Impact of environmental and innate factors on the food habit of Chinese perch Siniperca chuatsi (Basilewsky) (Percichthyidae)

Laboratory and field investigations were conducted to study the food habit of Chinese perch Siniperca chuatsi (Basilewsky) from first feeding through adult stage. Only fish larvae were consumed by Chinese perch larvae (2-21 days from hatching), and the presence of zooplankton did not have any significant effect on their survival rate. The ability of Chinese perch to feed on zooplankton is clearly limited by some innate factor. Instead of gill rakers, Chinese perch larvae have well-developed sharp teeth at the first feeding stage, and are well adapted to the piscivorous feeding habit unique to the larvae of Chinese perch, e.g. they bite and ingest the tails of other fish larvae. At the first feeding stage (2 days from hatching), daily rations were both very low, either in light or complete darkness. Although early-staged Chinese perch larvae (7-17 days from hatching) could feed in complete darkness, their daily rations were always significantly higher in light than in complete darkness. Late-staged Chinese perch larvae (21 days from hatching) were able to feed in complete darkness as well as in light, similar to the case of Chinese perch yearlings. Chinese perch yearlings (total length, 14-16 cm) consumed prey fish only and refused shrimp when visual cues were available (in light), but they consumed both prey when visual cues were not available (in complete darkness), suggesting that prey consumption by Chinese perch yearlings is affected by their sensory modality in predation. Both prey were found in the stomachs of similar-sized Chinese perch (total length, 14-32 cm) from their natural habitat, suggesting that shrimp are consumed by Chinese perch at night. Prey selection of Chinese perch with a length >38 cm, which consumed only fish in the field, appears to be based upon prey size instead of prey type. These results suggest that although environmental factors (e.g. light intensity) affect prey detection by Chinese perch, this fish is anatomically and behaviourally predisposed to prey on live fish from first feeding. This makes it a difficult fish to cultivate using conventional feeds.

Crustacean zooplankton distribution patterns and their biomass as related to trophic indicators of 29 shallow subtropical lakes

A comparative limnological study was carried out to present a snapshot of crustacean zooplankton communities and their relations to environmental factors to test whether there is a consistent relationship between crustacean biomass and trophic indicators among lake groups with similar trophic conditions. The study lakes showed a wide range of trophic status, with total phosphorus (TP) ranging from 0.008 to 1.448mgL(-1), and chlorophyll a from 0.7 to 146.1 mu g L-1, respectively. About 38 species of Crustacea were found, of which Cladocera were represented by 25 taxa (20 genera), and Copepoda by 13 taxa (I I genera). The most common and dominant species were Bosmina coregoni, Moina micrura, Diaphanosoma brachyurum, Cyclops vicinus, Thermocyclops taihokuensis, Mesocyclops notius and Sinocalanus dorrii. Daphnia was rare in abundance. Canonical correspondence analysis showed that except for four species (D. hyalina, S. dorrii, C. vicinus and M. micrura), almost all the dominant species had the same preference for environmental factors. Temperature, predatory cyclopoids and planktivorous fishes seem to be the key factors determining species distribution. TP was a relatively better trophic indicator than chlorophyll a to predict crustacean biomass. Within the three groups of lakes, however, there was no consistent relationship between crustacean biomass and trophic indicators. The possible reason might be that top-down and bottom-up control on crustaceans vary with lake trophic state. The lack of significant negative correlation between crustacean biomass and chlorophyll a suggests that there was little control of phytoplankton biomass by macrozooplankton in these shallow subtropical lakes. (c) 2007 Elsevier GmbH. All rights reserved.

Driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status

1. We studied driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status, the oligotrophic deep Lake Fuxian and the eutrophic shallow Lake Xingyun. 2. Phytoplankton samples were taken monthly for a year and phytoplankton species were sorted into the main taxonomic groups and associations proposed by Reynolds. A canonical correspondence analysis (CCA) was used to test the occurrence of these classification schemes and to determine their discriminatory power. 3. The results suggest that the major driving forces in Lake Fuxian were physical variables, and particularly the underwater light climate, whereas, nutrients were the important driving force in Lake Xingyun. 4. Top-down control through zooplankton grazing in Lake Fuxian was hardly ever a significant determinant itself, because of the scarcity of zooplankton and their low grazing efficiency of predation while a dominance of inedible cyanobacteria throughout the year rendered top-down controls ineffective failing in Lake Xingyun. Hence phytoplankton communities in both lakes appear to be regulated primarily by bottom-up controls.

Phytoplankton biomass in relation to nutrients and zooplankton in thirty subtropical lakes adjacent to the Yangtze River, China

A total of 30 shallow lakes, located along the middle and lower reaches of the Yangtze River, were studied to assess the relative importance of nutrients and zooplankton biomass in determining the phytoplankton biomass in subtropical China. Zooplankton biomass and nutrients both varied greatly in these lakes. Factor analysis and multiple linear regression showed that phytoplankton biomass was positively correlated with TN, NH4+, NO3- and TP, while it did not show any negative relationship to zooplankton biomass. Meanwhile, the phytoplankton biomass showed contrary relationships to the mass ratio of TN/TP in spring and summer, suggesting that in nutrient-richer lakes the dominant phytoplankton species have different preferences for TN/TP ratio. The insignificant top-down control of phytoplankton biomass may be attributed to the dominance of small-sized crustaceans and low crustacean biomass resulting from cyanobacterial dominance and planktivorous fish predation as well as other factors. Thus, it is likely that nutrients were more important than zooplankton biomass in explaining the total variance of phytoplaDkton biomass in these subtropical lakes.

Crustacean zooplankton size structure in aquaculture lakes: is larger size structure always associated with higher grazing pressure?

Crustacean zooplankton size structure in 27 aquaculture lakes was studied to test the hypothesis that larger size structure is associated with higher grazing pressure. Mean body length of crustaceans was positively correlated with increasing Chl a (r(2) = 0.40, P = 0.000) and TP (r(2) = 0.38, P = 0.000), contrary to the empirical studies. However, the ratio of zooplankton to phytoplankton biomass decreased significantly with increasing TP (r(2) = 0.27, P = 0.005) and mean body length (r(2) = 0.46, P = 0.000). Meanwhile, size structure showed no significant effect in explaining residual variations of phosphorus-chlorophyll relationship (P = 0.231). These results indicate that larger size structure was not always associated with higher zooplankton grazing pressure. It is likely that in aquaculture lakes crustacean zooplankton size structure was of minor importance in control of phytoplankton biomass, and it was mainly regulated by fish predation. The results showed in our study and the empirical studies might be a reflection of two different stages of lake eutrophication and fish predation intensity.

Negative effects of Microcystis blooms on the crustacean plankton in an enclosure experiment in the subtropical China

Effects of Microcystis blooms on the crustacean plankton were studied using enclosure experiments during July-September, 2000. Eight enclosures were set in the hypereutrophic Donghu Lake. Different nutrient concentrations through additional nutrient and sediment in enclosures were expected to result in different abundance of Micropystis. From July to early August, the phytoplankton community was dominated by Chlorophyta, Cryptophyta, Bacillariophyta and Cyanophyta other than Microcystis aeruginosa. M. aeruginosa showed a rapid increase during early August in all enclosures and predominated. Crustacean plankton was dominated by the herbivorous Moina micrura, Diaphanosoma brachyurum and Ceriodaphnia cornuta, and the predaceous Mesocyclops sp. and Thermocyclops taihokuensis. During the pre-bloom period, the dynamics of M. micrura population appeared to be mainly affected by the predaceous cyclopoids. With the development of Microcystis blooms, such interaction between M. micrura and cyclopoids seemed weakened, especially when the Microcystis biomass was high. But there was no apparent influence on the interaction between Leptodora kindti and its zooplanktonic prey. The density of two cyclopoids decreased with the enhancement of Microcystis. The density decline of M. micrura was caused by both predation and inhibition by Micropystis. The low food availability of other edible phytoplankton during the blooms led to low densities of both C. cornuta and D. brachyurum by late August. It appears that dense Microcystis blooms exert strong negative effects on the herbivorous cladocerans and the predaceous cyclopoids.

The impact of silver carp (Hypophthalmichthys molitrix) on the rotifer community in a eutrophic subtropical Chinese lake

From 20 April to 25 June in 1999, an enclosure experiment was conducted in Lake Donghu to assess the impact of planktivorous silver carp on the planktonic rotifer community. We set up four treatments with silver carp biomass at 0, 116, 176, and 316 g m(-2). Total rotifer density was significantly higher in the no-fish enclosure than in fish-present enclosures. Fish predation on the rotifers alleviated zooplankton competition and resulted in dominance of small zooplankton species (Anureaopsis fissa, Trichocerca pusilla and Moina micrura) in fish-present enclosures. However, some relatively larger species (Polyarthra vulgaris, Brachionus angularis, Brachionus calyciflorus, and Asplanchna spp.) showed higher densities in the no-fish enclosure than in fish-present enclosures.

Experimental study of trophic cascade effect of silver carp (Hypophthalmichthys molitrixon) in a subtropical lake, Lake Donghu: on plankton community and underlying mechanisms of changes of crustacean community

An enclosure experiment was carried out to test trophic cascade effect of filter-feeding fish on the ecosystem: growth of crustacean zooplankton, and possible mechanism of changes of crustacean community structure. Four fish biomass levels were set as follows: 0, 116, 176 and 316 g m(-2), and lake water ( containing ca. 190 g m(-2) of filter-feeding fishes) was comparatively monitored. Nutrient levels were high in all treatments during the experiment. Lowest algal biomass were measured in fishless treatment. Algal biomass decreased during days 21-56 as a function of fish biomass in treatments of low (LF), medium (MF) and high (HF) fish biomass. Crustaceans biomass decreased with increasing fish biomass. Small-bodied cladocerans, Moina micrura, Diaphanosoma brachyurum and Scapholeberis kingii survived when fish biomass was high whilst, large-bodied cladocerans Daphnia spp. and the cyclopoids Theromcyclops taihokuensis, T. brevifuratus, Mescyclops notius and Cyclops vicinus were abundant only in NF enclosures. Evasive calanoid Sinodiaptomus sarsi was significantly enhanced in LF, but decreased significantly with further increase of fish biomass. Demographic data indicated that M. micrura was well developed in all treatments. Our study indicates that algal biomass might be controlled by silver carp biomass in eutrophic environment. Changes of crustacean community are probably affected by the age of the first generation of species. Species with short generation time were dominant and species with long generation time survived less with high fish biomass. Evasive calanoids hardly developed in treatments with high fish biomass because of the ( bottle neck) effect of nauplii. Species abundance were positively related to fish predation avoidance. Other than direct predation, zooplankton might also be suppressed by filter-feeding fish via competition.

Enhancement of Moina micrura by the filter-feeding silver and bighead carps in a subtropical Chinese lake

The changes of cladoceran zooplankton from 1980 to 1996 were studied in a hypereutrophic subtropical Chinese lake, Lake Donghu, and an enclosure experiment was conducted to examine the possible role of the increased fish production in the enhancement of Moina micrura in the lake after mid-1980s. During the 1980s, the most striking event of the cladoceran community in the lake was that dominance of Daphnia was replaced by Moina following a steady increase in the production of planktivorous fish. This replacement was a direct result of increased fish predation, since our enclosure experiment indicates that Moina are less vulnerable to fish predation than Daphnia, and that increase in fish-stocking rate favors the development of M. micrura. The stronger resistance of M. micrura to fish predation may be attributed to its smaller body size and higher intrinsic growth rate than the daphnids. The present study has a strong parallel with the responses of zooplankton community to predators observed in many temperate lakes, and perhaps the only real difference is that in our lake the small rapidly growing cladoceran is Moina, rather than Bosmina or some other typical temperate take species. In the present study, the strong fish predation caused a shift from Daphnia to small zooplankton but not a corresponding increase in phytoplankton, which is in sharp contrast to what is expected with the classic "trophic cascade" process.

Long-term changes of planktonic rotifers in a subtropical Chinese lake dominated by filter-feeding fishes

1. The long-term changes (1956-1998) in density and species composition of planktonic rotifers were studied at two sampling stations (I, II) of Lake Donghu, a shallow eutrophic Chinese Lake densely stocked with filter-feeding fishes. Annual average densities of rotifers increased with an increase in fish yield and eutrophication, whilst species number decreased from 82 in 1962-1963 to 62 in 1994-1998. 2. During 1962-98, some species such as Anuraeopsis fissa, Polyarthra spp. (including P. dolichoptera & P. vulgaris), Trichocerca pusilla and Synchaeta oblonga increased their percentage in abundance remarkably, whilst the proportion of Keratella cochlearis decreased at two relatively eutrophic stations from 19 to 4.2% at Station I and from 30 to 3.2% at Station IL 3. The high r(max) of A. fissa probably made it more successful than other rotifers under high predation pressure by planktivorous fish. The decrease in the K. cochlearis population might be attributed partly to predation by Cyclops vicinus. 4. Small rotifers were less vulnerable to fish predation than large-sized cladocerans. Decreases in cladocerans coincided with increases in rotifers, suggesting that the indirect effect of fish predation on cladocerans might have partly contributed to the population development of rotifers in Lake Donghu during recent decades. 5. We also conducted surveys (1994-1998) of seasonal dynamics of rotifers at four sampling stations (I-IV) which have varied in trophic status after fragmentation of the lake in the 1960s. A total of 75 species were identified at the four stations. Both densities and biomass of rotifers were considerably higher in the two more eutrophic stations than in the two less eutrophic stations. This indicates that the population increase of rotifers at Stations I and II during recent decades might be partly attributed to eutrophication of the lake water.

Experimental and field studies of Mesocyclops notius (Copepoda : Cyclopoida) from a subtropical Chinese lake, Lake Donghu

This paper reports experimental and field studies on the cyclopoid Mesocyclops notius from subtropical Lake Donghu close to the Yangtze river. Mesocyclops notius, a dominant crustacean Zooplankter throughout tropical Australia, was previously considered to be endemic to Australia, but recently, Mesocyclops leuckarti in Lake Donghu was re-identified as M. notius. Laboratory culture experiments were conducted to reveal the effect of temperature (15, 20, 25 and 30 degreesC) on the development, growth and reproduction of M. notius. Temperature was inversely related to development times of eggs, nauplii and copepodites, body length and physiological longevity of adults, and brood size. Body length and physiological longevity of females were greater than those of males at the same temperature. No reproduction took place at 15 degreesC. Production and seasonal cycles of M. notius during 1980-1982 were studied at two sampling stations of Lake Donghu. At the mid-lake station, the annual production and production/biomass (P/B) ratio of M. notius varied between 6.0 and 18.0 g dry wt m(-2) year(-1) and 74.6 and 95.5, respectively. Mesocyclops notius reached their highest density peaks in the warm months (July-October), with a maximum density of 1256 individuals l(-1) at a littoral site. No reproduction and recruitment by AL notius took place during the cold months (December March) when the temperature of the lake water was < 15 degreesC. Mesocyclops notius were more abundant at a littoral station than at a pelagic station, possibly due to different food availability. The higher male:female sex ratio of M. notius at the littoral station was most likely caused by size-selective fish predation on larger females.

Impacts of filter-feeding fishes on the long-term changes of crustacean zooplankton in a eutrophic subtropical Chinese lake

Long-term changes In the crustacean zooplankton community (calanoid and cyclopoid copepods and cladocerans) were studied in Lake Donghu, a shallow and eutrophic Chinese lake. This lake had been earlier stocked with two pump Alter-feeding Ashes, silver carp (Hypopthalmichthys molitrix) and bighead carp (Aristichthys nobilis). During the 1950s and the mid-1980s, the ratio of copepods to cladocerans was relatively stable but showed a general increase thereafter. From the early-1980s to the 1990s, calanoid/cyclopoid ratios decreased obviously. In the 1990s, Cyclops vicinus, Diaphanosoma brachyurum, and Moina micrura were dominant the abundance of C. vicinus and M. micrura increased significantly; and D, brachyurum showed a substantial decrease. The study shows that under extremely high pressure of Ash predation, the species which could recover rapidly from fish predation would be the most likely to survive and increase their numbers.

Macrozoobenthos in 2 shallow mesotrophic Chinese lakes with contrasting sources of primary production

Comparative studies on macrozoobenthos were done in 2 shallow mesotrophic lakes in the middle basins of the Yangtze River, China: Lake Biandantang where macrophytes were abundant, and Lake Houhu where macrophytes were scarce Samples were taken monthly at 4 stations in each lake from April 1997 to March 1999, and a total of 67 and 31 tara of macrozoobenthos were recorded in Lake Biandantang and Lake Houhu, respectively. Both annual mean density and biomass of macrozoobenthos were higher in Lake Biandantang than in Lake Houhu: 780 vs 532 indivials/m(2) and 37.1 vs 25.9 g wet mass/m(2), respectively. Abundance of functional feeding groups followed the order: scraper > collector > predator > shredder in Lake Biandantang, and collector > predator > scraper > shredder in Lake Houhu. Only 1 density peak occurred from winter to early spring in Lake Houhu; however, in Lake Biandantang, there were 2 peaks, the winter peak and spring peak. K-dominance curves and Shannon-Wiener, Simpson, and Margelef indices indicated that macrozoobenthos were more diverse in Lake Biandantang than in Lake Houhu Our study suggests that, in shallow lakes, submerged macrophytes are essential for the maintenance of biodiversity of macrozoobenthos mainly because the macrophytes increase habit heterogeneity and availability of suitable food, and may also decrease predation by fish on the macrozoobenthos.

Long-term changes of Copepoda community (1957-1996) in a subtropical Chinese lake stocked densely with planktivorous filter-feeding silver and bighead carp

In contrast to the relatively well documented impact of particulate-feeding fish on zooplankton communities, little attention has been devoted to the impact of filter-feeding fish. Filter-feeding silver and bighead carp are the most intensively cultured fish species in Asia and comprise much of the production of Chinese aquaculture. However, little information is known about the impact of either fish on the zooplankton community. Long-term changes in the Copepoda community (1957-1996) were studied at two sampling stations of a subtropical Chinese lake (Lake Donghu) dominated by silver and bighead carp. For both calanoids and cyclopoids, the littoral station (I) was much more resource profitable than the pelagic station (II). There has been a tremendous increase in the annual fish catch over the past 30 years due to the increased stocking with fingerlings of the two carp species. There was a notably higher fish density at Station I than at Station II. Cyclopoid abundance was notably higher at Station I than at Station II during the 1950s to the 1980s, while the reverse became true in the 1990s. This is probably because when fish abundance increased to an extremely high level, the impact of fish predation on the cyclopoids became more important than that of food resources at the littoral station. At both stations, cyclopoid abundance was relatively low in spite of the presence of abundant prey. Similarly, calanoid density did not differ significantly between the two stations in the 1950s and 1960s, but was significantly lower at Station I than at Station II during the 1980s and 1990s. Such changes are attributed to the gradient of fish predation between the stations and an increasing predation pressure by the fish. The increased fish predation also correlated with a shift in summer-dominant calanoids from larger species to smaller ones. In conclusion, the predaceous cyclopoids are affected by fish predation to a much lesser extent than the herbivorous calanoids, and therefore increased predation by filter-feeding fish results in a definite increase in the cyclopoid/calanoid ratio. Predation by filter-feeding fish has been a driving force in shaping the copepod community structure of Lake Donghu during the past decades.

Changes of Leptodora kindti abundance (1957-1996) in a planktivorous fishes-dominated subtropical Chinese lake (Lake Donghu)

The changes of L. kindti density from 1957 to 1996 were studied in a shallow, eutrophic Chinese lake, Lake Donghu. Despite the fact that the fish yield of planktivorous fish (silver carp and bighead carp) has increased steadily, the population density of L. kindti has also increased since 1957 and peaked in 1982/1983, The increase of both fish and L. kindti densities during this period may have benefitted from a considerable increase in the densities of their zooplankton prey. and fish predation on L. kindti might have been minor. As the fish yield increased further, their predation began to suppress most zooplankton prey including L. kindti. The largely increased fish predation on L. kindti is also evidenced by the remarkable decline of their body length after 1984. The density of L. kindti was significantly higher at the pelagic station (II) than at the littoral station (I), although for L. kindti, the littoral zone was significantly more resource profitable than the pelagic zone. The gradient of fish predation (more fish in the littoral zone) is the most likely explanation, since L. kindti is reported to be a preferred prey for many planktivorous fishes. The maximum density of L. kindti was 1.78 ind./I (on Aug. 17, 1984) at Station I and 1.55 ind./I (on Sep. 13, 1985) at Station II, respectively, which are close to those in several other eutrophic lakes.