Key Technical Points and Precautions for Turtle-Fish Polyculture Explained

Turtle-fish polyculture is a method of turtle farming in which turtles are the main species and fish are stocked as a secondary crop. Experiments have shown that turtle-fish polyculture yields benefits 1 time or even several times higher than other polyculture methods. The following briefly describes its zoological principles, farming methods, and so on.

1 Zoological principles of polyculture

Turtle-fish polyculture refers to the mixed farming of turtles and fish in the same pond water body. From a zoological perspective, turtle-fish polyculture not only makes full use of the biological cycle of the water body, but also maintains the dynamic balance of the water body ecosystem. Turtles and fish can not only coexist, but also promote each other. In addition, because of low investment and fast capital turnover, it can be accepted by the vast number of farmers. It is a new pathway for high-benefit farming technology and has very good development prospects.

1.1 Turtle-fish polyculture can increase production

Turtles are reptiles that breathe with lungs and do not absorb dissolved oxygen from the water; they must frequently float to the water surface to take in oxygen from the air, while fish breathe with gills in the water. Therefore, in the same water body, turtles and fish do not come into conflict over the main environmental factor for survival - dissolved oxygen. Moreover, because turtles frequently engage in "air-exchange" activity, the dissolved oxygen levels in the surface water and bottom water can be balanced. This can both prevent supersaturated oxygen produced by vigorous photosynthesis of phytoplankton in the water body from escaping into the air and compensate for the "oxygen debt" of the deep water layer; it is beneficial to fish metabolism and can also promote the reproduction of plankton. At the same time, because of the activity of turtles at the pond bottom, organic matter settled at the pond bottom can be decomposed regularly. Even if pond water hypoxia occurs, it can reduce or avoid the danger of fish "pond turnover." The water body of a turtle-fish polyculture pond can regularly maintain a relatively high dissolved oxygen level, with a monthly average 35% higher than that of a control adult fish pond.

In turtle-fish polyculture ponds, when the ammonia produced by turtle metabolism reaches a certain concentration, it is unfavorable to the growth and development of turtles. However, because phytoplankton make large use of ammonia, it can play a role in purifying water quality. In this way, severe water quality pollution that affects the growth of turtles and fish is unlikely to occur.

Turtles will not harm healthy fish, but they can eat sluggish sick fish and dead fish. Therefore, turtle-fish polyculture can also play a role in preventing the spread of pathogens and reducing the occurrence of fish diseases. Under the same rearing conditions, the survival rate of fish in turtle-fish polyculture ponds is higher than that of fish in ponds with fish alone. In addition, turtles can also prey on bottom-dwelling animals such as mussels and snails in the pond, reducing ineffective consumption within the pond.

2 Polyculture methods

Polyculture methods include mainly farming market-sized turtles with market-sized fish as a secondary crop; farming juvenile turtles and fry; raising reserve broodstock turtles with market-sized fish as a secondary crop; and mainly farming mature broodstock turtles for egg laying with fry as a secondary crop. The following introduces the polyculture model of mainly farming market-sized turtles with market-sized fish as a secondary crop.

2.1 Polyculture pond

The area should not be too large; preferably 2-3 mu (667 sq m), with a pond depth of 1.5-2 m, a pond slope of 3:1, and pond bottom silt that should not be too thick, with a flat pond bottom. Anti-escape facilities should be complete. The fish feeding platform and the turtle feeding platform should be as far apart as possible to avoid competition for food between turtles and fish. The basking platform is set in the water on a sunny, wind-sheltered side facing south, 2 m from the embankment.

2.2 Stocking and matching ratios of turtles and fish

2.2.1 Stocking time. Because climates differ from place to place, stocking time also differs. In East China, fish are stocked around March, and turtles can be stocked in mid-May; in South China, fish and turtles are stocked successively in February and late April; in Central China, they can be stocked at the same time; in Northeast and Northwest China, it should be appropriately later.

2.2.2 Stocking of turtle seed. For stocking turtle seed, artificially farmed turtles are preferable, with a size of about 200 g each. Stocking density should be comprehensively considered according to the size of the stocked individuals, rearing area, and other conditions. Larger individuals can be stocked appropriately sparsely, while smaller individuals can be stocked at higher density; larger water surfaces can have lower density, and smaller water surfaces can have higher density. The stocking density is 1-2 turtles per sq m.

2.2.3 Stocking of fish seed. For fish seed stocking, both fish species combination and reasonable stocking density must be considered. As for species, silver carp, bighead carp, and other fish that feed on plankton should dominate, with appropriate combination of herbivorous and omnivorous fish; the stocking density is preferably 900 fish per mu.

2.3 Feeding management for polyculture

Turtles can be fed artificial compound feed. At the beginning, feed at 1%-2% of the turtle body weight at stocking, and afterward appropriately increase or decrease according to the feeding situation at the time; fish feed should be given according to the feeding habits of the stocked fish (mainly commercial feed and artificially planted Sudan grass). The feeding times for turtle feed and fish feed should be appropriately staggered. It is best to feed turtle feed about 30 minutes after feeding fish feed (mainly snails, fresh trash fish, and a small amount of compound feed; the feed is placed on a saddle-shaped feeding platform and fed at around 9:00 every day) to ensure that turtles eat. Under abnormal climate conditions, water should be added in a timely manner to prevent death of turtles and fish caused by reduced dissolved oxygen in the pond water. Add water once every 7-10 days, 20-30 cm each time; in high-temperature summer and autumn seasons, add water once every 2-3 days, and at the same time splash quicklime over the whole pond once every 20-30 days at 20-30 mg/kg. Normally, turn on the aerator frequently to prevent fish from being attacked by turtles after "floating head." When splashing quicklime and bleaching powder for disinfection, the tolerance capacity of turtles and fish should be considered: quicklime should not exceed 30 mg/kg, and bleaching powder should not exceed 15 mg/kg. In addition, dedicated personnel should be on duty, inspecting the pond in the morning and evening: first check water quality conditions, second check feeding conditions of turtles and fish, third check whether anti-escape facilities are damaged, and fourth check whether there is disease, while also doing well in flood prevention, wind prevention, and theft prevention. In addition to morning and evening inspections, one should walk around the pond as little as possible, especially at noon on sunny days when turtles are basking.