Detailed Explanation of the Experimental Methods for Farming Milkfish in Cement Ponds

1 Materials and Methods

1.1 Source of Experimental Fish

On May 12, 2001, milkfish fingerlings were shipped from Indonesia, transited through Malaysia, and arrived at the experimental site at 5 PM on the 14th. 3000 experimental fry were transported in 6 bags and 3 boxes using oxygenated live-water bags. Upon arrival, only 1380 survived, a survival rate of just 46%. The fry placed in the nursery pond died successively on the second and third days, leaving only just over 500 alive. The cause was determined to be prolonged transport time leading to death from carbon dioxide poisoning.

1.2 Conditions of the Experimental Pond

The experimental pond was an outdoor cement pond of 6×12×1.5 m3, with a cement bottom, flat pond floor, and convenient filling and drainage. The water source came from Bantou Reservoir in Xinglin Bay, with fresh water quality and ample water volume, pH of about 7, and dissolved oxygen above 5 mg/L. Before stocking, the pond was cleaned and disinfected, with a water depth of 0.8 m, filtered water filling, and water quality cultivation.

1.3 Stocking of Fry

When the fry arrived at the stocking site, they were placed in the experimental pond to adjust to water temperature for 20 min, then the bags were opened and the fish released. The stocking water temperature was 26.5°C. The fry were temporarily held in net enclosures in the experimental pond until normal, then dead and injured fry were removed and counted before entering the pond. At the same time, sampling measured the average body length at stocking as 3.27 cm and body height as 1.28 cm. Examination found no parasites on the body surface, with a small amount of silt on the gill filaments.

2 Daily Management

During the farming period, emphasis was placed on three key points: first, fry transport and cultivation; second, feeding management; third, disease prevention and treatment.

In daily management, efforts were made to achieve one diligence (pond patrol), two disinfections (water disinfection, tool disinfection), three observations (observing fish activity, feeding, and water color), four fixings (fixed time, fixed location, fixed quality, fixed quantity of feeding), and five preventions (preventing disease, escape, theft, water deterioration, and predators). Specifically, water temperature, pH, and DO changes were regularly monitored. Based on water quality conditions, water was changed on average once every 4 days, with water level controlled at 50-80 cm. During water changes, pond cleaning was combined with checking fish growth and health, and diseased or injured fry were promptly removed. Siphoning was used as appropriate to remove waste and feces. If the pond water became thick and turbid with transparency less than 25 cm, water was changed promptly to keep the water fresh and clear, appearing yellow-green.

Milkfish are omnivorous mouth-feeding fish that are primarily animal-based. Juveniles feed on phytoplankton or zooplankton, while adults are mainly plant-based but also eat small miscellaneous fish and shrimp, and can consume artificial compound pellet feed and natural organic bait. Plant-based feed includes leaves of withered melons and tuber plants, such as taro leaves, cassava leaves, sweet potato leaves, papaya leaves, cucumber leaves, as well as cucumber and pumpkin.

2.1 Feeding Management During the Fry Stage

To accelerate fry growth and ensure fresh water quality, during the fry stage they were mainly fed silk@#@254@#@, with a feeding amount of 1.5-2.5 kg/day. After half a month, they were switched to sea bass fry feed, with a feeding amount of 1.2-2.2 kg/day.

The feeding rate changed with water temperature, generally 4-8%. When water temperature was below 25°C, they were fed once daily in the evening; when water temperature was above 25°C, they were fed once each in the morning and afternoon, with the feeding amount set so that the feed was consumed within 1 h after feeding.

2.2 Feeding Management During the Adult Fish Stage

When fry grew to about 10 cm, they were transferred to adult fish rearing and fed tilapia No. 2 feed, twice daily in the morning and afternoon, with a feeding rate of 3-5%.

During management, quicklime (15 ppm) was used to adjust pH. To control water quality, reduce fertility, and adjust transparency, 50 silver carp were stocked as a complementary species.

2.3 Fish Disease Prevention and Treatment

During farming, no viral or bacterial fish diseases occurred. In the early stage, there was saprolegniasis caused by transport injuries; after autumn, due to fertile water and low transparency, anchor worm disease appeared, and after two applications of trichlorfon, it was