New directions in shrimp seed production
Producing shrimp larvae by cutting the eyestalks reduces the number of reproduction cycles and the quality of the shrimp. Applying a natural shrimp production method without cutting the eyestalks will solve the current problem of shrimp larvae, creating a uniform, disease-free shrimp population.
Change traditional methods
Currently, most shrimp breeding practices utilize the traditional method of cutting the eyestalks of female shrimp to stimulate molting, increase sexual maturity, and accelerate egg laying. This method is used because the eyestalks of shrimp (both male and female) contain the X organ complex (nodal gland), which directly controls the synthesis of gonadal growth inhibitory hormone (GIH) and molting inhibitory hormone (MIH). Therefore, cutting the eyestalks removes part of the X organ complex, thereby reducing the inhibitory effect on gonadal growth (GIH). However, despite the benefits, eyestalk removal has some limitations: shrimp only lay eggs 3-5 times before their reproductive life ends; the quality of subsequent reproduction gradually decreases.
Due to the closed thelycum of the tiger shrimp, cutting the eyestalks causes the female shrimp to molt, softening the reproductive organs, making it easier for the male to attach the spermatophore during mating. In contrast, the open thelycum of the whiteleg shrimp allows for reproduction even without molting. Based on this characteristic, the production of whiteleg shrimp larvae through natural farming has been successful and effective. This method involves a synchronized process, from selecting broodstock of traceable origin and disease-free to investing in integrated technical measures to produce whiteleg shrimp larvae that are less susceptible to diseases such as white spot disease, Taura syndrome, yellow head disease, muscle necrosis, and hepatopancreatic necrosis. Therefore, the shrimp's resistance, survival rate, and growth rate are higher compared to the eyestalk ablation method.
Applied in shrimp hatchery production.
The process of producing whiteleg shrimp larvae using the natural, non-eye-cutting method involves selecting broodstock of Hawaiian origin weighing over 45g/male and 50g/female. The acclimatization and rearing of the broodstock is a crucial stage, requiring adequate nutrition and controlled environmental parameters to ensure natural maturation. Managing environmental parameters (temperature, salinity) and using appropriate nutrition are considered key factors in the process, aiming for uniform, stable seed quality with superior characteristics compared to traditional methods.
In reality, shrimp in their natural habitat, without eyestalk ablation, can spawn more frequently over a longer period, producing more offspring. Therefore, researchers have studied how to stimulate shrimp spawning without eyestalk ablation. Globally, serotonin injections have been implemented in female shrimp, resulting in a 35.4% spawning rate on the first spawning cycle, six times higher than the control group. The rate of subsequent spawning cycles was 6.7%. Overall, the number of shrimp spawning induced by serotonin was seven times higher than the control group. While the spawning rate from serotonin injections was lower than that of shrimp with eyestalk ablation, after multiple spawning cycles, the eyestalk ablation shrimp could no longer be used for further shrimp seed production. In contrast, shrimp that spawned using serotonin continued to reproduce because they were not damaged, thus extending their reproductive lifespan.
After 1-2 months of intensive rearing, mature female shrimp are released into the male shrimp tank for mating, then transferred to the spawning tank. At this stage, it is essential to ensure the spawning tank has suitable temperature conditions, is quiet, and is free of light. After 36-40 hours, the nauplii are collected and transferred to the nursery to continue rearing into postlarvae.
This method has several advantages: Because the eyestalks are not cut, it does not harm the mother shrimp, and there is no need for the time-consuming recovery care required when eyestalks are cut. The number of Nauplius obtained is greater than 200 Nauplius/female, the time to transition from Nauplius to Postlarvae 12 is 18-19 days, 1-2 days shorter than the eyestalk-cutting method, and the length of Pl 8 (Postlarvae 8) is equivalent to Pl 10 in the eyestalk-cutting method. The shrimp larvae are of uniform quality, free from deformities, and healthy. Given the unregulated shrimp larvae market and rampant disease outbreaks, this method is considered a positive sign for the Vietnamese shrimp industry.
Vietnam Fisheries Resources - LY
