用鲢鳙直接控制微囊藻水华的围隔试验和湖泊实践

为了控制水体富营养化所形成的水华,国外经典的生物操纵论者提倡放养食鱼性鱼类以控制食浮游生物的鱼类,藉此壮大浮游动物种群,然后借助浮游动物遏制藻类.按照这条思路,以浮游生物为食的鲢和鳙应该是清除的对象.本文作者认为我国湖泊中危害性最大的是微囊藻水华,而浮游动物根本不能摄食这种水华,不如直接利用鲢鳙进行控制,因而1989-1992年间在武汉的东湖进行了三次原位围隔试验,2000年再度重复了一次围隔试验,结果证明,迄今在东湖中已消失18年的微囊藻水华,重新出现在不养鱼的围隔里.在养入一定密度的鲢或/和鳙的围隔中,就没有水华出现.已经出现水华的围隔,放入适当密度的鲢或/和鳙后,在短期内水华又复消失;而放入草鱼的围隔,则水华始终持续,不受影响.说明鲢和鳙能有效地遏制微囊藻水华.鲢、鳙遏制水华的有效放养密度(亦即有效生物量)为46-50g·m^-3.东湖湖泊中鲢、鳙的生物量,直到1985年才达到这个水平,所以1985年湖里反常地没有出现水华.往后的年份,东湖的鱼产量越来越高,也就是湖里鲢、鳙的生物量越来越大,所以迄今没有微囊藻卷土重来的机会.东湖的水质和其他非生物条件仍适于蓝藻水华的发生与发展,如果东湖鲢、鳙的产量下降到阈值以下,亦即降到1985年以前1000t水平,那么微囊藻及其它蓝藻水华的重来将是不可避免的.经典的生物操纵论学说和措施不能解决微囊藻水华猖獗的问题.相反,用滤食浮游生物的鲢和鳙直接遏制微囊藻却是有实验根据并已被渔业生产实践证明行之有效的.     

Experimental study of the impacts of planktivorous fishes on plankton community and eutrophication of a tropical Brazilian reservoir

We examined the impacts of three facultative planktivorous fishes, Congo tilapia (Tilapia rendalli), bluegill (Lepomis macrochirus) and tambaqui (Colossoma macropomum), and an obligate planktivorous fish, silver carp (Hypophthalmichthys molitrix) on plankton community and water quality of a tropical eutrophic reservoir, Paranoá Reservoir, Brasília, Brazil, conducting both laboratory selective grazing experiments and an enclosure experiment. The first two species inhabit this reservoir and the remaining two are recommended for introduction. The field experiment was performed in ten limnocorrals (2 m³ each) and lasted five weeks. During the enclosure experiment, silver carp suppressed copepod nauplii, cladocerans and rotifers while the presence of tilapia and bluegill were associated with increased rotifers density. The dominant blue-green algae,Cylindrospermopsis raciborskii (98% of phytoplankton biomass) was enhanced in the presence of bluegill, tilapia and tambaqui, but reduced in the presence of silver carp. This impact on plankton is in agreement with the results of the laboratory feeding trials. The observed alterations in water quality parameters in fish limnocorrals are discussed in relation to plankton community and eutrophication of this ecosystem. It is suggested that the control of the undesirable algaeC. raciborskii directly by silver carp grazing is a promising management tool.     

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.
2. During a summer experiment, a bloom of Anabaena flos-aquae developed (≈ 8000 cells mL⁻¹) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L⁻¹) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.
3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.
4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.     

Molecular cloning and characterization of alpha-class glutathione S-transferase gene from the liver of silver carp, bighead carp, and other major Chinese freshwater fishes

Two full-length cDNAs encoding glutathione S-transferase (GST) were cloned and sequenced from the hepatopancreas of planktivorous silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis). The silver carp and bighead carp GST cDNA were 920 and 978 bp in length, respectively, and both contained an open reading frame that encoding 223 amino acids. Partial GST cDNA sequences were also obtained from the liver of grass carp (Ctenopharyngodon idellus), crucian carp (Carassius auratu), mud carp (Cirrhinus molitorella), and tilapia (Oreochromis nilotica). All these GSTs could be classified as alpha-class GSTs on the basis of their amino acid sequence identity with other species. The three-dimensional structure of the silver carp GST was predicted using a computer program, and was found to fit the classical two-domain GST structure. Using the genome walker method, a 875-bp 5'-flanking region of the silver carp GST gene was obtained, and several lipopolysaccharide (LPS) response elements were identified in the promoter region of the phytoplanktivorous fish GST gene, indicating that the GST gene expression of this fish might be regulated by LPS, released from the toxic blue-green algae producing microcystins. To compare the constitutive expression level of the liver GST gene among the six freshwater fishes with completely different tolerance to microcystins, beta-actin was used as control and the ratio GST/beta-actin mRNA (%) was determined as 130.7 +/- 6.6 (grass carp), 103.1 +/- 8.9 (bighead carp), 92.6 +/- 15.0 (crucian carp), 72.3 +/- 7.8 (mud carp), 58.8 +/- 11.5 (silver carp), and 33.6 +/- 13.7 (tilapia). The constitutive expression level of the liver GST gene clearly shows that all the six freshwater fishes had a negative relationship with their tolerance to microcystins: high-resistant fishes (phytoplanktivorous silver carp and tilapia) had the lowest tolerance to microcystins and the high-sensitive fish (herbivorous grass carp) had the highest tolerance to microcystins. Taken together with the reciprocal relationship of constitutive and inducible liver GST expression level in some of the tested fish species to microcystin exposure, a molecular mechanism for different microcystin detoxification abilities of the warm freshwater fishes was discussed.     

保水渔业对千岛湖食物网结构及其相互作用的影响

为预防千岛湖连续暴发了2a(1998—1999)的蓝藻水华和改善千岛湖水质,于2000年起在千岛湖开展了以人工放养鲢鳙和控制凶猛鱼类为主要措施的保水渔业试验。作为试验的主要研究内容之一,通过构建1999和2000年千岛湖生态系统的Ecopath模型,比较分析了实施保水渔业对千岛湖生态系统食物网结构及其相互作用的影响。结果表明:实施保水渔业,使千岛湖中的银鱼和鲤生物量减少,而鲌类(主要是蒙古鲌)、鲴类和大眼华鳊等增加;使各种鱼类的捕食者和食饵生态位重叠指数下降;各主要鱼类的相互作用中,鲢、鳙对鳡、鲌的促进作用增强,鳡对鲌的抑制作用及鲌对虾类、银鱼和鲤等以及银鱼对浮游动物的抑制作用减弱,鳙对银鱼、大眼华鳊对鲤的抑制作用增强。这些影响,使千岛湖食物网结构更趋合理,如底层碎屑食性鱼类如鲴类等的增加,有利于营养物的再循环和再利用,从而增强了水体对营养物的净化作用。     

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     

In situ study on effect of food competition on diet shifts and growth of silver and bighead carps in large biomanipulation fish pens in Meiliang Bay, Lake Taihu

Silver and bighead carps were cultured in large fish pens to reduce the risks of cyanobacterial bloom outbreaks in Meiliang Bay, Lake Tauhu in 2004 and 2005. Diet compositions and growth rates of the carps were studied from April to November each year. Both carp species fed mainly on zooplankton (>50% in diet) in 2004 when competition was low, but selected more phytoplankton in 2005 when competition was high. Silver carp had a broader diet breadth than did bighead carp. Higher densities and fewer food resources increased diet breadths but decreased the diet overlap in both types of carps. It can be predicted that silver and bighead carps would be released from diet competition and shift to feed mainly on zooplankton at low densities, decreasing the efficiency of controlling cyanobacterial blooms. Conclusively, when silver and bighead carps are used to control cyanobacterial blooms, a sufficiently high stocking density is very important for a successful practice.     

Introduction and cage culture of exotic carps and their impact on fish harvested in Lake Begnas,Nepal

The suitability of exotic carps namely Aristichthys nobilis (Bighead carp), Hypophthalmichthys molitrix (Silver carp), Ctenopharyngodon idellus (Grass carp), Cyprinus carpio (Common carp) and Labeo rohita (Rohu) in a sub-tropical lake was evaluated. The impact of their introduction on native fishes was also studied. After the introduction and cage culture of exotic carps the total harvest reached 92 kg·ha^–1; an increase of 266% within eight years. The planktivorous bighead and silver carps were most successful. The harvest of the other three species was poor. Since the introduction of exotic carp the harvest of indigenous fishes declined by 42%. Considering the food habits of these fish, further stocking should be limited to bighead and silver carps to limit the adverse effects on the indigenous species.     

太湖梅梁湾大型控藻围栏对浮游甲壳动物群落结构的影响

2005年对太湖梅梁湾大型鲢、鳙控藻围栏内外浮游甲壳动物群落结构的季节变化进行了监测.结果表明:围栏内外的环境因子、浮游植物生物量、浮游甲壳动物种类组成无显著差异.但鲢、鳙放养对浮游甲壳动物的生物量产生了较大的影响,围栏内浮游甲壳动物的总生物量和枝角类的生物量显著低于围栏外.总体上,枝角类各种类的生物量受鲢、鳙放养的影响程度大于桡足类的种类.太湖梅梁湾浮游甲壳动物的季节演替明显,大部分种类只是季节性出现.冬季和春季以溞(Daphnia sp.)和近邻剑水蚤(Cyclops vicnus)等大型种类为主,夏季和秋季以象鼻溞(Bosmina sp.)、角突网纹溞(Ceriodaphnia cornuta)和中华窄腹剑水蚤(Limnoithona sinensis)等小型种类为主.典范对应分析表明,透明度、温度和浮游植物的生物量是影响浮游甲壳动物季节变化的主要因素.     

Comparative studies on the feeding selectivity of silver carp Hypophthalmichthys molitrix and bighead carp Aristichthys nobilis

Silver carp and bighead carp exhibited size-selection for food particles in aquarium experiments, but did not select their preferred species of plankton actively when they were distributed evenly in the water. They also possessed the capacity of selection for feeding area. The removal rates (% g⁻¹ fish weight) of silver carp for smaller plankton (phytoplankton) were higher than those of bighead carp. The removal rates by the latter for bigger plankton (zooplankton) were higher than those of silver carp, but for plankton about 70 μm dia. the rates by the two species were almost equal.     

In situ growth and photosynthetic activity of Cyanobacteria and phytoplankton dynamics after passage through the gut of silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), and Nile tilapia (Oreochromis niloticus)

The growth and photosynthetic activities of Cyanobacteria passed through the gut of silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), and tilapia (Oreochromis niloticus) were compared with those of phytoplankton taken directly from Lake Taihu during a 13-day in situ dialysis culture. After the first 3–5 days of reduced activity after excretion by silver carp and bighead carp, the photosynthetic activity of Cyanobacteria recovered and rose significantly higher (P < 0.01) than levels in the control population, whereas there was a notable reduction of photosynthetic activity after passage through tilapia gut. The phytoplankton biomass showed a 2- to 3-fold increase of growth, and extracellular polysaccharide production was also stimulated after passage through silver carp and bighead carp gut. Chlorophyta fluorescence was detected at much higher levels than that of Cyanobacteria and Bacillariophyta after passage through tilapia gut. Scenedesmus obliqnus and Chlamydomonas sp. contributed much to the growth of the Chlorophyta during the in situ cultivation. However, the total phytoplankton biomass showed a distinct reduction in the tilapia treatment during the culture. The study indicated that Nile tilapia feeding and defecation may help remove Cyanobacteria from the water column and favor a community shift to Chlorophyta.     

鲢、鳙肌肉生化成分的分析

同一季节收集的不同体长组的鲢、鳙肌肉的生化成分,随着鱼体的增长水分含量逐渐下降,而脂肪含量则逐渐增加,蛋白质、无氮浸出物及灰分变幅不大,且与体长变化无明显的从属关系;同一体长组的鳙肌肉水分高于鲢,而脂肪含量则低于鲢,蛋白质、灰分、无氮浸出物含量差异不大。同年收集的1+及2+龄鲢、鳙的肌肉生化成分随着季节的延续,水分含量逐步下降,蛋白质及脂肪含量逐步上升,无氮浸出物及灰分含量变化不大;1+龄鱼水分含量比2+龄鱼高,蛋白质及脂肪含量则比2+龄鱼低,其余成分含量差别不显著。       

Sediment Raking as a Tool for Enhancement of Phosphate and Productivity of Water in Tropical Pond System

Changes of orthophosphate in water, induced by raking of surface sediment in various ways, were compared. Twelve limnocorrals were installed in a shallow mesotrophic pond using four treatments with triplicate replication:(1) raking of surface sediment (R) by means of a rake for 5min per week (2) fish (F), by introducing six common carp and two silver carp per limnocorral, (3) raking plus fish (R+F) and (4) control (C), without raking and fishless. After day 122, treatments were reversed in limnocorrals byremoving (netting) or introducing fish and stopping or initiating raking. Samples of water and sediment were collected from each limnocorral at weekly interval and monitored for orthophosphate (OP), primary productivity, phosphate solubilizing bacteria (PSB) and sediment available phosphorus. Raking in presence of fish caused 280 and 160% increase in OP concentrations in surface and bottom water, respectively, as compared with raking in absence of fish. Net effects of fish and raking were 13-81 and 26-241%, respectively in surface water and 48-100 and 46-95% in bottom water. This implied that in bottom water, net raking effect was 13-161% greater than net fish effect. Increase in PSB population, due to raking plusfish (R+F) was 6-82% higher than increase by fish alone (F). Responses of available-P in sediment were opposite to that of water, being highest in concentration in control (C) followed by fish (F), raking (R) and raking plus fish (R+F). The primary productivity showed variations parallel with that of orthophosphate of water. This suggests that raking accelerated the transformations of available-P fromsediment to overlying water mediated through oxygen-dependent sediment water exchange mechanisms.     

Native bighead carp Hypophthalmichthys nobilis and silver carp Hypophthalmichthys molitrix populations in the Pearl River are threatened by Yangtze River introductions as revealed by mitochondrial DNA

Bighead carp Hypophthalmichthys nobilis and silver carp Hypophthalmichthys molitrix have been two economically important aquaculture species in China for centuries. In the past decades, bighead and silver carp have been introduced from the Yangtze River to many river systems in China, including the Pearl River, in annual, large-scale, stocking activities to enhance wild fisheries. Nonetheless, few studies have assessed the ecological or genetic impacts of such introductions on native conspecific fish populations. An mtDNA D-loop segment of 978 bp from 213 bighead carp samples from 9 populations and a 975 bp segment from 204 silver carp samples from 10 populations were obtained to evaluate genetic diversity and population integrity. Results from a haplotype network analysis revealed that most haplotypes of the Pearl River clustered with those of Yangtze River origin and only a small proportion were distinct, suggesting that both the native Pearl River bighead and silver carp populations are currently dominated by genetic material from the Yangtze River. The genetic diversity of Pearl River populations is high in both species because of this inter-population gene flow, but the diversity of native Pearl River populations is low. To preserve the native genetic diversity, stocking of non-native fingerlings should cease immediately and native Pearl River bighead and silver carp fish farms should be established. This research demonstrates the danger to native biodiversity across China because of the substantial, ongoing stock-enhancement activities without prior genetic assessment.     

Development of silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) genetic maps using microsatellite and AFLP markers and a pseudo-testcross strategy

Silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) are two of the four most important pond-cultured fish species inhabiting the major river basins of China. In the present study, genetic maps of silver carp and bighead carp were constructed using microsatellite and AFLP markers and a two-way pseudo-testcross strategy. To create the maps, 60 individuals were obtained from a cross of a single bighead carp (female) and a single silver carp (male). The silver carp map consisted of 271 markers (48 microsatellites and 223 AFLPs) that were assembled into 27 linkage groups, of which 22 contained at least four markers. The total length of the silver carp map was 952.2 cM, covering 82.8% of the estimated genome size. The bighead carp map consisted of 153 markers (27 microsatellites and 126 AFLPs) which were organized into 30 linkage groups, of which 19 contained at least four markers. The total length of the bighead carp map was 852.0 cM, covering 70.5% of the estimated genome size. Eighteen microsatellite markers were common to both maps. These maps will contribute to discovery of genes and genetic regions controlling traits in the two species of carp.     

Mortalities induced by the copepod Sinergasilus polycolpus in farmed silver and bighead carp in a reservoir

The frequency distributions of the parasitic copepod Sinergasilus polycolpus were examined in silver carp Hypophthalmichthys molitrix and bighead carp Aristichthys nobilis during a disease outbreak of the 2 species of fish in a reservoir in China. The mean abundance of the copepod was positively related with host length and age, and the overdispersion of the copepod in both silver and bighead carp was fitted well with negative binomial distribution. Although parasite-induced host mortality was observed, a peaked age-parasite abundance curve was not detected in the present parasite-host system. It is also proposed that this peaked age-abundance curve is unlikely to be observed in its natural host populations.     

主养鲢鳙非鲫高产鱼塘的初级生产力与能量转化效率的研究

分析测定了主养鲢鳙非鲫高产池塘浮游植物初级生产力的垂直、周日、周年变化及其与主要生态因素、鱼产量水平的关系。探讨了初级生产力在能量转化中的生态学效率:毛初级生产力对太阳辐射能的利用率为0.84％—1.64％;鲢鳙非鲫净产量对浮游植物净产量的直接利用率为8.46％—15.56％;太阳能转化为成产量的生态学效率为0.058％—0.156％。     

Prevalence of zoonotic trematodes in fish from a Vietnamese fish-farming community

The prevalence of fish-borne zoonotic trematode (FZT) metacercariae was investigated in fish farmed by rural households in Nghe An Province, located in northern Vietnam. In total, 716 fish, including tilapia (Oreochromis niloticus) and 6 carp species, i.e., grass carp (Ctenopharyngodon idellus), bighead carp (Aristichthys nobilis), mrigal (Cirrhinus mrigala), common carp (Cyprinus carpio), silver carp (Hypophthalmychthys molitrix), and roha (Labeo rohita), collected from 53 fish farms were examined. The overall prevalence of FZT metacercariae was 44.6%, ranging from 12.5% to 61.0% in fish species collected from grow-out ponds, which are the production system for growing fish from fingerling size to market size. The overall prevalence was 43.6% in fingerlings cultured in nurseries, ranging from 7.4% to 62.8% for different fish species. The FZT species recovered were heterophyids and echinostomatids and included Haplorchis pumilio, H. taichui, H. yokogawai, Centrocestus formosanus, Stellantchas musfalcatus, and Echinochasmus japonicus, all of which are intestinal flukes in humans, other mammals, and birds. This is the first report of H. yokogawai and E. japonicus in fish in Vietnam, and the first record for S. falcatus in northern Vietnam. Although a previous cross-sectional survey of the people living in these fish farm households revealed a very low prevalence of FZTs (< 1%), our results demonstrate that intestinal flukes are common in farmed fish in this area, suggesting that reservoir hosts such as dogs, cats, and pigs are more important in sustaining the life cycles of these flukes in fish farms than human hosts. This has implications for the effectiveness of control programs focused mainly on treatment of humans.     

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.     

Digestive enzyme pattern of two stomachless filter feeders, silver carp, Hypophthalmichthys molitrix Val., and bighead carp, Aristichthys nobilis Rich.

Activities of digestive enzymes (trypsin and amylase) of microplanktophagous silver carp, Hypophthalmichthys molitrix , and macroplanktophagous bighead carp, Aristichthys nobilis , were investigated in relation to pH in 10 different segments of the gut. In addition, the possible existence of 'classical' lysozyme in both species and cellulase in silver carp were scrutinized, but no activities were detected. Tryptic and amylolytic activities decreased sharply from fore-gut to hind-gut indicating an efficient reabsorption mechanism. Trypsin and amylase of both species had a pH optimum at 8.3 and 7.0 respectively. The relatively low pH of 6.4 in the fore-gut of silver carp did not support an efficient operation of these enzymes, which was compensated by a higher enzyme concentration as compared to bighead carp. The latter, however, showed a higher pH of 7.3 in the fore-gut and thereby maintained similar activities as silver carp. The distinction of herbivorous and omnivorous fish in terms of digestion mechanisms is discussed.