Iwahara is a type of maggot-shaped fish belonging to the subfamily Asteraceae. It is mainly found in the tributaries of the upper reaches of the Yangtze River, with larger populations in the middle and lower reaches of the Jialing River. From February to April, these fish migrate upstream to spawn in the tributaries. Due to their slow growth rate, adult individuals in the fourth instar typically weigh only around 0.5 kilograms. However, the construction of dams and barriers along the upper reaches of the Yangtze River has significantly hindered their migration to spawning grounds. As a result, wild populations have been gradually declining. In response, Iwahara has been classified as a vulnerable species in our country. Through years of research and experimentation, the author has developed a comprehensive artificial breeding technique for this fish. The following report outlines the methods and findings.
Materials and Methods: Broodstock Prenatal Cultivation
This study was conducted at a farm located in the Tongdian reservoir area of the Jialing River between 2002 and 2004, with the most successful results achieved in 2003. The broodstock was collected from the wild in the Jialing River and raised intensively in ponds. Fish weighing 1-2 kg were selected for breeding. Two months prior to the induction of spawning, they were fed fresh snail meat, and water flow was increased to stimulate natural behavior.
Preparation of Oxytocin Solutions
Three types of hormones were used in the process: human chorionic gonadotropin (HCG), luteinizing hormone-releasing hormone analogue (LRH-A), and domoxone (DOM). These agents were combined to induce spawning effectively.
Preparation of Artificial Insemination Equipment
Basic tools such as white basins, towels, feathers, physiological saline, troughs, needles, and cylinders were used to support the artificial insemination and hatching processes.
Identification of Male and Female Fish
Male Iwahara can be easily distinguished by the prominent bead on their mouth, dark-black fins, and protruding gonopores. In contrast, females have gray fins and an invaginated gonopore.
Artificial Oxytocin Induction
For females, a mixture of HCG (800 IU/kg), LRH-A (5 µg/kg), and DOM (50 mg/kg) was administered. Males received a dose based on their development status, with 1 ml of physiological saline injected per kilogram of body weight. The injection was delivered into the pectoral fin. After administration, the fish were placed in a circular spawning pond filled with large gravel to simulate natural conditions.
Post-Induction Artificial Insemination
The effect of the oxytocin usually took about 30 hours. Once the fish became calm after chasing each other, dry artificial insemination was performed. Eggs and semen were collected, mixed with a small amount of physiological saline, gently stirred with feathers, allowed to settle for two minutes, and then washed with normal saline two to three times before being transferred to the hatching stage.
Artificial Hatching Process
Fertilized eggs were placed in flat troughs at a density of approximately 10,000 eggs per square meter. They were treated with 1 ppm copper sulfate for sterilization and incubated with microfluidic water. The water flow rate was carefully maintained at 1.5 cm/s to ensure optimal hatching conditions.
Test Results
A total of 10 groups of broodstock were tested. On average, each female weighed 1.1 kg and produced over 12,000 fertilized eggs, with more than 7,000 successfully hatching.
Discussion
The trial revealed that Iwahara is a batch-spawning species, which means that the number of eggs produced per spawning event is relatively low, ranging from 0.2 to 0.4 million per kilogram of fish. Additionally, male semen production is limited, typically around 1 ml per kilogram. Therefore, when collecting males and females, it is important to check their maturity without squeezing the testes unnecessarily. This finding highlights the need for careful handling during artificial breeding to maximize success rates.
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