How should the timing of shrimp fry stocking and water temperature be managed to achieve high yields?
No matter what kind of aquaculture it is, farmers all hope to exchange the smallest investment cost for the largest profit margin. Therefore, for farmers, achieving high yield is the issue they care about most, so it is very necessary to reasonably master their living environment and living water temperature. Now let's take a look together.
When and at what water temperature should shrimp fry be stocked to achieve high yield
Taking into account various factors such as the patterns of climate change, the water temperature requirements for the growth of whiteleg shrimp (Litopenaeus vannamei) and black tiger shrimp (Penaeus monodon), and the water temperature requirements for the reproduction of feed organisms, it is generally believed that: to culture these two kinds of shrimp more safely and stably, early-spring stocking of fry along the coast of Zhanjiang, Guangdong, China should be around Qingming, that is, when the water temperature is stable above 18 degrees C. Even in a warm winter, fry should be stocked after mid-March; for the late crop, stocking should be completed before the Mid-Autumn Festival. Shrimp farmers generally believe that stocking fry early in spring and harvesting shrimp early offers a greater hope of making big money. But stocking shrimp fry too early means the water temperature is not suitable for shrimp growth, there are many diseases, and in the end there are few successes and many failures, contrary to one's wishes.
Water temperature requirements of shrimp
From the physiological requirements of whiteleg shrimp and black tiger shrimp, both species have a certain optimal water temperature range, and water temperature above 23 degrees C is their optimal water temperature. Only within the optimal water temperature range can they grow healthily and quickly; otherwise they grow poorly, leading to continuous outbreaks of disease.
According to statistics from 32 years (1960 to 1991) of measured water temperature data from the Zhanjiang Naozhou Marine Station, it can be seen that the water temperature in the coastal waters of Zhanjiang changes relatively slowly, with a small annual water temperature difference, and the lowest water temperature mostly appears in February. February to June is the warming period, and October to December cools fastest, with a cooling rate of 3 degrees C to 4 degrees C per month. July to August has the highest water temperature of the year, with a monthly average of 29 degrees C. Except for high-position shrimp ponds, other shrimp ponds in the Zhanjiang area are relatively shallow, mostly 1.0 m to 1.3 m. Water temperature in shallow shrimp ponds changes greatly, and in summer the water temperature can exceed the air temperature. In calm, low-pressure, muggy weather, pond water dissipates heat slowly, and the shrimp pond water temperature is higher than the air temperature. Water temperatures above 36 degrees C are common, and in some weather the shrimp pond water temperature even reaches 37 degrees C to 38 degrees C, exceeding the suitable temperature range for shrimp and causing long-term temperature discomfort for the shrimp. During the low-temperature period in winter, shrimp pond water is shallow, and the water temperature in the pond is much lower than the coastal sea water temperature, almost close to the air temperature.
Why it is not suitable to stock fry too early
Whiteleg shrimp and black tiger shrimp, the most widely cultured species in the South China Sea area, require water temperature above 18 degrees C to feed normally and grow normally, and only at 24 degrees C to 33 degrees C can growth reach an ideal state. From Table 2 it can be seen that in the coastal area of Naozhou, Zhanjiang, the water temperature is around 15 degrees C for most of January to February, all higher than the shrimp pond water temperature. Therefore, the sea water temperature in January to February is not suitable for the growth of these two kinds of shrimp. Moreover, when affected by cold air, the water temperature drops rapidly, light intensity is poor, water temperature is low, and salinity is high, which is unfavorable to algae growth and directly affects the growth of animal and plant feed in the shrimp pond. The water color of the shrimp pond is difficult to stabilize, and feed organisms can hardly meet the early feeding requirements of the shrimp. Because of feed organism growth, the ecological conditions of the pond water are also unstable. Therefore, early stocking of fry carries great risk. Even if the shrimp fry are not killed by cold, their growth is greatly restricted, the shrimp's constitution is weak, and they cannot withstand drastic changes in environmental factors later, making them prone to disease.
When is the right time to stock fry
Taking into account various factors such as the patterns of climate change, the water temperature requirements for the growth of whiteleg shrimp and black tiger shrimp, and the water temperature requirements for the reproduction of feed organisms, it is generally believed that: to culture these two kinds of shrimp more safely and stably, early-spring stocking of shrimp fry along the coast of Zhanjiang should be around Qingming, that is, when the water temperature is stable above 18 degrees C. Even in a warm winter, fry should be stocked after mid-March. Stocking shrimp fry around the Spring Festival is gambling-style production. Because tropical shrimp grow within a suitable water temperature range, and water temperature gradually rises (in a parabolic shape), the certainty of success is greater; if the water temperature changes in a wavy manner, it easily causes weak resistance in the shrimp and susceptibility to disease. Even if they do not die of disease, they grow slowly, consume more feed, and the cost is high, which inevitably affects economic benefits. From the annual water temperature change pattern along the coast of Zhanjiang, the water temperature begins to decline in September, and cools rapidly in October to November. Therefore, for late-crop culture of whiteleg shrimp, shrimp fry should all be stocked before the Mid-Autumn Festival. A simple and effective way to maintain water temperature in winter is to deepen the pond water. If the water depth can be maintained above 2 m, the water temperature will be more than 2 degrees C higher than in shallow shrimp ponds.
Compared over the same period, the coastal water temperature of Beihai, Guangxi, is 1 degree C to 2 degrees C lower than that of Zhanjiang, and the coastal water temperature of Fangcheng is about 1 degree C lower than that of Beihai. Therefore, in the northern part of the Beibu Gulf, early-spring stocking of fry is suitable after Qingming. The southern coast of Hainan Island is less affected by cold air, and except for avoiding the hot days of June to July, shrimp can be cultured year-round; the northern part is affected by cold air, and stocking of shrimp fry should begin in late February (that is, after Yushui). The air temperature of the Pearl River Estuary is about 2 degrees C lower than that of Zhanjiang. For shrimp ponds without greenhouse facilities, normal stocking of shrimp fry should be 10 days to 15 days later than in Zhanjiang. If there is a greenhouse over the shrimp pond and the water temperature can be maintained above 18 degrees C in winter, then there is little problem with when to stock shrimp fry. If the heat preservation capacity is poor, the most suitable time for stocking fry should also be managed as appropriate according to local climate change conditions. In early spring, the coastal water temperature of Shantou is more than 2 degrees C lower than that of Zhanjiang in the same period.
Therefore, stocking shrimp fry around mid-April is relatively suitable. In autumn, other coastal areas of Guangdong cool down earlier than Zhanjiang, and late-crop stocking of shrimp fry should be earlier than in Zhanjiang. By mastering the above stocking times, the time for culturing two crops of shrimp per year is also sufficient, and there is no need to stock fry too early in early spring and cause unnecessary economic losses. Because of shrimp deaths, the water sources of shrimp ponds or sea areas become polluted, causing shrimp diseases to occur frequently, which is extremely unfavorable to the development of the shrimp farming industry. Therefore, operators must act according to scientific guidelines so that the shrimp farming industry can develop sustainably.
Reasonably mastering the timing of shrimp fry stocking is very important for shrimp growth, and the survival of shrimp also has requirements for water temperature. Reasonably mastering the timing of shrimp stocking and the stocking water temperature can effectively reduce unnecessary economic losses, effectively save investment costs, and obtain more profits.