First, fry cultivation
The process of fry cultivation follows similar methods to those used for other fish species in artificial incubation. It begins when the newly hatched fry reach a total length of 2 to 3 cm and continues until they grow to about 6 to 7 cm. This stage usually lasts around 15 days. The tanks used are typically concrete or fiberglass, with a preferred volume of 1 to 4 cubic meters and a water depth of 40 to 60 cm. Initially, the stocking density is set at 5,000 per square meter, which is gradually reduced as the fish grow, ending at approximately 2,000 per square meter.
Water quality must be carefully maintained throughout this period. The temperature should remain stable between 20°C and 23°C, as temperatures above 24°C can be sub-lethal and 28°C is lethal. Below 11°C, survival rates also drop significantly. Dissolved oxygen levels should stay above 6 mg/L to support healthy growth. Feeding starts with live foods such as worms, which are gradually supplemented with Artemia nauplii, rotifers, and copepods as the fish develop. Artificial feeding is done 9 to 10 times daily, with each batch consisting of 3–5 grams of red worms or small animal feed per 1,000 fry.
From the third day after hatching, micro-particle feed is introduced. The initial particle size (S1) is less than 250 μm, increasing to S2 (less than 480 μm) as the fish grow. The daily feeding amount is 0.5–1.0 grams per 1,000 fish, divided into 10 feedings. During the first three days, S1 is used alongside natural food like Artemia filtered through an 80-mesh sieve. After that, S2 is introduced with a 60-mesh sieve. Copepods and Artemia nauplii are maintained at a concentration of at least 1,000/ml to ensure sufficient biological feed.
Second, fingerling rearing
This stage involves raising the fish from 6–7 cm to 12–20 cm, taking about 15 days. Outdoor ponds are suitable, with an area of 0.2 to 0.33 hectares and a water depth of 1.5 to 2 meters. Ponds should have good drainage and clean water, equipped with a 1.5 kW aerator. Before stocking, the pond is drained, cleaned with quicklime, and allowed to dry before introducing the fry. Initial stocking density is 1,000–1,500 per square meter, gradually decreasing as the fish grow, reaching 500 per square meter by the end of the cycle.
During this phase, the fish become more resilient, tolerating water temperatures between 2°C and 37°C, with an ideal range of 25°C to 32°C. Water quality is managed by fertilizing the pond before the next week to promote plankton growth. Soybean milk and bean dregs are added at 75 kg per hectare to support the development of natural food sources. Artificial micro-particle feed is introduced early, starting with S3 (less than 750 μm) and progressing to larger sizes like S5 (over 1,400 μm). The feeding rate is 1.5–7.0 grams per 1,000 fish per day, given 6 times daily. Zooplankton filtered through a 40-mesh sieve is also provided. As the fish mature, compound feed is introduced, with a daily ration of 8–10% of their body weight, fed 6 times a day. Regular monitoring and management of water quality and pests are essential to maintain high survival rates.
Third, disease prevention
During the fry stage, paddlefish are prone to diseases such as enteritis, stomatitis, acne, and hydromycosis. These can usually be treated effectively with appropriate medications. Fish measuring 10–15 cm are generally more resistant and rarely die. However, young fish are highly sensitive to drugs, especially heavy metal salts, so caution is necessary. In cases of severe worm infestation, formalin at 15–25% concentration can be used. If parasites are detected, a formalin bath of 2 g/m³ potassium permanganate or 75 ml/m³ water is recommended. Copper sulfate and chlorine-based chemicals should not be used during the early stages. Common antibiotics are limited to 4 g/m³. Regular health checks and prompt treatment are crucial to maintaining a healthy population.
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