Effect of stocking density on growth and serum concentrations of thyroid hormones and cortisol in Amur sturgeon, Acipenser schrenckii

This study investigated the effects of different stocking densities on growth and serum concentrations of thyroid hormones and cortisol in Amur sturgeon, Acipenser schrenckii. Fish were reared at low, medium, and high stocking densities (initial experimental densities were 0.30, 0.75, and 1.78 kg m⁻², respectively) for 70 days. The results showed that high stocking density had negative effects on growth and feeding efficiency, and altered serum levels of thyroid hormones and cortisol in Amur sturgeon. A significant decrease in specific growth rate was observed as stocking density was increased. The feeding rate decreased significantly in the medium and high density groups, indicating that high stocking density reduced the food consumption of sturgeon. Food conversion ratio increased with increasing stocking density, suggesting that high stocking density might inhibit fish growth through decreasing food conversion efficiency. Serum concentrations of total triiodothyronine, free thyroxine, and free triiodothyronine were inversely related to stocking densities, whereas serum total thyroxine level of sturgeon stocked at different densities remained stable. Also, higher stocking density resulted in an elevation of serum cortisol level, indicating that the sturgeon stocked at the higher density experienced density-dependent physiological stress. These results suggest growth suppression caused by high stocking density might be related to both crowding stress and the declines in peripheral circulating levels of thyroid hormones, as well as associated with the reductions in both food consumption and food conversion efficiency.     

A comparison of growth, survival rate, and number of marketable fish produced of swordtails, Xiphophorus helleri Heckel (Family Poeciliidae), between two types of culture systems

To test the effect of stocking density on growth, survival rates and size distribution of juvenile swordtails, Xiphophorus helleri Heckel, under different environmental conditions, fish were stocked at rates of 1, 3 and 6 fish I^?1. Growth was monitored over a 14-week period. Fish were weighed in six groups of 20 fish per tank. Size variation was determined at the end of the growth period by measuring the total length of each fish to the nearest mm. Fish were stocked in two different systems at three stocking densities (1, 3, and 6 fish I^?1) in replicate. The systems were an indoor aquarium system and a tunnel system under semicommercial conditions. In each system, increasing stocking rates resulted in a significant reduction of growth rates. In the aquarium system, survival rate was not related to stocking density, whereas in the tunnel system, fish at the highest stocking density had a lower survival rate than those kept at the two lower stocking densities. The number of marketable fish above a set size limit of 40 mm total length was not higher in fish stocked at 6 fish I^?1 than at 3 fish I^?1 at the end of the study. Therefore, a stocking rate of 3 fish I^?1 would be optimal. At the end of the study, fish were categorized into males, females and immature fish. Fish with a clearly visible gonopodium were classified as males, those with typical female characteristics as females, and small fish that were not yet differentiated as immature fish. The ratio of females to males was highly skewed in both systems, favouring a higher percentage of females. As stocking density increased, the female:male ratio was significantly reduced, which would result in a greater number of saleable pairs at increased stocking density. The implications of these results for the management of intensive production of swordtails are discussed.     

Evaluation of lethal and non-lethal sampling methods for the detection of white sturgeon iridovirus infection in white sturgeon, Acipenser transmontanus (Richardson)

Pectoral fin tissue of white sturgeon was investigated as a potential non-lethal sample source for the detection of white sturgeon iridovirus (WSIV) infection. Histopathology and polymerase chain reaction (PCR) results using fin tissue were compared with the standard lethal histopathology sampling method that utilizes head tissue. Tissues for each of the three sampling methods were collected weekly for 8 weeks from individual sturgeon undergoing an experimental cohabitation challenge with fish infected with the Abernathy isolate of WSIV. Non-lethal fin histopathological evaluation did not reveal infection during the first 3 weeks of sampling, while non-lethal PCR and the lethal method were variable. However, all three sampling methods were equally capable of identifying infection from 4 to 8 weeks post-exposure. Of the survivors tested, all were negative by PCR and the lethal method, and only one fish was identified as being positive by non-lethal fin histopathology. In another experiment, all three sampling methods were applied to asymptomatic WSIV carriers in a case study conducted at the Kootenai Tribal Sturgeon Conservation Hatchery. Results showed that both lethal and non-lethal fin histopathology were equally effective in detecting infection, but PCR was unable to identify this strain of WSIV. Depending on the virus isolate, these results suggest that non-lethal sampling of fin tissue (histopathology or PCR) is comparable with the lethal sampling method at identifying WSIV infection once infection is established, and under certain circumstances may provide an alternative to lethal sampling.     

Effects of Feeding Diets with and without Fish Meal on Production of Channel Catfish,Ictalurus punctatus,Stocked at Varying Densities

ABSTRACT

Animal protein, generally fish meal, has traditionally been used in the diet of channel catfish. However, our previous research indicates that animal protein is not needed for growing stocker-size catfish to food fish when the fish are stocked at densities typical of those used in commercial catfish culture. Whether this holds when fish are stocked at high densities is not known; thus, we conducted an experiment to evaluate the effect of feeding diets with and without fish meal to channel catfish stocked in earthen ponds at different densities. Two 32% protein-practical diets containing 0% or 6% menhaden fish meal were compared for pond-raised channel catfish, Ictalurus punctatus, stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48 g/fish were stocked into 30 0.04-ha ponds. Five ponds were randomly allotted for each fish meal level?×?stocking density combination. Fish were fed once daily to satiation for two growing seasons. There was a significant interaction between stocking density and fish meal for net production; net production increased in fish fed a diet containing fish meal compared with those fed an all-plant diet at the highest stocking density, but not at the two lower stocking densities. Net production of fish fed diets with and without fish meal increased as stocking density increased. Viewing the main effect means, weight gain decreased and feed conversion ratio increased for fish stocked at the two highest densities, and survival was significantly lower at the highest stocking density. Visceral fat decreased in fish at the two highest stocking densities. Body composition data were largely unaffected by experimental treatment except for a reduction in percentage filet fat in fish at the highest stocking density, and fish that were fed diets containing fish meal had a lower percentage fillet protein and a higher percentage fillet fat. It appears that at stocking densities two to three times higher than generally used, animal protein (fish meal) may be beneficial in the diet of channel catfish. In regard to stocking densities, high stocking results in higher overall production, but the average fish size decreased as stocking density increased.     

Effect of Stocking Density on Growth,Physiological Responses,and Body Composition of Juvenile Blunt Snout Bream,Megalobrama amblycephala

The impact of stocking density on growth performance, physiological indicators, and body composition of juvenile blunt snout bream in recirculating aquaculture system was investigated in this study. Juvenile blunt snout bream were raised at stocking densities of 75, 150, 225, 300, and 450 fish/m³ for 12 wk with three replicate tanks at each density. All treatment tanks were supplied with water from the same recirculating system to ensure uniformity of water quality across groups. This study has shown that higher stocking densities had a negative effect on individual growth performance. Final body mass, specific growth rate (SGR), and weight gain decreased significantly as stocking density increased. Individual body mass as well as body length were more uniform in fish stocked at densities of 75 and 150 fish/m³ than in other groups. Stocking densities of 225 and 300 fish/m³ resulted in significant increases in serum total protein, triglyceride, lactate, and cholesterol levels, whereas blood glucose concentrations decreased significantly. In addition, decreased body lipid content and increased body moisture content were observed at stocking densities of 300 and 450 fish/m³. Overall, a density of 150 fish/m³ resulted in higher SGR and more uniform size among juvenile blunt snout bream.     

Emigration of hatchery‐reared Pallid Sturgeon,Scaphirhynchus albus (Forbes and Richardson), through a Missouri River dam

The middle Missouri River (MMR; Fort Randall Dam, SD to Gavins Point Dam, NE‐SD) is stocked with hatchery‐reared pallid sturgeon, Scaphirhynchus albus (Forbes and Richardson), from upper Missouri River broodstock to aid recovery of this federally endangered species. Emigration of these fish through Gavins Point Dam restores genetic connectivity that likely existed pre‐impoundment but could lead to outbreeding depression in the future. Recapture data of hatchery‐reared pallid sturgeon stocked in the MMR were evaluated to improve understanding of pallid sturgeon emigration. From 2004 to 2015, 219 emigrants were caught: 4 stocked at age ≥2 years and 215 stocked at age ≤1 year. Emigration of the 2001‐2007 year classes stocked at age 1 was a consistent phenomenon and appeared higher than emigration of year classes stocked at ages 2–3. Little evidence suggested emigration was associated with an unusually high‐water event in 2011. The annual emigration probability of individuals stocked at age 1 estimated from multi‐state mark–recapture models was 0.05 [95% confidence interval = 0.04–0.06] for fish ages ≥1 year. This study suggests that alterations to stocking practices (e.g. stocking age) may affect emigration rates and, therefore, connectivity among pallid sturgeon populations.     

鲟鱼病原性疾病研究进展

鲟是地球上最古老的物种之一。我国自1991年后开始鲟类的商业化养殖,主要品种有引进的匙吻鲟、杂交鲟、小体鲟、俄罗斯鲟和西伯利亚鲟,黑龙江流域出产的施氏鲟、达乌尔鳇,以及施氏鲟和达乌尔鳇的杂交种等。随着养殖业的发展,鲟疾病不断增多,严重制约了养殖产业的健康发展。目前发现的鲟致病性病原有病毒、细菌、真菌和寄生虫等。概述了目前国内外鲟病原性疾病的研究进展,包括感染种群、致死率、临床症状、病原分离鉴定和药物控制等方面。目前对鲟病害的研究,在发病机制、免疫防治以及结合环境和营养因素的综合防控技术等方面还十分缺乏,应系统开展鲟疾病的流行病学、病原学、诊断技术以及防控技术研究。     

Effects of stocking density on survival and growth of juvenile tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> L.)

In two 120-day experiments, performed in the laboratory at 22°C, the effects of stocking density on the survival and growth of juvenile tench (Tinca tinca L.) were evaluated. Fish were kept in fibreglass tanks, supplied throughout with flow of artesian water, and fed a dry diet for salmonids, in excess, supplemented with restricted amounts of Artemia nauplii. In the first experiment four-month-old juveniles (0.31 ± 0.04 g and 32.00 ± 1.17 mm TL) were stocked at four densities—0.18, 0.88, 1.05, and 2.10 g l⁻¹. Survival was high (>89%) for all treatments. Final densities ranged between 1.10 g l⁻¹ (significantly lowest) and 10.46 g l⁻¹ (significantly highest). The density increase was significantly higher (611%) for fish stocked at the lowest initial density (0.18 g l⁻¹) than for fish stocked at 0.88, 1.05, and 2.10 g l⁻¹, for which the density increase averaged 457%. In the second experiment, 4.5-month-old juveniles (0.58 ± 0.17 g and 39.54 ± 0.83 mm TL) were stocked at three densities—1.05, 3.00, and 4.00 g l⁻¹. Survival was high (>96%) for all treatments. Final densities ranged between 4.08 and 16.53 g l⁻¹ and were significantly higher for greater initial densities. The density increase was greatest (413%) for fish stocked at the highest density (4 g l⁻¹) and was not significantly different for fish stocked at 1.05 and 3 g l⁻¹. Considering all the densities in the two experiments, for stocking at 4 g l⁻¹ the final density was 15 times higher than that reached after stocking at 0.18 g l⁻¹, without harmful effects on survival and growth. This final density (equivalent to 16.53 kg m⁻³) is in the range recommended for other fish species in this period under intensive conditions.     

The effect of stocking density on growth,survival and agonistic behaviour of African catfish

A high rate of sibling cannibalism is one of the principal obstacles in the rearing of larvae and juveniles of the African catfish Clarias gariepinus. This paper examines the underlying behavioural components of agonistic behaviour under culture conditions. Ten day old catfish larvae were stocked at 30 larvae l^–1 in three tank designs with different surface areas and equal volumes. Stocking densities were 1.2, 0.6 and 0.3 fish cm^–2 bottom surface. Growth did not differ between treatments. The highest mortality over 30 days was recorded at the medium density (0.6 larvae l^–1). Fish stocked at this density showed the highest rate of aggression, while there was no difference in aggression between the highest and the lowest stocking densities. The results indicate that stocking density should be at least as high as 1.2 larvae cm^–2 bottom surface area to obtain high production at best survival rates.     

Effects of Spirulina and plant oil on the growth and lipid traits of white sturgeon (Acipenser transmontanus) fingerlings

The aim of this research was to evaluate the efficiency of diets with Spirulina and plant oils (POs) inclusion for white sturgeon weaning and their effects on the fatty acid (FA) composition of fish flesh. Three isoproteic (45%) and isoenergetic (21 MJ kg^?1 DM) diets were formulated: one fish meal‐based diet integrated with fish oil (FMO) and two 40% Spirulina meal‐based diets integrated with corn (SPC) or soybean (SPS) oils respectively. One hundred and thirty‐five white sturgeon fingerlings (mean weight 17.5 g) were stocked randomly in nine fibreglass tanks. At the end of the trial, which lasted 71 days, the growth performance traits and somatic indexes were determined. The chemical composition, gross energy and FA profile were determined on the fish fillets. No significant effects were observed for the growth performances or fillet chemical composition. The FA profile of the fillets reflected those of the diets. In particular, the fillets of the fish fed with the SPC and SPS diets were lower in n‐3 FA, due to the substitution of fish oil (FO) with POs. It is possible to replace FO and meal in sturgeon; therefore, Spirulina meal integrated with POs could be a good alternative to sturgeon diet.     

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

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

养殖密度对流水养殖系统中俄罗斯鲟幼鱼生长的影响

为研究流水养殖系统中不同养殖密度对俄罗斯鲟幼鱼生长的影响,实验将初始体质量为(29.70±1.32)g的俄罗斯鲟幼鱼分置于2.5(SD1)、3.6(SD2)和4.7 kg/m3(SD3)3个养殖密度进行流水池塘(4.4 m×4.4 m×0.45 m)养殖,每个密度设3个重复,实验周期为90 d。结果显示:低密度组(SD1)幼鱼增重率(WG)、体长增长率(LG)、特定生长率(SGR)和饵料转化率(FCR)分别为362.01%±15.87%、55.88%±4.77%、(1.79±0.03)%d、114.95%±4.52%,显著高于高密度组(SD3)的272.30%±2.74%、46.34%±6.22%、(1.53±0.02)%/d、94.49%±1.96%,而SD3组幼鱼生长离散程度和死亡率显著高于SD1组幼鱼;随养殖密度增加,幼鱼体内蛋白和脂肪含量降低,水分和灰分含量升高,但是不存在显著性差异。研究表明,较高的养殖密度对俄罗斯鲟幼鱼的生长造成了显著的负面影响。     

Survival of stocked hatchery-reared brown trout, Salmo trutta L., fry in relation to the carrying capacity of a trout nursery stream

Abstract. During the period June 1982-84 hatchery-reared brown trout, Salmo trutta L., fry were Stocked into stretches of the Owendoher. a trout nursery stream on the east coast of Ireland. These experiments were designed to examine the survival of stocked fry and to estimate the carrying capacity of the system. During the first year fry were stocked into sectors already supptorting wild fish at densities normal for the system. In the following year fry numbers were artificially reduced prior to stocking with the hatchery-reared fish. Mortality of the stocked fry was high after release with less than 33% of the fish surviving beyond the first 3 weeks. No stocked fish survived after October 1982. In the second year, however, 2-9% of the fish survived. The best survival rates were achieved where wild fry numbers were lowest. Regardless of the initial stocking density the various experiments yielded autumn fry densities (0.07-0.7 fish/m²) similar to those at unstocked sites (0.1-0.62 fish/m²).
Stocking did not increase recruitment to the 1+ group and again 1+ densities (0.15-0.35 fish/m²) similar to unstocked sites (0.07-0.39 fish/m²) were obtained at the end of each year. These results suggest that spawning and recruitment in the Owendoher yield population densities approaching the maximum carrying capacity of the stream. The system appears to support a maximum summer fry density in the region of 1 fish/m² and a maximum autumn density of 0.7 fish/m².     

Effect of Stocking Density on Growth and Water Quality for Largemouth Bass Micropterus salmoides Growout in Ponds

Juvenile largemouth bass Micropterus salmoides , trained to accept artificial diets, were stocked into six 0.04-ha ponds at stocking densities of either 6,175 or 12,350 fish/ha. Fish were fed a floating custom-formulated diet, containing 44% protein, once daily to satiation for 12 mo (May 1994–May 1995). At final harvest, the total yield of fish was significantly greater (P < 0.05) and feed conversion ratio (FCR) was significantly lower, for bass stocked at the higher density (4,598 kg/ha and 2.3, respectively) than when stocked at the lower density (2,354 kg/ha and 3.3, respectively). There was no significant difference (P > 0.05) in average weight, length, or survival of bass stocked at the two densities. Averaged over the study period, there were no significant differences (P > 0.05) in total ammonia-nitrogen (TAN), nitrite-nitrogen, or un-ionized ammonia concentrations in ponds in which bass were stocked at the two densities. These data indicate that largemouth bass of the size used in this study are amenable to pond culture at densities of at least 12,350 fish/ha and that higher stocking densities may be possible.     

Development of Nursery Systems for Black Sea Bass Centropristis striata

Black sea bass (Centropristis striata) are territorial fish and cannibalism is a concern when rearing juveniles in intensive systems. Three studies were conducted to provide information for development of suitable tank nursery systems for juvenile black sea bass (3.6–4.5 cm; 0.8–1.7 g). Studies were performed at the Marine Resources Research Institute, Charleston, SC, using 1.5‐m diameter × 0.8 m deep tanks connected to recirculating seawater systems. The studies examined growth and survival at different stocking densities, selection and utilization of habitats, and, effects of water velocity on positioning and movement of fish. In study 1, fish were stocked at biomass densities of 126.7, 253.3, and 506.7 Wm³ and reared for 56 days with no habitats. No difference in growth was detected although fish reared at the lower densities had significantly lower mortality (mean 7.9%) as compared to those at the highest density (28.0%). At the highest density, cannibalism appeared to be a substantial cause of mortality. In study 2, three habitat types were used, (1) two‐tier structure constructed from plastic grating with 15 mm square openings (volume = 0.015 m³); (2) PVC pipe bundle (volume = 0.004 m³); (3) rock aggregate (volume = 0.008 m³). Of the habitats, the most utilized habitat (62.9%) was the two‐tier layered structure that allowed movement in all directions. The next utilized type was the pipe bundle (25.6%) with the openings inhabited by the largest juveniles in each tank. Overall, a mean of 18.2% of the fish were observed using habitats. Study 3 examined water velocities ranging from 0.01 to 0.12 m/sec. Most fish became concentrated in the tank bottom area having a water velocity in the range of 0.040.09 m/sec. At these velocities there were few aggressive interactions. Smaller fish inhabited the areas outside this velocity range. At the higher velocities, the small fish swam vigorously to maintain their position in the water column. At the low velocities, sporadic incursions of larger fish occurred presumably to attempt to cannibalize or to defend territory. Results from these studies help to define characteristics of nursery systems for rearing juvenile black sea bass.     

Effects of stocking density on mortality,growth and physiology of juvenile Amur sturgeon (Acipenser schrenckii)

To evaluate effects of stocking density on welfare of Amur sturgeon (Acipenser schrenckii), an experiment was designed using three initial stocking densities in flow‐through tanks (LSD = 3.7 kg m^?3, MSD = 6.9 kg m^?3, and HSD = 9.3 kg m^?3, respectively) for 60 days. Growth, body composition, and haematological and biochemical parameters were monitored. The mortality and feed conversion rate (FCR) were not affected by stocking density. However, the specific growth rate (SGR), final weight and weight gain in the HSD group were significantly lower than in the LSD and MSD groups. The hepatosomatic (HSI) and viscerosomatic indices (VSI) varied inversely with regard to stocking density. Stocking density did not affect crude protein levels in fish. In contrast, the total lipid level was significantly higher in the LSD group compared to the MSD and HSD groups. The levels of erythrocytes and haemoglobin were positively correlated with stocking density. Serum total bilirubin and urea in HSD group were significantly higher than in the LSD group while serum triglycerides showed opposite tendencies. Differences between treatments were not registered for glucose, total protein and albumin. In conclusion, higher stocking density resulted in increased immunosuppression and enhanced energy mobilization. The latter was necessary to enable Amur sturgeon to cope with crowding.     

Evaluation of Stocking Density during Second‐Year Growth of Largemouth Bass,Micropterus salmoides,Raised Indoors in a Recirculating Aquaculture System

Largemouth bass (LMB), Micropterus salmoides, are a highly desirable food fish especially among Asian populations in large cities throughout North America. The primary production method for food‐size LMB (>500 g) has been outdoor ponds that require two growing seasons (18 mo). Indoor, controlled‐environment production using recirculating aquaculture system (RAS) technologies could potentially reduce the growout period by maintaining ideal temperatures year‐round. Researchers conducted a 26‐wk study to evaluate optimal stocking densities for growout of second‐year LMB to food‐fish size in an indoor RAS. LMB fingerlings (112.0 ± 38.0 g) were randomly stocked into nine 900‐L tanks to achieve densities of 30, 60, or 120 fish/m³ with three replicate tanks per density. The RAS consisted of a 3000‐L sump, ¼ hp pump, bead filter for solids removal, mixed‐moving‐bed biofilter for nitrification, and a 400‐watt ultraviolet light for sterilization. Fish were fed a commercially available floating diet (45% protein and 16% lipid) once daily to apparent satiation. At harvest, all fish were counted, individually weighed, and measured. Total biomass densities significantly increased (P ≤ 0.05) with stocking rate achieving 6.2, 13.2, and 22.9 kg/m³ for fish stocked at 20, 60, and 120 fish/m³, respectively. The stocking densities evaluated had no significant impact (P > 0.05) on survival, average harvest weight, or feed conversion ratio which averaged 92.9 ± 5.8%, 294.5 ± 21.1 g, and 1.8 ± 0.3, respectively. After approximately 6 mo of culture, LMB did not attain target weights of >500 g. Observed competition among fish likely resulted in large size variability and overall poor growth compared to second‐year growth in ponds. Additional research is needed to better assess the suitability of LMB for culture in RAS.     

温度和重复运动对中华鲟游泳行为的影响

研究温度和重复疲劳运动对中华鲟游泳行为和能量代谢的影响,为中华鲟养殖环境水质量监测管理、物种保护和鱼道的设计等提供参考。在密封鱼类游泳装置中,利用速度递增法测定了不同温度(10、15、20和25℃)、流速条件下中华鲟(Acipenser sinensis)幼鱼(体长8.50~11.00 cm,体重5.10~8.80 g)的摆尾频率(TBF)、呼吸频率(RR),并同时测定了游泳过程中的耗氧率(M_(O_2))。结果表明:随着摆尾频率或呼吸频率的增加,中华鲟幼鱼的耗氧率增加,耗氧率与摆尾频率或呼吸频率呈指数相关(M_(O_2)=a×TBF~b;M_(O_2)=A×RR~B);随着温度增加,b值先减小后增加,15℃和20℃时b值较小;疲劳恢复后,第2次测试b值大于第1次;随着温度的增加,B值逐渐增加;疲劳恢复后,第2次测试B值小于第1次。游泳过程能量消耗随着温度的升高先降低后升高,15~20℃能量消耗较小。疲劳恢复后,第2次测试能量消耗大于第1次,游泳效率降低,特别是在10℃和25℃,15~20℃变化不明显。温度和重复游泳对中华鲟幼鱼游泳行为影响显著,温度不适宜和重复疲劳运动会产生叠加效应,导致游泳效率显著降低。     

Production of the Australian freshwater silver perch, Bidyanus bidyanus (Mitchell), at two densities in earthen ponds

Silver perch fingerlings (mean weight 15.3 g) were stocked at densities of 21 000 and 7000 fish/ha in six 0.1-ha earthen ponds and cultured for 10 months. There were three replicate ponds for each density. Ponds were aerated for at least 11 h a day and water was added every 4 weeks to replace that lost by evaporation and seepage. Fish were fed a formulated diet containing 35% crude protein at 4% body weight per day for the first 4 weeks and at rates up to 3% thereafter. The mean annual production rate of 9819 kg/ha of fish stocked at 21 000/ha was significantly higher (P < 0.01) than the annual rate of 3699 kg/ha of fish stocked at 7000/ha. The maximum daily production and growth rates achieved in any pond over a 1-month period during summer were 97.7 kg/ha and 5.1 g/fish, respectively. Stocking density did not significantly (P > 0.05) affect survival rate (treatment means for 21 000 and 7000 fish/ha: 92.8 and 94.7%), daily growth rate (0.2–3.3 and 0.3–3.4 g/fish), weight at harvest (434.9 and 473.2 g), food conversion ratio (1.9:1 and 1.8:1) and cost of feeding ($A1.55 and $A1.47/kg), suggesting that higher stocking densities and production rates are possible. Water temperatures ranged from 11.1 to 30.0 °C. Significantly (P < 0.05) slower growth during December was associated with concentrations of NH₃-N up to 0.65 mg/l. The results demonstrate that silver perch is an excellent species for semi-intensive culture in static earthen ponds with the potential to form the basis of a large industry in Australia, based on high-volume, relatively low-cost production.     

The Influence of Stocking Density on the Swimming Behavior of Adult Atlantic Cod,Gadus morhua,in a Near Shore Net Pen

Cage design and stocking density are important aspects of aquaculture farm design, therefore understanding how fish behave at different stocking densities is critical information for farm managers. In this study, high resolution acoustic telemetry was used to investigate the swimming behavior of adult Atlantic cod, Gadus morhua, that were stocked at four densities (5, 10, 25, and 45 kg/m³). Acoustic tags were placed into the abdominal cavity of five fish per density treatment so their swimming behavior could be continuously monitored throughout the study. An array of hydrophones made it possible to calculate the position of each fish in three dimensions, at ～2–5 sec intervals, for 4–30 d. Three underwater cameras were used to obtain additional data about the distribution of fish in the cage during the daytime. At the lowest density, the cod spent the majority (64.3 ± 0.08%) of their time in the bottom third of the net pen. As density increased, the fish moved higher in the water column, and this behavior was most evident at night, at all densities. At no time throughout the entire study were there any obvious occurrences of schooling behavior, even at the highest density (45 kg/m³).