鲤鱼种和鲢鳙对池塘浮游生物的影响

本文根据１９９０年－９月对９个鱼池的研究,报道鲤鱼种和鲢鳙对浮游生物的影响,结果表明：鲤鱼种使浮游植物和浮游动物生物量增加,浮游植物大型化,浮游动物小型化,并使浮游植物多样性增加,浮游动物多样性下降;鲢鳙密度增加,浮生物小型明显,微型藻类和超微在在浮植物中所占比重显著增加,小型浮游动物（原生动物和轮虫）在浮游动物中比重也明显增;鲢鳙密度对浮游生物多样性和浮游生物量的影响具有阶段性,当鲢鳙密度低时,     

Feeding and control of blue-green algal blooms by tilapia (Oreochromis Niloticus)

Outbreak of blue-green algal blooms, with associated unsightly scum and unpleasant odor, occurs frequently in eutrophic lakes. We conducted feeding experiments to study ingestion and digestion of Microcystis aeruginosa by tilapia (Oreochromis niloticus) under laboratory conditions and field testing to reduce Microcystis blooms by stocking tilapia in Lake Yuehu and other eutrophic waters in Ningbo, China between 2000 and 2003. Our results show that tilapia was capable of ingesting and digesting a large quantity of Microcystis. Digestion efficiency ranged from 58.6 to 78.1% at water temperature of 25 °C. Ingestion rate increased with increasing fish weight and water temperature. Intensive blooms occurred in Lake Yuehu in both 1999 and 2000. The lake was stocked with silver carp (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis) and a freshwater mussel (Hyriopsis cumingii) at a total biomass of 9.8 g m⁻³ in early 2001, and tilapia at 3–5 g m⁻³ in April of 2002. From June to October, average phytoplankton density decreased from 897.6×10⁶ cells l⁻¹ in 2000 to 291.7×10⁶ cells l⁻¹ in 2001 and 183.0×10⁶ cells l⁻¹ in 2002. Compared to 2000, the annual average phytoplankton biomass in 2001 and 2002 decreased by 48.6% and 63.8%, respectively. The blue-green algal biomass which made up 70% of the total phytoplankton biomass in 2000 was reduced to 22.1% in 2001 and 11.2% in 2002. Meanwhile, Secchi depth increased from 20–50 cm to 55–137 cm during the same time period. Similar results were observed in some other eutrophic waters. For example, algal bloom disappeared about 20 days after tilapia fingerlings were stocked (8–15 g m⁻³) to a pond in Zhenhai Park. Chlorophyll a concentration and phytoplankton production declined dramatically whereas water transparency increased substantially. However, the impacts of tilapia on nitrogen and phosphorus dynamics in natural lakes need further investigation. Our studies revealed that stocking tilapia is an effective way to control algal blooms in eutrophic waters, especially in lakes where nutrient loading cannot be reduced sufficiently, and where grazing by zooplankton cannot control phytoplankton production effectively.     

Aquaculture of fry and fingerling of pike-perch (Stizostedion lucioperca L.) — a short review

This review presents a short survey of pertinent literature on rearing methods of pike-perch fry and fingerlings in ponds, net cages and tanks. The traditional pond culture results in variable numbers of fingerlings, which are sometimes small and are therefore of limited value for stocking. Fingerling production can be increased by manipulating the succession of zooplankton and by stocking adequate quantities of fry in the pond. Culture in illuminated net cages in lakes seems to be a possibility to produce advanced fry. The rearing of larvae in tanks following controlled propagation is initially based on feeding natural plankton. The artificial diet can only be used successfully several weeks later at fingerling size (4–5 cm). High mortality rates of fry and symptoms of food deficiency in liver cells indicate unsatisfactory quality of larval diets tested until now. Lack of an adequate artificial feed considerably hampers further development of intensive rearing of fry. Growth of fry and fingerlings is strongly temperature dependent. Growth is rather poor at 16–18°C and best between 26–30°C. Although there is a short stage of positive phototropism in fry, older pike-perch generally prefer dim light. There is no food uptake at high light intensity and mortalities will occur under such conditions. More research is needed on adequate diets which consider the ontogenetic development of the digestive organs of young fish.     

Changes in abundance of larvae of the four domestic Chinese carps in the middle reach of the Yangtze River, China, before and after closing of the Three Gorges Dam

The four domestic Chinese carps, i.e. grass carp (Ctenopharyngodon idella), black carp (Mylopharyngodon piceus), silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), cast their drifting eggs in the running water of the Yangtze River. In 1997 ~ 2005, a systematic study on the dynamics of the abundance the larvae of the four domestic Chinese carps was performed in the middle reach of the Yangtze River, close to Sanzhou city. It was calculated that in breeding seasons from early May to late June every year the abundance of fry drifting through the section of Sanzhou was 3.59 billion in 1997, 2.75 billion in 1998, 2.15 billion in 1999, 2.85 billion in 2000, 1.90 billion in 2001, 1.90 billion in 2002, 406 million in 2003, 339 million in 2004 and 105 million in 2005 respectively. Several environmental parameters related to the dynamics of larval abundance were also examined simultaneously. The construction of the Three Gorges Dam near Yichang between the upper and middle reaches of the Yangtze River has apparently had a drastic influence on the abundance of fish larvae.     

The relevance of size parameters as indicators of fishery exploitation in two West African reservoirs

Fish communities living within the artificial reservoirs of Manantali and Selingue in Mali are compared after the monitoring of small-scale fishery landings over 13 months (May 2002–June 2003). The fishing pressure constitutes the main difference of these two similar reservoirs. The effects of fishing on the structure of the fish communities are analyzed by using fish size spectra and derived indicators. In Selingue Reservoir, the fishing gears mostly target smaller species (mean length of 165 mm) than in Manantali Reservoir (mean length of 210 mm). Unlike in Selingue, the size structure does not change between seasons in Manantali. In Selingue, fishing practices that target the fish recruitment of the year constitute a structuring factor of the fish sizes observed in the catches. In spite of similar values of the slopes of the global fish communities’ size spectra between the two reservoirs, they clearly display an intense exploitation at Selingue. Then, size-based spectra indicators represent a potential tool for assessing the impact of fishing on fish communities in small-scale fisheries.     

一种优良淡水鱼——团头鲂(Megalobrama amblycephala)的繁殖和饲养

团头鲂原是一种野生的草食性淡水鱼类,从1960年起对它进行了一系列的观察试验,肯定它有以下六个优点:(1)在池养条件下,性腺能发育成熟;(2)以各种草类为主要食料;(3)抗病力强、成活率高;(4)容易捕捞、起水率高;(5)含肉量高,脂多、味美;(6)一年半可长至商品规格。试验结果证明团头鲂可以作为新的养殖对象,同时也提供了一套繁殖、饲养管理方法。1964年到1973年已有二十一个省市先后进行移殖饲养,有的已就地繁殖、推广。本文系历年试验和部分移殖经验的总结。       

Ontogenetic shift in dietary preference and low dietary overlap in rohu (<Emphasis Type="Italic">Labeo rohita</Emphasis>) and common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) in semi-intensive polyculture ponds

In order to investigate ontogenetic changes in diet and diet overlap between rohu (Labeo rohita) and common carp (Cyprinus carpio) in polyculture ponds, food preferences of different size classes of these fishes were quantified. Rohu diet consisted of both phytoplankton and zooplankton, and there was a distinct ontogenetic shift in the relative importance of these food items. Zooplankton was the dominant food for rohu up to 20.6 cm total length (TL) and then gradually decreased in importance as fish grew. Phytoplankton was initially a minor component of rohu diet but gradually increased in importance and became the dominant food for rohu at 24.2 cm TL. Phytoplankton biovolume in rohu guts was positively correlated with fish size (TL). Chesson’s α indicated that rohu of all sizes preferentially selected Cladocera and avoided Cyanophyceae and Euglenophyceae. Young rohu initially preferred Rotifera and Copepoda but gradually switched to Bacillariophyceae and Chlorophyceae. Common carp diet consisted of phytoplankton, zooplankton, and benthic macroinvertebrates, but was dominated by benthic macroinvertebrates (63–92% of total diet). As common carp grew, the proportion of zooplankton ingested decreased and the proportion of benthic macroinvertebrates increased. Benthic macroinvertebrate biovolume in common carp guts was positively correlated with fish size. Common carp of up to 15.4 cm TL preferentially selected zooplankton, but common carp larger than 18.9 cm TL avoided this food item. Common carp of all sizes avoided phytoplankton. A low dietary overlap was found between rohu and common carp (Schoener overlap index: 0.08–0.35), probably due to ingestion of smaller quantities of zooplankton by the latter. Dietary overlap also decreased with increasing rohu and common carp size because of divergent ontogenetic shifts in dietary preferences of the two species.     

Feeding behavior of black carp Mylopharyngodon piceus (Pisces: Cyprinidae) on fry of other fish species and trematode transmitting snail species

Fish raised in aquaculture ponds may get infected with fishborne zoonotic trematodes (FZT) during the nursing stage. Freshwater snails serve as intermediate hosts for FZT and we wanted to explore the possibility of controlling snails by stocking nursery ponds with a few juvenile specimens of the mollusc-eating fish, black carp (Mylopharyngodon piceus). Obviously, the risk that black carp might also prey on the juvenile fishes in nursery ponds should first be assessed. Laboratory trials showed that all size classes of juvenile black carp consumed fry of common carp (Cyprinus carpio) even when offered snails as food; the odds of survival of fry from tanks with medium sized and large black carp was 5.6% and 39.9%, respectively of that of fry in tanks with small sized black carp. Since the large black carp also consumed fewer snails than medium sized fish, we believe that large specimens were stressed in the experimental aquaria. Under semi-field conditions, presence of the black carp had no effect on survival of fry of Oreochromis niloticus and C. carpio both in the absence and presence of snails as alternative food. The black carp consumed most snails offered with the exception of some of the large snails. We conclude that under field conditions, predation by black carp on fish fry is minimal and field trials in nursery ponds are warranted. Due to the risks that black carp pose to native imperiled snails and other molluscs, trials should be restricted to ponds within the fish’s native or existing range.     

Outdoor stocking density in free-range laying hens: radio-frequency identification of impacts on range use

The number and size of free-range laying hen (Gallus gallus domesticus) production systems are increasing within Australia in response to consumer demand for perceived improvement in hen welfare. However, variation in outdoor stocking density has generated consumer dissatisfaction leading to the development of a national information standard on free-range egg labelling by the Australian Consumer Affairs Ministers. The current Australian Model Code of Practice for Domestic Poultry states a guideline of 1500 hens/ha, but no maximum density is set. Radio-frequency identification (RFID) tracking technology was used to measure daily range usage by individual ISA Brown hens housed in six small flocks (150 hens/flock – 50% of hens tagged), each with access to one of three outdoor stocking density treatments (two replicates per treatment: 2000, 10 000, 20 000 hens/ha), from 22 to 26, 27 to 31 and 32 to 36 weeks of age. There was some variation in range usage across the sampling periods and by weeks 32 to 36 individual hens from the lowest stocking density on average used the range for longer each day (P<0.001), with fewer visits and longer maximum durations per visit (P<0.001). Individual hens within all stocking densities varied in the percentage of days they accessed the range with 2% of tagged hens in each treatment never venturing outdoors and a large proportion that accessed the range daily (2000 hens/ha: 80.5%; 10 000 hens/ha: 66.5%; 20 000 hens/ha: 71.4%). On average, 38% to 48% of hens were seen on the range simultaneously and used all available areas of all ranges. These results of experimental-sized flocks have implications for determining optimal outdoor stocking densities for commercial free-range laying hens but further research would be needed to determine the effects of increased range usage on hen welfare.     

Consequences of the size structure of fish populations for their effects on a generalist avian predator

Size-structured interspecific interactions can shift between predation and competition, depending on ontogenetic changes in size relationships. I examined the effects of common carp (Cyprinus carpio), an omnivorous fish, on the reproductive success of the red-necked grebe (Podiceps grisegena), an avian gape-limited predator, along a fish size gradient created by stocking distinct age-cohorts in seminatural ponds. Young-of-the-year (0+) carp were an essential food source for young grebes. Only adult birds were able to consume 1-year-old (1+) fish, while 2-year-old (2+) fish attained a size refuge from grebes. Amphibian larvae were the principal alternative prey to fish, followed by macroinvertebrates, but the abundance of both dramatically decreased along the carp size gradient. Fledging success was 2.8 times greater in ponds with 0+ versus 1+ carp; in ponds with 1+ carp, chicks received on average 2.6–3 times less prey biomass from their parents, and over 1/3 of broods suffered total failure. Breeding birds avoided settling on 2+ ponds. These results show that changes in prey fish size structure can account for shifts from positive trophic effects on the avian predator to a negative impact on the predator’s alternative resources. However, competition did not fully explain the decrease in grebe food resources in the presence of large fish, as carp and grebes overlapped little in diet. In experimental cages, 1+ carp totally eliminated young larvae of amphibians palatable to fish. In field conditions, breeding adults of palatable taxa avoided ponds with 1+ and older carp. Non-trophic interactions such as habitat selection by amphibians or macroinvertebrates to avoid large fish may provide an indirect mechanism strengthening the adverse bottom-up effects of fish on birds.     

鳜春季、夏季和秋季按季节人工繁育模式的研究

为满足不同地区、不同季节鳜(Sinierca chuatsi)养殖需要, 实现均衡上市的苗种供应要求, 研究通过对两批亲鱼在不同季节各进行4次交替人工催产, 按月建立苗种繁育模式。结果显示, 池塘中自然培育的亲鱼, 卵巢成熟系数出现2个峰值, 而网箱中培育的亲鱼, 经过4次人工催产, 出现4个成熟系数峰值, 产卵量和出苗量与成熟系数峰值正相关。以二繁的成熟系数、产卵量和出苗量最高, 显著高于其他三次(P<0.05), 二繁、三繁和四繁的受精率、孵化率和苗种培育成活率均较高, 显著高于一繁(P<0.05), 温度是影响一繁受精率、孵化率和苗种培育成活率的主要因素。产后亲鱼成活率随人工繁殖次数增加而下降, 其中以一繁的成活率最高, 达93.33%, 显著高于三繁和四繁(P<0.05)。综上结果表明, 通过按季节分梯次人工繁育模式解决鳜苗种生产的均衡供应是可行的。这为转变鳜的养殖方式提供了科学依据, 也为其他鱼类苗种的均衡生产提供了借鉴意义。     

Predation of zebra mussels by round gobies, Neogobius melanostomus

Preliminary gut analysis of a recent Great Lakes invader, the round goby, Neogobius melanostomus (7.0–8.4 cm), collected from the Detroit River, showed that they ate zebra mussels (58%), snails (6%), and other invertebrates (36%), including aquatic insects (Hexagenia), softshelled crayfish, and zooplankton. Because zebra mussels, Dreissena polymorpha, predominated as prey, we investigated the ability of round gobies to consume different size classes of zebra mussels. In laboratory experiments, we examined feeding preferences of three size classes of round gobies (5.5–6.9 cm; 7.0–8.4 cm; 8.5–10.3 cm standard length) on four different size classes of zebra mussels (6.0–9.9 mm, 10.0–12.9 mm, 13.0–15.9 mm, 16.0–18.9 mm). All sizes of round gobies ate zebra mussels < 10.0 mm. Only the largest size class of round gobies ate larger zebra mussels (10.0–12.9 mm) when all prey sizes were presented. The association between the total mass of zebra mussels available and the amount consumed by round gobies increased positively up to about 6.5 g of available mussels and then levelled off. Round gobies consumed an average of 1.0 g of mussels in 24 h. There was a significant positive relationship between gape size and standard length of round gobies. Although larger round gobies (over the size range of fish in our study) are able to consume larger zebra mussels, small mussels were preferred. Our findings suggest that the preference of small zebra mussels by round gobies has the potential to alter the size structure of zebra mussel populations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding,production and marketing of golden tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> (L.)) in Gan Shmuel Fish Breeding Center,Israel

A first attempt to introduce tench (Tinca tinca (L.)) to Israel, followed by comparative growth experiments, was carried out in 1947. A batch of 200 fingerlings, which were supposed to serve later as brood fish, was imported from Switzerland to Fish Culture Experimental Station at Sdeh Nahum. However, after 2 years tench were considered unsuitable for culturing in Israel and the trials were abandoned. Two factors affected negatively these historically early trials: (1) Tench was just second exotic species introduced to Israel some years after introduction of the common carp, and the Israeli fish farming expertise at that time was low. (2) The Independence War temporarily delayed advancement of aquaculture. A second introduction of tench was performed in 1992, when a golden mutant of tench was imported to Gan Shmuel Fish Breeding Center (GS-FBC) from the Research Institute of Fish Culture and Hydrobiology at Vodňany, Czech Republic. Currently, GS-FBC is the only Israeli fish hatchery that maintains golden tench as a part of breeding program as well as a number of other varieties of ornamental fish and species, all of them produced mostly for export. Tench (800–1,000 g) females are maintained separately from males, in order to prevent uncontrolled reproduction. Routinely, in April, the fish are transferred indoors and induced to spawn artificially with a single injection of GnRH synthetic analog—DAGIN. Dry method of stripping is used to obtain eggs and sperm. After fertilization the sticky eggs are spread in a single layer on walls of 230 dm³ cylindrical incubators provided with conical bottom, or they are degummed using a solution of milk/water. At a water temperature of 24°C, hatching (70% hatching rate) occurs 36–40 h after fertilization. The larvae absorb their yolk sac 2–3 days after fertilization and they start feeding on small size (200 μm) Artemia nauplii. At the age of 7–10 days, if fry are retained indoors, they are fed with regular size Artemia and starter feed, or are released into a nursing 0.5–1.0 ha pond. Usually, the fish are grown to the marketing size (5–15 cm) and exported abroad, mainly to Europe. About 100,000 golden tench fingerlings, with a total value of € 40,000 are produced and marketed annually.     

An evaluation of government‐recommended stocking systems for sustaining pastoral businesses and ecosystems of the Alpine Meadows of the Qinghai‐Tibetan Plateau

China introduced the “Retire Livestock and Restore Grassland” policy in 2003. It was strengthened in 2011 by additional funding for on‐farm structures. On the Qinghai‐Tibetan Plateau (QTP), fences were erected, livestock excluded from degraded areas, rotational stocking introduced, nighttime shelters were built, forages grown, and seed sown. However, the effectiveness of these actions and their value to Tibetan herders has been questioned. We conducted a sheep stocking experiment for 5 years in an Alpine Meadow region of the QTP to evaluate stocking options recommended by Government. Cold and warm season stocking each at three rates (0, 8, and 16 sheep/ha) and continuous stocking at 0 and 4 sheep/ha were compared. We measured live weights of sheep, plant species richness and evenness, root biomass and carbon (C), nitrogen (N) and phosphorus (P) contents of the 0–10 cm of soil. We found that resting grassland from stocking during the warm season for later cold season stocking significantly reduced plant species richness and evenness and root biomass but not soil C, N, and P. During cold season stocking, live weights of sheep declined whether at a stocking rate of 8 or 16 per ha. In contrast, sheep continuously stocked on grassland at 4 per ha gained weight throughout both the warm and cold seasons and plant species richness and evenness were maintained. Warm season stocking at 8 and 16 sheep/ha increased plant species richness and root biomass but reduced plant species evenness. Resting these alpine grasslands from stocking in the warm season has adverse consequences for plant conservation. Fencing from stocking in the warm season is not justified by this study; all grassland should be judiciously stocked during the warm season to maintain plant species richness. Neither resting nor stocking during the cold season appears to have any adverse consequences but sheltering and in‐door feeding of sheep during the cold season may be more profitable than cold season stocking with use of open nighttime yards.     

Effect of recreational-fisheries management on fish biodiversity in gravel pit lakes,with contrasts to unmanaged lakes

Gravel pit lakes are novel ecosystems that can be colonized by fish through natural or anthropogenic pathways. In central Europe, many of them are managed by recreational anglers and thus experience regular fish stocking. However, also unmanaged gravel pits may be affected by stocking, either through illegal fish introductions or, occasionally, by immigration from connected water bodies. We sampled 23 small (< 20 ha) gravel pit lakes (16 managed and 7 unmanaged) in north-western Germany using littoral electrofishing and multimesh gillnets. Our objective was to compare the fish biodiversity in gravel pit lakes in the presence or absence of recreational fisheries. Given the size of the sampled lakes, we expected species poor communities and elevated fish diversity in the managed systems due to regular stocking of game fish species. Our study lakes were primarily mesotrophic and did not differ in key abiotic and biotic environmental characteristics. Lakes of both management types hosted similar fish abundances and biomasses, but were substantially different in terms of fish community structure and species richness. Fish were present in all lakes, with a minimum of three species. Higher α-diversity and lower β-diversity was discovered in managed gravel pit lakes compared to unmanaged lakes. Consequently, recreational-fisheries management fostered homogenization of fish communities, by stocking a similar set of fish species desired by anglers such as piscivorous fish and large bodied cyprinids. However, unmanaged gravel pit lakes were also affected by human-mediated colonization, presumably by illegal fish releases. Hardly any non-native species were detected, suggesting that recreational-fisheries management did not foster the spread of exotic species in our study region.     

Studies on the role of exogenous proteolytic enzymes in digestion processes in fish

Studies were carried out on the proteolytic activity of the fry of common carp, rainbow trout, grass carp, and whitefish, as well as on the activity of digestive organs of adult common carp and rainbow trout. Activity of exogenous enzymes in relation to endogenous ones was assessed on the basis of the proteolytic value of fish food and the activity of digestive organs. It was found that the share of proteolytic enzymes of natural food in the digestion process in fish was high. Beginning from a weight of 50–100 g for common carp and 10 g for rainbow trout, the relation between the daily enzymatic ration and the weight of fish indicates the cooperation of an approximately constant amount of exogenous enzymes.     

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.     

A mark-recapture population estimate for invasive silver carp (<Emphasis Type="Italic">Hypophthalmichthys molitrix</Emphasis>) in the La Grange Reach,Illinois River

Invasive silver carp (Hypophthalmichthys molitrix) populations have expanded greatly in the Upper Mississippi River System (UMRS) since their introduction in the early 1970s. We conducted a Chapman-modified, continuous Schnabel mark-recapture population and biomass estimate for silver carp (106–901 mm) in the La Grange reach, Illinois River during 2007–2008. We estimated a total of 328,192 (95% CI 231,226–484,474) silver carp (2,544 per river km 1,792–3,756) comprising 705 (95% CI; 496–1,040) metric tons of biomass (5.5 metric tons per river km 3.8–8.1). Long Term Resource Monitoring Program (LTRMP) data from the La Grange reach showed an exponential increase in silver carp catches since 1998, with an intrinsic rate of increase approaching 84%. In 2008, silver carp comprised about 51% of the total LTRMP annual fish collection. To our knowledge, this large river reach may contain the greatest ambient densities of wild silver carp in the world. Our findings provide a target for reduction efforts and also emphasize the importance of the La Grange reach as a source population for potential expansion of the species to the Laurentian Great Lakes.     

姚江鱼类种群生态特点和鱼产力估量

本文根据1976-1977年的调查研究,讨论姚江鱼类种群生态特点,并参照对杭州青山水库的一些调查及中国科学院水生生物研究所对武昌东湖的研究,估量姚江的鱼产力,旨在为拟定增产措施提供科学根据。       

Culture-based fisheries in minor perennial reservoirs in Sri Lanka: variability in production, stocked species and yield implications

Sri Lanka is blessed with a large number of irrigation reservoirs. Depending on their hydrological regimes they are broadly categorized into perennial and seasonal reservoirs, and are secondarily used for inland fisheries. The Ministry of Fisheries and Aquatic Resources in Sri Lanka initiated a programme to introduce culture‐based fisheries in minor perennial reservoirs (< 250 ha) whereby 15 minor perennial reservoirs situated in eight administrative districts were selected for introduction of culture‐based fisheries in its initial year of implementation. These reservoirs were stocked with fish fingerlings of catla Catla catla, rohu Labeo rohita, common carp Cyprinus carpio, Nile tilapia Oreochromis niloticus and post‐larvae of freshwater prawn Macrobrachium rosenbergii. Stocking commenced in 2004; stocking data from 2004, 2005 and 2006 are considered in this study. Stocking densities varied from 217 to 870 ha^?1 year^?1, with an average density of 425 ha^?1 year^?1. Fish catch statistics for 2005, 2006 and 2007 were considered; high variability in fish yield among reservoirs as well as in some reservoirs between the years were observed. Mean annual fish yield from all 15 reservoirs increased from 57.3 to 208.1 kg ha^?1 year^?1 after the introduction of culture‐based fisheries. Overall fish production in all 15 reservoirs increased by 263%, ranging from 42.8 to 1344%. Overall contributions of Nile tilapia, catla, rohu, common carp and freshwater prawn to fish harvest were 47.4, 27.2, 16.9, 4.3 and 0.7%, respectively. Biomass gain per fingerling stocked with respect to catla, rohu, common carp and freshwater prawn are 0.51, 0.42, 0.26 and 0.04 kg, respectively, indicating attractive monetary gains through stocking of these species. Results indicate the viability of culture‐based fisheries in minor perennial reservoirs. Possible reasons for high variability in fish yield and areas for follow‐up studies are discussed.