Growth performance of juvenile Russian sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) at two stocking densities in net cages

The growth performance of juvenile sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) was studied in experimental net cages (2 m × 2 m × 2 m) in freshwater Sapanca Lake. Fertilized eggs were imported from Krasnodar, Russia in January 2001. Two experimental stocking densities were employed (12 and 8 ind. m⁻³). Sturgeon were hand‐fed a pelleted commercial trout feed twice daily throughout the 203‐day experiment period. Fish were grown at ambient temperature (12.7–28.5°C) and natural photoperiod. Initial and final mean body weights were 279.5 g (±31.27) and 1112.8 g (±234.77) in the first group, and 271.1 g (±28.21) and 1140.5 g (±213.31) in the second group, respectively. Results were a fourfold biomass density increase in both trials from an initial 3.48 to 12.4 kg m⁻³ (high density) and 2.2 to 8.8 kg m⁻³ (low density). Mean specific growth rate (SGR) was determined as 2.69% day⁻¹ in both groups. Mean condition factor (CF) at the end of the experiment was 0.36 ± 0.05 in the high‐density group and 0.41 ± 0.05 in the low‐density group. Mean feed conversion ratio (FCR) was calculated to be 5.7 and 5.8, respectively. Survival was 92.7% in the first group (high density) and 96.1% in the second group (low density). The results demonstrated that sturgeon juveniles can be raised in cages and that growth performance (CF, SGR and FCR) and mortality of sturgeon were not significantly different at the two stocking densities (P > 0.05) tested.     

网箱养殖密度对虹鳟甲状腺激素及血脂指标的影响

为研究网箱养殖密度对虹鳟甲状腺激素及血脂指标的影响, 测定了血液中游离甲状腺激素T3(FT3)、游离甲状腺激素T4(FT4)、甘油三酯(TG)和总胆固醇(TC)含量, 检测了高密度胁迫对肝脏和肠中 IGF-Ⅰ和肝脏、肾脏中TR-表达的影响。结果显示, 随着养殖密度的升高FT3和FT4的含量逐渐降低, 并且在11月份之前含量与养殖时间成正相关性; 血清中TG含量随着密度的升高而降低, TC随着密度升高而升高, 并且与温度存在负相关性, 在11月份时密度处理组3(GR3)中的TG含量显著低于密度处理组1(GR1), 翌年1月份时3个密度处理组间都存在显著性差异(P 0.05); 而IGF-Ⅰ和TR-也随着养殖密度的增加表达量逐渐降低。结果说明高密度网箱养殖作为一种环境胁迫因子使得血清中FT3和FT4含量降低, 从而影响虹鳟鱼的生长发育, 这一现象与特定生长率(SGR)的变化趋势一致。甲状腺激素含量的降低使得TR-表达量降低, 实验中IGF-Ⅰ的表达与甲状腺激素含量也存在相关性, 甲状腺激素是否调控IGF-Ⅰ的表达有待于进一步的研究。       

Anadromous trout threatened by whitefish gill‐net fisheries in the northern Baltic Sea

We estimated the effect of the gill‐net fisheries targeted at whitefish (Coregonus sp.) on anadromous sea trout, Salmo trutta, in the Gulf of Bothnia, Baltic Sea using separate data for fish species. The analysis of sea trout captures was based on tagging and recapture data collected in 1998–2011, while whitefish data were derived from individual samples of commercial fisheries from the same period. The mesh sizes used in gill‐net fishing and the seasonal and temporal distributions of recaptured sea trout and sampled whitefish were compared in the northern and southern Gulf of Bothnia. The trout had typically spent 1–2 years at sea, and they were mainly immature with a median body length of 40–43 cm at the time of recapture in gill nets. Despite the increase in the minimum permitted landing size from 40 to 50 cm in 2008, the median length of recaptured trout remained unchanged during the study period. Most (59%) of the gillnetted trout were caught in the southern Gulf of Bothnia in gill nets with mesh sizes of 40–45 mm, which were also used in the whitefish fishery (72%). In the northern Gulf of Bothnia, nets with a smaller mesh size of 25–39 mm took 83% of the whitefish catch and 39% from recaptured trout. In both areas, the overlap in mesh sizes used to gill‐net catch whitefish and sea trout increased during the study period. There were clear seasonal and areal differences in the relative probability of sea trout being captured in gill nets, suggesting that carefully tailored spatial and temporal restrictions on gill‐net fisheries could provide a tool to protect young sea trout without causing intolerable difficulties for the fisheries targeting other species.     

Direct estimates of the selectivity of a multimesh and a series of single gillnets for brown trout

Hatchery brown trout Salmo trutta (1406) of length 5–20 cm were released into a 7.5 ha shallow lake. They were recaptured with 28 multimesh gillnets of a type proposed for use in the Nordic countries and 42 single gillnets of mesh size 8–22 mm (knot to knot). Corrected for the effect of different twine thicknesses, the single nets showed the highest selectivity for 16.5 mm and smaller meshes and the multimesh nets for the larger meshes. The height of the selectivity curves increased exponentially with mesh size, and most distinctly for the multimesh nets. Over a limited range of mesh sizes the selectivity of the two types of net did not differ much. Extended over mesh sizes 10.0–55.0 mm, the catching abilities of the two types of net became considerably different.     

饲料蛋白源和养殖密度对草鱼生长性能、体成分和血清生化指标的影响

为探究饲料蛋白源和养殖密度对草鱼生长以及生理健康的影响,以初始体质量为(5.36±0.18) g的草鱼(Ctenopharyngodon idella)为试验对象,采用双因素正交实验,研究饲料非粮蛋白源(豆粕、乙醇梭菌蛋白、黄粉虫、棉籽浓缩蛋白和小球藻)和初始养殖密度(0.11、0.16和0.21 kg/m³;对应为20、30和40尾/网箱)及其交互作用对草鱼生长性能、体成分和血清生化指标的影响。养殖试验在池塘网箱(1.0 m×1.0 m×1.5 m)中进行,养殖周期为60d。结果表明:随着养殖密度的增加,各蛋白源组草鱼饲料系数均呈增长趋势,特定生长率、增重率和蛋白质效率和肝体比均呈降低趋势。在不同养殖密度下,黄粉虫组饲料系数均显著高于其他蛋白源组(P<0.05),特定生长率、增重率和蛋白质效率均显著低于其他蛋白源组(P<0.05)。当养殖密度为0.11和0.16 kg/m³时,试验草鱼生长性能接近,其特定生长率显著优于0.21 kg/m³密度组(P<0.05)。饲料蛋白源和养殖密度对草鱼全鱼水分和粗蛋...     

养殖密度对史氏鲟稚鱼生长的影响

养殖密度对史氏鲟生长影响的研究结果表明 ,在养殖密度分别为 0 .2 32、0 .6 6 5、1.34 7和 2 .46 9kg·m-2 的流水环境中 ,各密度组的史氏鲟稚鱼的生长表现为不等速性 ,但生长离散没有加剧 .试验持续 2 8d后 ,各组的生长表现出显著差异 ,生长效率、特定生长率和日增重都随密度的增大而降低 ,而饵料转化率和净增重随密度的增大而增大 .特定生长率 (SGR)与养殖密度 (D)之间存在着显著的负相关     

A morphological and geometric method for estimating the selectivity of gill nets

We propose a new method for estimating gill net selectivity which estimates the probabilities leading to retention by analyzing both the fish morphology and the mesh geometry. This method estimates the number of fish approaching and contacting gill nets of different mesh sizes as an intermediate step towards computing the selectivity. Instead of assuming an underlying probability distribution as in indirect methods, we split the entire interaction between a fish and the gill net into several stages, each with its own probability. All the necessary parameters to compute these probabilities can be obtained from measurements of the fish, knowledge of the mesh geometry, and catch data from different mesh sizes. The framework offers three pathways for computing the total number of fish contacting the gill nets and has the capability to use both wedged and entangled fish in the analysis. As a proof of concept, the method is applied to catch data for cod (G. morhua) and Dolly Varden (S. malma) to estimate the number of fish contacting the gill nets in both cases. By estimating the number of fish contacting the gill net in addition to the selectivity, this method provides an important step towards deriving estimates of fish density in a particular fishery from gill net measurement.     

Mesh-size effects on drift sample composition as determined with a triple net sampler

Nested nets of three different mesh apertures were used to study mesh-size effects on drift collected in a small mountain stream. The innermost, middle, and outermost nets had, respectively, 425 µm, 209 µm and 106 µm openings, a design that reduced clogging while partitioning collections into three size groups. The open area of mesh in each net, from largest to smallest mesh opening, was 3.7, 5.7 and 8.0 times the area of the net mouth. Volumes of filtered water were determined with a flowmeter. The results are expressed as (1) drift retained by each net, (2) drift that would have been collected by a single net of given mesh size, and (3) the percentage of total drift (the sum of the catches from all three nets) that passed through the 425 µm and 209 µm nets. During a two day period in August 1986, Chironomidae larvae were dominant numerically in all 209 µm and 106 µm samples and midday 425 µm samples. Large drifters (Ephemerellidae) occurred only in 425 µm or 209 µm nets, but the general pattern was an increase in abundance and number of taxa with decreasing mesh size. Relatively more individuals occurred in the larger mesh nets at night than during the day. The two larger mesh sizes retained 70% of the total sediment/detritus in the drift collections, and this decreased the rate of clogging of the 106 µm net. If an objective of a sampling program is to compare drift density or drift rate between areas or sampling dates, the same mesh size should be used for all sample collection and processing. The mesh aperture used for drift collection should retain all species and life stages of significance in a study. The nested net design enables an investigator to test the adequacy of drift samples.     

鱼溶浆、酶解鱼溶浆和酶解鱼浆完全替代鱼粉对黄颡鱼生长的影响

为了探究鱼溶浆、酶解鱼溶浆和酶解鱼浆完全替代鱼粉后对黄颡鱼(Pelteobagrus fulvidraco)生长的影响, 在黄颡鱼实用型日粮配方模式下, 以28%的日本级蒸汽鱼粉为对照(FM), 按照FM组鱼粉蛋白质量的15%、30%和45%三个梯度, 分别添加鱼溶浆(SW15、SW30和SW45)、酶解鱼溶浆(SWH15、SWH30和SWH45)、酶解鱼浆(FPH15、FPH30和FPH45)完全替代鱼粉, 设计共10组等氮等能日粮, 每组设定3个重复, 在池塘网箱中养殖初始体重(18.68±0.10) g /尾黄颡鱼60d。结果显示: (1)以FM为对照, SW的3个试验组黄颡鱼的SGR降低9.89%—20.33%(P<0.05), FCR增加18.79%—44.85%(P<0.05); SWH试验组中SWH15和SWH45的SGR相对FM组分别降低8.79%和14.84%, FCR相对FM组增加16.97%和27.88%, 差异显著(P<0.05); FPH试验组中FPH15和FPH45的SGR相对FM组降低13.18%和15.38%, FCR相对FM增加30.30%和29.70%, 差异显著(P<0.05); (2)SWH30和FPH30组的SGR、FCR与FM组无显著差异(P>0.05); (3)相对于SW, 同等添加量SWH的SGR增加4.40%—9.39%, FCR降低9.81%—15.31%(P<0.05); (4)与FM组的FIFO值相比, SW30、SWH30和FPH30的FIFO值仅为0.67、0.61和0.60, 降低67.67%—70.15%(P<0.05)。结果表明: 在黄颡鱼日粮中, 8.5%添加量的酶解鱼溶浆(干物质)、8.2%添加量的酶解鱼浆(干物质)可以完全替代鱼粉(28%), 而相应的FIFO值分别比鱼粉组降低了69.95%和70.15%; 酶解鱼溶浆对黄颡鱼的生长效果优于鱼溶浆。日粮中过高或过低添加量的鱼溶浆、酶解鱼溶浆和酶解鱼浆都会导致黄颡鱼的生长速度和饲料效率下降。     

Effects of salinity on the growth and nutrient retention in silver perch, Bidyanus bidyanus (Mitchell 1838) (Teraponidae)

The silver perch, Bidyanus bidyanus, is a native Australian freshwater fish of the highest aquaculture potential. The species is known to tolerate a certain extent of salinity. Silver perch juveniles were fed a commercial diet (45% protein) and reared at salinities 0, 4, 8 and 12 in order to assess weight gain, specific growth rate (SGR), food conversion ratio (FCR) and nutrient retention at these four salinities. Fish reared at salinity 4 (P < 0.05) showed the best weight gain, SGR, FCR and a significantly better performance. Nitrogen and phosphorus retention were also significantly better in fish reared at salinity 4 (P < 0.05).     

Sampling and filtration efficiency of two commonly used plankton nets. A comparative study of the Nansen net and the Unesco WP 2 net

The paper presents the results from a study in which two commonlyused plankton nets, the Nansen net and the WP 2 net, were compared.The study was performed at six stations in the Baltic Sea andthe samples were collected during seasons of both high and lowparticle abundance. The comparison included both qualitativeand quantitative filtration capacity of the nets under differentenvironmental conditions. Different mesh sizes were also tested.The results show that the Nansen net has an efficiency of 50–70%compared to the WP 2 net under favourable conditions. When conditionsare unfavourable, i.e. during periods of high particle abundanceor during long hauls, the efficiency may be as low as 25–30%.The mesh size of the nets proved to be of decisive importancefor the qualitative composition of the samples. Most of thesmaller size fractions such as rotifers, copepod nauplii andyoung copepodites passed through the 160 and 200 µm meshes.The 90 µm nets sampled these fractions well but with thedrawback of retaining vast amounts of phytoplankton at certaintimes of the year.     

Length–weight relationships of 19 freshwater fishes from the Upo Wetland in South Korea

The length–weight relationships (LWRs) for 19 freshwater fish species in Upo Wetland, South Korea, were analyzed. Fish samples were collected quarterly using scoop‐nets (5 mm mesh), casting nets (7 mm mesh) and a fixed shore net (15 mm mesh) from 2007 to 2014. LWRs data for three species have not yet been listed in FishBase.     

A comparison of bridled and bridle‐less ichthyoplankton nets in a variable flow estuarine environment

The effectiveness of bridled and bridle‐less plankton nets for sampling ichthyoplankton from a fixed structure in a variable flow environment was examined. From 22 June to 19 September 2011, larval and juvenile fishes were collected weekly during night flood tides from the Moon River, an estuarine tidal creek south of Savannah, Georgia, USA. Passive horizontal tows were made from a fishing pier using two ichthyoplankton nets, each with a 1 m diameter hoop and 1 mm mesh. A bridled plankton net was configured with a tow rope attached to a traditional three‐point bridle anchored to the hoop and a closed, 1 L collection jar at the cod end. A bridle‐less net was configured with a tow rope and a float tied to the top of the hoop while a weight was tied to the bottom of the hoop. The cod end of the bridle‐less net had an open collection bucket with 1 mm mesh. Nets were deployed simultaneously in the water column, just below the surface, for three consecutive 30‐min tows. For each sampling date, pair‐wise comparisons of nets were performed on mean values of fish abundance, species richness, species diversity, and species evenness. Mean abundance was the only consistent difference between bridled and bridle‐less nets, with the bridle‐less net having on average 4.870 times more fishes. Species richness (as measured by both number of species and Margalef's species richness index) tended to be greater in the bridle‐less net, but not significantly greater. Species diversity (Shannon‐Wiener diversity index) and species evenness (Pielou's evenness index) were also not significantly different between the two nets.     

Effect of artificial baits on the catch efficiency of monofilament gill nets

Greater success in catching fish with gill nets is possible if more the fish are attracted to the nets. Bait has been successfully used to lure fish into the gill nets. With the aim of increasing the catch efficiency of monofilament gill nets, a study was conducted between January 2009 and December 2010 to test the effect of artificial baits on the efficiency of 40, 50 and 55 mm monofilament gill nets in the Keban Dam Lake (Elaz??/Turkey). The catch rate of the baited nets was compared to similar nets without bait. Baited nets caught 482 fish (71.8% of the total, seven species). Non‐baited nets caught 189 fish (28% of the total, seven species). The majority of fish (238) were caught using baited gill nets with 40 mm mesh. The most commonly caught species was Capoeta trutta. The differences between the baited gill nets and non‐baited gill nets were statistically significant (P < 0.05). Finally, it was understood that artificially baited monofilament gill nets had higher catch efficiencies than non‐baited monofilament gill nets. Unlike most natural baits, artificial baits are re‐usable and thus more economical in the long term.     

A comparison of four types of sampling gear used to collect shovelnose sturgeon in the Lower Missouri River

We compared variability in catch per unit effort (CPUE) and size structure of shovelnose sturgeon Scaphirhynchus platorynchus collected in 2003 and 2004 with stationary winter gill nets, drifted trammel nets, hoop nets, and otter trawls in the Lower Missouri River, USA to determine the most precise types of gear to collect all sizes of sturgeon so that refinements of long‐term monitoring protocols can be made. A total of 1947 net sets or trawls collected 8743 shovelnose sturgeon, with 67% of the fish collected during winter gill netting (16% of total samples). Mean coefficient of variation (CV) among all months for juvenile (age 3 and younger; <250 mm fork length) sturgeon was highest for gill nets and lowest for otter trawls (P = 0.0008). Mean CV of subadult and adult shovelnose sturgeon (≥250 mm) was highest in hoop nets compared to other gear types (P = 0.0002). All gear and mesh sizes collected the most common sizes of shovelnose sturgeon (500–600 mm), but only otter trawls and trammel nets collected fish <150 mm. The higher precision of winter gill nets and summer otter trawls led to fewer samples needed to detect changes in CPUE as compared to hoop and trammel nets. Sampling only with types of gear that do not collect younger shovelnose sturgeon may hinder management decisions that rely on recruitment trends to determine the effects of management actions (e.g. channel modifications).     

The influence of a longer photoperiod on growth parameters of European sea bass Dicentrarchus labrax (Linnaeus, 1758) reared in sea cages

The aim of this study was to investigate the effects of a long‐term photoperiod (15L : 9D) on both the somatic growth and husbandry parameters of sea bass Dicentrarchus labrax. Experiments were conducted in triplicate in high density polyethylene (HDPE) floating cages with net depths of 14 m and diameters of 20 m. Experiments were performed with approximately 170 000 sea bass with initial average weights of 110.63 ± 3.12 g and 110.26 ± 29.70 g for the experimental and control groups, respectively. Beginning in April 2008, extended artificial lighting was used in the experimental cages for 13 months; the control group received no additional illumination. At the end of the experiments, the average weights of the experimental and control groups were 362.13 ± 7.72 and 310.34 ± 18.15 g, respectively. Specific growth rate (SGR) was relatively high in the experimental group compared to the control fish. Feed conversion ratio (FCR) was 2.02 and 2.21 for the experimental and control groups, respectively, with significant differences also found between these groups (P < 0.05). Moreover, gonadal fish weight in the control group was significantly higher than in the experimental group, with the gonadosomatic index fluctuating within a 1.71‐fold increase.     

Effect of exposure to cadmium on the tropical freshwater prawn Macrobrachium rosenbergii

The effect of cadmium (Cd) on mortality, resistance and bioaccumulation in the tropical freshwater prawn Macrobrachium rosenbergii from Egypt were studied. Survival of prawns exposed to Cd doses over 60 μg l^?1 were significantly lower than that of prawns exposed to lower doses. After 96 h prawns exposed to >40 μg l^?1 of Cd had a greater reduction in total haemocyte count and phagocytic activity than those exposed to lower concentrations. Bioaccumulation of Cd in the gills, hepatopancreas and muscles was variable. Cadmium accumulated significantly in the gills and hepatopancreas, but Cd accumulation in the muscles increased only marginally. Macrobrachium rosenbergii manifested histopathological alterations in the gills, hepatopancreas and muscles when exposed to various concentrations of cadmium.     

Effect of the probiotic Bacillus subtilis on the growth and food utilization of tilapia (Oreochromis niloticus) and prawn (Macrobrachium rosenbergii) under laboratory conditions

Three experiments were conducted to analyze the effect of the probiotic Bacillus subtilis on the growth of juvenile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii). The experiments were conducted under laboratory conditions, minimizing the indirect effects of the probiotic on the water quality and leaving only the possible bactericidal and digestion-support effects. A model of stress was also designed in tilapia to compare the effect with tilapia under normal conditions. The dose in the food was 0.1% of the probiotic (5 x 10(8) CFU/g and 99.9 % maltrine) in the dry diet. Every 14 days the animals were weighed in group (tilapias +/- 0.1 g, prawns +/- 0.001 g) to estimate average body weight. In the first experiment (tilapia) the specific growth rate (SGR) and the feed conversion ratio (FCR) were bad in relation with the factor probiotic, but the differences were not significant. In the second experiment (tilapia) both the SGR and the FCR deteriorated with the addition of B. subtilis to the diet; the difference was significant to 94%. The stress factor, on the contrary, caused a notable worsening of both the growth and the food utilization. In the experiment with prawns the addition of B. subtilis caused a light deterioration of the growth and of the food utilization, with a statistical probability of mistake of 10% in case of the growth. During the experiment the direct effects over the digestive system should have prevailed, either by the contribution of macro- and micronutrients, or by the enzymes that contribute to the digestion. The negative effect due to the addition of the probiotic to the food was small (about 10% in both the SGR and the FCR) being difficult to detect statistically. The reports on the positive action of probiotics on the growth in aquatic animals have been conducted mainly in ponds, and our information does not contradict directly a possible positive action of B. subtilis in this type of systems. Since the effect on the digestive system seems to be relatively small, in those environments the effect might be compensated by other positive effects on water quality, and by bactericidal effects on pathogenic bacteria.     

Growth and body composition of rohu, Labeo rohita (Hamilton), fed compound diet: winter feeding and rearing to marketable size

A 122‐day growth trial was conducted to observe the impact of polyhouse in winter on growth, conversion efficiencies and body composition of fingerling Labeo rohita (7.9 ± 1.1 cm; 4.60 ± 0.18 g). Fish were stocked (1.5 m^?2) in polyhouse and outdoor concrete tanks (250 m²) in duplicate and fed a compound diet [35% crude protein (CP)] to apparent satiation twice daily, at 09.00 and 17.00 hours. A natural photoperiod was maintained during the trials. At the end of the trials, polyhouse‐reared fish produced significantly (P < 0.01) higher values for weight increment, specific growth rate (SGR %), protein efficiency rate (PER), protein productive value (PPV) and better feed conversion ratio (FCR). Polyhouse‐reared fish showed higher (P < 0.01) CP and fat, and lower (P < 0.01) moisture and ash contents in the muscle. In the second part of the study, which also lasted 122 days, polyhouse‐reared young L. rohita (21.7 ± 1.3 cm; 127.8 ± 0.69 g) were raised to marketable size in outdoor earthen ponds (500 m²) at a stocking density of 0.37 m^?2 to examine the effects of feeding traditional feed mixture and compound diet (30% CP) on growth and body composition of fish. Labeo rohita fed the compound diet showed higher (P < 0.01) values for weight increment, SGR (%), PER and PPV, and better (P < 0.01) FCR than those fed traditional feed. Proximate composition of fish muscle showed higher (P < 0.05) CP and fat, and lower (P < 0.05) moisture and ash contents in fish fed the compound diet. The results suggest that polyhouse may be used successfully to culture L. rohita during winter, and that thereafter the fish may be reared in earthen ponds using the compound diet to obtain better production.     

虾-鱼-贝-藻生态优化养殖及其水质生物调控技术研究

建立了一种虾、鱼、贝、藻多池循环水生态优化养殖模式及水质生物调控系统,包括对虾养殖、鱼类养殖、贝类养殖和大型海藻栽培等4个不同功能养殖区,1个水处理区以及1条应急排水渠。通过在封闭循环系统内不同池塘中放养生态位互补的经济动植物对虾池水环境进行生物调控。结果表明,循环水养殖系统内虾池水层悬浮物数量、COD值、氨态氮和硝酸态氮含量比对照组对虾单养池明显降低(P<0·01)。养殖排放水不处于富营养化状态(E<1)。对虾饲料产出对虾0.667kg·kg-1、罗非鱼0.037kg·kg-1、牡蛎0.738kg·kg-1、江蓠0.437kg·kg-1,净增产值2.01元。投入产出比由对虾单养的0.588降低为优化生态养殖的0.235。该养殖模式不仅实现了虾池水环境的生物调控与养殖用水的零排放,且显著提高了饲料利用率和经济效益,具有防病、环保、高效等优点。