Since the beginning of this year, Hainan Province has continued to suffer from high temperatures and little rain. Freshwater resources and its scarcity have greatly affected the cultivation of tilapia. In this period, the day-to-day management of aquaculture is well underway, and in particular maintaining the stability of pond water quality is particularly critical.
In the â€œFront of Aquaculture Frontierâ€ visit in Hainan in late June, I learned from the Hainan Bolu Aquatic Products that the Hainan News Channel recently reported that a non-native Zhejiang Taizhou fisherman operating over 100 mu of fish ponds in Wenchang Wengtian and Luo Fei in 4 fish ponds. Occurrence of fish breeding accidents, 140,000 kg of fish died all night. The farmer reported the case locally and the police went to investigate and collect evidence. However, the results of the inspection of dead fish and water samples have not yet been concluded.
Ji Shengrong, general manager of Baolu, believes that this type of accident is likely to be related to the deterioration of the water environment caused by persistent high temperatures in Hainan since the drought and drought this year. In particular, the freshwater resources in Wenchang are very scarce, plus the management practices of farmers. Improper use of drugs and other factors.
High temperature and drought, severe farming situation
It is understood that by the end of June, the average rainfall of Hainan Island this year is only 372.25 millimeters, which is 31% lower than the average for many years. Although it has entered the flood season, Hainan's hot and rainy weather continues. The Wenchang area, as a dense area for tilapia breeding, has always been one of the hardest-hit areas since the Streptococcus outbreak in 2009 due to the lack of large reservoirs and rivers and the shortage of freshwater resources.
In the afternoon of the same day, the reporter of â€œFishery Frontierâ€ also accompanied Chen Zibin, sales manager of Baolu Road, and Wang Jian, a technician of Baolu Aquatic Slope Service Station, visited the farmers and conducted some basics on the fish ponds where the fish farmers had several fish. The results of water quality measurement showed that the ammonia nitrogen, pH and other values â€‹â€‹of the water were all too high, and the pH was even closer to 9.5. Chen Zibin explained that the resulting high pH is mainly due to the high water temperature and strong light in summer, and the water body is prone to eutrophication, resulting in a large outbreak of blue-green algae. Wang Jian said that this type of situation is not uncommon in the Wenchang area, and that this blue-green algae encounters a large number of deaths in the wake of abrupt changes in the weather, which can cause problems such as lack of oxygen and algae decomposition and water quality, which can easily lead to breeding. The accident occurred.
Oxygen, water transfer to maintain a good water environment
And how should farmers respond to this situation? Wang Jian said that in the case of high temperatures, farmers first need to do a good job of oxygenation. At present, in order to save costs, many farmers need only one aerator for the 56-acre fishpond and they rarely turn on oxygen. These practices are undesirable, usually on a sunny afternoon (1-3 points). The aerators should be opened in the middle of the night and the aquarium should be increased accordingly. It is advisable to allow the water to circulate. In addition, when the water quality is poor, it is necessary to reduce or stop the feeding. "Because the fish is quite fragile at this time, the appetite for feeding is very low, and the feed water will spoil the water quality."
During the high temperature season, when algae over-proliferate and the pH of the water is too high, many farmers will often use disinfectants, algaecides, etc. to prevent diseases and regulate water quality. However, there are risks in this way. It is often seen that the dose is small and no effect is seen, and farmers often increase the dose to cause a culture accident. Of course, the safe way is undoubtedly to advise the qualified fish farmers to change the water properly. However, for situations like Wenchang, where there is no water change, one can improve the water body by splashing out antidote products such as organic acids. Chen Zibin said that acetic acid can also quickly reduce the pH of the water, but the duration is short, and it will rebound after three or two days. Regularly sprinkling microbial preparations such as EM bacteria and enzyme bacteria to regulate water quality is one of the feasible methods. The proliferation of beneficial bacteria inhibits the over-proliferation of algae, decomposing organic matter and improving the body of water. However, Wang Jian also reminded farmers that if they use inferior products, the nutrients used by the beneficial bacteria will be used by the algae, which will lead to more vigorous algal blooms. In this regard, Cai Zengshanâ€™s engineer at Wuhan Heyuan Green Bioengineering Co., Ltd. also believes that the best way is through microbial regulation, but he also agrees that the current microbial preparations are poorly regulated due to lack of effective supervision, and the brands are numerous and uneven in quality. From the appearance, it is difficult to discriminate whether the product quality is good or bad. When farmers purchase, they can't blindly try to buy cheap products, but they should choose a good word of mouth or a product that has worked well.
Sustained high temperatures coupled with harsh farming conditions, Streptococcus can be said to be explosive. In this regard, Chen Zibin believes that in addition to the day-to-day management work of the farmers, the ponds that put the seedlings need to be poisoned and the water should be released before they are released. When stocking, the stocking density should be reasonably controlled according to the water quality; Ponds should fish out as soon as possible to avoid the various risks of high temperature period.
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