Techniques for rearing summer fry fish: stock one main fish species, do not introduce carp, and combine feed with fertiliser for intensive feeding

Summer fry fish are small and delicate, with a weak ability to withstand adverse environments. In addition, at this stage the summer fry undergo a dietary transition, and their digestive system structure and function are not yet fully developed, so their digestive capacity is poor. If rearing methods are improper, mass mortality will occur. Through experiments, the author found that adopting the following rearing methods can significantly increase the survival rate and rearing efficiency of summer fry.

Scientific stocking and rational matching: the traditional rearing method is mainly polyculture of multiple species. However, from production practice, because fish have different feeding habits, this rearing method easily causes uneven feeding among the fish species, so the survival rate of the fry is relatively low, generally around 40%. Moreover, this rearing method is also prone to individual growth differences, intensifying the survival competition pressure among different fish species, inhibiting normal growth of the fry, and resulting in low rearing yield.

Through years of continuous experiments, we found that stocking one species as the main species, with a stocking quantity accounting for more than 90%, generally 15,000 to 20,000 fry per mu, while matching about 10% of other fish species according to the feeding habits and inhabiting water layers of different fish species, to make full use of water space and bait resources, can significantly improve rearing efficiency. When releasing the fry, the following points should be noted:

First, release the main@#@233@#@species, and after 5 to 7 days release the matching species, so as to avoid adverse effects of the matching species on the main species.

Second, select and release the larger-sized fry as much as possible in the same pond, to ensure good growth performance of the fry.

Third, strictly guard against mixing in carp fry. Because carp fry have a strong ability to compete for food, under the same size and the same rearing conditions, carp grow nearly 10 times faster than other fish (summer fry are generally reared for an average of 85 days). They not only pose a threat to the survival of the main reared fish, but also stir up the bottom mud and sand, damaging water quality.

Fourth, strictly disinfect and fertilise the water. Before releasing the fry, the pond must be thoroughly disinfected with quicklime, filled with water to 1.4 to 1.6 m, and given sufficient base fertiliser: 200 kg of organic fertiliser, 15 kg of urea, and 30 kg of phosphate fertiliser per mu, to cultivate natural food for the summer fry after they enter the pond.

Combining feeding with fertiliser and intensifying feeding: improve the feeding method according to the physiological characteristics of summer fry during the dietary transition period.

First, feed sufficient high-quality feed. To ensure the nutritional needs for rapid growth of summer fry, the feed protein content should reach more than 30%. The feed formula ratio is: fishmeal 15%, soybean cake 40%, sesame cake 30%, @#@245@#@ powder 15%. Mix the above feeds evenly, add water and knead into feed balls of moderate hardness, and place them on the feeding table. The feeding amount should be based on the feed being finished within 1 to 1.5 hours. Gradually increase the feeding amount afterwards.

Second, apply supplementary fertiliser in time according to whether the water is rich or poor. Supplementary fertiliser should mainly be inorganic fertiliser, matched with a small amount of organic fertiliser, which can both increase the dissolved oxygen content and provide abundant natural bait. This rearing method combining feeding with fertiliser can increase the growth rate of the fry and reduce production costs. Generally, in only about 20 days, the size of summer fry can reach more than 5 g. At this point, the summer fry have basically acquired the feeding habits of adult fish. After 2 to 4 days of "feeding training", most young fish develop the habit of rising to the water surface to compete for food, and then pellet feed with a diameter of 2 mm can be fed.

Separate into ponds in time to promote growth: after a period of intensive feeding, summer fry grow larger individually. If they are not separated into ponds in time, growth is often inhibited due to excessive density and deterioration of the living environment, and the survival rate will also be reduced. Therefore, they should be separated into ponds in time to reduce density, so as to keep the population individuals uniform and increase the survival rate. When separating into ponds, use a fish sieve to screen out the larger fry for cultivation in dedicated ponds, or they can be placed in adult fish ponds with lower density for rearing. Through netting and pond separation, small fish are prevented from competing for food with large fish, and after the fish are stimulated and exercised by crowding, they expel excess water from the body and secrete large amounts of mucus, enhancing disease resistance and adaptability to adverse environments. However, netting and sieving operations should be gentle, to prevent scratching the fish body and causing infection.