Introduction to three methods for harvesting warm-water fish

I. Seine netting method

This is currently a relatively common harvesting method for "warm-water fish." The net is generally made of nylon, or the middle section is made of nylon. The net length should be about 1.5 times the width of the pond surface, the net height should be about 2 times the pond water depth, and the mesh size should be such that none of the pond fish get gilled in the net. The advantages of this harvesting method: first, it catches all types of pond fish, which can meet the demands of different fish vendors; second, during the seining process, the bottom mud and pond water are stirred up, which plays a role in fertilizing the water and aerating it. Of course, this harvesting method also has obvious disadvantages: first, the process of seining and sorting the fish is rather long, which inevitably brings several adverse consequences. First, the labor intensity is too high; completing one seining operation requires at least more than 10 people. Second, the fish are easily injured, which can lead to the occurrence of fish diseases. In addition, because the fish-sorting operation takes too long, there may be fish deaths from oxygen deprivation during the process. Second, the catch rate for some fish is not high, especially in the high-temperature full-water season, when the catch rate for common carp, crucian carp, and grass carp is very low. Therefore, it is generally believed that the seine netting method is more focused on catching upper-layer fish and is relatively suitable for "fertilized-water fish" culture ponds with silver carp and bighead carp as the main fish.

Now, in response to the problems in the seining process, people have introduced two improved methods: first, using large-mesh nets for seining. The net used is determined according to the size of the fish to be harvested; fish that have not reached market size basically pass through the mesh and do not get caught in the net, thus shortening the operation time and avoiding the occurrence of oxygen deprivation. This method still cannot avoid injury to the fish. In particular, black carp and grass carp between fingerling and adult size are often prone to getting gilled in the net. These gilled fish generally have gill injuries, basically cannot survive, and even if they barely @#@136@#@ have extremely poor economic value. Second, using the fish-gathering purse seine method, that is, 2 to 3 hours before seining, add fresh water to the pond so that most of the pond fish gather and move in the fresh-water area. At this time, it is only necessary to surround the net in the corner of the pond where water enters to complete the harvesting work, thus greatly shortening the seining time. Because the operation is carried out in the fresh-water area, it will not cause fish deaths from oxygen deprivation. However, this method is only suitable for use in the early stage when the pond water is relatively low. At this time, the pond fish have an obvious response to the stimulation of fresh water, and the purse seine effect is very good. By the full-water midsummer season, the pond fish do not respond strongly to the stimulation of fresh water, and often very good results cannot be obtained.

II. Lift-net method

This is a method of harvesting "warm-water fish" that only began to be promoted after the use of compound feed in aquaculture. The size of the lift net used is 16 m x 16 m. The specific procedure is: first place the lift net on the bottom of the feeding area, use a feeding machine to feed, so that the fish gather on the surface of the lift net, and then lift the net to catch the fish. The advantages of this fishing method are that it is simple to operate and greatly shortens the working time; the whole process takes only about 40 minutes, thereby reducing injury to the fish. In addition, under normal weather conditions, this method has a very high catch rate for feeding fish. Generally, at least 60% to 70% of the feeding fish can be lifted into the net each time, making it especially suitable for the culture requirement of catching the large and leaving the small. Of course, this method also has its disadvantages: first, the target of harvesting is limited; it is only effective for feeding fish, and its catch rate for silver carp is almost zero. Second, it is obviously affected by climate. Because the fish school must be concentrated through feeding, in the early morning of extremely hot or rainy weather, it is often impossible to gather the fish because of oxygen deprivation. Third, it has relatively high requirements for pond water depth. In ponds with a water depth of less than 1.5 m, the fish school often cannot concentrate to feed because of the influence of the lift net on the pond bottom, making it impossible to complete the harvesting work. Fourth, the preparation time in the early stage is relatively long. To achieve the ideal harvesting effect, the lift net generally must be placed on the bottom of the feeding area 1 to 2 days in advance so that the fish school can adapt.

III. Cast net method

The "cast net" is a fishing net commonly used in the past. One person standing on a boat or on the shore can complete the fishing operation by casting the net into the water. Each cast takes about 5 to 10 minutes, and the fishing area depends on the skill of the operator, generally about 20 to 30 sq m. The greatest advantage of this method is that it saves manpower; generally at most only 2 people are needed to operate it, and the fish caught by this method are complete in variety. Its greatest disadvantage is that it is not conducive to large-scale harvesting; generally at most only 100 to 150 kg can be harvested each time. Second, the fish caught are severely damaged, because the fish-sorting work of this method must be completed on a boat or on the shore, which is very damaging to the fingerlings left in the pond. Third, this operation is highly technical and often must be completed by specialized personnel. Therefore, the value of promoting this method has become smaller and smaller. Through the above analysis, everyone can determine the fishing method according to their own actual needs. Ponds mainly for fertilized-water fish should mainly use seine netting for harvesting; ponds mainly for compound feed aquaculture are generally better with lift nets; and for some small adult-fish ponds or fishing ponds mainly for entertainment and leisure, the cast net method is also a feasible and practical method.