First, the basic situation of rivers
The drainage trough where water often flows on land is called a river. Large velocity, unstable water level, high sediment concentration and few aquatic organisms are the common characteristics of rivers. But the hydrological and environmental conditions of different rivers are very different.
The hydrological conditions of the Yellow River, the Yangtze River and other large rivers are very complicated, especially in the middle and upper reaches, where the water flow is very fast and the water level changes greatly. Only some species of aquatic organisms have low biomass and poor fishery utilization performance. The plankton in the river mainly flows in from the connected still water, and only some diatoms grow by themselves. The downstream conditions have improved, and plankton and benthos (chironomid larvae and oligochaetes) have gradually increased, but they are much less than lakes and reservoirs.
Shanxi River mainly refers to the upper reaches and tributaries of mountain streams and rivers. This kind of river has large water level difference, low water temperature, thin water quality and extremely poor bait organisms. Only on the basis of transformation and development can it be used in fishery production.
Small river ditches in plain areas, especially those in water network areas, are generally located in densely populated areas, with gentle water flow, relatively small water level change, fertile water quality, abundant plankton, benthic organisms and even aquatic vascular plants, and a large number of village domestic sewage and nutrients from surrounding farmland, which are very suitable for farming.
The second is the proliferation and release of fish in large rivers and the protection of resources.
The hydrological characteristics of large rivers determine that the fishing methods are mainly fish proliferation and release and resource protection. The so-called release refers to putting seedlings into natural waters and listening to their natural growth and reproduction to obtain the reproduction of resources. However, in China, the four fry can't reproduce naturally in lakes and reservoirs, and the fish-stopping equipment is limited to a certain range. Under the management of people, production can only increase production and can't realize the regeneration of resources, so it is called stocking. The discharge of major rivers in China is rarely done, but Zhejiang Province has done a good job in this respect. For example: 197 1, 12, 1972, from April to May, about 300,000 silver carp and bighead carp were released to the Oujiang River, and from July to September/kloc-0. Since the artificial release of Qiantang River in 1958, the catch of the four major fishes has increased from 8% before release to 40% (1972).
The Wusuli River and Tumen River have also carried out artificial release of salmon, and achieved certain results. The release of salmon in Japan, the United States and other countries has a history of 100 years, and the effect is remarkable. The length of juvenile fish released in Japan is 3.4-5.9 cm, and the regression rate of 1974- 1983 is 4. 1-6.3%. Only by controlling soil erosion and sewage discharge, reducing sediment content and water pollution, and at the same time restricting fishing, can the problem be fundamentally solved.
Except for the reservoirs built on the big rivers, there are few ways to cultivate fish in the big rivers. In recent years, metal cage fish culture in Sichuan can be set in rivers with high velocity, such as Fujiang River and Jialing River. This method of raising fish is to make an iron boat with sealed cabins at both ends, an empty frame and a metal net, and put a cage in the empty frame to raise fish. It is characterized by strong water flow resistance and high yield.
Three. Fishery development in mountainous rivers
Because of the special environmental conditions of rivers in mountainous areas, it is difficult to raise fish. However, according to the specific situation, fish farming can be artificially transformed and developed.
In places with good conditions, small reservoirs or ponds can be built to implement comprehensive fish farming, including fertilization and fish feeding combined with animal husbandry.
You can use the natural terrain in mountainous areas to build running water fish farms. Due to the large gap between streams and rivers in mountainous areas, it is easy to find a suitable site to build a running water fish farm, and introduce natural running water to obtain high yield without consuming energy. If the water temperature is low, you can raise valuable salmon and trout.
In some mountainous areas of Hubei Province, it is also a good development direction to try to cultivate giant salamander (giant salamander) by using mountain rivers.
Four, plain small rivers and ditches to raise fish
The rivers and ditches in the plain have excellent conditions and can be used for cage culture and fish farming.
(1) Stop feeding
In order to raise fish, fences or bamboo foils should be set up upstream and downstream of a river, and then fish should be raised in the fences.
1. Fence structure has three forms: bamboo foil, mesh foil or barrier net. Bamboo foil is suitable for rivers with slow water flow and small water depth, and blocking net is suitable for wider and deeper rivers. Its design and construction methods are the same as those of lakes and reservoirs.
2. The main purpose of river cleaning in the enclosure is to remove silt and fierce fish. The bottom pollution can be removed by dredgers or small dredgers, and it can also be removed manually in dry season and dry season. Removing sludge will improve the water environment and prevent water quality from deteriorating. The fierce fish in the river are mainly red goblet, Mongolian red goblet and snakehead, which can be cleaned by drugs, hook fishing and repeated trawling to ensure the safety of stocked fish.
3. Fish stocking Because of the fertile water quality, abundant plankton and debris in the small plain river, the water body has been in a state of directional exchange, and the dissolved oxygen is also sufficient. Natural baits such as aquatic plants, snails and clams are easily collected around, so there are two ways to stock them:
(1) Silver carp and bighead carp are fed with abundant plankton, and other fish are properly matched, so little or no feeding is required. Silver carp and bighead carp (4:6) account for about 70% of the total stocking, and the remaining 30% are mainly herring, grass carp, bream, bream, crucian carp and carp (carp, crucian carp and bream account for about 20%). Due to the great requirement of fishing equipment for water capacity, the total length of the four major fish species is required to be above 13.3cm, and the second-instar fish species (mainly grass carp and black carp) account for a certain proportion, the total length of bream and bream is above 9.9 cm, and the total length of carp and crucian carp is above 6.6 cm. The stocking amount should be flexibly controlled according to the water surface size, water quality and other specific conditions. 200-300 fish/mu can be released in poor conditions, 300-500 fish/mu can be released in good conditions, and the stocking quantity of some rivers can be higher.
River fish culture area 1.40 mu in Nanning, Guangxi. During the period from September 65,438+0.956 to March 65,438+0.957, 65,438+0.1.00000 fish were released, with an average of 65,438+0.294 fish per mu. Bighead carp accounts for 28%, with the specification of10-16.5cm. Carp accounts for 23%, with the size of 2.6cm.: Grass carp accounts for 5%, and the specification is10-16.5cm.1957. In April, 48 tons of adult fish were caught, with an average yield of 342.5kg per mu.
(2) Edible fish accounts for a large proportion, and the main source of bait is aquatic plants, snails and clams collected artificially in the surrounding waters. This fish culture method has a small area and is cultivated according to the method of enclosing fish in lakes. The difference is that the proportion of silver carp and bighead carp is larger than that of the fish around the lake, which can generally reach 30-50%.
For example, in Wuxian Aquaculture Farm in Jiangsu Province, the river 18 mu, and the average water depth 1.5 meters. 1.976 herring was the main feed, grass carp, carp, silver carp, bighead carp and crucian carp were fertilized, and the yield per mu was 650.2 kg. Among them, herring accounts for 52. 1%, grass carp accounts for 3.3%, carp accounts for 15.3%, and silver carp, bighead carp and crucian carp account for 29.3%.
4. River basin management The most important thing in river basin management is to manage fishing equipment. Once the fishing equipment is damaged, the fish will escape, and the consequences will be unimaginable. Wood blocks, bamboo chips, etc. Dirt must be inspected, maintained and removed in time. Ships often cross some rivers, so a special person should be appointed to manage the lifting pulley. In addition, we must do a good job in theft prevention, flood control and pollution prevention.
(2) Other fish farming methods
According to the river conditions, silver carp and bighead carp cages can be set up in rivers with abundant plankton and low flow rate, and they can be cultured entirely with natural bait. For example, the rivers near villages and towns in Pingtan District, Tongliang County, Sichuan Province have fertile water quality, small water level change and slow water flow. Set up silver carp and bighead carp cages, and the yield per mu is 1992- 1993, equivalent to1-20,000 kg. Rivers with better water quality can also be caged to raise edible fish.
In the aqueduct with water flowing all year round, fish can be cultured in metal cages. This fish culture method is as follows: the bank on one side of the channel is widened and reconstructed at the place where the cage is installed, and then a box of 40-60 square meters is enclosed with a metal net, and intensive culture is carried out with reference to the measures of running water fish culture and cage fish culture, and the output can reach more than 150 kg/square meter. At present, this form of fish farming is very common in Meishan, Sichuan.