Effect of dietary microminerals in early weaning diets on growth,survival, mineral contents and gene expression in gilthead sea bream (Sparus aurata,L) larvae

In previous studies, combined inclusion of Zn, Mn and Se in early weaning diets improved larval growth, but suggested a potential toxicity by one of these elements. The present study aimed to determine the effect of the single inclusion of Zn, Mn, Se or Cu, their combination (Control+) or their absence (Control?) on larval diets. At the end of the trial, survival was significantly (p < .05) lowest in fish fed C+ diet (17.16 ± 7% mean ± SD), followed by that of larvae fed Mn diet (21.91 ± 7%). The highest survival was obtained by Cu diet (35.27 ± 15%), followed by C? diet (34.58 ± 9%). Cu and Se supplementation significantly improved total length and body weight, in comparison with the C? fish. On the contrary, fish fed Mn and C+ showed the lowest growth. Supplementation with Zn or Cu significantly increased CuZnsod, whereas gpx was significantly upregulated in fish fed Se and C+ diets. ARA/EPA level was significantly highest and DHA/EPA lowest in larvae fed the Cu diet in fish fed C+ diet. The results pointed out the importance of supplementation with Cu, as well as Se and Zn, on early weaning diets for gilthead sea bream, and the potential toxic effect of Mn.     

Effects of Cu,Zn and Cd on larval development and respiratory metabolism of pacific abalone (Haliotis discus hannai)

Trochophore and veliger are vulnerable pelagic larvae and susceptible to environmental toxicants, which are extremely crucial for the population renewal. Cu, Zn and Cd pollution are common elements in metal pollution in coastal areas. Though Pacific abalone is the main economic mollusc in China, its larval response to metals remains unclear. To understand this, the effect of Cu, Zn and Cd toxicity on malformation classification and respiratory metabolism of trochophore and veliger are analysed and measured in this paper. The 48 hr EC₅₀ for abalone trochophore was (18.9 ± 1.0) μg/L for Cu, (65.1 ± 0.3) μg/L for Zn and (1,377.8 ± 68.9) μg/L for Cd respectively. The LC₅₀ of veliger was (45.8 ± 0.9) μg/L for Cu, (50.0 ± 0.9) μg/L for Zn and (1,049.3 ± 37.6) μg/L for Cd respectively. Trochophore died with no shell at 128 μg/L Cu, yet remained alive with multiple broken‐shell bodies at 128 μg/L Zn and failed to form well‐developed shells at 20,480 μg/L Cd. All veliger died with complete shells at the mentioned concentrations. A self‐made device was used to study the effect on respiratory metabolism. The respiratory metabolism level was significantly fluctuating under Cu and Zn exposure and declined under Cd. The results indicated a decreasing order of the metal toxicity to trochophore and veliger as follows: Cu > Zn ? Cd. Cu and Zn were the main causes of shell abnormality, and Cd was less toxic. Moreover, the affected respiratory has a negative impact on further larval development.     

上海地区池塘沉积物中氮、磷、有机碳及重金属风险评价

为综合评估上海地区池塘沉积物环境质量状况,2016-2019年对上海地区36个养殖场池塘采集沉积物样品360个,检测和分析沉积物中总氮（TN）、总磷（TP）、总有机碳（TOC）及重金属Cu、Zn、Pb、Cd、Cr、Hg和As含量。研究结果表明,池塘0~10 cm层和10~20 cm层沉积物中TN、TP、TOC及各重金属均值分布无显著差异（P>0.05）,0~20 cm层沉积物（干重）中TN、TP和TOC平均含量分别为（873.37±352.45）mg/kg、（685.66±199.66）mg/kg和（6.62±3.05）mg/g,三者相关性显著。综合污染指数法和有机指数法评价结果表明,池塘沉积物中氮和有机物质的累积量较低,磷累积量相对较高,均低于其他地区高产池塘。池塘沉积物中Cr、Cd、Cu和Hg样品超标率分别为6.42%、3.21%、4.13%和1.38%,Zn、Pb和As无超标现象。地质累积指数、潜在生态危害指数法和一致性沉积物质量基准评价结果表明,上海地区池塘沉积物中重金属整体上处于清洁等级、低潜在生态危害状态,预测不会引发生物毒性效应。     

Fe、Zn、Cu不同组合对岩原鲤生长、体组成和血清生化指标的影响

试验选用体长(8.16±0.14)cm,体重(7.91±0.12)g的岩原鲤(Procypris rabaudi),经76 d的养殖试验,研究添加Fe、Zn、Cu不同组合水平的7组实用日粮对岩原鲤生长、体营养组成和血清生化指标的影响。试验鱼种630尾,随机分成7个组,每组3个重复,每个重复30尾。结果显示:饲料中添加Fe、Zn、Cu能够提高岩原鲤的生长性能和抗氧化能能力。当Fe、Zn、Cu的添加量分别为140、50、5 mg/kg时,增重率、特定生长率、饲料蛋白质效率、超氧化物歧化酶(SOD)活性和总抗氧化能力(T-AOC)最高,饲料系数最低。适量添加Fe、Zn、Cu能够显著提高岩原鲤的免疫能力。当Fe、Zn、Cu的添加量分别为200、90、4 mg/kg时岩原鲤血清溶菌酶活力最高。结果表明,岩原鲤饲料中Fe、Zn、Cu的最适添加量分别为140、50、5 mg/kg。     

Pharmacokinetics and physio‐metabolic response of single and multiple dose of fenbendazole in Labeo rohita (Hamilton, 1822) fingerlings

An experiment was carried to determine the plasma fenbendazole (FBZ) concentration and physio‐metabolic responses in juveniles of Labeo rohita (90 ± 4 g) after oral administration of single doses at 10, 20 and 50 mg, 20 mg FBZ/kg b.wt. in multiple times on 1st, 3rd and 7th day. The blood samples were collected at 0.5, 1, 2, 4, 8, 12, 24, 30, 48, 72, 96 and 120 hr, after single‐dose administration, and regularly (upto 15 day) in multiple dose. Plasma FBZ concentration was determined up to the limit of detection (LoD) of 0.09 µg/ml by HPLC. There was no parent drug detected in plasma for administration of 10 mg FBZ/kg b.wt. The drug attained the peak concentration (C_max) 1.85 and 3.09 µg/ml in plasma at 4 hr (T_max) after administration of 20 and 50mg FBZ/kg b.wt. respectively. Plasma FBZ was detectable up to 96 and 120 hr with concentration 0.09 ± 0.007 and 0.098 ± 0.006 µg/ml, respectively, after single‐dose administration of 20 and 50mg/kg b.wt. In case of multiple‐dose administration, the maximum concentration of FBZ was 1.01 ± 0.03 µg/ml on 7th day that was less than to the single dose at 50 mg/kg b.wt. However, FBZ was detected up to 11 day after multiple doses. The study revealed that the hepatic antioxidant enzymes activities like superoxide dismutase, catalase and glutathione‐S‐transferase were significantly affected by increasing FBZ in single and multiple doses. The results of the present study could reveal that single‐ or multiple‐oral administration of FBZ at 20 mg/kg b.wt. in feed as antihelminthic drug in L. rohita could be considered as the safe dose.     

Formaldehyde degradation in denitrifying woodchip bioreactors: Effects of temperature,concentration and hydraulic retention time

Formalin is applied in certain aquaculture systems to control parasites infestations as well as bacterial and fungal diseases. This study investigated the capacity of end-of-pipe denitrifying woodchip bioreactors to remove potentially harmful amounts of residual formaldehyde (FA) from aquaculture effluents. Formaldehyde was readily removed by experimental- and field-scale denitrifying woodchip bioreactors and the removal of FA was found to be a combination of an initial adsorption of FA to woodchip surfaces (52 ± 2.8 g FA/m³ woodchips) and microbial degradation. Volumetric FA removal rates reaching 261 ± 27 g FA/m³/d were found at FA inlet concentrations of 90 mg FA/L and hydraulic retention times (HRT) of 5 h. High FA removal efficiencies ranged from 88.3 ± 4.6–99.8 ± 0.2% found for FA inlet concentrations –up to 105 mg FA/L and HRTs between 3.4 and 15 h. Microbial FA degradation rates in woodchip bioreactors were positively correlated to temperature with a Q₁₀ value of 2.27 and a corresponding Arrhenius temperature coefficient of 1.086 for the investigated temperature range of 7–23 °C. At a commercial, outdoor recirculating aquaculture system (RAS) three full-scale woodchip compartments, achieved an average volumetric FA removal rate of 29.4 ± 0.2 g FA/m³/d and a removal efficiency of 82.5 ± 0.8% during the first 24 h following addition of FA. The results demonstrated that woodchip bioreactors are efficient in removing residual FA from RAS effluents and that nitrate removal was transiently enhanced during FA removal.     

Effects of stocking density on the survival,growth and physical injury of Marsupenaeus japonicus juveniles in a flowing water aquaculture system

Stocking density is a biotic factor affecting the production of cultivated animals in aquaculture. Herein, a rearing trial was conducted to investigate the impact of stocking density on the survival, growth performance and physical injury of Marsupenaeus japonicus juveniles in a flowing water aquaculture system. Five stocking densities were examined in this study, that is, 10, 20, 40, 80 and 160 individuals/m². Throughout the experiment, ammonia nitrogen and nitrite concentrations ranged from 0.02 ± 0.006 mg/L to 0.08 ± 0.035 mg/L and 0.002 ± 0.001 mg/L to 0.076 ± 0.021 mg/L respectively. The survival rate, specific growth rate (SGR), weight gain (WG), absolute growth rate (AGR) and coefficient of variation for weight (CV) across the stocking densities ranged from 90.38 ± 3.20% to 94.33 ± 4.73%, 1.42 ± 0.16%/day to 1.53 ± 0.05%/day, 1.09 ± 0.19 g to 1.15 ± 0.16 g, 0.018 ± 0.003 g/day to 0.019 ± 0.004 g/day and 16.21 ± 5.78% to 35.09 ± 10.68% respectively. Within the investigated densities, the survival rate and the abovementioned growth parameters were not significantly (p > .05) affected by the stocking density, consequently, a higher stocking density resulted in a significantly (p < .05) greater final biomass. The results regarding physical injury showed that the antennal breakage rate displayed a tendency of a positive correlation with the stocking density. Overall, the current study provides basic data for establishing a viable intensive farming system for M. japonicus and a promising indicator for easily assessing the crowding stress status of M. japonicus.     

北部湾钦州港近江牡蛎重金属污染分析

为近江牡蛎的食用安全及养殖环境监督管理提供科学依据,2015年7—11月在北部湾钦州港采集近江牡蛎样品,利用原子荧光光度计和原子吸收光谱仪测定近江牡蛎体内重金属含量,分析其污染程度。结果显示,调查海域牡蛎体内重金属平均含量从高到低依次为ZnCuCdCrAsPbHg,其中Zn、Cu含量较高,平均值分别为532.03、126.96 mg/kg。Cu参照《无公害食品水产品有毒有害物质限量》(NY 5073-2006),发现除了7月2号站样品未超标,其余样品均超标,超标率达89%。As参照《食品安全国家标准食品中污染物限量》(GB 2762-2012),发现总超标率为11%,仅7月3号站样品存在超标。Pb、Hg含量较低,其平均值分别为0.02、0.009 mg/kg。重金属富集系数揭示近江牡蛎对Zn、Cu、Cd、Cr富集严重。膳食暴露评估方法显示,重金属的膳食摄入量低于联合国粮食和农业组织的食品添加剂联合专家委员会(JECFA)推荐的暂定每周摄入量,钦州湾近江牡蛎属于安全食用范围。     

The dietary zinc requirement of a benthic fish Paramisgurnus dabryanus

This study was conducted to assess the dietary zinc (Zn) on growth and antioxidant capacity of adult Paramisgurnus dabryanus. Zinc methionine (ZnM) of grade levels (0, 20, 40, 80, 120 and 160 mg/kg diet respectively) was supplemented, providing actual dietary Zn concentrations of 24.38, 28.03, 31.68, 38.98, 46.28 and 53.58 mg/kg diet respectively. P. dabryanus with an initial body weight of 5.21 ± 0.15 g were fed these Zn supplemented diets for 8 weeks. Results showed that the weight gain (WG) and specific growth rate (SGR) increased with increasing dietary Zn levels from 24.38 to 31.68 mg/kg, and then decreased above these levels. The hepatopancreas index (HIS) was the highest at 31.68 mg/kg, followed by 38.98 mg/kg. The enzymatic antioxidants in plasma and hepatopancreas firstly increased, and reached the peak at 31.68 or 38.98 mg/kg, then kept stable with the increase of dietary Zn levels. On the contrary, the content of MDA firstly decreased, and then increased. According to WG and T‐AOC in plasma, the Zn requirement was determined to be 32.02 and 32.24 mg/kg, respectively, based on regression analysis. The relatively low dietary Zn requirement of P. dabryanus may involve in the evolutional adaption of metal absorption and utilization to their habitat.     

Comparison of bacterial communities in channel catfish Ictalurus punctatus culture ponds of an industrial ecological purification recirculating aquaculture system

The industrial aquaculture pond system has gradually replaced the use of traditional earthen pond, as it causes less pollution and is more economical. In this study, an industrial ecological purification recirculating aquaculture system consisting of the water source pond, high‐density culture ponds, a deposit pond, and ecological purification ponds for channel catfish cultivation was established. Twelve water samples from different ponds were sequenced, and the bacterial communities were analysed. The abundances of Cyanobacteria and Merismopedia varied in different functional ponds of the system. The water quality was stable after two months of cultivation at 1.89 ± 0.22 mg/L total nitrogen, 1.1 ± 0.08 mg/L NH₄‐N and 0.43 ± 0.1 mg/L total phosphorus. The fish weight increased in a nearly linear manner, reaching 237.63 ± 23.8 per fish at day 120. An analysis of the environmental parameters, water quality and fish weight suggested that the system had an effective water purification process. Canonical correspondence analysis showed that the community was affected at the genus and phylum levels by different environmental parameters. We identified several dominant beneficial bacteria with nutrient removal abilities. Overall, our results demonstrated that the ecological purification recirculating aquaculture system had notable effects on water quality improvement and promoted changes in bacterial populations. These results provide important information on the microbial ecology of pond industrial eco‐aquaculture systems.     

Effects of high temperature on the growth of European whitefish (Coregonus lavaretus L.)

The effect of three different temperatures on growth in a first progeny generation, hatchery reared, subarctic population of European whitefish (Coregonus lavaretus L.) were investigated. The whitefish (start weight 444 g, ±SD 125 g) were reared for 60 days at three constant temperatures; 15, 18 and 21°C and under ambient light regimes for 70°N latitude. The results showed that temperature had a significant influence on the growth of the fish with the highest increase in weight increment occurring at 18°C (mean final weight 656 g ± SD 151 g) compared with the growth of fish held at 15°C (mean final weight 591 g ± SD 143 g) and 21°C (mean final weight 505 g ± SD 121 g). The cumulative per cent mortality of the fish during the experimental period increased with increasing temperature, from 10% at 15°C to 30% at 21°C. The present study indicates that the optimal temperature for farming of European whitefish is somewhere between 15 and 18°C rather than between 18 and 21°C.     

Biodegradation potential of aquaculture chemotherapeutants in marine sediments

The commercial chemotherapeutant formulations SLICE^® and AlphaMax^® [active ingredients emamectin benzoate (EB) and deltamethrin respectively] are used in fin fish aquaculture to control parasitic sea lice. In some regions, the use of these substances has drawn concern from the commercial fishing industry regarding potential adverse effects on non‐target organisms. In the present work, biodegradation of EB and deltamethrin, and their commercial formulations, was investigated over 135 days at 4 and 10°C in fresh marine sediments collected from underneath an active open net‐pen salmon farm. EB incubated as either pure substance or commercial formulation was recalcitrant at both temperatures under abiotic and biotic conditions. Deltamethrin incubated alone or as its commercial formulation degraded slowly at 10°C (t_1/2 = 330 ± 107 and 201 ± 27.1 days respectively). At 4°C, deltamethrin degradation was only significant following incubation as commercial formulation (t_1/2 = 285 ±112 days). Degradation rates of EB and deltamethrin as pure substances versus their commercial formulations were not statistically different. Depletion of deltamethrin was observed in 10°C inactive sediments indicating that transformation occurred (at least in part) via an abiotic pathway. Overall, these data provide further insight into the fate and persistence of EB from the ongoing use of SLICE^® in British Columbia's salmon aquaculture industry. AlphaMax^® is not registered in Canada but is used in other salmon farming countries to control sea lice.     

Quantitative dietary copper requirement of juvenile Siberian sturgeon,Acipenser baerii,and effects on muscle composition and some enzymatic activities

An 8‐week feeding trial was conducted to quantify dietary copper (Cu) requirement of juvenile Siberian sturgeon, Acipenser baerii. Five isonitrogenous diets were formulated to provide actual dietary copper values of 1.8, 5.7, 10.1, 15.9 and 28.3 mg Cu per kg diet. Experimental diets were fed to the Siberian sturgeon (27.57 ± 0.24 g) in triplicate to apparent satiation for 8 weeks. At the end of experiment, weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) were significantly increased with increasing dietary Cu level up to 10.1 mg/kg and then decreased with further increases in dietary Cu level (p < .05). The Cu concentration in the liver and cartilage was positively correlated with the respective concentrations in the diet (p < .05), while muscle and serum Cu concentrations remained significantly unchanged (p > .05). Superoxide dismutase and glutathione peroxidase had the highest activities in serum of fish fed with 15.9 and 28.3 mg Cu per kg diet, respectively. Analysis by the broken‐line regression of SGR, crude protein content and superoxide activity demonstrated that the optimum dietary Cu requirements in juvenile Siberian sturgeon were 9.51, 9.58 and 16.10 mg/kg diet, respectively.     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.     

Dietary copper requirements of juvenile grouper, Epinephelus malabaricus

To quantify dietary copper (Cu) requirements in grouper, Epinephelus malabaricus, copper sulfate was added to the basal diet at 0, 1, 2, 4, 6, 8, 10 and 20 mg Cu/kg diet providing the actual dietary value of 0.11, 1.66, 2.41, 4.37, 6.56, 8.97, 11.03 and 20.05 mg Cu/kg diet, respectively. Each diet was fed to triplicate groups of grouper (initial body weight 13.35 ± 0.01 g) in a recirculated rearing system for 8 weeks. The Cu concentration in rearing water was monitored during the feeding period and ranged from 1.0-1.5 μg/l. Weight gain (WG) and feed efficiency (FE) were higher (P < 0.05) in fish fed diets with 4.37 and 6.56 mg Cu/kg diet than those in fish fed diets with ≥ 11.03 and ≤ 1.66 mg Cu/kg diet. Hepatic thiobarbituric acid reactive substances (TBARS) value was lowest in fish fed diets with 4.37 and 6.56 mg Cu/kg diet, intermediate in fish fed diets with 11.03 and ≤ 1.66 mg Cu/kg diet, and highest in fish fed the diet with 20.05 mg Cu/kg diet. Differences between each of the three groups were statistically significant (P < 0.05). Both hepatic copper-zinc superoxide dismutase (Cu-Zn SOD) and plasma ceruloplasmin activities in fish fell into four groups. Cu-Zn SOD value was highest in fish fed the diet with 6.56 mg Cu/kg diet, second highest in fish fed the diet with 8.97 mg Cu/kg diet, intermediate in fish fed the diet with 20.05 mg Cu/kg diet, and lowest in fish fed the diet with 0.11 mg Cu/kg diet; plasma ceruloplasmin was highest in fish fed the diet with 6.56 mg Cu/kg diet, second highest in fish fed diets with 2.41, 4.37 and 8.97 mg Cu/kg diet, intermediate in fish fed diets with ≥ 11.03 mg Cu/kg diet, and lowest in fish fed diets with ≤ 1.66 mg Cu/kg diet. All values in each of the four groups were significantly different from the values of three other groups (P < 0.05). Analysis by broken-line regression of WG, hepatic SOD activity and TBARS value and linear regression of whole-body Cu retention of the fish indicate that the adequate dietary Cu concentration in growing grouper is about 4-6 mg Cu/kg diet.     

A preliminary study on the use of mannan oligosaccharides (MOS) in freshwater crayfish, <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz, 1823 juvenile diets

The effects of dietary mannan oligosaccharides (MOS) on the survival and growth of Astacus leptodactylus juveniles were evaluated. Experimental diets were prepared by using supplementation of 0 (Control), 1.5, 3.0, and 4.5 g MOS kg⁻¹ commercial trout larvae diet containing 43 g kg⁻¹ protein and 15.74 g kg⁻¹ lipid. A. leptodactylus juvenile with an average total length of 3.6 ± 0.46 cm (TL) and average weight of 1.25 ± 0.43 g was stocked in 0.2-m² aquariums at a rate of 50 crayfish/m² and reared for 60 days at 22.8°C. The experiment consisted of four treatments with three replicates each. Each aquarium contained ten crayfish. Crayfish juvenile fed with 0, 1.5, 3.0, and 4.5 MOS attained 6.15 ± 0.49, 5.94 ± 0.29, 7.34 ± 0.39, and 5.94 ± 0.27 cm final total length and 50, 56.67, 46.67, and 50% survival rates, respectively. Moreover, molting frequencies in 0, 1.5, 3.0, and 4.5 g kg⁻¹ MOS groups were detected as 44.44, 61.11, 83.33, and 38.88%, respectively. At the end of the experiment, a general enhanced growth performance (P < 0.05) and feed conversion ratio were observed in crayfish fed on the diet containing 3.0 g kg⁻¹. Crayfish juveniles fed with 3.0 g kg⁻¹ MOS had the highest final length (7.34 ± 0.39 cm), although their survival was the lowest (46.67%) compared to other treatments but not significant. Specific growth rates were significantly different (P < 0.05) among the treatment groups at the end of the 60-day experiment. There were no significant differences (P > 0.05) in percentage moisture, protein, and ash (wet-weight basis) in the tail meat of A. leptodactylus juvenile among treatments (diet) that averaged 82.3, 16.1, and 1.2%, respectively. However, lipid value was significantly different among the diets P < 0.05), with values between 0.13 and 0.32. From the current results, it could be advised to use MOS at the rate of 3.0 g kg⁻¹ in A. leptodactylus juvenile diets.     

Conditioning,maturation and year‐round natural spawning of orange‐spotted grouper,Epinephelus coioides (Hamilton, 1822), in recirculating aquaculture system

The present experiment was aimed at studying the conditioning, maturation and natural spawning of orange‐spotted grouper, Epinephelus coioides, in a recirculatory aquaculture system (RAS). Thirty fish (n = 30; 3.35 ± 0.05 kg) were stocked in a circular tank of 125 m³ capacity fitted with an RAS for conditioning and broodstock development. After 15 days, 15 fish were implanted with 17 α methyl testosterone and letrozole at the rate of 5 mg and 0.2 mg/kg body weight, respectively, for conversion from female to male. The gonadal development started after 1 month, and by 90th day, 63.53 ± 3.78% and 2.07 ± 0.84% of the oocytes attained a size of 400–500 μm and 500–600 μm respectively. Natural spawning commenced in the RAS from 4th month onward after stocking and spawning continued round the year. The spawning pair showed courtship behaviour with a typical vertical burst of swimming just before release of gametes. The total number of eggs spawned during 1 year was 47.23 million with spawning frequency varying form 5 to 13 times per month. The association of spawning events with new moon day (lunar cycle) weakened as time progressed. The mean monthly fertilization and hatching rates varied from 77.80 ± 3.34% to 83.70 ± 1.76% and 82.80 ± 4.21% to 88.33 ± 1.39% respectively. The study proved that RAS is an efficient system that provides a stable, controllable and conducive environment for year‐round natural breeding of orange‐spotted grouper.     

Partial utilization efficiencies of protein and methionine by barramundi (Lates calcarifer) in response to dietary methionine source and form

An experiment was conducted with barramundi (Lates calcarifer) juveniles (initial weight 10.3 g ± 0.3 g) to examine the partial efficiency of utilization of methionine (Met) from intact protein (fishmeal or lupin protein concentrate) and a crystalline DL‐Met source. Fish were fed at one of three ration levels: Low (0.4 g/fish/day), Moderate (0.8 g/fish/day) and High (1.6 g/fish/day). Those fed the fishmeal‐based diet (Diet FML) at the highest ration level grew to an average weight of 37.3 ± 0.46 g, whereas those fed the Lupin Protein Concentrate (LPC)‐based diet fortified with all EAA (Diet LPCM) at the highest ration level grew to 25.4 ± 2.27 g. The weight of the fish fed the LPC diet with no additional Met (Diet LPC) even at the highest ration level declined over the course of the experiment resulting in a final weight of 9.2 ± 0.88 g, clearly demonstrating the impact of dietary Met deficiency. The partial efficiency of protein utilization was also significantly reduced when Met was limiting (a coefficient of 0.06, compared to 0.39 in the Met‐supplemented LPC diet). The results suggested that the partial efficiencies (coefficients) of both Met and protein utilization in diets where crystalline Met is the primary source of Met (Diet LPCM: 0.26 and 0.39 respectively) were significantly poorer than from an intact protein source (Diet FML: 0.89 and 0.67 respectively) when Met is provided in excess.     

Effects of dietary zinc level on performance,zinc status,tissue composition and enzyme activities of juvenile Siberian sturgeon,Acipenser baerii (Brandt 1869)

This study conducted to evaluate the effect of dietary zinc (Zn) levels on feed utilization, tissue Zn composition and serum enzyme activities of juvenile Siberian sturgeon, Acipenser baerii. Five isoenergetic and isonitrogenous semi‐purified diets were formulated with increasing Zn sulphate (ZnSO₄.5H₂O) level to provide the actual Zn values of 14.7 (control), 20.8, 27.3, 37.7 and 46.4 mg/kg diet. Each diet was assigned to three groups of 20 experimental Siberian sturgeons with uniform size (initial weight of 26.52 ± 0.94 g) for a period of 8‐week feeding trial. Results showed that growth performance and muscle protein content were significantly increased with increasing dietary Zn level up to 27.3 mg/kg (p < .05), beyond which they remained significantly unchanged (p > .05). Muscle lipid content significantly declined with increasing dietary Zn level. While muscle and serum Zn contents were not significantly changed among treatments (p > .05), liver Zn content tended to rise with increasing dietary Zn supplementation. Alkaline phosphatase, superoxide dismutase and glutathione peroxidase activities were also raised with increasing dietary Zn level. The adequate amount of dietary Zn requirements for the Siberian sturgeon was estimated to be 28.24 mg/kg based on the relative growth rate and 34.60 mg/kg based on the liver Zn content.     

Effects of dietary zinc sources and levels on growth performance,tissue zinc retention and antioxidant response of juvenile common carp (Cyprinus carpio var. Jian) fed diets containing phytic acid

Plant protein‐based diets are widely used for common carp (Cyprinus carpio var. Jian). The plant source antagonist, such as phytate, negatively affects the bioavailability of trace minerals, but this aspect was not considered in previous studies on this species. A 10‐week growth trial was conducted to investigate the effects of inorganic Zinc (ZnSO₄·7H₂O, Zn‐S) and organic Zn (2‐hydroxy‐4‐(methylthio) butanoic Zinc, Zn‐M) on growth performance, Zn retention and antioxidant responses of common carp (initial weight 10.0 ± 0.03 g). Eleven semi‐purified diets containing 7 mg/kg phytic acid were prepared with 0, 5, 20, 35, 50 and 65 mg/kg Zn from Zn‐S and Zn‐M (12.8 mg/kg Zn in basal level), respectively. The results showed that either Zn‐S or Zn‐M inclusion improved growth performance, vertebral Zn deposition and antioxidant responses of fish. The Zn requirement based on WGR, vertebrae Zn and plasma SOD were 47.0, >77.8 and 48.5 mg/kg, and 63.3, 42.2 and 36.8 mg/kg, respectively, with Zn‐S and Zn‐M as Zn sources. The relative bioavailability of Zn‐M was 2.44‐ (vertebrae Zn deposition) and 1.74‐fold (plasma SOD activity) the availability of Zn‐S in the diet of common carp. The lower growth performance and poor bioavailability in vertebrae of Zn‐S group were related to the chelating of zinc with phytic acid.