Key Technical Points for Large-Scale Fry Rearing of Pufferfish

Pufferfish eggs are small, with an egg diameter of only about 1.1 mm; the gonadosomatic index is high and the number of eggs carried is large, which creates the prerequisite conditions for large-scale fry rearing. For large-scale fry rearing, the following technical steps should also be well controlled:

First, having a sufficient number of broodstock with well-developed gonads is the prerequisite for obtaining enough high-quality eggs. Only when the number of broodstock is sufficient can the number of eggs used for fry rearing be guaranteed; only when the gonads of the broodstock are well developed can the quality of the eggs be guaranteed. Neither can be lacking. The number of broodstock can be satisfied through holding or selecting and retaining from reserve parents; the quality of the broodstock needs to be ensured by creating a suitable ecological environment and using a method combining physiology and ecology to intensify cultivation, so that the gonads of the broodstock develop well, thereby ensuring the quality of the broodstock and ultimately ensuring both the quantity and quality of the broodstock eggs.

Second, accurately grasping the timing of induced spawning and the effect time is the prerequisite for normal fertilization of the eggs and for improving the fertilization rate. During induced spawning, the environmental factors required for induced spawning should be ensured, and the timing of induced spawning should be grasped; induced spawning should be carried out when the eggs have developed to the end of stage IV. The type and dosage of drugs used during induced spawning should also be appropriate so as to ensure the transformation of eggs from the end of stage IV to stage V; otherwise, there may be no spawning or overripening, leading to failure of induced spawning. Accurately grasping the timing is equivalent to increasing the number of broodstock (or saving the amount of broodstock used), and this is especially important for units with insufficient broodstock.

Third, a suitable hatching environment is beneficial to the healthy development of fish embryos and to the later rearing of fry. The hatching container should be non-toxic, and the temperature, salinity, pH value, light intensity, etc. during hatching should be suitable. The water should be changed frequently, and the daily water exchange rate should reach 100%, which is beneficial to improving the hatching rate. During artificial propagation by the research group the author belongs to in 1999, the hatching rate of fertilized eggs from many groups of broodstock reached more than 95%.

Fourth, during fry rearing, attention should be paid to the type, density, and feeding method of the bait.

The water quality should remain fresh; in this way, the fry will feed actively, be healthy, and grow quickly. In the bait series for pufferfish fry rearing, special attention should be paid to the type of bait and the timing and method of diet transition, as these are the main factors affecting fry rearing. If the bait is not palatable and the diet transition is poor, cannibalism may occur, which can lead to a fry mortality rate of 50% or even higher, and may ultimately lead to failure of fry rearing.

As long as fry rearing units have specific technical measures and operating procedures in the above four aspects and grasp all aspects of each technical step, then large-scale fry rearing of pufferfish can certainly succeed; conversely, a mistake in any one step will affect the output of pufferfish fry and may even lead to failure of fry rearing. If the operation is successful, after artificial insemination of one 1.5 kg female broodfish, the number of obtained fry can reach 100,000.