Water quality requirements and management measures of aquaculture in aquatic ponds

With the development of high density and intensive water quality aquaculture production, the change frequency of aquaculture water quality is accelerated, resulting in eutrophication of pond water quality. Coupled with the increase of pond water pollution sources, water quality management is more important than in the past. The quality of water quality is closely related to aquaculture output, diseases and economic benefits. Comprehensive management should be adopted in water quality management to make water quality conditions meet the requirements of aquaculture objects.

1. Pond water quality requirements

A good pond of fish requires a good pool of water, and the water quality of fish culture is summarized as "fat, live, cool and tender".

1.1 Fertilizer

The concept of "fertilizer and water" is mostly based on the total amount of plankton or the number of digestible phytoplankton. "fat" mostly refers to strong water color and high plankton. In order to avoid the interference of abiotic suspended matter in the water, it is necessary to stand on the ridge of the upwind pool. The transparency of the general fat pool should be about 20-30cm. This is equivalent to the total amount of phytoplankton in the water is above 20mg/L.

1.2 active

"living water" means that the color and transparency of the water often change, and the activity is caused by the changes of organisms in the water. It is observed that the most typical living water is the change of water color caused by the proliferation of genicularia. Genicularia belongs to Xanthophyta, which is a kind of flagellate algae, which swims fast and has significant phototaxis. It often moves vertically and horizontally with the change of light intensity in the daytime. The upper and lower water layers are evenly distributed in the early morning, and gradually concentrate to the surface layer after sunrise. Most of them are concentrated in the surface layer before and after noon, and then gradually sink and disperse. The transparency can be different between 9 o'clock and 13:00 7cm. When the algae gather on one side or corner of the fish pond, half the pond is red and half green. We often see different shades of water in ponds, such as dark cloud-like water masses formed by flagellates. All flagellate algae have a similar phenomenon, and the number of surface layer is generally more in the afternoon than in the morning.

1.3 Shuang

"Shuang" means that the water quality is refreshing, the water color is not too strong, and the transparency is not lower than that of 25cm. The reasons for low transparency are either extremely high plankton, dominant cyanobacteria (cyanobacteria are generally concentrated on the surface), or too much sediment and other suspended matter. Suspended solids and excessive algae that can not be used by fish in the water are all factors that affect filter feeding. The amount of phytoplankton in well-growing ponds is generally less than 100 mg/L, and more than 100 mg/L is roughly the dividing line between "fertile water" and "old water" in flagellate algae ponds. However, the biomass of "Fei Shui" phytoplankton in cyanobacteria ponds often exceeds that of 200mg/L.

1.4 tender

"tender" means that the water quality is fat but not old, which means that the algae cells in the water are not aging, and there are not many cyanobacteria. There are mainly two kinds of so-called water "old", one is yellow or brown, the other is white. The yellowing or browning of the water color is due to the aging of the algae cells. the composition of the algae in the water does not change, but the lutein and carotene in the cells increase. From the appearance, the water color is yellow and brown. Farmers call this water old tea (yellowish brown) and yellow wax water (withered yellow with green). The faint whitening of the water color is mainly a manifestation of the growth of cyanobacteria, especially those small cyanobacteria such as Microcystis powdery, Chlorella aeruginosa, etc.). The pH value of this kind of water is very high, usually above 9-10, the transparency is very low, usually less than 25-20cm, and the alkalinity decreases rapidly with the increase of turbidity intensity during the day. Thus it can be seen that the whitening of water color is the result of bicarbonate forming carbonate crystals due to the lack of carbon dioxide. At the same time, the increase of pH promoted the growth of cyanobacteria.

2.1 remove silt and improve sediment

Too much silt can easily worsen water quality and cause fish disease. Healthy aquaculture keeps the sludge around 5cm, while exposing to the dry and cracked bottom of the pond or freezing the bottom of the pool for several days, applying quicklime 100-150kg per 667m2.

2.2 reasonable stocking density

The quantity of fish species should be determined according to the conditions of the pond, the species and specifications of fish species, the supply of bait, the techniques of feeding and management, etc.

2.3 Control of feeding amount

According to the total feeding amount of the whole year and the size of the fish body, determine the monthly feeding amount; according to the season, weather, water color, fish activity and feeding situation, determine the daily feeding amount, generally make the fish eat up to 80% full.

In the culture ponds of healthy aquatic products, the use of drugs should strictly follow the relevant regulations of pollution-free aquatic products, and use fish drugs with "three effects" (high efficiency, quick effect and long effect) and "three small" (low toxicity, small side effects and small dosage). Calculate the dosage accurately and release it reasonably. Prevent the abuse of fishery drugs, blindly increase the dosage or increase the frequency of drug use, and prolong the time of drug use.

2.5 regular replacement of new water

It is necessary to timely inject and change water, improve the water quality of the pond, keep the water fresh and replenish the dissolved oxygen in the water body. The water can be changed every 15 days, at least once a week during the peak fish growing season from June to September. Every time you change the water 30cm, you should first discharge the pool water and then add new water.

The probiotics of Yunye em, nitrifying bacteria, thiobacillus, lactic acid bacteria, yeast and Gram-positive actinomycetes can be used to improve the biological method of water, so as to make the water quality reach the standard of "fat, live, tender and cool", improve the immune function of fish and prevent the occurrence of bacterial fish disease.

Turn on the aerator at the right time to improve the dissolved oxygen in the water and maintain the excellent environment of the pond water. The law of starting the aerator is generally as follows: start the aerator at noon on a sunny day (11:00 to 14:00), open in the morning on a cloudy day, open in the middle of the night in continuous drizzle, but not in the evening; open early in the floating head, and open every day in the floating head season; open in time after rotation, with less wind and more open, and so on. The start-up time is: long start-up time in the middle of the night and short start-up time at noon; after fertilization, the weather is muggy, the pond area is large, the fish carrying capacity is large, and the start-up time should be long; without fertilization, the weather is cool, the pond area is small, the fish load is small, and the boot time is short.

The suitable range of pH for freshwater aquaculture is 6.5-8.5, and the optimum range is 7.2-8.0.