Growth and food habits of hybrid carp, Ctenopharyngodon idella×Aristichthys nobilis, from aerated and non- aerated ponds

Hybrid grass carp fry ( Ctenopharyngodon idella × Aristichthys nobilis ) were stocked into 0·04 ha ponds with and without paddlewheel aeration. Fish in the paddlewheel and non-paddlewheel pond, preyed upon identical organisms, but in different proportions. Fish in the paddlewheel ponds grew at significantly greater rates.     

Growth and energy budget in young grass carp, Ctenopharyngodon idella Val., fed plant and animal diets

Young grass carp held under laboratory conditions were fed either duckweed or tubificid worms. Food consumption ( C ), faecal production ( F ), excretion ( U ), metabolism ( R ) and growth ( G ) were estimated for fish fed both diets. Fish fed tubificid worms had higher growth rates than those fed duckweed, in terms of wet weight, dry matter, protein, lipid and energy. Fish fed duckweed consumed more wet and dry matter than did the fish fed tubificids, but rates of protein and lipid consumption were lower. The energy budget was estimated to be 100C = 9 F + 8 U + 61 R + 22 G for fish fed tubificids, and 100C = 35 F + 5 U + 51 R + 9 G for fish fed duckweed. Linear relationships existed between specific growth rate in wet weight and rate of food absorption (consumption minus faecal production) in dry matter, protein or energy. Food type did not have a significant effect on these relationships. It was concluded that differences in growth rate between grass carp fed different diets were mainly caused by differences in absorption rate.     

Dietary lipid requirement on non-specific immune responses in juvenile grass carp (Ctenopharyngodon idella)

This study aimed to evaluate the dietary lipid requirement and its effects on liver oxidative status and non-specific immune responses of juvenile grass carp (Ctenopharyngodon idella). Purified diets with five dietary lipid levels (0%, 2.5%, 5%, 7.5% and 10%, fish oil/corn oil = 1:1) were each fed to triplicate groups of grass carp (mean initial weight: 6.57 ± 0.01 g) in a recirculating rearing system maintained at 27.5 ± 0.5 °C for 10 weeks. Percent weight gain was highest (P < 0.05) with 5% lipid and lowest in fish fed the lipid free control diet. Feed efficiency (FE) and protein efficiency ratio (PER) in fish followed the same pattern of percent weight gain. Fish fed with lipid containing diets had better non-specific immune response indexes (e.g. phagocytic activity, plasma peroxidase and lysozyme activity) and low-level of liver oxidation status than fish fed with the control diet. But excess dietary lipid supplement would bring over metabolic burden to liver. After the feeding trial, fish were challenged by Aeromonas hydrophila. Fish fed control diet obtained significantly (P < 0.05) lower survival rate. The survival rate was highest with 7.5% lipid. The results of this study indicated that proper dietary lipid supplementation enhanced the immune response of grass carp and improved the survival rate in the bacterial challenge, but excess dietary lipid may elevate liver oxidation rates of grass carp. Analysis by second-order regression of percent weight gain indicated that the optimal dietary lipid level in juvenile grass carp (6.6–35.5 g) is about 6.5%.     

The effect of rice seeding rate and fish stocking on the floodwater ecology of the rice field in direct-seeded,concurrent rice-fish systems

Concurrent, rice-fish systems in the Mekong Delta, Vietnam, are characterized by a rice field surrounded by a trench. Rice is direct seeded and fish are reared in polyculture. The most common species for polyculture are silver barb Barbodes gonionotus (Bleeker), common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.). In a 1996–97 rice-fish experiment, the effects of (1) absence or presence of such a polyculture, and (2) different rice-seeding rates (100 and 300 kg pre-germinated rice per ha) on the field floodwater ecology were studied. Fish obtained from local nurseries were stocked in six out of 12 rice-fish plots at the Co Do experimental rice-fish station (10°10 N and 105°20 E). Silver barb, common carp and Nile tilapia were stocked in polyculture at densities of 3150, 310 and 550 fish ha^–1, respectively. About 50% of the observed variation in the floodwater could be attributed to the fish stocked and to rice-seeding rate. The above-ground dry weight of the rice plants increased in the presence of fish and by an increase in rice-seeding rate. Greater shading by denser plants resulted in changes in variables related to aquatic primary production, including the amount of chlorophyll-a, dissolved oxygen concentration and pH. The presence of fish quadrupled the ammonium concentration, but decreased that of ortho-phosphate. Though fish increased the ammonium concentration, this did not result in a higher aquatic photosynthesis. Light, not ammonium, was the most limiting factor. However, increased ammonium concentrations in the presence of fish did have a positive effect on the density of Euglenophyta and the amount of chlorophyll-a, though only at the lower rice-seeding rate. At the higher rice-seeding rate, light seemed to be lacking. At the lower rice-seeding rate, fish also had a significant effect on the Cladocera–Rotifera ratio. Rotifera numbers increased as fish stimulated phytoplankton. We also demonstrated that fish most probably do not reduce ammonia volatilization losses. The lower rice-seeding rate seemed better for fish production than the higher rate: at the lower rate, dissolved oxygen concentrations were higher throughout the rice cycle. In addition, the amount of chlorophyll-a and the density of Euglenophyta were higher at the lower rice-seeding rate. Finally, we could show that even at high rice-seeding rates, fish had an impact on the aquatic environment. Fish access to the field is not hindered by dense rice stands.     

The effect of rice-seeding rate and fish stocking on the floodwater ecology of the trench of a concurrent,direct-seeded rice-fish system

Concurrent rice-fish systems in the Mekong Delta, Vietnam, are characterized by a rice field surrounded by a trench (on average 1000 m², covering 15–20% of the field surface). Rice is direct seeded and fish are reared in polyculture. The most common species for polyculture are silver barb Barbodes gonionotus (Bleeker), common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.). In a 1996–1997 dry season experiment, the effects of (1) absence or presence of a fish polyculture, and (2) two different rice-seeding rates (100 and 300 kg pre-germinated rice per ha) on the trench floodwater ecology were studied. Fish were stocked in six out of twelve rice-fish plots at the Co Do experimental rice-fish station (10° 10 N and 105° 20 E). Silver barb, common carp and Nile tilapia were stocked in polyculture at densities of 3150, 310 and 550 fish/ha, respectively. Several hydrological and biological parameters of the trench floodwater were measured. About 65% of the observed variation in the trench floodwater could be attributed to the fishes stocked and changes in rice-seeding rate. The presence of a fish polyculture increased the water turbidity of the trench floodwater, mainly through suspension of mineral and organic material through fish perturbation. At the lower rice-seeding rate, this resulted in a lower primary production. Photosynthetic activity, dissolved oxygen am and pm showed significant decreases, but only at the lower rice-seeding rate in the presence of fish. Fish polyculture presence resulted in lower ortho-phosphate concentrations, higher phytoplankton communities and higher Protozoa numbers, most probably due to a higher availability of nutrients through fish defecation and perturbation. The rice-seeding rate had a significant impact on pH am, pH pm and temperature pm readings. The survival rate for Nile tilapia and the gross production for Nile tilapia and common carp was higher at the lower rice seeding rate, most probably due to a better aquatic environment of the field. In terms of fish production, the trench floodwater environment was better than the field floodwater. The trench is a very important part of the rice-fish system. It serves as a refuge and supplies reasonable amounts of phytoplankton and zooplankton to the fish.     

Influence of food ration, copper exposure and exercise on the energy metabolism of common carp (Cyprinus carpio)

The present study was conducted to extend the understanding of the combined physiological effects of different food rations in combination with sublethal levels of copper in common carp (Cyprinus carpio). Fish acclimated to low (0.5% body weight) and high (5% body weight) food rations were exposed to 1 microM copper for a period of 28 days and kept for a further 14 days in copper free water to examine their recovery. Measurements of oxygen consumption, ammonia excretion and ammonia accumulation in plasma and muscle were done at various time intervals during the experimental period. Overall, oxygen consumption and ammonia excretion rates were significantly affected by food ration in both copper free and copper exposed fish. Additional challenges, such as copper exposure and/or exercise, significantly increased plasma and muscle ammonia in the fish fed a high food ration. Muscle ammonia levels in general responded slower (first increase after 72 h) and recovered within 2 weeks of exposure. There was a significant correlation between plasma ammonia levels, muscle ammonia levels and ammonia excretion rates. Influence of copper in terms of ammonia excretion and plasma ammonia accumulation was observed in high ration fish but low ration fish remained unaffected. This clearly indicates that ammonia metabolism was significantly influenced by copper in this group of fish showing that during unfavourable environmental conditions a high amount of food supply may turn deleterious to fish.     

Evaluation of natural food for planktivorous fish in Lakes Phewa, Begnas, and Rupa in Pokhara Valley, Nepal

Six floating 4-m³ cages stocked with 40 silver carp per cage (three cages) and 40 bighead carp per cage (three cages) were placed in each of the three subtropical Lakes Phewa, Begnas, and Rupa. The fish were cultured, without supplying artificial feed, from August 1994 to December 1995. Fish growth was positively correlated with water temperature, and a slight loss in weight occurred in January when water temperature fell below 16°C in all the lakes. Fish growth was better in Lake Phewa than in Lakes Begnas and Rupa, where food might not have been sufficient or of a quality to sustain fish growth. The fish fed on mostly indigestible phytoplankton, Microcystis aeruginosa in Lake Begnas and on Tabellaria fenestrata and Microcystis aeruginosa in Lake Rupa, which can lead to poor fish growth. The maximum growth rate of silver carp (5.8 g day⁻¹) and bighead carp (4.7 g day⁻¹) occurred in Lake Phewa when Ceratium hirundinella and Peridinium spp. were abundant from August through October. The food particles found in the gut were mostly similar in silver and bighead carp, though Cladocerans (Bosmina longirostris) were observed sparsely in the gut contents of bighead carp only. Received: May 21, 1999 / Accepted: September 28, 1999     

Effects of fish density on planktonic communities and water quality in a manipulated forest pond

We examined the effects of fish on lower trophic levels in a small pond in eastern Finland. The pond was divided into four sections with plastic curtains and stocked with crucian carp (Carassius carassius); two sections had low (4.4–5.5 g m^–3) and two high (10.4–13.7 g m^–3) densities of fish. In the summer of 1987, the pond was sampled weekly for phyto- and zooplankton until the fish were removed by rotenone in September after a three month experiment. Fish density as well as the extent of macrophyte cover had a considerable impact on planktonic communities and water quality. Mean zooplankton biomass was significantly lower and phytoplankton biomass higher, at high fish density. Water transparency was correlated negatively with chlorophyll-a at low fish density but turbidity appeared to reduce transparency at high fish density. The composition and dynamics of the plankton also differed at different fish densities. The mechanisms behind these effects, and the influences of habitat and fish behaviour on the results, are discussed.     

Biology and management of grass carp (Ctenopharyngodon idella,Cyprinidae) for vegetation control: a North American perspective

Summary The grass carp is one of the largest members of the family Cyprinidae. In their native habitat, grass carp typically reach weights of 30–36 kg, but fish have been reported up to 181 kg. Successful reproduction is a function of temperature, age/size, and water conditions. Fish reach maturity when about 4 years old (4–5 kg). Spawning occurs when water temperature rises above 20°C. Because grass carp eggs are semipelagic, current during spawning is required to keep eggs in suspension while they incubate. In general, successful spawning takes place under rising water conditions in very long rivers. Fecundity is very high in normal diploid individuals; females may produce over one million eggs in a season. In triploid fish, eggs and sperm are produced, but the incidence of viable offspring (even when mated with diploids) is very low.Grass carp fry begin feeding on microscopic animals and gradually switch to plant material as they grow. Adult diploids, triploids, and hybrids ( grass carp x bighead carp (Hypophthalmichthys nobilis, Cyprinidae)) are all herbivorous. Feeding is strongly affected by temperature. Active feeding begins as temperatures rise above 7–8°C and consumption peaks at 20–26°C. Whereas triploids feed at nearly the same rate as diploids, hybrids feed at substantially lower rates. Therefore, vegetation control is most efficiently achieved with diploid or triploid fish. These fish may consume more than their own weight in plant material each day. However, feeding rate (and hence vegetation control) is affected by the forage that is available. Grass carp exhibit strong preferences for different macrophyte species depending on the aquatic system (i.e. the same plant species is not always the most preferred). Hydrilla verticillata and similar species are almost always among the most preferred species, and control or elimination is usually assured if adequate stocking densities are used. Vegetation control has been reported with stocking densities as low as six fish per vegetated ha.Grass carp currently appear to be the most effective biological control on aquatic vegetation. However, in order to avoid ecological disaster, care should be taken to limit their use to sterile forms and to prevent their invasion of ecologically sensitive areas, such as waterfowl staging areas and threatened or endangered species habitat.     

不同草鱼池塘混养系统结构优化的实验研究

研究采用陆基围隔实验法,对草鱼(Ctenopharyngodon idellus)、鲢鱼(Hypophythalmichthys molitrix)、鲤鱼(Cyprinus carpio)和凡纳滨对虾(Litopenaeus vannamei)不同混养系统的养殖产量、投入产出比、氮磷利用率和综合养殖效果进行了研究。实验设置6个处理组,分别为草鱼单养(G)、草鱼和鲢鱼二元混养(GS)、草鱼、鲢鱼和鲤鱼按照不同比例放养的三元混养(GSC1和GSC2)和草鱼、鲢鱼和凡纳滨对虾按照不同比例放养的三元混养(GSL1和GSL2)。研究结果表明,各处理组总产量在770480—11492.50 kg/hm2之间;饲料系数在1.00—1.38之间,以GSC1最低,各处理组之间差异显著(P<0.05)。N、P总相对利用率在2.01—7.37之间,以GSL2最高,G最低;投入产出比在1:1.41—1:2.12之间,以GSL2最高,G最低;综合效果指标在0.59—1.39之间,以GSL2最高,G最小。研究结果表明,混养组能显著提高养殖系统的产量,降低饲料系数,提高N、P利用率,从而有效提高草鱼养殖的经济效益和生态效益。     

综合养鱼高产池塘的溶氧变化周期

根据1979—1984年对主养鲢、鳙、非鲫,主养青、草鱼,主养青鱼3种养殖结构类型高产鱼池溶氧变化周期的系统研究,揭示了高产养鱼池塘溶氧的昼夜、垂直、水平变化及季节变化周期,分析了光合作用、呼吸作用、扩散作用在高产养鱼池塘溶氧动力学上的地位和作用。对高产养鱼池塘的溶氧收入、支出及平衡情况进行了定量研究,在主要饲养季节,测得晴到多云天、晴天的溶氧来源分别为:浮游植物光合产氧占86.0和95.3%,大气扩散溶入占14.0和4.7%;氧的消耗分别为:“水呼吸”消耗氧占72.0和72.0%,鱼类呼吸消耗氧占22.0和13.1%,淤泥中生物呼吸消耗氧占2.9、5.5%,扩散逸出占3.1、8.8%。文中还对溶氧变化周期与养鱼池塘管理的环境控制、结构控制之间的关系进行了分析。       

Effects of different fish species and biomass on plankton interactions in a shallow lake

Thirty-six enclosures, surface area 4 m², were placed in Little Mere, a shallow fertile lake in Cheshire, U.K. The effects of different fish species (common carp, common bream, tench and roach) of zooplanktivorous size, and their biomass (0, 200 and 700 kg ha^–1) on water chemistry, zooplankton and phytoplankton communities were investigated. Fish biomass had a strong effect on mean zooplankton size and abundance. When fish biomass rose, larger zooplankters were replaced by more numerous smaller zooplankters. Consequently phytoplankton abundance rose in the presence of higher densities of zooplanktivorous fish, as zooplankton grazing was reduced. Fish species were also significant in determining zooplankton community size structure. In enclosures with bream there were significantly greater densities of small zooplankters than in enclosures stocked with either carp, tench and, in part, roach. When carp or roach were present, the phytoplankton had a greater abundance of Cyanophyta than when bream or tench were present. Whilst top-down effects of fish predation controlled the size partitioning of the zooplankton community, this, in turn apparently controlled the bottom-up regeneration of nutrients for the phytoplankton community. At the zooplankton–phytoplankton interface, both top-down and bottom-up processes were entwined in a reciprocal feedback mechanism with the extent and direction of that relationship altered by changes in fish species. This has consequences for the way that top-down and bottom-up processes are generalised.     

Size-structured effects of common carp on reproduction of pond-breeding amphibians

The role of fish in driving amphibian communities has been widely recognized. However, little is known about size-structured interactions between amphibian and fish populations. This study compared the taxonomic occurrence and densities of larval amphibians between unstocked ponds and ponds stocked with different age cohorts of common carp Cyprinus carpio differing in average body size. The average total densities of early and late breeding anurans known to be vulnerable to fish were by 1–2 orders of magnitude greater in the presence of young-of-the-year carp than that of older cohorts. The probabilities of occurrence of the most common taxa did not differ between ponds stocked with young-of-the-year fish and ponds free of carp, but were significantly larger in those ponds than in ponds stocked with large-size cohorts. No significant differences between pond categories were found for densities of unpalatable Bufo bufo larvae. In aquatic systems harbouring size-structured fish populations, a fish age/size gradient may explain differential habitat suitability for breeding amphibians better than the fish presence/absence dichotomy. When dominated by young cohorts incapable of predation or of adverse habitat alteration, fish-abundant waters are suitable for amphibian reproduction. Conversely, even a ‘non-predatory’ fish, after attaining large body size, may exert a detrimental impact on amphibian breeding success. These findings may be particularly important for amphibian conservation at pond fisheries characterized by spatial separation of age/size distributed stocks.     

Feeding behaviour of yearling and older hybrid grass carp

Hybrid grass carp resulting from the cross of a female grass carp, Ctenopharyngodon idella (Val.), and a male bighead carp, Hypophthalmichthys ( Aristichthys ) nobilis Rich., 12–18 months old ( c . 300 mm T.L.) were studied in a two-part experiment to determine feeding preference and total daily consumption fish^-1 on selected species of aquatic plants. Fish were maintained in circular pools with 6840·8 1 of water inside a temperature-controlled greenhouse. Preference tests were conducted at three temperature ranges; 25–28° C, 17–20° C and 12–15° C. Based on the time to complete consumption or the relative quantity consumed, the most preferred plant was Lemna gibba when in combination with six other species. Chara sp., Najas guadalupensis and Potamogeton peciinatus were readily consumed and considered to be of about equal preference. Ceratophyllum demersum and Myriophyllum brasiliense were least preferred. Hybrid grass carp generally consumed as much plant material species^-1 and in the same order of preference at the 12–15°C range as they did at 25–28° C. In the second part, mean daily consumption (g) fish^-1 at 25·7–31·0° C for five plant species tested separately was as follows: Chara sp. 369·8; Lemna gibba 178·2; Najas guadalupensis 172·6; Hydrilla verticillata 106·4 and Ceratophyllum demersum 8·8.     

Population genetics of pike,genus <Emphasis Type="Italic">Esox</Emphasis> (Actinopterygii,Esocidae), in Northern Italy: evidence for mosaic distribution of native,exotic and introgressed populations

Biomanipulation, or management actions aimed to structure biological communities to achieve certain goals, has often been used in the restoration of aquatic ecosystems. In 2000, The Nature Conservancy acquired the Emiquon Preserve, which included two former Illinois River floodplain lakes, to restore these ecosystems. Restoration included stocking to establish a native fish community commensurate with historical records. Largemouth bass (Micropterus salmoides, bass) were also introduced to control poor water clarity and invasive common carp (Cyprinus carpio, carp). We summarized fish community characteristics and tested whether bass contributed to water clarity maintenance and limited carp during 2007–2014. The fish community was dominated by species stocked in greatest abundance, 13 of 32 species initially stocked have not been collected, and species diversity increased. No carp were observed in bass diets, water clarity declined significantly, and carp relative abundance increased. Increasing water levels during 2008–2009 diffused bass predation potential upon zooplanktivorous fishes and carp and weakened potential trophic cascading interactions. Our findings suggest that water level management, greater stocking of piscivores to maintain predator densities, prevention of gizzard shad (Dorosoma cepedianum) introduction, and/or a more diverse fish community including other native piscivores may be required to achieve long-term restoration goals.     

Estimating the stocking potential of fish in impoundments by modelling supply and steady‐state demand

1. Fish stocking is an increasingly common management tool for freshwater and marine environments and is often used to create and maintain fisheries in closed waters. The densities at which fish are stocked can have a large impact on a stocking programme’s success and sustainability. Stocking densities in impoundment sport‐fisheries, for example, are often based on social or practical factors, and ecologically based stocking models are needed to assist the selection of stocking densities that are appropriate for the environment. 2. In this study, stocking density is calculated with a numerical model that balances the supply of prey production with the energetic demand of stocked fish. The model aims to deliver outcomes over a range of potential management objectives, by providing specific consumption scenarios that represent the trade‐off between population abundance and individual body size in stocked fisheries. 3. The model uses a steady‐state population approach to calculate stocking density, which optimises population consumption by maintaining a consistent biomass distribution and encourages sustainable stocking by considering the energetic needs of all cohorts. Carrying capacity is represented by the steady‐state stocking density under a minimum consumption scenario (when fish meet only their minimum energetic needs). The comparison between a desired consumption rate and the existing level of production is used to assess the status or ‘health’ of the existing population and is used to determine whether stocking can occur and whether stocking densities can be sustainably increased. The probability of incorrectly assuming populations are achieving a given consumption level is also estimated, which is an ideal approach for interpreting multiple probability distributions. 4. A Monte‐Carlo analysis of uncertainty was used to provide a probability distribution of stocking density of Australian bass (Macquaria novemaculeata) in three Australian impoundments under various seasonal and consumption scenarios. The likely consumption rates of the existing populations were determined using historical stocking densities, which showed that the three populations were of reasonable health, although one impoundment may be overstocked. The steady‐state stocking densities depended on the desired consumption rate, and there was an eightfold difference in the stocking density aimed at providing large ‘trophy’ fish and the density required to reach carrying capacity. 5. Model outputs of existing abundance and biomass density agreed with empirical estimates of abundance and relative density in these impoundments, which provides support to the model’s accuracy. This supply–demand approach to estimating the range of appropriate stocking densities shows promise as a decision‐support tool for stocked impoundments and other closed fisheries.     

Effects of temperature and stocking density on food consumption and growth of grass carp Ctenopharyngodon idella, Val.

Grass carp were raised in 227 1 indoor tanks at 12.8, 18.3, 23.9 and 29.4° C temperatures, each experimental condition received five fish. Five grass carp were also raised in a 1135 1 tank maintained at 29.4° C representing low stocking density (29.4° C-L). Food consumption, food conversion, and growth of carp were not different among the 18.3, 23.9, and 29.4° C experimental conditions with identical stocking density. The least growth and food consumption were noted for the fish at the 12.8° C temperature. The fish at the low stocking density had the best growth and maximum food consumption.     

Impact of Juvenile Stocking Size on the Major Carp Production in a Minor Reservoir,Bibinagar, India

The present study deals with the impact of juvenile stocking sizes of the major carp on production in a minor reservoir, Bibinagar, Nalgonda, India. Reservoir surface area equaled over 23.8 ha and water from the reservoir was used for irrigation and fisheries. Four experiments were conducted for 4 years from 2000–2001 to 2003–2004. The experiments were planned in such a way that every year juvenile stocking size was held constant and subsequent fish production analyzed. During the first year’s experiment (2000–2001) a stocking size of 25–30 mm (fry) was maintained. Similarly 50–55 (advanced fry), 75–80 mm (fingerling) and 100–105 mm (advanced fingerling) were stocked during 2001–2002, 2002–2003 and 2003–2004 respectively. Uniform yearly stocking densities (2000/ha) were established in each experiment in the month of July and fish were harvested in June of the subsequent year. Major carp production was enhanced with larger stocking size. Yearly productions equaled 144.00, 231.48, 632.91 and 1005.03 kg/ha/year with the above stocking sizes. Variation in stocking sizes had significant (P<0.05) effects on fish production. The number of fish per kg production decreased gradually with increases in stocking size with an average value of 3.97. Reservoir production of catla was the most abundant species, followed by rohu, common carp, mrigal and grass carp. These results show that stocking size has a great impact on fish production and the stocking of advanced fingerlings will provide maximum carp production in minor reservoirs in India.     

主养草鱼高密度池塘溶氧收支平衡的研究

采用原位生态学的方法测定广东省中山市9口主养草鱼高密度池塘中浮游植物光合作用产氧量、水柱呼吸耗氧量、底泥呼吸耗氧量和鱼呼吸耗氧量, 并用数学模型计算增氧机增氧量及用差减法计算大气扩散作用引起的得氧或失氧, 对高密度养殖池塘中溶氧收支平衡状况进行了研究。结果显示: 在水深为1.5-2.0 m的主养草鱼高密度池塘中, 光合作用产氧量随着水深的增加而显著降低(P0.05), 底层出现负值呈现氧债现象。水呼吸耗氧量在表层、中层和底层之间没有显著差异(P0.05)。表层水光合作用产氧量显著大于水呼吸耗氧量(P0.05), 而中层和底层水光合作用产氧量却显著小于水呼吸耗氧量(P0.05)。在主养草鱼高密度池塘溶氧的收入中, 浮游植物光合作用产氧量、增氧机增氧量和大气扩散溶入氧量分别占总溶氧来源的44.7%、42.3%和13.0%, 机械增氧作用已接近光合作用, 成为溶氧来源的主要贡献者; 在池塘溶氧的支出中, 水呼吸、鱼呼吸和底泥呼吸耗氧量分别占总耗氧量的45.9%、45.0%和9.1%, 鱼呼吸耗氧与水呼吸耗氧相当, 成为水体中氧气的主要消耗者。结果表明在草鱼高密度养殖过程中, 合理使用机械增氧是池塘溶氧管理的有效措施。       

Oxygen consumption, ammonia excretion and protein use in response to thermal changes in juvenile Atlantic salmon Salmo salar

Experiments were designed to examine the effects of various temperature challenges on oxygen consumption and ammonia excretion rates and protein utilization in juvenile Atlantic salmon Salmo salar . Fish acclimated to 15° C were acutely and abruptly exposed to either 20 or 25° C for a period of 3 h. To simulate a more environmentally relevant temperature challenge, a third group of fish was exposed to a gradual increase in temperature from 15 to 20° C over a period of 3 h ( c. 1·7° C h⁻¹). Oxygen consumption and ammonia excretion rates were monitored before, during and after the temperature shift. From the ammonia excretion and oxygen consumption rates, protein utilization rates were calculated. Acute temperature changes (15–20° C or 15–25° C) caused large and immediate increases in the oxygen consumption rates. When the temperature was gradually changed ( i.e. 1·7° C h⁻¹), however, the rates of oxygen consumption and ammonia excretion were only marginally altered. When fish were exposed to warmer temperatures ( i.e. 15–20° C or 15–25° C) protein use generally remained at pre-exposure (15° C) levels. A rapid transfer back to 15° C (20–15° C or 25–15° C) generally increased protein use in S. salar . These results indicate that both the magnitude and the rate of temperature change are important in describing the physiological response in juvenile salmonids.