The role of dietary Clostridium autoethanogenum protein in the growth, disease resistance, intestinal health and transcriptome response of Pacific white shrimp under different stocking densities

With the rapid development of intensive farming mode and the high price of fishmeal (FM), finding alternatives to FM and exploring the application under different stocking densities has become a focus of current research in aquaculture. In this research, the ability of Pacific white shrimp (Litopenaeus vannamei) to utilize Clostridium autoethanogenum protein (CAP) at different stocking densities was investigated from the aspects of growth, disease resistance, intestinal health and transcriptome response. A 3 × 2 factorial design stocking experiment was conducted, using L. vannamei fed diets of two protein sources (FM and CAP) at three stocking densities with 100 per m3 (low, LSD), 200 per m3 (medium, MSD) and 300 per m3 (high, HSD) for 8 weeks. At the end of the feeding trail, the growth performance and the resistance to Vibrio parahaemolyticus of shrimp decreased with the increase of stocking density, and dietary CAP could promote the effects at the same stocking density when compared with the FM group, with more notable enhancement effect at high stocking density was observed. There was a significant interaction between stocking density and protein source on the activities of alkaline phosphatase (AKP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), catalase (CAT), superoxide dismutase (SOD), lysozyme (LYS), amylase and lipase, most of which were significantly different between CAP and FM groups only at high stocking density. Analysis of 16S rDNA sequencing showed that dietary CAP increased the alpha diversity of intestinal microbiota, inhibited the colonization of pathogenic bacteria and enhanced the abundance of beneficial bacteria. Transcriptomics results showed that DEGs in the FM vs CAP group at the same stocking densities were mainly enriched in immune and metabolism-related pathways including Toll and Imd, PI3K-Akt, and JAK/STAT signaling pathway. Pearson correlation analysis revealed significant correlation between the top ten intestinal bacteria at the genus level and markedly enriched DEGs, also more were detected under high density situations. In conclusion, dietary CAP could not only promote the growth of shrimp, but also improves the immunity and metabolism, and maintains the intestinal health of shrimp when compared with dietary FM, along with more pronounced improvement effect at high-density stocking. The results implied that CAP had a great potential as a novel protein source in shrimp intensive aquaculture.

Climatic events and disease occurrence in intensive Litopenaeus vannamei shrimp farming in the Mekong area of Vietnam

As recurrent disease outbreaks impart economic adversity across the global shrimp farming sector in general, and in Asia in particular, clarifying determinants of outbreak susceptibility carries significance for sustainability in economic growth and social and environmental prospects. This study employs logistic regression to assess the probability of disease occurrence in intensive white leg shrimp (WLS) (Litopenaeus vannamei) aquaculture under the impact of explanatory factors grouped in (1) farmers' perceptions of climatic events, (2) adaptation measures (3) farmer biodata, (4) farm site characteristics, (5) biosecurity measures, and (6) culture method. The analysis was performed using a survey of 267 Vietnamese small-scale intensive shrimp farms in the Mekong region. Significant contributors to lowering the chance of shrimp disease occurrence include (1) regularly carrying out feed conversion ratio calculations, (2) increasing participation in training programs and extension services, (3) implementing adaptive measures related to changes in feeding schedules, and (4) increasing stocking density. The main risk factors increasing the chance of shrimp disease are the duration of the crop and more years in operation. This quantitative evidence contributes to identifying important focal points for policymakers and intensive shrimp farmers in monitoring and managing the shrimp industry under the potential impacts of climate change.

Effects of Stocking Density on the Growth Performance, Physiological Parameters and Antioxidant Status of Juvenile Common Carp (Cyprinus carpio L.) Reared in the Cage system

Stocking density is one of the most important factors influencing growth performance, health status and welfare of fish in aquaculture. This research was carried out to investigate the effect of different stocking densities on growth performance, feed utilization, survival rate, haematology, serum biochemistry and serum antioxidants enzyme responses in common carp juveniles (Cyprinus carpio L.) reared in outdoor cage culture. The fish were randomly stocked in four density groups; 7F fish/0.2m3 (Control group), 14F fish/0.2m3, 21F fish/0.2m3 and 28F fish/0.2m3 in 12 cylindrical cages (0.2m3) in concrete pond, with three cages in each density for 84 days. The results of the 14f density group significantly improved the FW, WG, SGR, FCR, FCE, PER, FI, PI, WBC, RBC, Hct, GSH and SOD activities. The 21F and 28F had significant impacts on FW, WG, SGR, FCR, FCE, PER, FI, PI, glucose, cortisol, ALT, AST, ALP, TG, MDA and GSH increased significantly with increasing stocking density. In contrast, the survival rate, TP, TG, HDL, GPx and SOD activities were significantly decreased. In general, the results demonstrated that the best stocking density is 14F fish/0.2m3 which provided a better growth performance and health status of C. carpio cultured in the cage in the concrete pond.

Intensification of Amazon River Prawn Hatchery

The effects of the intensification on the performance of the Amazon River prawn hatchery carried out in a simple recirculation system were investigated. Newly hatched larvae were stocked in 120 L tanks at 80, 100, 120 and 140 larvae L−1 in a closed recirculating system. The experiment used a randomized block design with five replicates. An exponential equation was adjusted to express the relationship between the stocking density and productivity (postlarvae L−1). The development, larval quality, survival and postlarval (PL) dry weight did not significantly differ among the treatments (p &gt; 0.05). When 80 larvae were stocked, the productivity (54 ± 11 PL L−1) was lower than those at higher densities (p &lt; 0.05). Stocking 120 and 140 larvae L−1 resulted in higher productivities (75 ± 18 and 80 ± 17 PL L−1, respectively) with a lower use of Artemia nauplii to produce each postlarvae (~1200 Artemia nauplii PL−1). The maximum mean M. amazonicum postlarval production estimated by the exponential model was 93 PL L−1. This means that despite the increase in stocking density, productivity tends to stabilize. The results showed that M. amazonicum tolerates high intensification in recirculating hatchery systems based on a crushed shell bed biofilter, and the intensification optimizes Artemia use.

Dietary papaya peel extract ameliorates the crowding stress, enhances growth and immunity in Labeo rohita fingerlings.

This study was designed to determine the effects of papaya peel extract (PPE) supplementation on the growth and immunophysiological responses of rohu fingerlings at different stocking densities. In this study, three isonitrogenous (307.2-309.8gkg-1 protein) and isocaloric diets (16.10-16.16MJ digestible energy kg-1) were prepared using three different inclusion levels (0, 5, and 10gkg-1) of PPE. Four hundred and five rohu fingerlings (mean weight: 4.24g ± 0.12) were randomly distributed into nine treatment groups in triplicates viz. low (10nos 75 L-1 or ≈ 0.565kg/m3), medium (15nos 75 L-1 or ≈ 0.848kg/m3), and high (20nos 75 L-1 or ≈ 1.13kg/m3) following a completely randomized design. The study found that increasing stocking density negatively affected fish growth indices, such as weight gain percentage (WG%), feed efficiency ratio (FER), specific growth rate (SGR) and survival. In contrast, dietary PPE supplementation improved growth indices and survival (p < 0.05). We also observed that aminotransferase, lactate (LDH), and malate dehydrogenase (MDH) activity increased with stocking density, whereas 5 and 10gkg-1 PPE supplementation reduced LDH and MDH activity (p < 0.05). PPE supplementation positively affected serum indices, decreased glucose levels, and increased respiratory burst activity (p < 0.05). Interferon-gamma (IFN-γ) expression was highest in the low- and medium-stocking density groups fed with 5gkg-1 PPE, which also increased total immunoglobulin and myeloperoxidase activity while decreasing malondialdehyde concentration (p < 0.05). The results revealed that 5gkg-1 dietary PPE supplementation could be used as a growth promoter and immunostimulant to improve immuno-physiological responses at low and medium stocking densities.

Ecosystem-based fishery enhancement through pen culture of Indian major carp Labeo catla in a tropical floodplain wetland of North Eastern Region, India, during COVID pandemic.

The present study was conducted with the objective of developing ecologically and economically feasible pen culture protocols for Labeo catla as an alternate income source for wetland fishers in the context of the COVID-19 pandemic. Yearlings of L. catla (12.33 ± 1.99 cm mean total length and 26.05 ± 6.57 g mean weight) were reared in HDPE pens (500 m2 area each) at three different stocking densities of 3 (SD3), 6 (SD6) and 9 (SD9) no. m-2 in triplicates. Fishes were fed with floating pelleted feed containing 28% crude protein and 5% crude lipid two times daily at 1.5-3% of body weight. During the culture period, fish grew from 26.05 ± 6.57 to 434.61 ± 30.63 g, 306.13 ± 10.68 g and 221.13 ± 14.92 g, respectively, at stocking densities of 3, 6 and 9 no. m-2 respectively. Weight gain percentage and specific growth rate declined with increase in stocking density. Gross fish yield increased with increase in stocking density and was highest at SD9 (657.92 ± 53.55 kg pen-1), while net fish yield increased initially from SD3 to SD6 (594.31 ± 29.72 kg pen-1) and then declined with further increase in stocking density. Important water quality parameters influencing fish growth were measured, and significant difference (p > 0.05) was not observed between treatments (inside pens) and reference site (outside pen at 10-m distance). Weight gain was positively correlated (p < 0.05) to water temperature (r = 0.989) and total phosphorus (r = 0.81). Benefit cost ratio and net return was highest at SD3 (1.61; US $518.88, respectively). Stocking density of 3 no. m-2 can be considered economically feasible for table fish production of L. catla in pens. Post pen culture, monthly income of fishers increased by 10.76-179.11%, with a mean increase of 90.57%, compared to the period of first COVID-19 wave in India. The present findings can provide an impetus for effective utilization of pen enclosures for income generation and livelihood enhancement of small-scale wetland fishers during pandemic.

Efficiency of using chitosan complex in feeding technology for broiler chickens under conditions of increased stocking density

Efficiency of using chitosan complex in feeding technology for broiler chickens under conditions of increased stocking density

Effect of stocking density on growth, survival and cannibalism of juvenile pikeperch, Sander lucioperca (L.), in a recirculating aquaculture system

The effect of stocking density on the rearing performance of pikeperch juveniles was studied. Three separate experiments (I, II and III) were conducted with fish of an initial average body weight of 1.3, 6.7 and 19.2 g, respectively. Each experimental design consisted of three treatments (three replicates) with different initial stocking densities (low, medium and high). Experiments lasted 28 days in a recirculating aquaculture system (21°C, 24L:0D) with an initial stocking density of 0.78, 1.04 and 1.30 kg m−3 in experiment I, 2.68, 4.02 and 5.36 kg m−3 in experiment II, and 3.84, 7.68 and 11.52 kg m−3 in experiment III. The results of our study showed that in experiment I, the use of a stocking density of 1.04 kg m−3 resulted in the highest body weight and survival, as well as the lowest feed conversion ratio and cannibalism. In experiments II and III, the pikeperch growth rate decreased, and their feed conversion ratio increased gradually with increasing stocking density. Our study demonstrated that based on growth parameters, densities of 1.04, 2.68 and 3.84 kg m−3 can be used for pikeperch with an initial body weight of 1.3, 6.7 and 19.2 g, respectively.

Stocking density affects culture performance and economic profit of adult all-female Chinese mitten crabs (Eriocheir sinensis) reared in earthen ponds

As female Chinese mitten crab (Eriocheir sinensis) generally offer the higher edible yield, greater nutritional value, and consequently, higher market price compared to males, therefore all-female monosex culture has been popularized for the farming E. sinensis. However, the optimal stocking density remains unknown for all-female culture of E. sinensis. The present study was conducted to evaluate the effect of different stocking densities (D1.3: 1.3 inds/m2, D1.9: 1.9 inds./m2, D2.5: 2.5 inds./m2 and D3.8: 3.8 inds./m2) on growth performance, gonadal development, and economic profits of all-female E. sinensis during nine months culture period. The results showed that all growth parameters including mean body weight, body weight gain (BWG) and specific growth rate (SGR), exhibited an inverse relationship with stocking density. However, stocking density did not have a significant effect on the percentage of puberty molting, gonadosomatic index (GSI) and hepatosomatic index (HSI). At the end of the experiment, the survival rate significantly decreased with the increasing stocking density, while both final production yield and economic feed conversion ratio (eFCR) significantly increased with stocking density (P < 0.05). Profitability analysis showed that total cost and total return increased significantly with the stocking density, but the highest net profit (129.68 × 103 CNY/ha) and return-on-investment (ROI, 87.65%) were achieved at the D2.5 group. Overall, these results suggested that the optimal stocking density might range from 1.9 to 2.5 individuals/m2 in grow-out ponds for all-female mono-culture of E. sinensis.

Growing smaller fish for inclusive markets? Increasing stocking density and shortening the production cycle of Nile tilapia in cages on Lake Victoria

Fish farmers aim to maximise fish weight relative to the feed inputs needed to turn a profit. Yet, many farmers in Africa lack the cash flow to grow large fish and many consumers prefer, or are limited to purchasing, small fish. This study aimed to intentionally produce small tilapia in cages by assessing the effects of higher stocking densities and shorter growth cycles on production and financial efficiency. An experiment with 3 treatments and 6 replicates took place on Lake Victoria. The first treatment (T1) used a stocking density of 2.9 ± 0.3 kg per m−3 and aimed to produce fish to an average body weight (ABW) of 400 g (final ABW = 500.33 ± 31.01 g after 138 days). Treatment two (T2) did the same but with double the stocking density (5.9 ± 0.3 kg per m−3), resulting in a final ABW of 439.22 ± 22.22 g over 138 days. The third treatment (T3) partially harvested 50% of the cage (after 76 days) once reaching an ABW of 230.92 ± 22.55 g. The remaining fish in T3 were on-grown for a total of 138 days (final ABW = 499.86 ± 15.95 g). A fourth production scenario (M1) based on data from T3, modelled a 100% harvest after 76 days of culture. There were no significant differences in mortality between treatments. There were no statistical differences in the feed conversion ratio (FCR) between T1 (1.51 ± 0.03) and T2 (1.49 ± 0.02), though T3 was statistically lower (1.46 ± 0.02; p = 0.03). Cages in T1 had a higher proportion of fish between 400 and 599 g while fish in T2 were mostly between 300 and 499 g. T3 had a bimodal distribution with most fish either in 200–299 g or 400–499 g. There was little effect on average price per kg for T1 (3.0 ± 0.01 USD) and T2 (2.98 ± 0.01 USD), though T3 (2.89 ± 0.04 USD) was significantly lower (p = 0.001). Overall, T2 had significantly higher gross margins (17% ± 2.08) than T1 (13% ± 2.3, p = 0.021) and T3 (7.2% ± 2.43, p = 0.001), while M1 had the lowest gross margins (−11.8% ± 5.5). The results suggest that farmers can increase stocking densities. Some farmers can use partial harvesting strategies or shorter cycles to produce small tilapia and achieve faster cash flows, though the economic margins are lower. Such approaches can provide opportunities for poorer farmers and consumers.

Phenethylamine Is a Potential Density Stress Pheromone in Turbot (Scophthalmus maximus)

Pheromones play a vital role in regulating fish behavior, including reproduction, aggregation, hazard recognition and food location. To gain a better understanding of chemical communication in fish produced by density changes, this study analyzed the metabolites released by turbot (Scophthalmus maximus) under different stocking densities. The experiment was conducted at low (LD: 3.01 kg/m2), medium (MD: 6.62 kg/m2) and high (HD: 10.84 kg/m2) densities for 15 days. High-throughput non-targeted metabolomics (LC-MS/MS) was used to identify variations in metabolites released into the aquatic environment by turbot at different densities. Results showed that 29 and 47 metabolites were significantly upregulated in the MD and HD groups, respectively, compared with the LD group. Among them, hexadecanedioic acid, xanthine, phenethylamine, proline and styrene were significantly upregulated in the MD vs. LD, HD vs. MD and HD vs. LD. The VIP diagram of OPLS-DA alignment showed that phenethylamine was the most important metabolite shared by MD vs. LD, HD vs. MD and HD vs. LD. Key gene changes in the GH/IGF-1 signaling pathway, HPI axis of turbot were studied using qRT-PCR for density treatment. The results demonstrated that the expression of GH, GHR and IGF-1 was significantly lower, while the expression of CRH and ACTH was higher in the HD group. Additionally, plasma levels of cortisol, glucose, triglycerides and T3 were also highest in the HD group compared with the LD and MD groups. Phenylethylamine concentration was positively correlated with the HPI axis and negatively correlated with the GH/IGF-1 signaling pathway. To investigate the impact of phenethylamine accumulation on turbot, an acute treatment experiment with phenethylamine was set up. Its concentration in the aquatic environment was set at 0 (CON), 10−7 (LP) and 10−5 (HP) mol/L via exogenous addition, and turbot were exposed to these environments for 2 days. There was a high degree of concordance between the GH/IGF-1 signaling pathway (GH, GHR, IGF-1), HPI axis (CRH, ACTH) and plasma physiological changes (cortisol, glucose, triglycerides, T3) in the phenethylamine-treated group and the density-treated group. Therefore, accumulation of phenethylamine with increasing stocking density may be a potential cause of density stress. Phenylethylamine has a dose-dependent and trace effect as a pheromone.

Effect of Stocking Density on the Post-larval Production of &lt;i&gt;Macrobrachium rosenbergii&lt;/i&gt; in A Two-Phase Larval Rearing System

The effect of stocking density on the post-larval production of Macrobrachium rosenbergii has been studied. A two-phase larval rearing technique involving high-density rearing of early larvae for 10-12 days followed by low-density rearing of advanced larvae (stage VI) was followed. In the first phase of rearing, the stocking density did not show any effect on survival. However, in the second phase of rearing, percentage of survival decreased with increasing stocking density. Post-larval production per litre was found to be maximum at a stocking density of 55/1, and both higher and lower stocking densities resulted in decreased production per litre of the medium.