A method for artificial cultivation of northern loach fry using euglena as opening bait

Abstract

The application discloses a kind of artificial breeding method of northern loach fry with oocystis as opening bait, which is to sprinkle and inoculate oocystis into the water of breeding pond before the northern loach fry is out of membrane, the natural water temperature of the water of breeding pond is 17-19 ℃, the density of phytoplankton and the number of oocystis in the water are detected regularly, and at least 80% of the phytoplankton of oocystis is used as the opening bait of northern loach fry, so that the fry is active in opening feeding, and the feeding ratio can reach 100%. Suitable breeding density and the density of phytoplankton can ensure normal feeding of northern loach fry and sustainable reproduction of phytoplankton, so as to effectively decompose ammonia nitrogen and sub-salt in water, improve water quality, and make the survival rate of northern loach fry reach 89%, which is helpful for large-scale artificial breeding of northern loach.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture fry cultivation technology, specifically relating to a method for artificially cultivating juvenile northern barbel loach using Algae oocystis as the initial feed. Background Technology

[0002] Northern Loach ( Barbatula nuda The northern barbel, belonging to the order Cypriniformes, family Cobitidae, and genus Barbatula, is a small, cold-water edible fish with tender, delicious flesh, making it very popular. While the northern barbel is still primarily caught naturally in the market, overfishing has led to a sharp decline in its natural resources, resulting in a supply shortage. Therefore, researchers have been dedicated to developing artificial breeding methods for the northern barbel.

[0003] The artificial breeding method for Northern Loach is similar to that of other fish: fertilized eggs are obtained from parent fish, hatched, and the larvae are introduced into a pond and fed initial feed until they reach juvenile stage. Then, formulated feed is used to raise the juveniles to larvae and adults. The larval stage is a period of transition from endogenous to exogenous nutrition, an early stage of active nutrition, making the initial feed crucial. Rotifers and formulated feeds are commonly used as initial feeds. Chinese patent application No. 201710645475.X discloses a "Formulated Feed for Northern Loach," which states that it is "particularly suitable for the digestive physiology of Northern Loach, has good palatability, high feed utilization, and fast growth rate, enabling Northern Loach to reach marketable size in the same year...". However, because most freshwater fish larvae have incomplete digestive functions, ordinary formulated feeds can affect larval growth and survival rates, thus restricting the large-scale artificial breeding of Northern Loach.

[0004] *Oocystis* is a common genus of green algae, belonging to the order Chlorococcales, suborder Acoenobianae, and family Oocystaceae. It typically lives in cellular aggregates and has been reported to effectively remove ammonia nitrogen from water and inhibit Vibrio growth. It is a high-quality algae for fertilizing and regulating pond water quality and is commonly found in fish farming ponds as food for rotifers and cladocerans. It is generally believed that freshwater fry cannot break down the cell walls of algae and therefore cannot absorb their nutrients. To date, there are no reports of artificial breeding methods for northern barbel loach fry using *Oocystis* as their first food source. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems existing in the prior art by providing a method for artificially cultivating juvenile northern barbels using *Oocystis suis* as the initial feed.

[0006] The technical solution of the present application is a method for artificially breeding northern loach larvae using oocystis as the opening bait, which is performed according to the following steps:

[0007] Step 1. Before the northern loach larvae are hatched, oocystis is inoculated into the water in the breeding pond, the natural water temperature of the breeding pond is 17-19℃, and the density of phytoplankton and the number of oocystis in the water are detected by regular sampling;

[0008] Step 2. When the density of phytoplankton in the water in the breeding pond is at least 100,000 / L and the number of oocystis accounts for at least 80% of the total number of phytoplankton in the water, the northern loach larvae on the third day after hatching are put into the breeding pond, and the northern loach larvae are bred for 26-34 days using the phytoplankton in the water as the opening bait, and the breeding density is less than 5 million per mu.

[0009] The density of phytoplankton and the number of oocystis in the water in the regular sampling of step 1 are detected according to the following method: regularly taking a metered volume of the upper water body in the breeding pond, filtering with a 300-mesh plankton net, collecting the sediment and observing and counting under a microscope to obtain the density of phytoplankton and the number of oocystis in the water.

[0010] In the present application, at least 80% of the phytoplankton is oocystis, which is used as the opening bait for the northern loach larvae. The larvae are active in feeding and the feeding proportion can reach 100%. The appropriate breeding density and the density of phytoplankton can ensure normal feeding of the northern loach larvae and sustainable reproduction of the phytoplankton, thereby effectively decomposing ammonia nitrogen and salt in the water, improving water quality, and making the survival rate of the northern loach larvae reach 89%, which is helpful for large-scale artificial breeding of the northern loach. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic diagram of the feeding opening bait proportion of the northern loach larvae in the embodiment and the comparative example of the present application.

[0012] Figure 2 is a comparison diagram of the total length, body length, body weight and survival rate of the northern loach larvae in the embodiment and the comparative example of the present application.

[0013] Figure 3 is a staining diagram of the digestive tract of the northern loach larvae in the embodiment and the comparative example of the present application.

[0014] Figure 4 is a comparison diagram of the pepsin and trypsin activity of the northern loach larvae in the embodiment and the comparative example of the present application. DETAILED DESCRIPTION

[0015] The method for artificially breeding northern loach larvae using oocystis as the opening bait according to the present application is performed according to the following steps:

[0016] Step 1. Before the northern loach fry is hatched, the oocyst algae is sprayed into the water of the breeding pond in the morning on a sunny day, and the spraying amount of the oocyst algae can be determined according to the hatching time of the northern loach fry, the reproduction speed of the oocyst algae and the target density of the phytoplankton. The natural water temperature of the water in the breeding pond is 17-19℃, the pH is 7.53-7.70, the dissolved oxygen is 8.5-8.9 mg / L, and the NH4 + The content of -N is 0.09±0.02 mg / L, and after the pond water is light green, a measured volume of the upper water body of the breeding pond is regularly taken, filtered by using a 300-mesh plankton net, the sediment is collected and observed under a microscope, and the density of the phytoplankton and the number of the oocyst algae in the water are obtained by calculation;

[0017] Step 2. When the density of the phytoplankton in the water of the breeding pond is at least 100,000 pieces / L and the number of the oocyst algae accounts for at least 80% of the total number of the phytoplankton in the water, the northern loach fry on the third day after hatching is put into the breeding pond, and 1-2 hours after being put into the pond, 100% of the northern loach fry can open the mouth to feed to satiety. The northern loach fry is bred for 26-34 days by using the phytoplankton in the water as the opening feed, and the breeding density is less than 5 million pieces / mu.

[0018] Experiment:

[0019] Comparative Examples 1 and 2 are two groups of breeding ponds which are the same as the embodiment of the present application. The natural water temperature, pH, dissolved oxygen, NH4 + -N content and breeding density of the water in the breeding ponds are consistent with those of the embodiment of the present application. Different from the embodiment of the present application, the oocyst algae is not sprayed into the water of the breeding pond before the northern loach fry is hatched, but the northern loach fry on the third day after hatching is put into the breeding pond to feed the opening feed. The opening feed of Comparative Example 1 is mainly rotifer (the proportion of rotifer is more than 90%), and the opening feed of Comparative Example 2 is artificial feed (crude protein > 29%, crude fat > 3%), which is purchased from Zhejiang Yida Biological Technology Co., Ltd. and has a particle size of 0.08-0.1 mm, and is fed to satiety.

[0020] The northern loach fry with the same number of individuals is bred for 7 days according to the method of the embodiment of the present application, Comparative Example 1 and Comparative Example 2, respectively. The feeding opening feed proportion of the northern loach fry, the body length (individual and average value) of the northern loach fry, the body weight and the survival rate of the northern loach fry are detected, the digestive tract of the northern loach fry in each group is dyed, and the pepsin and trypsin activities of the northern loach fry are determined according to the method of the prior art. The results are shown in Figures 1-4 , Figures 1-4 Zoo in the figure is Comparative Example 1, Algae is the embodiment of the present application, and AD is Comparative Example 2, P < 0.05.

[0021] The open feeding proportion of the northern brook lamprey larvae in the embodiment of the present application and the comparative examples is shown in Fig. Figure 1 The results show that the open feeding of the open feed is active, and the feeding proportion can reach 100%, which is significantly higher than that of the comparative examples 1 and 2.

[0022] The comparison of the body length, body weight and survival rate of the northern brook lamprey larvae in the embodiment of the present application and the comparative examples is shown in Fig. Figure 2 Figure 2 A is a full length diagram of the northern brook lamprey larvae in the three experimental groups, B is a body length diagram of the northern brook lamprey larvae in the three experimental groups, C is a final body weight diagram of the northern brook lamprey larvae in the three experimental groups, and D is a survival rate diagram of the northern brook lamprey larvae in the three experimental groups. The results show that the full length, body length, final body weight and survival rate of the northern brook lamprey larvae in the embodiment of the present application are higher than those of the comparative examples 1 and 2, and the survival rate is 89%.

[0023] The staining diagram of the digestive tract of the northern brook lamprey larvae in the embodiment of the present application and the comparative examples is shown in Fig. Figure 3 The results show that the northern brook lamprey larvae in the embodiment of the present application contain digested oocyst algae in the intestinal tract, the folds are obviously increased, and the intestinal villi begin to appear.

[0024] The comparison of the pepsin and trypsin activity of the northern brook lamprey larvae in the embodiment of the present application and the comparative examples is shown in Fig. Figure 4 Figure 4 A is a comparison of pepsin activity, and B is a comparison of trypsin activity. The results show that the pepsin and trypsin activity of the northern brook lamprey larvae in the embodiment of the present application is significantly improved compared with the comparative examples 1 and 2.​​

Claims

1. A method for artificially raising juvenile Northern Loach using *Oocystis suis* as the initial feed, characterized in that... Follow these steps: Step 1. Before the larvae of the northern barbels hatch, spray and inoculate the culture pond water with Algae oocystis. The natural water temperature of the culture pond water is 17-19℃. Regularly sample and test the density of phytoplankton and the number of Algae oocystis in the water. Step 2. When the density of phytoplankton in the culture pond is at least 100,000 / L and the number of Oocystis is at least 80% of the total number of phytoplankton in the water, the juvenile Northern Whiskers, which are 3 days after hatching, are introduced into the culture pond. The juvenile Northern Whiskers are then cultured for 26-34 days using the phytoplankton in the water as their first food, with a culture density of less than 500,000 fish / acre.

2. The method for artificially cultivating juvenile Northern Loach using *Oocystis suis* as the initial feed according to claim 1, characterized in that... The periodic sampling and testing of the density of phytoplankton and the number of oocysts in the water in step 1 is carried out as follows: a measured volume of water from the upper and middle layers of the aquaculture pond is periodically taken, filtered using a 300-mesh plankton net, the sediment is collected and observed and counted under a microscope to obtain the density of phytoplankton and the number of oocysts in the water.

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