2.1 Research on the over-wintering technology of fish in the seawater solar pond

The area of the solar pond is 6000 m2 and the gradient is in 1.8. The interior of the pond is trapezium-structured, in which there are three contrast districts. The water is 4m deep in district □, 3.5m deep in district □ and 3m deep in district □. See fig 4

During the process of designing and constructing the pond, optimizing and simulating the ecological environment suitable for fish in seawater is attached importance to. In the temperature-preserving area, trapezium-shaped structure is adopted to provide fish with the convenience and freedom to choose suitable Living space. It is because that a large quantity of poisonous gas is accumulated continuously in the high-temperature zone during the operation of the solar pond.

Bulldozers, digging machines and slurry pumps are combined to work to construct the solar pond. The underground depth of the pond is 3.5m and upground depth is 0.5m. The upper slope of the pond is protected by cement board. The treatment of leakage-prevention is not adopted at the bottom of the pond, thus the underground brine is adopted to be poured into the solar pond and the salt concentration is regulated and controlled at about 25%o. The depth of water poured in pond for the fist time should be suitable for raising and managing young aquatic products, then go on pouring in water to 3/4 of the depth of the pond and should maintain the water level. When water temperature drops to 15°C,(It happens during the first-ten-day period of November) People should pour fresh water into the pond of about 20cm to 30cm, then pay attention to the change in weather. Fresh water of 20cm to 30cm should be poured into the pond before the cold current or at the time of the cold current. The depth of the fresh water should reach 60cm to 80cm when December arrives.

The crux of the safe working of the seawater solar pond is to maintain the existence of salt gradient and to upkeep good physico-chemical, biological factors of the heat-preserving areas. Fresh water should be added timely once the solution of the surface mixes. In winter, the ice surface

should be kept clean and accumulated snow is strictly forbidden in order not to affect photosynthesis and the effects of integrating and preserving heat.

In order to study and explore the law of change in physico-chemical factors in the seawater solar pond, water temperature, salt concentration, dissolved hydrogen, PH and so on are monitored regularly. See graph

Form the winter of 2001 to the spring of 2002, the working conditions of the seawater solar pond is fine and the salt gradient is controlled well. The temperature reaches 10.0”C, which is 4.0”C higher than the lowest working temperature. It meets the demand of the over-wintering of cultivation objects in the seawater of warm water kind in the Northern Part of China.

However, the physico-chemical target of the lower convective zone of solar pond exceeds limits, especially, the dissolved bydrogen in the water drops to zero. In the year of 2002, several measures were taken to improve the content of the dissolved hydrogen and better the water quality at the bottom.1) Develop and install the underwater hydrogen-increase devices at the interior of the solar pond.2) Design water circulating plastic pipeline at the bottom of solar ponds. The problems of water changing foul and low dissolved hydrogen are solved successfully through the two above-mentioned measures and the output of the over-wintering fish achieves 250kg per mu.