Effects Of Stocking Density Research Articles

High-light pronounced the effects of stocking density on photosynthesis and nutrients uptake of the bloom-forming green alga, Ulva linza

High-light pronounced the effects of stocking density on photosynthesis and nutrients uptake of the bloom-forming green alga, Ulva linza

Intra-cohort cannibalism and aggressive behavior in tropical gar (Atractosteus tropicus) larvae: Effects of stocking density and starvation

Cannibalism in early fish developmental stages is a biological phenomenon affecting aquaculture, so seeding density and feeding schemes play a fundamental role in its optimal control. The objective of this research was to evaluate two initial stocking densities, 0.7 larvae/L (D7) and 1.4 larvae/L (D14), which were fed (F) and not fed (NF) in tropical gar (Atractosteus tropicus) larvae on growth, attacks, survival, and digestive enzyme activity, digestive morphology, and oxidative enzymes and aggressiveness gene expression. A total of 420 larvae (0.022 ± 0.003 g; 1.52 ± 0.10 cm) were placed in 70 L tanks connected to a recirculation system. Treatment F larvae were fed a formulated food. D14F larvae had the highest final weight, total length, and specific growth rate (SGR) (p < 0.05). The highest survival percentage was in D7F larvae (46.19 ± 2.74) (p < 0.05). The highest frequency of attacks occurred in D14F larvae (26.66 ± 0.82) (p < 0.05). The coefficient of variation (CV) and size heterogeneity (SH) were higher in D7F larvae (13.56 ± 1.80; 0.81 ± 0.10) (p < 0.05). The F larvae started attacks at 8 days after hatching (DAH), while the NF larvae showed it at 10 DAH. The difference in weight between the attacker and the attacked was 16.44 ± 9.75% and in total length 12.28 ± 4.57% (p < 0.05). Acid and alkaline protease, trypsin, and lipase activities presented differences between both factors, as well as the interaction between them. D14F larvae presented the highest Glutathione peroxidase (GPX) activity (p < 0.05), while D7-NF larvae registered the highest catalase (CAT) activity (p < 0.05). Superoxide dismutase (SOD) activities only showed differences between F and NF larvae (p < 0.05). The liver presented the highest percentage of area with melanomacrophage centers (MMC) in D7-NF larvae, and hepatocytes with the highest area were recorded in D14F larvae (p < 0.05). In gut, the highest enterocytes were recorded in D14F larvae (p < 0.05). cat, cck, and gpx expression did not show difference between feeding regimes. The expression of sod1 and sod2 in D7F and D14F treatments presented the highest expressions (p < 0.05). D7F larvae presented higher expression of avp1, crh, htr1, sstr1, th and tph1 genes (p < 0.05). Our results show that A. tropicus larvae D14F presented the highest growth and morphometric parameters and decreased CV and SH, which shows a more homogeneous growth. Regarding cannibalism, fed larvae (D7F, D14F) presented cannibalism in a greater proportion than unfed larvae regardless of density, however, it is necessary to analyze other physiological and social factors that could be related to the aggressiveness and cannibalism of the species.

Effect of Stocking Density during CO2 Stunning of Pigs on Induction Time and Activity Level Measured Using AI.

During the CO2 stunning of pigs, a variation in their reaction to the gas and the duration of the induction period is observed. The stunning process can be affected by several conditions, such as stressful events and previous experiences, but the stocking density in the gondola may also have an impact. The objective was to investigate the effect of stocking density on the stunning process under commercial conditions. To quantify the pigs' reactions under industrial settings with a stocking density of up to eight pigs pr. Gondola (3.91 m2), the activity level was measured using an AI solution. Compared with a simulation of the expected induction period, a significantly longer induction period was found in gondolas containing seven and eight pigs (p < 0.001) but not when the gondolas contained three or four pigs. Both high and mean activity levels were significantly higher when stocking density was increased from three or four pigs to seven or eight pigs. The stunning process was thus negatively affected when increasing the stocking density. More knowledge is needed to explain this effect and to make statements on optimal stocking density. The measured activity levels may be a useful tool for obtaining information under commercial conditions and for documenting animal welfare.

Effects of strain and stocking density on leg health, activity, and use of enrichments in conventional broiler chicken production

Conventional broiler production needs to evolve towards more animal-friendly production systems in order to meet increasing consumer concerns regarding animal welfare. Genetics and stocking density are 2 of the most promising leads to make this change possible. In this study, 6 strains with different growth rates (42-61 g/d) were reared at contrasting densities: 37 kg/m² (HD) and 29 kg/m² (LD). At the same body weight of 1.80-1.95 kg, we evaluated how growth rate and stocking density influenced broiler behaviors (general activity, interactions with enrichments), broiler health (mortality, leg problems, cleanliness and plumage growth) and litter quality. Density did not affect body weight, mortality or behaviors. For all strains, LD was associated with a lower prevalence of hock burns, a better gait score, and improved litter quality and broiler cleanliness. For the 3 strains most affected by pododermatitis, a lower prevalence was observed in LD than in HD pens. Fewer birds were inactive and more birds were standing and interacting with the enrichments (as proposed in the experiment) as soon as the growth rate was lower than that of the control strain (Ross 308). Others welfare indicators such as gait score, plumage growth improved as well. Litter humidity decreased with growth rate, contributing to better leg conditions and cleaner breasts. The prevalence of hock burns and certain behaviors (i.e., the proportion of birds grooming or walking/running) were not affected by growth rate. The proportion of birds foraging was higher at a lower growth rate. These results suggest that reducing growth rate as a preliminary measure, and reducing density as a supplementary one, would improve conventional broiler welfare.

Effects of Different Stocking Densities on the Growth, Antioxidant Status, and Intestinal Bacterial Communities of Carp in the Rice–Fish Co-Culture System

Common carp (Cyprinus carpio) is a freshwater fish commonly farmed in rice fields, yet there were few studies on the intestinal functions and microbial community structure of common carp in the rice–carp co-culture system. Therefore, this study aimed to explore the effects of different stocking densities on the growth, antioxidant status, and intestinal bacterial composition of common carp in this system. This study was divided into three different stocking densities, including low density (LD, 10 fish, 52.9 g/m2), medium density (MD, 20 fish, 105.8 g/m2), and high density (HD, 30 fish, 158.7 g/m2), with a culturing period of 60 days. The results indicated that HD treatment inhibited the growth of common carp, as evidenced by the reduced final weight, WG, and SGR. In serum, the TG content in the HD group and the Cor content in the MD group were significantly increased. Meanwhile, HD treatment induced oxidative stress, manifesting specifically as increased SOD and CAT activities in the intestine or serum while reducing Gpx, GSH, and T-AOC in the serum. The 16S rDNA analysis indicated that the Simpson and Shannon indices of intestinal microbiota in the HD group were significantly higher than those in the LD group. At the phylum level, Proteobacteria, Cyanobacteria, and Firmicutes were dominant microbial communities in two groups. In addition, there was a significant difference between the two groups in the abundances of Actinobacterota and Bifidobacterium. Based on growth performances, biochemical indicators, and microbial diversity in rice–carp co-culture, low density (52.9 g/m2) may be more suitable in the rice–carp co-culture systems. In summary, this study contributes to a better understanding of common carp response to different stocking densities in the rice–carp co-culture system.

Haematological, biochemical and oxidative stress parameters of New Zealand rabbits housed at different stocking densities

The aim of this study was to investigate the effects of different stocking densities on oxidative stress, some hematological and biochemical blood parameters in New Zealand rabbits, and to determine the ideal cage area where rabbits can live without being stressed. A total of 36 1–month–old mixed sex New Zealand weaned rabbits were selected for the study. The rabbits were placed in cages at different densities of stocking. Experimental groups were 1 rabbit per cage (C1), 2 rabbits per cage (C2) and 3 rabbits per cage (C3). There was no significant differences between groups in terms of RBC, HGB, HCT, MCV, MCH, WBC, neutrophils, lymphocytes, monocytes, eosinophlis, basophlis, AST, ALT, trigliseride, cholesterol, HDL and LDL parameters (P&gt;0.05). C2 group had lower count of PLT comparing C1 and C3 groups. C1 group had the highest value for MCHC (P&lt;0.05). As oxidative stress parameters, there was no significant differences between IMA and TAS parameters (P&gt;0.05). C2 group had the lowest value in terms of SOD (P&lt;0.05). In conclusion C2 group was determined more advantageous in terms of breeding and welfare, since C1 group does not support social needs of the animals and C3 group leads to increased stress levels due to reduced individual space and restricted movement.

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.

The effect of stocking density and crude protein level on performance, carcass characteristics, nitrogen use, and ammonia emissions of the Indonesian native chickens

This was study aimed to investigate the impact of stocking density and crude protein level on the performance, carcass characteristics, nitrogen (N) use, and ammonia emissions of Sentul Selected (Sensi)-1 Agrinak chickens. A total of 504 chickens were used in the 70-day analysis using a random ized block design with factorial pattern of 3 × 3 which was arranged in nine treatments and four repli cates. The administered treatment covered two factors, including stocking density (A) and crude pro tein level (B). The treatments were administered when chickens reached 5 weeks of age. The results showed that different stocking density significantly influenced (p&lt;0.05) the average weekly feed con sumption per chicken at 6, 7, 8, and 9 weeks, but not at 5, 6, and 10 weeks. However, varying crude protein levels showed no significant effect on carcass weight, giblet weight, and total edible parts. There was also no significant interaction observed between stocking density and crude protein level in relation to carcass weight and edible parts. Furthermore, no significant differences were found in giblet and carcass weights between the two groups (p&gt;0.05). The results showed that feeding Sensi-1 Agrinak chickens with a lower crude protein level of up to 14% did not compromise their performance, meat quality, protein digestibility, or ammonia emissions, but affected carcass characteristics.

Effects of stocking density and salinity on the flavour performance and muscle microstructure of black tiger shrimp (Penaeus monodon) post larvae

Effects of stocking density and salinity on the flavour performance and muscle microstructure of black tiger shrimp (Penaeus monodon) post larvae

Effects of different stocking densities on growth, nutritional quality, stress and antioxidant response in Labeo rohita; cultured in in-pond raceway system.

A 171-day long experimental trial was undertaken to study intricate physiological response of rohu (Labeo rohita) under stress caused by high stocking density in In-pond raceways system (IPRS). Fingerlings of rohu (initial body weight: 250 ± 1.20 g) were cultured at three different stocking densities; low density (LD) (2.27 kg/m3), medium density (MD) (3.79 kg/m3) and high density (HD) (5.30 kg/m3) in raceways of IPRS production system. Each treatment was in triplicate. Fish growth exhibited a decline in HD treatment statistically as its average weight gain/fish/day was 4.21 g as compared to MD (4.82 g) and LD (4.74 g). Nutritional profile of rohu indicated by the content of crude protein, fatty acids, and profile of amino acids was up to the set dietary benchmarks. Survival rate of fish in all the treatment groups was greater than 99%. The elevated cortisol levels observed in the HD treatment in contrast to the other treatments suggested the presence of stress. The levels of superoxide dismutase, catalase and glutathione peroxidase were also higher in HD as compared to other treatments. However, there were no difference in the level of MDA between the three treatments. Activity of amylase, protease was significantly different in treatment whereas the difference in lipase activity was found to be insignificant. It can be concluded that medium stocking density i.e. 3.79 kg/m3 outperformed the high density (5.30 kg/m3) in different aspects of this study. Nevertheless, additional research is imperative to ascertain whether any intermediate stocking density between medium (3.79 kg/m3) and high (5.30 kg/m3) such as 4 kg/m3, 4.5 kg/m3, or 5 kg/m3, could potentially serve as suitable options for rohu. It is also suggested that brood stock of rohu should be genetically improved to obtain stress resilient fingerlings which will perform better at high stocking density at large scale production level.

Effect of Stocking Density on Survival and Growth of Brown Meagre Sciaena umbra (L.) Larvae

Effect of Stocking Density on Survival and Growth of Brown Meagre Sciaena umbra (L.) Larvae

Cage-Free Pullets Minimally Affected by Stocking Density Stressors

Management choices during the pullet phase can affect behavior, welfare, and health later in life, but few studies have evaluated the pullet phase, particularly in extensive housing systems. This study was a 2 × 2 factorial randomized complete block design (RCBD) with two strains and two stocking densities. The Lohmann LB-Lite and Lohmann LSL-Lite were housed on the floor at high-stocking density (619–670 cm2/bird) and low-stocking density (1249–1352 cm2/bird), which changed with age from 2 to 16 weeks of age (WOA). Bird-based measures of appearance, blood parameters, organ measurements, and production values were evaluated. Stocking density alone affected (p &lt; 0.05) only relative bursal weight (% of body weight)—3.32% in the low-density versus 3.08% in the high-density group. High-stocking density was correlated with decreased uniformity (high—89.33 ± 0.24%; low—90.41 ± 0.24; p &lt; 0.02) and worse feather coverage in the brown strain. High-stocking density was correlated with greater uniformity (High—90.39 ± 0.24%; Low—88.47 ± 0.24%; p &lt; 0.001) and better feather coverage in the white strain. This study’s feed conversion ratio (FCR) was improved by 0.07 in the low-stocking density for both strains. The remaining parameters were affected by strain and age only. Thus, while stocking density effects vary slightly depending on the strain used, cage-free pullets had limited negative effects at both the high and low-stocking densities tested in this study; there were few to no changes in the numerous bird-based welfare parameters tested.

Effects of Stocking Density and Pre-Slaughter Handling on the Fillet Quality of Largemouth Bass (Micropterus salmoides): Implications for Fish Welfare.

There is currently insufficient acknowledgment of the relationship between fish welfare and ultimate fillet quality. The purpose of this study was to assess the impacts of pre-slaughter handling and stocking density as fish welfare markers on fillet quality of largemouth bass (Micropterus salmoides). Fish from three stocking densities of 35, 50, and 65 kg·m-3 were reared in a recirculating aquaculture system (RAS) for 12 weeks and received commercial feed. Ultimately, the fish were either stunned with percussion on the head (control group) or subjected to air exposure for 3 min (anoxia group) before stunning and subsequent collection of blood and fillet samples. Western blot analysis revealed the degradation of actin in both groups. Additionally, higher oxidation progress and lower hardness and pH were observed in anoxia compared to the control group. We observed higher hardness at 35 kg·m-3 in anoxia compared to 50 and 65 km-3. The initial hardness values at 35, 50, and 65 km-3 were 1073, 841, and 813 (g) respectively in the anoxia group. Furthermore, the anoxia and control groups had rigor mortis after 6 and 10 h, respectively. Cortisol and glucose levels, and oxidative enzymes activity were higher in anoxia than in the control group. In conclusion, oxidation induced by anoxia likely plays a crucial role as a promoter of the quality deterioration of largemouth bass fillets.

83 Effect of stocking density on F1 gilt reproductive performance

Abstract Replacement females are the future of a farm, and their development can impact production. Currently, replacement gilts are housed in many different environments. Stocking density of replacement females is one factor that varies across production systems. Therefore, the objective of this study was to evaluate the effect of different stocking densities on replacement gilt reproductive performance. At 10 wk of age, DNA L241 females (n = 824; DNA Genetics, Columbus, NE) were randomly allotted to finishing pens with 3 different stocking densities. Each stocking density consisted of 12 pens of 0.71 m2 (n = 360), 0.93 m2 (n = 264), and 1.25 m2 (n = 204). Heat detection started at 20 wk of age with fence line exposure for 2 wk at 15 minutes per pen. Within pen boar exposure occurred from 22 to 31 wk of age for a minimum of 10 min per pen. Starting at 20 wk of age, females that exhibited red and swollen vulvas or standing estrus were recorded. Body weight, backfat, and loin depth measurements were collected at estrus detection. A blood progesterone assay was performed on all females at 24 wk of age. Further blood progesterone assays were performed at 27, 29 and 31 wk of age on any female for which progesterone was not detected on previous assays. Females were mated on their 2nd estrus if they were at least 136 kg or on their first estrus if they were over 145 kg. Body weight was recorded at the time of mating. For females that cycled by 31 wk, females in the 0.71 m2 treatment cycled significantly earlier than the 0.93 m2 treatment, 147 vs 153 d post-weaning respectively (P &amp;lt; 0.05). No difference was detected in age at mating; however, gilts in the 0.71 m2 treatment were 5.9 kg and 8.2 kg lighter than the 0.93 and 1.25 m2 treatments respectively (P &amp;lt; 0.01). At 31 wk of age 60% of the 0.71 m2, 71% of the 0.93 m2, and 77% of the 1.25 m2 treatments had cycled according to visual heat detection. However, according to the progesterone assay, at 31 wk of age 75% of 0.71 m2, 81% of the 0.93 m2, and 84% of the 1.25 m2 had cycled. The accuracy of visual heat detection compared with progesterone assay were 79.4% for 0.71 m2, 77.3% for 0.93 m2, and 85.8% for 1.25 m2 treatments. Overall, the 1.25 m2 treatment resulted in heavier females at mating, a greater rate of females cycling, and a more accurate detection of females cycling than the 0.71 m2 treatment. Swine producers can improve the percentage of females detected in estrus and mated in the desired period by providing additional rearing space during gilt development.

219 Effect of stocking density on F1 gilt grow-finish performance

Abstract As replacement rates in the swine industry have increased, gilt development units have increased the number of females developed in the same allotted space. The impact of decreasing space is not well understood on the developing gilt. Therefore, the objective of this study was to evaluate differences in grow-finish performance for developing gilts housed at different stocking densities. At 10 wk of age 824 F1 females (DNA L241, DNA Genetics, Columbus, NE) were randomly allotted to 12 pens per treatment of either 0.71 m2 (n = 360), 0.93 m2 (n = 264), or 1.25 m2 (n = 204). Body weights (BW) were individually collected at 10, 24, and 31 wk of age. Backfat and loin depth were measured using an Exxago Ultrasound between the 10th and 11th rib at 24 and 31 wk of age. Feed consumption was measured at the pen level using a Feed Logic system. Mortality date, reason, and BW were recorded throughout the grow-finish phase. At 10-wk of age, there was no significant difference in BW between the treatments. Differences in BW were observed between treatment 0.71 m2 at 119.3 kg compared with 0.93 m2 and 1.25 m2 at 123.4 kg and 125.6 kg, respectively (P &amp;lt; 0.01). All stocking densities were significantly different (P &amp;lt; 0.01) at 31 wk of age with 0.71 m2 at 142.4 kg, 0.93 m2 at 152.4 kg and 1.25 m2 at 156.5 kg. Backfat and loin depth were significantly different at 24 wk for 0.71 m2 compared with 0.93 m2 and 1.25 m2 (P &amp;lt; 0.05). At 31 wk of age, all treatments were significantly different for backfat with 0.71 m2 at 16.1 mm, 0.93 m2 at 18.0 mm and 1.25 m2 at 19.1 mm (P &amp;lt; 0.05). Feed conversion was not different across treatments from 71 d of age until 84 d of age and from 84 until 111 d of age. However, feed conversion was significantly different from 111 d until 167 d of age for 0.71 m2 at 3.83 compared with 1.25 m2 at 3.40 (P &amp;lt; 0.10). Mortality was not different between treatments (P &amp;lt; 0.05). Gilts that were assigned to the least square foot treatment grew slower and had decreased backfat and loin depth. This could potentially impact the timing of the estrus detection and matings in the replacement gilt population. Overall, producers looking to improve the BW of females entering the breeding herd should evaluate increasing the space allotted per female in their gilt developer.

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.

Aquaculture Performance and Genetic Diversity of a New [(Crassostrea hongkongensis ♀ × C. gigas ♂) ♂ × C. hongkongensis ♀] Variety of the Oyster "South China No. 1" in Beibu Gulf, China.

Crassostrea hongkongensis is an economically important bivalve found in various parts of the South China Sea. A new interspecific backcross ([(Crassostrea hongkongensis ♀ × C. gigas ♂) ♂ × C. hongkongensis ♀]) variety was bred by the South China Sea Institute of Oceanology which named "South China No. 1". This study aims to explore the effects of stocking density on the growth performance of "South China No. 1", compared their growth performance and genetic diversity to C. hongkongensis, and found the best place breeding site for "South China No. 1" in Beibu Gulf. The results showed that stocking a density of 20 oysters/substrate can significantly increase the shell height, shell width, total weight, survival rate, daily shell height gain and daily body mass gain. It was found that the shell height and total weight of "South China No. 1" cultured in Fangchenggang were significantly higher than that of those in Beihai and Qinzhou from September 2018 to November 2018. Similarly, the shell width of oysters in Fangchenggang and Qinzhou was also significantly higher in September 2018, and the interaction between site and stocking density had significant effects on the shell width in March 2018 and November 2018. In addition, the shell height and shell width of "South China No. 1" were significantly higher than that of C. hongkongensis in all three sites. At all three sites, the phytoplankton community structure was mostly dominated by Bacillariophyta. In the Hardy-Weinberg equilibrium test, for the seven populations and ten microsatellites, in 10 of the 70 groups, the segregation distortion was significant. These results suggest that a stocking density of 20 oysters/substrate can promote the shell height, shell width and total weight of "South China No. 1" in Beibu Gulf, China. "South China No. 1" has better growth performance compared with C. hongkongensis. Fangchenggang is a suitable place to cultivate the "South China No. 1" breed according to the total weight and sum of all algal genus abundances. The results of this study can be used as a reference to further understand the stocking density and genetic diversity of the "South China No. 1" breed in Beibu Gulf, China.

Effects of Chronic Stress from High Stocking Density in Mariculture: Evaluations of Growth Performance and Lipid Metabolism of Rainbow Trout (Oncorhychus mykiss).

(1) Background: In aquaculture, chronic stress due to high stocking density impairs animals' welfare and results in declined fishery production with low protein quality. However, most previous studies evaluated the effects of high stocking density on trout in freshwater rather than seawater. (2) Methods: Juvenile trout were reared for 84 days in circular tanks under three stocking densities, including low density ("LD", 9.15 kg/m3), moderate density ("MD", 13.65 kg/m3), and high density ("HD", 27.31 kg/m3) in seawater. The final densities of LD, MD, and HD were 22.00, 32.05 and 52.24 kg/m3, respectively. Growth performance and lipid metabolism were evaluated. (3) Results: Growth performance and feeding efficiency were significantly reduced due to chronic stress under high density in mariculture. The digestive activity of lipids was promoted in the gut of HD fish, while the concentration of triglycerides was decreased in the blood. Furthermore, decreased acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), increased hormone-sensitive lipase (HSL) concentrations, and activated hepatic β-oxidation processes were observed in trout under HD. Redundancy analysis showed that glycerol and HSL can be used as potential markers to evaluate the growth performance of trout in mariculture. (4) Conclusions: We showed that chronic high stocking density led to negative effects on growth performance, reduced de novo synthesis of fatty acids, and enhanced lipolysis.

Determination of optimal temperature, salinity, and stocking density combinations for larval growth and survival of diploid, triploid, and tetraploid Fujian oyster (Crassostrea angulata)

For nurseries, thriving larvae mean higher incomes. Three factors - temperature, salinity and stocking density - are critical to the success of larval rearing. However, the effects of these three factors on the performance of diploid, triploid and tetraploid Crassostrea angulata larvae have not yet been comprehensively investigated. In this study, the combined effects of temperature (T, 12.0–35.0 °C), salinity (S, 10.0–38.0 psu) and stocking density (D, 0.5–10.0 ind. ml−1) on the accumulated growth rate (AGR) and survival rate (SR) of diploids (DD), triploids (DT) and tetraploids (TT) C. angulata larvae were comprehensively assessed using a central composite design and response surface methodology. The results revealed that suitable temperature-salinity-stocking density combinations significantly increased the AGR and SR of larvae from all three groups, while unsuitable environments (e.g., ultra-high temperature - extra-high salinity -high stocking density combinations or ultra-high temperature - extra-low salinity - high stocking density combinations) significantly reduced the AGR and SR of the larvae, albeit to different magnitudes. The optimal temperature-salinity-stocking density combinations were obtained by model optimization. The maximum AGR and SR of DT reached at 23.6 °C, 26.5 psu and 0.5 ind. ml−1 combinations with values of 17.13 μm day−1 and 64.81%, respectively. The combinations of 24.0 °C - 25.89 psu - 1.99 ind. ml−1 and 25.9 °C - 25.96 psu - 0.5 ind. ml−1 were the optimal breeding conditions for DD and TT (DD: AGR = 13.10 μm day−1, SR = 63.55%; TT: AGR = 10.11 μm day−1, SR = 25.89%). In addition, validation experiments were carried out under the obtained optimum conditions. The AGR and SR of DD, DT and TT obtained from the validation experiments were basically in conformity with the maximum AGR and SR obtained under the theoretically predicted conditions. Moreover, the growth and survival of tetraploids remained lower than those of diploid and triploid counterparts, even under optimal breeding conditions. This means that more attention should be paid to the tetraploids so as to safeguard the succession of this fragile population. The application of the findings of this study will help to improve the breeding efficiency of C. angulata with different ploidies in larval culture.

Effect of stocking density of Snakeskin gourami (Trichopodus pectoralis) in polyculture system with Black apple snail (Pila polita)

The experiment determined the effect of stocking density of snakeskin gourami in the polyculture model with black apple snails. The experiment included four treatments corresponding to four densities of fish (ind./m2): (i, Control): 0, (ii) 3, (iii) 5, and (iv) 7; snails were stocked at 150 snails/m2; each treatment was triplicated. The initial fish’s weight was 12 ± 0.3 g, and the snail’s weight was 0.15 ± 0.01 g. After 120 days of the experiment, the survival rate of fish was 100% in all treatments, whereas the survival rate of snails ranged from 80.22 to 82.44%, and there were no significant differences (p&gt;0.05). Snails in the control treatment obtained the highest specific growth rate (2.68 %/day) and productivity (0.54 kg/m2). In contrast, the specific growth rate and productivity of fish obtained the highest number in treatment iv, with 0.98 %/day and 0.24 kg/m2, respectively. The highest profit was recorded in the treatment with 7 fish/m2, and this was significantly different (p&lt;0.05) compared to the control and 3 fish/m2 treatment. Results from this study showed that the stocking density of 5 fish/m2 was suitable to enhance productivity of both snail and snakeskin gourami in polyculture system.