Establishing an eyeball-weight relationship for Litopenaeus vannamei using machine vision technology

This study aimed to establish a shrimp eyeball-weight relationship model for Litopenaeus vannamei using machine vision technology. A total of 295 shrimp were sampled from a recirculating aquaculture system (RAS). The long-axis length (d), body length (L), and body weight (W) of each individual was measured. The long axis length of the shrimp eyeball was identified and measured using machine vision technology. Continuous fitting and piecewise fitting models were used to construct the eyeball-weight relationship model for L. vannamei. The continuous fitting relationship model was described as: W = 38.865d^2.7914, while the piecewise model was described as: d < 2 mm, W = 0.0326d^3.7363, R² = 0.9288; 2 mm ≤ d < 3.9 mm, W = 0.0401d^3.104, R² = 0.9629; 3.9 mm ≤ d < 5.8 mm, W = 0.0421d^3.0311, R² = 0.9216; 5.8 mm < d, W = 0.103d^2.6226, R² = 0.9457. The root mean square error (RMSE) of the piecewise fitting model (0.0244, 0.1575, 0.5034, 0.7072) was smaller than the continuous fitting model (0.8229). The correlation coefficient (R²) of the piecewise model (0.9288, 0.9629, 0.9216, and 0.9457) was similar to that of the continuous fitting model (R² = 0.9621). The results indicated that the piecewise fitting model is suitable for calculating the biomass of L. vannamei in RAS and provides a novel way of estimating the biomass of L. vannamei cultured in RAS. The piecewise fitting model can also provide the foundation of evaluating the production of shrimp using underwater image recognition in intelligent aquaculture systems.     

The effects of density and artificial substrate on intensive shrimp Litopenaeus vannamei nursery production

Recirculating aquaculture systems (RAS) can be installed indoors, allowing year-round production of tropical animals in nearly any climate. A nursery phase is commonly used in Litopenaeus vannamei production since it allows for enhanced biosecurity and better quantification of animals while reducing space requirements. However, it is unclear whether animal density and inclusion of artificial substrate may improve shrimp performance during the nursery phase. In this experiment, we compared shrimp production parameters in two stocking densities with or without the use of an artificial substrate by creating four treatments: low-density LD; 1500 PL/m⁻³, low-density with substrate LDS, high-density HD; 3000 PL/m⁻³), and high-density with substrate (HDS). The LDS and HDS treatments included 0.46-m² of high-density polyethylene 2.5-cm mesh as a substrate, which increased the tank surface area by 21 %. Each treatment was randomly assigned to four 160-l culture tanks, each with a biofilter. The shrimp had an initial weight of 4 mg and were grown for 50 days. The low-density treatments had significantly higher dissolved oxygen (DO) and pH than the high-density treatments (P ≤ 0.001). Specifically, LDS had the highest DO and pH followed by the LD, HD, and HDS treatments, respectively. High-density treatments had significantly higher NO₂-N levels than low-density treatments during week 2 of the experiment when an unusually high concentration of nitrite was observed. FCR was significantly lower in both low-density treatments than in high-density treatments. At harvest, the total biomass (kg m⁻³) was significantly higher in high-density treatments than in low-density treatments (P ≤ 0.001), and the HDS treatment had a significantly greater biomass output than HD. Producers should consider artificial substrate and higher densities during nursery production to maximize shrimp production; however, the effects on water quality should also be taken into account.     

电解与紫外协同去除工厂化养殖循环水中氨氮效果研究

为探究电化学氧化法在工厂化循环水养殖系统中处理水质的效果及影响因素,在前期试验得到最佳条件(温度25℃、电流密度40 A/m2、水流速度300 m L/min)下,以不同初始氨氮质量浓度和固体悬浮颗粒物的模拟养殖水以及实际养殖水为研究对象,探讨了加入低压紫外汞灯后电解与紫外协同去除氨氮的效果。结果表明:电解紫外协同处理氨氮效果明显优于单独电解法,运用本系统处理氨氮初始质量浓度分别为4、7、10 mg/L的模拟养殖水时,氨氮去除效率相对于单独电解时分别提高45.0%(p0.05)、36.0%(p0.05)和20.0%(p0.05);电解紫外协同去除氨氮效率受氨氮初始质量浓度、水体中的固体颗粒悬浮物、实际养殖水等因素影响,随着氨氮初始质量浓度及水体中固体悬浮颗粒物的升高,氨氮的去除效率降低,达到同种去除效率所需的时间延长,当处理固体悬浮颗粒(SS)分别为100、150、200 mg/L的模拟养殖水时,氨氮的去除效率随着SS的升高而降低,相对于仅含氨氮的模拟养殖水,氨氮的去除效率分别降低51.7%(p0.05)、65.5%(p0.05)和72.4%(p0.05);在处理实际养殖水时,氨氮的去除速率明显降低,去除完全所需的时间延长,在本系统中电解紫外对氨氮、亚硝氮、固体悬浮颗粒物的去除具有较好效果,去除率分别为97.8%、96.9%和92.1%。     

脱二氧化碳装置对循环水养殖系统pH的影响

为了调节循环水系统中养殖水体的pH,根据气体交换原理,设计一种脱二氧化碳(CO_2)装置。采用该装置去除养殖水体中的CO_2,并对由于CO_2含量累积造成的pH下降进行调节,使养殖鱼类处在一个适宜的pH环境中。试验时水温控制在(25±0.5)℃,每1 h取水样测1次pH,每4 h测1次碱度。水样取自养鱼桶内的水,检测前先对水样用40μm孔径针头过滤器进行过滤处理,实验周期24 h。结果显示,循环水系统加装脱二氧化碳装置能有效去除CO_2,使水体稳定在一个适宜的pH范围(7.39~7.42);CO_2质量浓度呈降低趋势,24 h后由开始的13.16 mg/L降低到7~8 mg/L,降低近50%,而不加装脱二氧化碳装置的循环水系统CO_2质量浓度持续上升,24 h后增加到37 mg/L左右,pH持续降低,最终降低到6.72~6.81。研究表明,脱二氧化碳装置能够有效去除水体中的CO_2,使水体pH维持在一个适宜鱼类生长的范围。     

大西洋鲑循环水养殖水体异养细菌组成的研究

采集养殖池水样,选取Zobell 2216E琼脂培养基、溶菌肉汤琼脂培养基、硫代硫酸盐柠檬酸盐胆盐蔗糖琼脂培养基、脑心浸液琼脂培养基、胰蛋白胨大豆琼脂培养基、营养琼脂培养基6种常见固体培养基进行细菌分离培养,以平板菌落计数法和菌落外观形态特征辨别及16SrRNA基因测序方法进行异养菌计数和种类组成分析。结果显示:(1)养殖池水体异养菌可分为4大类,分别属于变形菌门(包括α-、γ-变形菌纲)、厚壁菌门、拟杆菌门、放线菌门,其中以γ-变形菌纲为优势菌群。按属分类大多为假交替单胞菌属和弧菌属。(2)不同培养基分离菌落数量2216E培养基溶菌肉汤琼脂培养基胰蛋白胨大豆琼脂培养基脑心浸液琼脂培养基营养琼脂培养基硫代硫酸盐柠檬酸盐胆盐蔗糖琼脂培养基,且2216E培养基菌落数极显著高于其余5种培养基(P0.01);2216E培养基所分离细菌的种类最多,分属于12个属,假交替单胞菌属为优势类群,占比50%,弧菌属仅占3.13%;脑心浸液琼脂培养基、溶菌肉汤琼脂培养基、胰蛋白胨大豆琼脂培养基所分离细菌均以弧菌属为优势菌群,分别占33.33%、60%、25%;硫代硫酸盐柠檬酸盐胆盐蔗糖琼脂培养基所分离细菌仅分属于1个属,即弧菌属;营养琼脂培养基无弧菌,但有假单胞菌分离出。     

鳗鲡循环水高密度养殖试验研究

利用室内封闭式循环水养殖系统对欧洲鳗鲡进行高密度养殖试验。结果表明,10 522尾平均体重为55.6 g(18P)的欧洲鳗鲡养殖159 d,成活率达99.7%,总重由584.6 kg增加到1478.0 kg,均重达143.2 g(7.0P),养殖密度从13.0 kg/m3提高到32.8 kg/m3,共投饵1 263.2 kg,鳗鲡增重893.4 kg,饵料效率达70.7%。采用添加营养液和低负载预培养生物膜,使鳗鲡进入系统后水质平稳变化,降低了养殖初期因水质变化剧烈而发生事故的风险。试验阶段养殖池水体氨氮0.03～1.28 mg/L、亚硝态氮0.02～0.75 mg/L、硝态氮1.21～99.60 mg/L,溶氧控制在5～7 mg/L、pH以碳酸氢钠调节稳定在7.0～7.7、水温在23.8～32.4℃间,系统的日换水量在5%内,各水质指标均处于鳗鲡适宜范围内。养殖期间发生2次指环虫病害,利用中草药和无残留药物进行防治,效果良好。利用循环水养殖系统养殖鳗鲡,创造最适的水环境理化条件,在快速生产绿色安全水产品的同时有效节水和减少污水排放。研究亮点:国内首次中试规模(养殖水体45 m3),高密度(32.8 kg/m3)进行了欧洲鳗鲡的循环水养殖试验。养殖试验时间达159 d,鳗鲡达到了商品规格。在中试规模条件下,联合运用预培养生物膜和低负载培养生物膜的方法快速构建了具有稳定硝化功能的生物过滤器。首次比较了不同日换水率条件下,循环水养殖欧洲鳗鲡水体氨氮、亚硝酸盐氮和硝酸盐氮的变化情况。     

Comparing biofloc,clear-water,and hybrid nursery systems (Part I): Shrimp (Litopenaeus vannamei) production,water quality,and stable isotope dynamics

Indoor, intensive, nursery-based recirculating aquaculture systems (RAS) can provide high-quality juvenile shrimp for indoor or pond-based production systems in a biosecure manner. However, it is unclear what type of RAS is most appropriate for indoor shrimp nurseries. This study compared three types of RAS nurseries: biofloc (BF), clear-water (CW), and hybrid (HY). Each treatment included four, randomly assigned 160 L (0.35-m²) tanks that were stocked with 3000 post-larvae shrimp m⁻³. The post-larvae (PL10) shrimp had an initial average weight of 7 ± 0.0 mg and were grown for 48 days. The BF tanks included external settling chambers as the only filtration mechanism. The CW tanks had settling chambers, foam fractionators, and external biofilters to fully clarify the water and process nitrogenous waste. Hybrid tanks included settling chambers, and external biofilters to maintain some suspended solids along with external biofiltration. Overall, the CW treatment had significantly higher dissolved oxygen (DO) and pH levels than the BF and HY systems. The HY treatment had significantly higher DO than the BF treatment. Nitrite concentration was significantly higher in the HY treatment than the CW treatment. Turbidity in the BF treatment was significantly higher than the other treatments. On the final sample date, the BF treatment had significantly higher nitrite and nitrate concentrations than the other treatments. Differences between treatments in terms of shrimp survival, mean harvest weight, specific growth rate, and feed conversion ratio were not significant. The final weight of the shrimp at 48 days for the BF, CW, and HY were 670 mg, 640 mg, and 590 mg respectively. A stable isotope mixing model indicated that, in the BF treatment, 13% of the C and 34% of the N in harvested shrimp tissue may have originated from biofloc material, signifying some nutrient recycling. The nitrification process was more effective with the inclusion of an external biofilter. All three system types appear suitable for RAS shrimp nursery production although consideration should be given to water quality consistency and filtration costs.     

Evaluation of three types of structured floating plastic media in moving bed biofilters for total ammonia nitrogen removal in a low salinity hatchery recirculating aquaculture system

Three different commercially available structural plastic media were evaluated in triplicate in moving bed biofilters under low salinity (11–12 ppt) warm water culture conditions and two different feed loading rates. The culture system consisted of nine separate modules that include a double drain fish culture tank paired to a moving bed biofilter. The biofilters were filled with 0.11 m³ of one of three different types of floating plastic structured media. The three types of media evaluated were K1 kaldnes media, MB3 media, and AMB media. Volumetric total ammonia nitrogen (TAN) removal rates (g TAN removed/m³ media-day), TAN removal efficiency, and biofilm kinetic constants, K_i (h⁻¹) were determined for the three media types at two different daily feed load rates of 3.5 and 8.2 kg feed/m³ media. The feed provided was a 4.8 mm slow sinking marine grower diet pellet (45% protein, 17% fat). Average (±standard deviation, SD) volumetric TAN removal rates (VTR) at the lower feed load for the three media types were 92.2 ± 26.3, 86.1 ± 27.5, and 82.5 ± 25.9 for the MB3, AMB, and K1 kaldnes media, respectively. At the higher feed load the average VTR for the three media types was 186.4 ± 53.7, 172.9 ± 47.8, and 139.9 ± 38.9 for the MB3, AMB, and K1 kaldnes media, respectively. Influent TAN concentrations varied by the feed load rate and ranged from 0.55 to 0.93 mg/L and 0.83 to 1.87 mg/L for the low and higher feed loads, respectively. The percent TAN removal rates for the MB3 media was the highest of the three media types at both the low and high feed load rates averaging 12.3% and 14.4%, respectively. The MB3 media was selected for use in the moving bed biofilters because of the greater VTR and removal efficiency results for use in the 0.11 m³ moving bed biofilters of the hatchery recirculating aquaculture system.     

Important influent-water quality parameters at freshwater production sites in two salmon producing countries

Further growth in Atlantic salmon (Salmo salar) aquaculture production is expected, and as a response to limited freshwater resources, recirculating aquaculture systems (RAS) are increasingly applied in smolt production. Knowledge of the general composition and quality of inlet-water is important for designing water-treatment to obtain optimal water quality in both flow-through and RAS systems. Based on water quality surveys in Norway (96 water sources, 1999–2006) and Chile (120 water sources, 2006–2008) inlet-water quality was evaluated. Norwegian smolt production is characterized by almost exclusively utilizing surface waters as inlet-water sources, with lake inlets constituting 88% and river inlets 12%. This results in large seasonal variations in both temperature, and inlet-water quality. In Chile, production is based on inlet-water from groundwater wells (32%), natural springs (40%) and rivers (28%). Norwegian inlet-water quality shows significantly lower pH and buffering capacity. The content of total organic carbon and total nitrogen is generally higher in Norway, while the levels the main metals of concern, aluminium (Al) and iron (Fe), show large between-site variability in both countries. In low pH waters in Norway, the concentration of inorganic (labile) aluminium exceeds recommended level (10 μg/L) in 15% of the samples. The Norwegian database documents highly variable production intensity in smolt production. The measured levels of carbon dioxide (CO₂, 11.6 ± 6.2 mg/L) and total ammonia nitrogen (TAN, 499 ± 485 μg N/L) (mean ± SD), exceed current legislative recommendations in 30% and 10.5% of the cases, respectively. RAS technology has the potential to improve a variable water quality if it proves reliable for the time intervals and production volumes needed. Thus, if necessary adjustments in water treatment to the local water quality are implemented, RAS production may well constitute a substantial part of smolt production in the future.