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Chapter 27. Possible effects of the proposed eastern transfer route on the fish stock of the principal water bodies along the course

Yu Xuefang
Institute of Hydrobiology, Academia Sinica, Wuhan, China

THE DAMAGE DONE to the ecosystem by human activity has become a topic of intense worldwide concern. The mass interbasin transfer of water from the Chang Jiang, a major item in China's economic construction plan, would impinge upon the natural environment and people's lives in the four valleys of the Chang Jiang, the Huai He, the Huang He and the Hai He. This project must be investigated from all sides before we can make the scientific appraisal and prognosis of its potential adverse effects which is essential to appropriate planning.

This chapter is based on an initial study of the influence of the south-to-north transfer on the fish stock of the water bodies along the East Route.

WORKING METHOD

At different times between October/November 1978 and October/ November 1979, we carried out on-site investigations of the main water bodies along the East Route: the Hai He, Dongping Lake, Nansi Lake (comprised of Weishan Lake, Zhaoyang Lake, Nanyang Lake and Dushan Lake), Luoma Lake, Hongze Lake, Baima Lake, Baoying Lake, Gaoyou Lake and the lower reaches and estuary of the Chang Jiang. We investigated and collected a large amount of data on the history and the present condition of these water bodies. In 1980, we further investigated the biology and environmental habits of several species of migratory fish in the lower reaches and estuary of the Chang Jiang, including Coilia ectenes (J. et S.) Hilsa reevesii (Rich.) and Coilia mystus (L.). We collected data on past fish catches and on previous flows, water levels, current velocities and water temperatures in the lower reaches of the Chang Jiang. In October of the same year, we recorded statistics on the fish catch near the pumping station at the water transfer headworks and estimated the relationship between past catches of the migratory fish and the flow of the Chang Jiang. (For a list of common English names for some of the fish mentioned, see appendix to this chapter, page 388.)

The hydrological data are copied from the reference room of the Chang Jiang Basin Planning Office. The relevant figures for fish catches are taken from the following two sources: first, from fishing communes in different stretches of the river, with comparatively long histories, sound organization and complete records; second, from fishing brigades in different stretches of the river which have relatively stable production. At the same time, we also referred to records of the amount of fish caught during past years by individual boats with similar production conditions.

THE GENERAL CONDITION OF THE PRINCIPAL WATER BODIES ALONG THE TRANSFER ROUTE

In the lower reaches of the Chang Jiang the river is broad with many shoals. The beaches are wide and the current is slow. This results in many good fishing grounds. In these waters, the species of pure freshwater fishes are similar to those in the middle reaches of the river. The most common economic fishes are Leiocassis longirostris (Gunther), Leiocassis crassilabris (Gunther), Leiocassis crassirostrils (Regan), Cyprinus carpio (L.) Hypophthalmichthys molitrix (C. et V.), Mylopharyugodon piceus (Rich.), Elopichthys bambusa (Rich.), Silurus asotus (L.), Silurus soldatovi merionalis (Cheng), Psephurus gladius (Martens), Parabramis pekinensis (Basil.), Culter erythropterus (Basil.) and Erythroculter. In addition, there are the rare Hilsa reevesii, the delicious Coilia mystus and the high-yielding Coilia ectenes and Hemisalanx prognothus (Regan), as well as the Anguilla japonica (T. et S.) and Fugu obscurus (Abe). Their fishing season is concentrated and they are abundant so that they occupy a key position in China's fishing industry.

The estuary of the Chang Jiang is over 80 km wide (from the Haimen promontory to the Nanhui outlet). The waters of the estuary form a freshwater current of the Chang Jiang due to the river's runoff into the sea. This creates a low brine (saline freshwater) area whose size and movement change with the magnitude of the runoff, stretching to the northeast near Cheju Island when it is strong. The rich nutrient salts and organic matter here are constantly flowing into the sea with the runoff (see Table 1) and constitute an excellent environment for the reproduction of plankton and zoobenthos. This is also a superior feeding ground for various kinds of young fish.

In these waters live not only brackish water fish but also marine and freshwater species. Besides the migrating fish mentioned above, others of economic value are Lateolabrax japonicus (Cuv. et Val.), Trachidermus fasciatus (Heckel), Harpodon nehereus (Hamilton), Collichthys lucidus (Rich.), Cynoglossus gracilis (Gunther), Synechogobius ommaturus (Rich.), Dasyatis akajei ( Muller et Henle), Mugil so-iuy (Basil.) and Mugil cephalus (L.). Seven of China's most important marine fishing grounds are located in the offshore areas near the estuary (Figure 1).

The lakes along the East Route are all shallow, with a general depth of 2 to 4 metres. Weeds flourish here (about 70,000 kg/ha wet weight). Along the banks are luxuriant belts of economic aquatic plants, especially reeds Phragmitis communis (Trin.) and wild rice Ziznia latifolia (Turcz). These cover over 200,000 ha of Hongze Lake. The amount of dissolved oxygen is high in these lakes, where the water is slightly alkaline, with an average pH of 7.5 to 8.5. Nutrient salts are rich (see Table 2) and plankton and zoobenthos flourish.Hongze Lake contains an average of 2,080 zooplankton and 115,482 phytoplankton per litre and has a total quantity of benthos of more than 170,000 tons. These lakes are excellent grounds for numerous species of fish to feed, grow and reproduce and form the core areas for aquatic production in Jiangsu and Shandong provinces.

Table 1. Water Quality of the Estuary of the Chang Jiang

  Temp. (C) pH Ammonia
nitrogen
(mg/l)
Nitrous
nitrogen
(mg/l)
Chlorides
(mg/l)
Dissolved
oxygen
(mg/l)
Oxygen
consumption
(mg/l)
Maximum 33.3 8.0-8.3 0.27-6.36 0.05-0.29 1760-3260 8.40-11.13 4.18-21.26
Minimum 5.5 6.0-6.2 0.05 0.01 4.0-11.0 1.00-5.87 1.02-2.75
Average 18.9-19.4 7.44-7.70 0.09-0.67 0.02-0.08 595-899 5.85-7.51 2.49-5.21

Note: The chloride data are from 1979; the remainder from 1978.
Source: Shanghai General Hydrologic Station

Figure 1. Fishing Grounds at the Outlet of the Chang Jiang

Table 2. Water Quality Data for the Three Lakes Along the East Route

Lake and the date
of investigation
Value pH SiO2
(mg/l)
PO4
(mg/l)
NO3
(mg/l)
Dissolved
Oxygen
(mg/l)
Oxygen
consumption
(mg/l)
  Maximum 8.6 24.3 0.18 1.32 10.8 5.0
Hongze Lake Minimum 6.8 4.2 0.03 0.03 4.0 1.76
Aug. 1973 Average - 7.92 0.10 0.45 7.4 2.98
Luoma Lake Maximum 9.5 21.5 0.08 2.02 9.93 2.42
Apr. & Aug. 1976 Minimum 8.1 0.0 0.0 0.3 8.82 1.70
Baima Lake Apr. 1978 Average 8.4 9.09 0.03 0.3 - 4.19

Source: Nanjing Institute of Geography

This chapter analyzes the changes in the environments of the above waters which would be brought about by the proposed south-to-north water transfer project. Specifically, it looks at changes in the fish ecology and the possible effects on the various links in the fish lifecycle, and predicts changes in the fish resources of these water bodies so that we can take those factors into consideration in planning the project and try to remedy the unfavourable consequences.

THE RELATION BETWEEN THE RUNOFF IN THE CHANG JIANG AND THE FISH STOCK IN THE LOWER REACHES

AND THE ESTUARY

The initial plan to transfer water to the north involves pumping 1,000 m/second and transferring 30.0 km/annum from the Chang Jiang. This amount equals 1/10 to 1/IS of the total water in the river curing the dry season and 1/38 to 1/51 of the flood season flow (see Table 3). This reduction in runoff after the transfer will affect the hydrological and chemical conditions of the lower reaches, especially in the estuary and offshore. These changes will be reflected in the activities and migration routes of some fishes.

Table 3. Comparison Between the Average Monthly Runoff of the Chang Jiang from 1958 to 1977 and the Amount of Water to be Transferred

Month Average
monthly runoff
(km)
Percentage of
runoff to be
transferred
Season
December 37.09 6.9 dry season
January 26.51 9.6
February 25.54 9.0
March 38.01 6.7
April 60.38 4.1
May 97.36 2.6 flood season
June 104.54 2.4
July 131.31 1.9
August 109.25 2.3
September 95.79 2.6
October 88.37 2.
November 60.46 4.1

THE FISH IN THE ESTUARY AND OFFSHORE WATERS

The reduction in area of the freshwater current in the Chang Jiang estuary will cause the salinity in those waters to increase, the silt content to decrease, the transparency to be higher, the ocean tides to move upstream and the runoff of chemical and organic matter to be reduced (including nutrient elements such as silicon and iron). This could lead to a deterioration in the feeding conditions of the young of economic fishes such as Hilsa reevesii, Coilia mystus, Coilia ectenes, Hemisalanx prognothus and Acipencer sinensis. This is because the amount of forage organisms will decline and the feeding grounds will shrink, affecting the quality and quantity of the recruit population of these fishes.

After these waters become more saline, there could be an increase in the kinds and numbers of salt-tolerant organisms available as food for the fishes. This would directly cause changes in the species, population and distribution of those fishes which are nourished by this organic matter. Deeper sea fishes such as Pneumatophorus japonicus (Houttuyn), Decapterus maruadsi (T. et S.) and the Scomberomorus species might tend to move towards the shore.

Some fish species spawn in the brackish water area during the transition period from the dry season to the flood season. These include the Hemisalanx prognothus, which arrive at the estuary in early March and begin to spawn in large quantities in the middle of March when the chloride content of the water is below I, 114 mg/litre. The Coilia mystus comes to the estuary in late April and begins to spawn in early May (Ichthyology Laboratory, 1976; Chen and Huang, 1963). With the slackening of runoff induced by the proposed transfer, the brackish water area would be reduced in size and these fishes would have to move into the inner parts of the estuary to spawn; otherwise they would be unable to breed normally not having suitable spawning conditions.

The data show that a change in the amount of runoff in the Chang Jiang will result in changes in the hydrological conditions of the littoral area of the Dong Hai and the south Huang Hail The form of the seven fisheries in these areas and the composition of the schools of fishes will change correspondingly. This effect will be somewhat greater in particular during the winter dry season (December to March) when the transferred water would constitute 7 to 10 per cent of the total runoff. For example, Trichiurus haumela (Forskal), located in the south Huang Hai and the Dong Hai, often change the location of their grounds during the Shengshan winter flood season owing to shifts in the interface of the fresh littoral water of the Chang Jiang and the ocean water. Alternations in the amount of water of the Chang Jiang in the estuary and offshore may influence the migration routes of Pseudosciaena crocea (Rich.), Pseudosciaena polyactis (Bleeker) and Trichiurus haumela (Forskal), causing some difficulties or losses to the fishing industry.

MIGRATORY FISH

In the study of the migratory fish species, many scholars have observed that the external factors which influence the migration of fish species are complicated and usually interrelated. Water current and the amount of water are always the factors receiving the greatest attention, however. This is reflected in the opinion of China's fishermen that the larger the amount of water in the Chang Jiang and the farther that freshwater flows into the sea, the more spawning colonies of migratory fish species such as Hilsa reevesii and Coilia ectenes will be attracted into the Chang Jiang. We are attempting to investigate the relation between the runoff of the Chang Jiang and the number of Hilsa reevesii, Coilia ectenes, Coilia mystus and Hemisalanx prognothus.

In order to ascertain the influence of the amount of runoff on the spawning migration into the river, we have measured and calculated the correlation between the amount of runoff in the Chang Jiang in the fishing season and the fish catch for past years. To investigate the relation between the runoff of the Chang Jiang and the number of Hilsa reevesii during the period of physiological adaptation before they enter the estuary from the sea, we have calculated the correlation between runoff in winter (from November to January) before they enter the Chang Jiang and the amount of fish caught after they enter the river.

The relationship between runoff and the spawning time of Hilsa reevesii as well as the fattening period of their fries and young fishes can be reflected in whether or not their filial generation flourishes. We have made a comparative analysis, based on age-structure data of Hilsa reevesii in 1973, 1974 and 1975, between the catch of three-year-old fish (first reaching sexual maturity) and the runoff in the Chang Jiang during both the spawning period (June to July) and the fattening period for fry and young fish (August to October) in 1970, 1971 and 1972 (the respective years of birth of the three generations).

Our calculations show no close correlation between the runoff of the Chang Jiang and the catch of the several migrating fish species (Table 4). But with the different runoff volumes in the Chang Jiang in 1970, 1971 and 1972, when three generations of Hilsa reevesii were born, we observe corresponding differences in the numbers of the three generations of fish. The average runoff of the river in 1970 from June to August and from August to October were both greater than in 1971 and 1972 (see Table 5). It is quite probable that this provided excellent conditions for Hilsa reevesii to spawn and to be fattened because the greater volume and velocity of water are both beneficial to Hilsa reevesii, as it lays eggs that drift with the current. These conditions raised the rate of fertilization of the roe and their rate of survival. In addition, when the amount of water was greater, so was the inundated area, so that a large number of growing young fish fattened in the vast inundated shoals of the lakes connected with the river where the forage base was rich. Even if young Hilsa reevesii went downstream from the lakes into the estuary in succession after September, sufficient food was also guaranteed them there because of the large volume of water. Thus the number and quality of this generation were increased greatly and it became the dominant age class in the catches of 1973, 1974 and 1975 (see Table 6). We can see that this generation grew well and attained sexual maturity evenly, with the vast majority mature by the age of three. The runoff in the river fell in 1971 and again in 1972. In consequence, the two generations born in these years were much fewer in number than the generation born in 1970. Therefore we conclude that amount of runoff in the Chang Jiang has a closer relationship with the filial generation than with the parental generation of Hilsa reevesii. This phenomenon needs to be understood more deeply. As we lack data on other migratory fish species, we need to carry out further studies on them.

Table 4. Correlation Results Between the Average Flow at Datong Station and the Amount of Four Fish Species Caught in the Spawning and Migration Seasons (partial data from 1956-1979)

Aquatic
Products
Organization
Fish
Hilsa
reevesii
Coilia
ectenes prognothus
Hemisalax
mystus
Coilia
Jiangsu Province
The fishery commune of
Jingjiang County
(based on catch per boat)
-0.08 -0.01 -- 0.33
The fishery commune of
Jingjiang County
-0.11 -0.01 0.24 0.23
Aquatic Products -0.14 0.12 0.69 -0.15
Administrative Bureau
for Diversification
Jiangdu County
-0.34 0.27 -- 0. 11
Administrative Bureau
for Diversification,
Changshu County
-- -- 0.17 --
The fishery commune of
Bangjiang County
0.16 0.49 0.37 --
Anhui Province
Huajin Fishery Brigade
Dangtu Commune
-0.40 0.08 -- --
Hongqi Fishery Brigade
Dangtu Commune
-0.06 -0.03 -- --
Datong Fishery Commune, Tongling County -0.34 0.13 -- --

Note: Except where indicated, calculations are based on total catch.

Table 5. The flow at Datong Station

  June to August
(The spawning period for
Hilsa reevesii)
August to October
(The fattening period for
Hilsa reevesii)
1970 49,300 m/sec 41,300 m/sec
1971 38,000 27,800
1972 31,200 25,500

Table 6. Age Composition of the Chang Jiang Hilsa reevesii (Rich.). 1973- 1975

  3 years old 4 years old 5 years old years 6 years old years
  Total % Total % Total % Total %
1973 1,504 80.78 280 18.62 9 0.60 -- --
1974 1,015 17.73 789 77.73 46 4.57 -- --
1975 284 28.52 63 22.18 134 47.18 6 2.12

Source: Investigation and Study of the Changjiang Hilsa Reevesii (Rich).

THE EFFECT OF THE PUMPING STATION ON THE FISH

The inlet for the south-to-north water transfer project is situated at Sanjiangying, over 230 km from the estuary of the Chang Jiang, while' the pumping station for diverting the river's water is at Jiangdu near Yangzhou, 20 km from Sanjiangying and connected to the latter by two small tributaries, the Jia Jiang and the Mangdao He. Except for the seasonal migratory fishes in the mainstream of the Chang Jiang, fishes are generally more active in the tributaries because there are relatively few ships and boats there and forage organisms are more abundant. Especially from June to September the tributaries serve as feeding grounds for youngfish. On October 13-14, 1980, we cast 60 purse nets with dense meshes to catch fish, and in 40 minutes caught 4 to 5 kg of various kinds of young fish with body lengths of 5.9 to 25.5 cm (the vast majority were 6 to 11 cm long). There was a total of 32 species, among which 11 are of economic significance, including Ctenopharyngodon idella (C. et V.), Anguilla japonica (T. et S.), Carassius auratus (L.), Hypophthalmichthys molitrix (C. et V.), Aristichthys nobilis (Rich.), Parabramis pekinensis (Basil.) Coreius heterodon (Bleeker) and Mylopharyngodon piceus (Rich.). We surmise that the reason we did not find any young Hilsa reevesii was because the sample was taken late in the season.

In our opinion, the pumping station for water transfer could have the following effects on fish resources:

The membranes of fish eggs will probably break and die as the water is pumped through the intake pipes, turbines and outlet pipes, undergoing several repeated sudden changes from negative pressure to positive pressure and back. But the current velocity is relatively slow in the lower reaches of the Chang Jiang and is generally not suitable for those fishes which breed floating eggs. The breeding grounds of Ctenopharyngodon idella, Mylopharyngodon piceus, Hypophthalmichthys molitrix and Aristichthys nobilis are located in the middle or upper reaches of the river where the current is swift. After being laid, their fertilized eggs will have grown into young fish by the time they have floated to the water transfer inlet, so they will probably not be greatly affected.

According to the data, summer-flower fingerlings [xiabua yazhong] are not hurt when they pass through a centrifugal hydraulic turbine. Therefore we assume that a large quantity of young fish will be pumped into the inland rivers when we transfer water. There are two kinds of situation here. In one, the young of pure freshwater species can not only exist in the inland rivers, but can find better fattening conditions in inland rivers and lakes than in the Chang Jiang, so they can augment the fish resources there. On the other hand, the migratory fishes such as the young of the Hifsa reevesii will finally die in fresh water if they cannot go down to the sea at the suitable time. According to an August 1978 investigation, a large number of young Hilsa reevesii were pumped in through the pumping station. Below the Wanfu sluice gate, one boat of the Jiangdu Fishery Brigade could catch 100 to 150 kg of young Hilsa reevesii in one day. The brigade as a whole had a daily catch of 400 to 500 kg. If we calculate at the rate of 600 fish per kg, 200,000 to 300,000 young Hilsa reevesii were caught at this one place alone. Therefore, during the season from July to October in which young Hilsa reevesii go to the Chang Jiang, an extremely large number of fingerling Hilsa reevesii are pumped inland. Even if they are not caught after they are pumped in, they will die because they cannot go down the Chang Jiang to the sea. The recruit population of Hilsa reevesii will certainly be damaged and the quantity of this resource will decline.

We are told that large economic fish which pass through the hydraulic turbines such as Anguilla japonica, Mylopharyngodon piceus and Hypophthalmichthys molitrix all die because the pump blades cut them into pieces. Big fishes have better swimming ability and are better equipped to escape from harm than young fishes, so fewer are likely to be pumped into the steel conduits of the hydraulic turbines. Nonetheless, the fishery resources must be damaged to a certain extent.

With the transfer of water to the north at a rate of 1,000 m/sec, more fishes will be pumped in than at present. This must be given serious consideration, together with definite protective measures.

CHANGES IN THE BIOCOMMUNITY OF THE "TRANSIT LAKES" AFTER THE TRANSFER OF WATER

In the 1950s there were 100,000 ha of water plants such as reeds and wild rice in Hongze Lake. But after the Sanhe gate was built and stored water, the elevation of the water level and reclamation left only 20,000+ ha. According to the initial water transfer planning, the water level of Hongze Lake will rise by another 0.5 to 1.0 m and that of Nansi Lake by 1.0 to 1.5. This would make it difficult for some emergent hydrophytes to grow (Chen and He, 1975). At the same time, the silt content of the water to be transferred is high. This is unfavourable to the photosynthesis of phytobenthos and thus affects its growth. What is more, the projected passing of a large flow of water through the transfer route lakes will constantly dilute their original rich organic matter and nutrient salts and reduce the water temperature, checking the reproduction of plankton. This will directly affect the various links in the lifecycle of fishes.

First, forage for the fish will not be as available as before. The reduction in aquatic weeds will cause forage conditions to deteriorate for herbivorous fish species such as Ctenopharyngodon idella, Parabramis pekinensis and Megalobrama terminalis (Rich.). Fattening conditions will worsen for their young as well as for those economic fish which feed on plankton, such as Hypophthalmichthys molitrix and Aristichthys nobilis. The availability of forage affects the growth rate of fish.

Second, the spawning area will be markedly reduced for those fish species that lay their eggs on aquatic weeds, placing great limitation on the reproduction of Cyprinus carpio, Carassius auratus, Megalobrama terminalis and other fishes. Therefore, the passing of transfer water through the lakes will affect the herbivorous fish species and those fishes that take plankton as their staple food. The death rate of their young will rise, the surviving individual fish may grow slowly and their physical constitution will become worse. The reduction in spawning grounds will lead to further declines in the fish stock.

On the other hand, some small fishes in the lakes that have low economic value, such as Coilia brachygnathus (K. et P.), Neosalanx tangkahkeii taihuensis (Chen) and Protosalanx hyalocranius (Abbott) will have better conditions for reproduction because they can spawn in gently flowing water with a smooth surface. Their number will increase and they could become the predominant fish species in those lakes, replacing species with high economic value such as Ctenopharyngodon idella, Mylopharyagodon piceus, Hypophthalmichthys molitrix, Aristichthys nobilis, Cyprinus carpio, Carassius auratus, Parabramis pekinensis and Megalobrama terminalis. These impacts of the proposed water transfer would bring comparatively large losses to lake fishery and the local populace.

CONCLUSIONS

The proposed transfer of water to the north will reduce the runoff in the Chang Jiang, resulting in changes in the hydrologic conditions of the waters of the estuary and offshore areas. The increase in salinity and the reduction in the nutrient element in the runoff may lead to the following unfavourable effects:

(1) The fattening conditions for the young of Hilsa reevesii, Coilia ectenes, Coilia mystus, Hemisalanx prognothus and Acipencer sinensis will worsen and this will affect the quality and quantity of the recruit populations of those species.
(2) After the salinity of these waters increases, the salt-tolerant species and numbers in the components of the fish food could increase and deeper sea fish species such as Pneumatophorus japonicus, Decapterus maruadsi and Scomberomorus could move towards the shore.
(3) With the reduction in the brackish area, some fish species that spawn in this environment such as Hemisalanx prognothus and Coilia mystus may possibly migrate to the inner part of the estuary of the Chang Jiang to spawn. They may also find it difficult to reproduce normally owing to the lack of suitable spawning conditions.
(4) A change in the runoff of the Chang Jiang will result in a change of hydrologic conditions in the littoral area of the Dong Hai as well as in the south Huang Hail The form of the seven fishing grounds and the composition of the fish schools here will change accordingly. The migration routes of Pseudosciaena crocea, Pseudosciaena polyactis and Trichiurus haumela will probably change and this will create some difficulties and losses to the fishing industry.

Our calculation of the correlations between the past runoff of the Chang Jiang and the catch of four species of migratory fish, and between the winter runoff in the Chang Jiang and the catch of those species in the following year shows no close relationship between runoff and catch. There is a close relationship, however, between runoff and the number in the filial generation of Hilsa reevesii.

When the pumping station for the water transfer inlet is in operation, a large amount of young fish, some big fishes and possibly some fish eggs will be drawn in. When fish eggs pass through the hydraulic turbine, the sudden changes of pressure are very likely to cause the membranes to break and the eggs to die. Big fishes such as Anguilla japonica, Mylopharyngodon piceus and Hypophthalmichthys molitrix will be cut into pieces by the pump blades when they pass through the hydraulic turbines. Young fish will not be affected. If they are of pure freshwater species, they will increase the resources in inland rivers and lakes after they are pumped into them. If they are migratory fishes that have crossed the estuary (mainly young Hilsa reevesii), they will inevitably die in the freshwater owing to the fact that they cannot go downstream and enter the sea in season.

After the transfer of water, the water level of such transit lakes as the Hongze will rise by 0.5 to 1.5 metres. This will dramatically reduce aquatic weeds, the eutrophic water bodies will be continuously diluted, the water temperature will drop and plankton will diminish. This could lead to the following:

(1) The availability of forage will decline for the young of herbivorous fish species such as Ctenopharyngodon idella, Parabramis pekinensis, Megalobrama terminalis and of the plankton-eating economic fish species as well as the adult Hypophthalmichthys molitrix and Aristichthys nobilis. Their growth conditions will worsen and the death rate of young fish will rise.
(2) Those fish species that lay eggs on aquatic weeds, including Cyprinus carpio, Carassius auratus and Megalobrama term in alis will encounter worse spawning conditions. The survival rate during the embryonic period will drop and the fish resource will decline.
(3) Small fishes, such as Coilia brachygnathus, Neosalanx tangkahkeii taihuensis and Protosalanx hyalocranius which make their habitat in smooth water surfaces and spawn in gentle flowing currents will receive better conditions for existence. They could develop into the predominant fish species and take the place of the comparatively larger fishes such as Ctenopharyngodon idella, Mylopharyngodon piceus, Hypopthalmichthys molitrix, Aristichthys nobilis, Cyprinus carpio, Carassius auratus, Parabramis pekinensis and Megalobrama terminalis, which have higher economic value.

References

Chen Hongda and He Chuhua, 1975, "The biomass of aquatic plants with vascular bundles in Dong Hu (East Lake), Wuchang, and their rational utilization in fishery", Acta Hydrobiologica Sinica, pp. 410-420.

Chen Peishun and Huang Henian, 1963, "Data on the morphology and ecology of fish on the surface of the Chang Jiang delta", Acta Hydrobiologica Sinica, No. 3, pp. 93-98.

Ichthylogy Laboratory, Hubei Institute of Hydrology, 1976, Fish of the Chang Jiang, Science Press, Beijing.

APPENDIX

Common English names for some of the fish mentioned

Hilsa reevesii hilsa herring
Coilia mystus anchovy
Cyprinus carpio carp
Hypophthalmichthys molitrix silver carp
Mylopharyngodon piceus black carp
Psephurus gladius paddlefish
Erythroculter skygazer
Hemisalanx prognothus white bait
Anguilla japonica Japanese eel
Lateolabrax japonicus suzuki
Dasyatis akajei red sting ray
Mugil so-iuy mullet
Mugil cephalus striped mullet
Acipencer sinensis Chinese sturgeon
Pneumatophorous japonicus Japanese mackerel
Decapterus maruadsi Maruaji
Pseudosciaena crocea yellow croaker
Ctenopharyngodon idella grass carp
Carrassius auratus cruscian carp
Carassius auratus big head
Aristichthys nobilis hairtail
Megalobrama terminalis triangular bream

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