Increasing Stocking Density Research Articles

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.

Effect of Copper Supplementation on Performance, Eggshell Quality and Heterophil: Lymphocyte Ratio in Aged Laying Hens Housed at Different Stocking Densities

This study was conducted to determine the effects of additional dietary copper on performance, eggshell quality and heterophil: lymphocyte ratio in aged laying hens housed at different stocking densities. For this purpose, 216 Nick Chick laying hens of 106 weeks of age, were housed at three different stocking densities i.e. 500, 417 and 357 cm2/hen, respectively and copper (0, 150 and 300 mg/kg) was added in the basal diet for a period of 10 weeks using a 3x3 factorial arrangement. The effect of the treatments on body weight gain, feed intake, damaged eggs, specific gravity and eggshell breaking strength were not significant (P>0.05). However, eggshell thickness was improved (P<0.05) with increasing stocking density in the aged laying hens. Additionally, added copper had a significant effect on egg production (P<0.05), egg weight (P<0.01), egg mass (P<0.01), feed conversion ratio (P<0.01) and eggshell weight (P<0.01). While added copper had a significant adverse effect on eggshell weight, the addition of copper had a significant positive effect on performance parameters. Highest stocking density resulted in increased (P<0.05) heterophil: lymphocyte ratio. Addition of 150 and 300 mg/kg copper in the diet of the birds kept at 500 cm2/hen stocking density reduced heterophil: lymphocyte ratio as compared to other groups. It may be concluded that supplementation copper in the diet of aged laying hens decreased stress under normal stocking density, while stress was increased to the birds under high stocking density.

Adverse Husbandry of Maraena Whitefish Directs the Immune System to Increase Mobilization of Myeloid Cells and Proinflammatory Responses.

Adverse life circumstances evoke a common “conserved transcriptional response to adversity” (CTRA) in mammalian leukocytes. To investigate whether this pattern is preserved in lower vertebrates, maraena whitefish (Coregonus maraena) were exposed for 9 days to different stocking densities: ~10 kg/m3 (low density), ~33 kg/m3 (moderate), ~60 kg/m3 (elevated), and ~100 kg/m3 (high). Transcriptome profiling in the liver and kidney of individuals from each group suggested that crowding conditions activate stress-related signaling and effector pathways. Remarkably, about one-quarter of the genes differentially expressed under crowding conditions were involved in the activation of immune pathways such as acute-phase response and interleukin/TNF signaling attended by the simultaneous reduction of antiviral potency. Network analysis confirmed the complex interdigitation of immune- and stress-relevant pathways with interleukin-1 playing a central role. Antibody-based techniques revealed remarkable changes in the blood composition of whitefish and demonstrated the correlation between increasing stocking densities and elevated number of myeloid cells together with the increased phagocytic activity of peripheral blood leukocytes. In line with current studies in mammals, we conclude that crowding stress triggers in whitefish hallmarks of a CTRA, indicating that the stress-induced molecular mechanisms regulating the immune responses not only are conserved within mammals but were established earlier in evolution.

Environmental impact assessment of an Italian vertically integrated broiler system through a Life Cycle approach

Poultry meat represents one of the most popular meat products in the world and its production is expected to increase significantly in the next decades. The Italian broiler sector is characterized by a vertically integrated intensive production system and a high final weight of broilers in comparison to the other European countries. The Life Cycle Assessment method was used to estimate environmental impacts (Global Warming Potential; Acidification; Eutrophication; Terrestrial ecotoxicity; Non-renewable fossil energy) of 1 kg of broiler carcass weight at slaughterhouse gate in an Italian integrated broiler group. Moreover, the effects of final live weight and stocking density on the impacts were studied. Broiler fattening resulted the most impactful phase for all the impact categories, contributing on average for 87% of impacts. Conversely, the hatchery, breeder rearing and slaughtering phases moderately concurred to impact categories. Heavy broilers (roasters) showed the higher impacts per kg live weight compared to light and medium live weight broilers mainly due to the worse feed conversion ratio. The main contribution to environmental impacts in the fattening phase was feed production and processing; in particular purchased protein feeds, mainly soybean meal, were the greatest single contributor to all impact categories. The reduction of final live weight of Italian broilers from 2.6 kg to 1.6 kg could lower the total Global Warming Potential of the Italian broiler sector by about 12%. In the scenario analysis the increasing stocking density up to the maximum allowed determined only slight effects on the environmental impacts per kg carcass weight.

Growth Performance and Body Composition of Aspikutum: A New Hybrid of Asp, Leuciscus aspius ♀, × Caspian Kutum, Rutilus frisii ♂, Cultured under Different Stocking Densities in Circular Concrete Tanks

AbstractThe first step for rearing the newly produced hybrid of Asp, Leuciscus aspius ♀, × Caspian Kutum, Rutilus frisii ♂ (so‐called “Aspikutum”) is to understand essential production requirements such as stocking density. For this purpose, fish (60.4 g) were held at five stocking densities of 2, 4, 6, 8, and 10 kg/m3 in circular concrete tanks (603 L) for a period of 56 d. The culture system was maintained at natural temperature and photoperiod. Fish were fed thrice a day using a commercial diet. At the end of the trial, growth indices, including final mean weight, weight gain, and specific growth rate, were significantly higher at the density of 10 kg/m3 compared with 2 kg/m3 (P&lt; 0.05). Feed intake was significantly greater at 10 kg/m3 compared with 2 kg/m3 (P&lt; 0.05); however, feed efficiency, protein efficiency ratio, protein productive value, and hepatosomatic index remained unchanged among the stocking densities (P&gt; 0.05). Increased stocking density caused significant increase in body protein and fat contents (P&lt; 0.05). Condition factor in higher densities (8 and 10 kg/m3) was significantly higher compared with 2 kg/m3 (P&lt; 0.05). The results indicated that rearing this hybrid in the studied weight range at high density of 10 kg/m3 or more is possible without negative impacts on growth performance and body composition.

Growth, egg production and hatching success of Acartia tonsa cultured at high densities

Acartia tonsa is a calanoid copepod with high potential as live feed for marine aquaculture. However, its usage remains limited at an industrial scale, with cost effective production being conditional on successful culture at high density. The present study took an integrated approach to provide further insight on the effects of A. tonsa stocking density on copepod growth and adult reproduction, specifically egg production and egg hatching success. The effect of stocking density was studied by following the growth and survival of A. tonsa copepods, from egg hatching to maturity, on cultures initially stocked with 250, 400, 1000, 3000 and 6000copepods l−1. Additionally, the effects of high-density rearing, of adults kept at 100, 250, 500 and 2500copepods l−1, on egg production and hatching success were also evaluated over a 5-day period.Higher stocking densities were shown to have no unfavourable effect on copepod growth, though mortality significantly increased with density, from ≤2.5%d−1 at densities of ≤1000copepodsl−1 to 3.5–4.0%d−1 at 3000–6000copepodsl−1. Individual egg production decreased with increasing stocking densities, from 28eggsfemale−1d−1 at 100copepodsl−1 to 7eggsfemale−1d−1 at 2500copepodsl−1. However, total yield still increased with stocking density, with the cumulative egg production at 2500copepodsl−1 being 4 times the production at lower densities (from 100 to 500copepodsl−1). Though adult rearing density had no effect on 96-h hatching rate (60 to 69%), a density-dependent late hatching was observed on eggs produced by adults grown in dense cultures (500–2500copepodsl−1), with 48-h hatching success significantly decreasing with increasing densities (from 37% to 1%).In spite of the negative effect of stocking density on survival during growth and egg production, the magnitude of these effects does not compromise the use of high density cultures. Future research should focus on the improvement of production systems, as the ability to rear calanoid copepod species at large scale would present a major advancement in larviculture of marine fish species. Supporting statementThe present research focused on the effects of A. tonsa stocking density on copepod growth and adult reproduction, specifically egg production and egg hatching success. This is the first study on A. tonsa high-density culture from copepod growth to egg production and hatching. It further provides new insight on the viability of using high-density cultures for egg production and its impact on hatching success, essential for the commercial production of this species

Stocking density limits for post-smolt Atlantic salmon (Salmo salar L.) with emphasis on production performance and welfare

For the development of commercial scale semi-closed sea systems for farming post-smolt Atlantic salmon (Salmo salar), further knowledge is required on the interaction between fish density, farming conditions and fish welfare. In this experiment post-smolts (115.0g±13.6) were stocked at 5 different densities (25, 50, 75, 100 and 125kgm−3), and kept at these densities for 8weeks. All treatments received an equal specific flow rate of 0.6Lkg fish−1min−1 of flow-through seawater (fully oxygenated, salinity 34‰ and temp. 9.3°C) and water oxygen (O2), pH, carbon dioxide (CO2) and total ammonia nitrogen (TAN) levels were monitored in the outlet and kept within recommended limits. Over the 8week period, specific growth rate (SGR %) was significantly reduced in stocking densities of 50kgm−3 and above. Increasing density from 100kgm−3 to 125kgm−3 lead to a 42% decrease in SGR. Between 50kgm−3 and 125kgm−3 there was a correlation between reduced feed intake and increased stocking density and there was a linear increase in feed conversion ratio (FCR) with stocking density (25kgm−3 to 125kgm−3). At the end of the 8week period primary and secondary stress responses such as elevated plasma levels of cortisol, sodium, pCO2 and decreased plasma pH were observed in the highest density treatment compared to other treatments. In combination with the reduced SGR in the highest density treatments these results indicate an allostatic overload i.e. the environment has exceeded the adaptive ability of the fish with chronic adverse effects on fish welfare. Stocking densities of 100kgm−3 or more also increased pelvic fin damage and the prevalence of cataracts was higher in the 125kgm−3 treatment. In conclusion, our results suggest that at this temperature and fish size it is feasible to rear Atlantic salmon post-smolts in densities up to 75kgm−3 without compromising performance and welfare. Statement of relevanceThe data presented here are highly relevant for Aquaculture as further knowledge is required on the interaction between fish density, and fish welfare for the development of commercial scale semi-closed sea systems for post-smolt Atlantic salmon farming.

Effect of stocking density on water and soil quality, growth, production and profitability of farming Indian major carps

Indian major carps (IMCs), catla (Catla catla); rohu (Labeo rohita) and mrigal (Cirrhinus mrigala) were cultured at stocking densities of 20000 (T1), 35000 (T2) and 50000 (T3) fingerlings ha-1 for a period of 300 days in nine numbers of polythene lined ponds having an average water area of 150 m2. Stocking ratio of catla, rohu and mrigal were 4:3:3. Fishes were fed 35% protein diet twice daily. Water pH was maintained within the ideal range (6 - 9) by intermittent liming. Significantly lower (p&lt;0.05) levels of dissolved oxygen and higher values of total ammonia- nitrogen were recorded at higher stocking densities compared to lower ones. Significantly higher (p&lt;0.05) specific growth rate (SGR) and lower feed conversion ratio (FCR) were recorded in T1 compared to T2 and T3. However, maximum production was recorded in T3 followed by T2 and T1. Highest values of investment as well as income were recorded in T3 followed by T2 and T1. However, the maximum net return was obtained in T1 (`140147±7048) followed by T3 (` 133694±7931) and T2 (`101944±4857). Further, significantly higher (p&lt;0.05) profitability (PI) was recorded in T1 (85.51%) compared to T2 (45.03%) and T3 (45.04%). The results clearly showed that profitability of the culture system could not be increased only by increasing stocking densities.

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

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

Effects of feeding frequency and density on growth, energy budget and physiological performance of sea cucumber Apostichopus japonicus (Selenka)

Feeding frequency and density are two of the most important factors that directly affect the growth and physiology of sea cucumber Apostichopus japonicus. In the present study, a 60-day experiment was conducted to evaluate the effects of feeding frequency (1 time, 2 times and 3 times per day) and stocking density (D10, D20, D40 and D60) on growth performance, feed utilization, endocrine response and energy budget of sea cucumber. The results revealed that there was no significant interaction between feeding frequency and stocking density on final weight and specific growth rate (SGR). The maximum SGR occurred at treatment of stocking density D10 with feeding thrice per day. Stepwise multiple regression analysis showed that SGRW and SGRE increased with increasing feeding frequency, and decreased with the increase of stocking density. Density had significant influence on coefficient of variation (CV) for the sea cucumber body weight. For D10 and D20, no significant difference in CV was found between different feeding frequencies. Feed intake, energy intake and feces production rate were significantly affected by feeding frequency, stocking density and their interaction. Density also had significant influence on food conversion efficiency and protein efficiency ratio. Apparent digestibility coefficients of crude protein and crude lipid exhibited remarkable descending trends as stocking density increased. The energy for growth decreased and energy required for metabolism increased with the increase of stocking density, suggesting that crowding stress modified their energy allocation by inhibiting the accumulation of growth energy and accelerating energy consumption of sea cucumber. Cortisol level in coelomic fluid of sea cucumber significantly increased with the increase of stocking density, which could generate energy to satisfy the increasing demand of stress-related energy. Lactate level significantly elevated, and glucose level in coelomic fluid and glycogen in muscle showed remarkable descending trends from D10 to D60, implying long-term energy consumption under high stocking density. Feeding frequency had significant influence on glucose, glycogen and cortisol levels. To some extent, increasing feeding frequency could effectively reduce coefficient of variation of sea cucumber, especially under high stocking density. Statement of relevance•In the present study, a 60-day experiment was conducted to evaluate the effects of feeding frequency (1 time, 2 times and 3 times per day) and stocking density (D10, D20, D40 and D60) on growth performance, feed utilization, endocrine response and energy budget of sea cucumber.•Increasing feeding frequency could effectively reduce coefficient of variation of sea cucumber.•The present study provided valuable information for the intensive culture of A. japonicus.

Effects of egg stocking density on egg hatchability, larval quality and water quality for pinfish, Lagodon rhomboides , and pigfish, Orthopristis chrysoptera

Pinfish (Lagodon rhomboides Linnaeus) and pigfish (Orthopristis chrysoptera L.) are relatively new, cultured species commonly used as marine baitfish in the south-eastern United States and currently have no defined protocols for egg incubation. Thus, experiments were conducted to determine efficient egg stocking densities during static and flow-through incubation that yielded higher quality larvae. Eggs of each species were incubated statically at 250, 500, 1000 and 2000 eggs L−1, and after incubation, egg hatching success, larval survival to first feeding, larval morphometrics and water quality were assessed. Stocking densities above 250 eggs L−1 led to significant reductions in pinfish hatching success and water quality degradation, evident from decreased dissolved oxygen and pH levels and increased nitrogenous wastes. Increased stocking densities for pigfish also resulted in significant water quality degradation, although hatching success was unaffected up to a density of 1000 eggs L−1. A high flow-through water exchange rate of 2000% daily resulted in significant reductions in nitrogenous wastes and greater stability in dissolved oxygen and pH levels during incubation when compared to static treatments of the same egg density. Additionally, the high exchange rate of 2000% was critical in maintaining high hatching success and larval survival to first feeding at stocking densities of 1000 eggs L−1 for pinfish and up to 4000 eggs L−1 for pigfish. No clear patterns in larval morphometrics were observed among stocking densities. Static incubation densities of 250 and 1000 eggs L−1 are recommended for pinfish and pigfish, respectively.

Effect of grazing on vegetation and soil of the heuweltjieveld in the Succulent Karoo, South Africa

We asked how historical and recent grazing intensity affect the patchy landscape of the heuweltjieveld in the semi-arid biodiversity hotspot Succulent Karoo. The study was carried out on a communal farmland 80 km south-west of Springbok, in Namaqualand. Heuweltjies are roughly circular earth mounds that are regularly distributed in this landscape. We sampled plant species and life-form composition, diversity measures, habitat and soil variables in 100 m2 plots, placed in three visually distinguishable heuweltjie zones (centre, fringe, and matrix) and distributed across grazing camps with different recent and historic grazing intensities. Differences between heuweltjie zones were assessed with ANOVAs and multiple linear regressions. The effect of past and recent grazing intensity on soil and plant variables was analysed by Generalized Linear Models for each heuweltjie zone separately. The three zones constituted clearly distinguishable units in terms of vegetation and soil characteristics. Soil pH and cover of annual plants increased from matrix to centres, while total vegetation cover, species richness and perennial plant cover decreased in the same direction. Historic (pre-2000) grazing patterns had the strongest effects on fringes, showing the strongest soil and vegetation-related signs of overutilization with increased stocking density. Centres showed signs of overutilization irrespective of the stocking density. The much shorter exposure to recent grazing pattern (post-2000), which was nearly inverse to the historic grazing pattern, showed increase of vegetation cover (centres) and species richness (matrix) with recent grazing intensity. We interpret these effects as still visible responses of the lower grazing intensity in these camps during the historic period. No recovery under recent grazing was observed at any of the zones. We conclude that irrespective of their conducive growing conditions, once transformed to a disturbed state, heuweltjie centres recover slowly, whereas the less impacted soil and vegetation of fringes are more responsive than centres and matrix.

Influence of stocking density on the performance, carcass characteristics,hemato-biochemical indices of Vanaraja chickens

A total 90 Vanaraja experimental birds were divided into three respective groups based on floor density viz., G1 (16 birds/m2), G2 (12 birds/m2) and G3 (8 birds/m2). No significant difference in average live weight and carcass weight was observed between groups. Average feed consumption, feed conversion ratio (FCR) and dressing percentage in G2 and G3 was significantly (P&lt;0.05) higher as compared to G1. There were no significant effect (P&gt;0.05) of stocking density in the carcass characteristics except the heart weight. There were non significant differences among groups for total protein, albumin, globulin and A:G ratio. Blood glucose was significantly (P&gt;0.05) higher in group G1 as compared to G2 and G3. Blood cholesterol level increased with increase in stocking density but not significantly. Blood parameters eosinophil, monocyte, basophil counts and H:L ratio were not affected by the stocking density. Hb concentration increased non-significantly with increased stocking density. Vanaraja birds from 8 birds/m2 to 12 birds/m2 give the better growth performance, FCR and dressing percentage without change in blood biochemical and hematological indices.

The effect of feeding frequency, water temperature, and stocking density on the growth of river puffer Takifugu obscurus reared in a zero-exchange water system

The effects of daily feeding frequency (Exp I), water temperature (Exp II), and stocking density (Exp III) on the growth of river puffer, Takifugu obscurus, juvenile fish of 10 and 40 g in body weight were examined to develop effective techniques to produce river puffer in a non-exchange water system. In Exp I, fish were fed commercial floating feed with 45 % protein one to five times per day to apparent satiation each by hand daily for 8 weeks at 25 °C. In both the 10- and 40-g size groups, the final body weight, daily feed consumption, and weight gain of fish fed one meal per day were significantly lower than those of fish fed five meals per day (P < 0.05). However, there were no significant differences in the final body weight, daily feed consumption, and weight gain among fish fed two, three, and five meals per day. Feed efficiency showed decreasing tendency with increasing size of fish. In Exp II, fish of 10 and 40 g in initial body weight were reared with the commercial feed at 15–30 °C for 8 weeks. The weight gain of fish increased with raising water temperature up to 25 °C and decreased drastically at 30 °C for both sizes. The Q10 of specific growth rate was decreased with raising water temperature from 5.04 (temperature interval, 15–20 °C) to 0.66 (25–30 °C) for the 10-g fish and from 4.98 to 0.31 for the 40-g fish. In Exp III, the effect of stocking density on growth was examined with fish of 10 and 40 g in initial body weight. The final body weight for initial stocking densities of 4, 8, and 12 kg/m3 was significantly higher than that of 20 kg/m3 for the 10-g fish, and the final stocking density reached 10.1, 19.2, 28.7, and 39.9 kg/m3, respectively. For the 40-g fish, the final body weight for initial stocking densities of 3 and 6 kg/m3 was significantly higher than that of 9 and 15 kg/m3 and the final stocking density reached 7.38, 13.5, 17.1, and 27.5 kg/m3, respectively (P < 0.05). In both groups, weight gain tended to decrease with increasing stocking density; however, survival showed no significant difference.

Short communication: Short-term changes in stocking density did not alter meal characteristics of lactating Holstein dairy cattle

The study objectives were to determine the effect of short-term increases in stocking density and milking on meal duration, meal frequency, and time between meals and to determine the bioequivalence of different meal criterions in a competitive environment. Forty-eight Holstein dairy cows were allotted to 1 of 4 groups (n=12 per group). Stocking density treatments of 100 (one cow per freestall and headlock), 113, 131, and 142% were assigned to groups using a 4×4 Latin square with treatments imposed for 14-d periods. On d 11 of each period, feeding time was recorded for 24h using 10-min scan samples from direct observation. Meals were defined as repeated observations of eating with a maximum of 20, 30, or 40min of not eating between observations constituting the same meal. A new meal was established when a cow was observed feeding and then not feeding for greater than 2 (20min), 3 (30min), or 4 (40min) observations. To evaluate diurnal effects, the 24-h period of data was divided into 8-h intervals (based on milking time); morning (0400–1200h), afternoon (1200–2000h), and night (2000–0400h). Feed delivery occurred daily at 0430h, with feed pushed up throughout the day. A mixed linear model was used to determine the effect of stocking density and time of day on meals per day, meals per hour, meal duration, time between meals, and meal duration 2h before and after milking. Regardless of stocking density, meal duration, meal frequency, meals per hour, and time between meals did not differ. Regardless of stocking density, mean meal duration was longer during the morning and afternoon compared with night. Meal duration was also greater after milking compared with before milking, regardless of stocking density. These results suggest meal length decreased throughout the day, relative to feed delivery, with periodic increases in length due to return from milking. Meals per hour, meal duration before and after milking, and meal frequency established bioequivalence for the 20-, 30-, and 40-min meal criteria. Bioequivalence was not met for meal duration when the meal criterion was increased from 20 to 40min. Short-term increases in stocking density of 14-d duration did not affect the feeding pattern of lactating dairy cows, indicating that mid-lactation dairy cows can compensate for reduced feed bunk access during short-term overstocking. When calculating feeding behaviors, including meal frequency and time between meals, using a meal criterion of 20, 30, or 40min resulted in similar outcomes when using 10-min scan samples. Future studies should investigate changes in other behaviors, such as resting, which may be altered to compensate for reduced access to the feed bunk.

Co-culturing green sea urchins (Strongylocentrotus droebachiensis) with mussels (Mytilus spp.) to control biofouling at an integrated multi-trophic aquaculture site

In a field study, five different stocking densities (i.e. 0, 30, 60, 90, 120ind.net−1 or 0, 2.46, 4.91, 7.37, 9.82ind.m−2) of adult green sea urchins (Strongylocentrotus droebachiensis) were randomly assigned to 30 predator-exclusion nets (i.e. n=6) around cultured mussels (Mytilus spp.) to test the effect of urchin density on biofouling intensity (percent net occlusion) and urchin/mussel growth. After 174days of culture, nets in all treatments containing sea urchins were significantly less fouled than those in the control treatment without urchins. Fouling intensities on nets with the two highest stocking densities of urchins (90 and 120ind.net−1) were approximately 40% less than that on nets with urchins held at the lowest stocking density (30ind.net−1) and 45% less than that on nets without urchins. The differences in fouling intensity among nets with 60, 90, and 120ind.net−1 were not statistically significant. While fouling was significantly reduced in the presence of urchins compared to the control treatment with no urchins, it was not completely eliminated since they were only able to access the inside surface of the nets. Sea urchin somatic and gonad growth declined with increasing stocking density, but there was no significant difference in mussel growth at the different urchin stocking densities. Mussels and sea urchins can be successfully co-cultured with no food input, but there may be a trade-off between the effectiveness of biofouling control and sea urchin growth. Statement of relevanceThis paper examined the use of sea urchins (Strongylocentrotus droebachiensis) to mitigate biofouling in mussel (Mytilus spp.) aquaculture and the effect of sea urchin density on biofouling coverage and mussel growth. Treatments containing sea urchins showed significantly less fouling than a control treatment without urchins. Urchin density had no significant effect on mussel growth.

Effects of stocking density, light and perches on broiler growth.

The aim of this study was to determine the effect of stocking density, light intensity and light color on broiler growth. The experiment consisted of four 35-day phases during each of which 320 chickens were surveyed. The research was performed at stocking densities of four and six birds/m2 . Illuminances of 15 and 30 lx were obtained through commercial lamps with 4000 K and 6000 K color temperatures. Lighting was used 17 h a day, between 06.00 and 23.00 hours (17 L:7 D). The results showed a decrease in body, carcass, breast and thighs weight (P < 0.05) with the increase in stocking density. Body weight decreased by 10.5% and carcass weight decreased by 9.4% at six birds/m2 stocking density. Contrastingly, no differences were found for the tested light colors. Increasing illuminance from 15 to 30 lx caused a 1.9% decrease in body weight. The analysis of the effect of perches revealed that using perches significantly increased body (2.5%) and breast weight (11.8%). The interactions between light intensity or color and stocking density and between light intensity and light color were analyzed.

Effect of shrimp stocking density and graded levels of dietary methionine over the growth performance of Litopenaeus vannamei reared in a green-water system

This study evaluated the effect of shrimp stocking density, dietary methionine (Met) content and their interaction over the growth performance of juveniles of Litopenaeus vannamei reared under a green-water system. Five diets were formulated to contain increasing levels of Met (0.48, 0.62, 0.72, 0.81 or 0.94% on a dry matter basis, DM) and Met+Cysteine (Cys) (0.96, 1.09, 1.19, 1.28 or 1.40% DM, respectively) by supplementing a basal diet low (5%) in fishmeal with graded levels (0, 0.11, 0.21, 0.31, and 0.41% as fed basis) of dl-methionyl-dl-methionine, a dipeptide of Met. Each of the five diets were fed four times daily for 70days to five replicate groups of 1.97±0.14g initial body weight shrimp, stocked at 50, 75 or 100 animals m−2. At harvest, both dietary Met and shrimp stocking density statistically affected shrimp performance. The increase in stocking density significantly increased FCR and yield, while reducing shrimp weekly growth and final body weight. Final shrimp survival was higher than 90% and unaffected by stocking density. Dietary Met and Met+Cys content by supplementation with the dipeptide of Met, positively affected final shrimp survival, apparent feed intake, FCR and yield. Growth rate of shrimp was significantly affected by an interaction between dietary Met content and stocking density, being highest (1.56±0.04gweek−1) in shrimp fed diets with 0.62% Met (1.09% Met+Cys) reared at a stocking density of 50 animals m−2. Within groups of 50 and 100 shrimp m−2, final shrimp body weight was progressively increased up to 0.72% Met (maximum of 16.80±1.95g). Within 75 shrimp m−2, final shrimp weight was highest at 0.81% Met (16.59±1.88g). Beyond this level, no benefit could be detected in final shrimp weight. Natural food collected from tank walls contained between 21.5 and 26.2% CP, 0.25–0.28% Met and 0.58–0.69% Met+Cys and may have thus contributed to meeting shrimp Met requirements, at least at lower stocking densities. This study has shown that under green water, an enhanced shrimp performance was obtained in diets containing between 0.72 (1.19% Met+Cys) and 0.81% Met (1.28% Met+Cys), being 29 and 38% of this total Met provided as supplemental dipeptide of Met. Statement of relevanceShrimp stocking density affects dietary methionine level.

Influence of Stocking Density on Growth Performance, Antioxidant Status, and Physiological Response of Juvenile Turbot, Scophthalmus maximu, Reared in Land‐based Recirculating Aquaculture System

AbstractThis study aimed to assess the effects of stocking density on the growth, antioxidant status, and physiological response of juvenile turbot. Turbot (average initial weight 70.0 ± 5 g) were reared at three different initial densities (low density [LD], 5.13 ± 0.03 kg/m2; medium density [MD], 7.71 ± 0.11 kg/m2; and high density [HD], 10.8 ± 0.12 kg/m2) for 80 d. At the end of this trial, the final densities were 13.2 ± 0.10, 19.9 ± 0.15, and 25.7 ± 0.12 kg/m2 in the LD, MD, and HD groups, respectively. The growth performances were adversely influenced by a high stocking density. Levels of cortisol, glucose, cholesterol, triglyceride, glutamate pyruvate transaminase, and glutamate oxalate transaminase in the plasma significantly increased in HD treatment. Results of oxidative stress analyses showed that there was a clear decrease in superoxide dismutase, glutathione peroxidase, catalase, glutathione, and total antioxidant capacity, and an obvious increase in malondialdehyde in plasma and/or liver of turbot reared in HD group (P &lt; 0.05). Overall, the results indicated that increasing stocking density reduced the growth performance, modulated the physiological response, and induced oxidative stress in turbot.

Using Evolutionary Operation technique to evaluate different management initiatives at herd level

The purpose of this project was to exemplify the use of Evolutionary Operation (EVOP) technique at herd level to test the effect of change in the herd's normal management procedure. As pigs are day active animals, it is assumed that an increase in the activity level during the night will indicate that the pigs are forced to change their normal diurnal rhythm to adapt to the conditions. Thus change in the diurnal pattern of drinking was used as a potential indicator of stress/resource limitations in the pen. A three way factorial experiment with 714 crossbred pigs (34.3±4.1kg) was carried out. The variables were: stocking density (14 or 18 pigs per pen), number of straw allocations (one allocation of 140g straw per pig/day or four daily allocations of 35g straw per pig) and allocation of pigs to pens (randomly or by size). The pigs were fed a libitum. Water consumption and temperature at pen level were continually measured during the experimental period (29 days). The day was divided into two 12-h periods: “day” (from 0700h to 1859h) and “night” (from 1900h to 0659h), and the proportion of the water consumption during the night of the total water consumption was calculated at pen level. Data were analysed using a linear mixed effect model. The average daily water consumption was 4.52±0.24l per pig per day. On average, 26.0% of the total amount of water was consumed during the night. An increasing stocking density increased the proportion of water consumed during the night by 2.0 percentage points (P=0.01). A random distribution of the pigs instead of sorting them by size at pen level reduced the proportion of water consumed during the night by 2.3 percentage points (P=0.03), while no significant effect of the number of straw distributions (P=0.36) or interactions was found. Looking at the daily water consumption, no effect of stocking density (P=0.32), straw allocation (P=0.85) or sorting the pigs (Randomly versus sorted by size, P=0.11) was found. Groups with small pigs had a lower water intake compared with groups with large or randomly sorted pigs (P<0.01). The results show that the use of an EVOP design at herd level using change in the diurnal rhythm as response variable can be used to give a fast indication of the optimal combination of production factors within the herd.