Trionyx sinensis or the Chinese Soft-shell Turtle

Phylum Chordata



Sketch of Trionyx sinensis
Class Reptilia
Order Testudines
Family Trionychidae
Measurements

25 cm, 600 g
Distribution Southeast of Russia, China, Mongolia, eastern Parts of Inida, Korea, Japan  
Diet Dentrobena, Nightcrawler and other Lumbricidae, Fish, Insects
Protection Status none

Introduction

The pond culture of freshwater turtle species began at the turn of the last century in small farm systems. Several turtle species have been produced commercially including the Soft-shell Turtle (Trionyx sinensis), the Red Ear Slider, the Diamond Back Terrapin and the Green Sea Turtle. The Soft-shell Turtle and Diamond Back Terrapin are cultured solely for food, the Red Ear Slider for the pet industry, and the Green Sea Turtle for food, leather and decorative products. Some Soft-shell Turtles are sold to individuals for pets as well.

Habit

The Chinese Soft-shell Turtle, Trionyx sinensis (Fig.1and2), has a plain carapace on the back. The abdomen corselet is coated with leather-like skin. The carapace, head, and limbs of this species are greyish green in adults and patterned in juveniles, whereas the plastron is white in adults and has black blotches in juveniles. The Chinese Soft-shell Turtle has a snorkel-nose, salient eyes and a long, highly mobile and flexible neck. The long neck and the protruding nose enable them to reach the surface of the water and 'Snorkel' with the minimum of surface disturbance, thus concealing themselves and their hiding place from predators. Male soft shells are generally smaller than the females, the females being larger to allow for the development of eggs.
Fig.2: Chinese Soft-shell Turtle. Source

Description

The Chinese Soft-shell Turtle is one of the approximately 225 species of freshwater turtles of the world. It is most commonly found in lakes, streams, ponds, drainage canals, creeks, especially when there is a muddy bottom, as well as in marshlands. The wide range of habitats in which they are found, gives them great versatility and increased chances of survival.
Little is known about the natural behaviour of the Chinese Soft-shell Turtle. This species of turtle is almost wholly aquatic and spends 90% of its time in the water. It is very shy and prefers to hide under aquatic hides or dig into a soft substrate underwater and leave just the nose exposed. The mating of the Soft-shell Turtle is difficult. Upon reaching sexual maturity males pursue females, often biting at the neck and limbs in an attempt to subdue her and so allow him to mount. Soft-shell Turtles feed primarily on fish, crustaceans, mollusks, insects, and seeds of marsh plants. Little is also known of natural predators, though it is thought that there are predators of both juveniles and eggs. Additionally, adults have been observed eating their young. The development of the Chinese Soft-shell Turtle is pictured in Fig.3.
Fig.3: Development of the Soft-shell turtle.
1.eggs;2.hatching;3.baby turtle;4.juvenile turtle;5.winter hibernation;6.adult turtle.
Source
The Soft-shell Turtle digs a hole and hibernates in the mud at the bottom from October to April or May, when temperatures drop below 12°C. In the wild it is mainly crepuscular, although, in a captive environment, they are usually more active during day time. The mean weight of a male or female adult is about 1kg and they reach a size of approximately 25cm (10inches). This species is oviparous, and depending on the region of origin, the sexual maturity occurs between one to six years. The breeding occurs generally in March or April and the nesting follows in May after approximately sixty days of incubation. One female can lay ten to twenty eggs per batch, depending on the spawner size, and about sixty to eighty eggs per year. This clutch size is fairly large, so the chance of genetic survival is high.
The longevity of the Chinese Soft-shell Turtle in natural populations is unknown, but in captivity this species can live for 25 to 30 years. The geographic range of this species covers central and southern China, south-eastern Russia and Mongolia, as well as eastern India, Korea, Vietnam, Taiwan and areas of Japan. Feral populations that have escaped or been introduced have been recorded in areas of Hawaii and Florida. To date the
Soft-shell Turtles introduced to Hawaii have not been found as a threat to the endemic species, this does not mean that through increased research this species will not be found to be invasive.

Cultivation

Chinese Soft-shell Turtles are particularly cultured in Taiwan, China and Korea. In both China and Japan its turtle meat is a delicacy with nutritional and medical values.
They are generally cultured in ponds with a mud bottom. The ponds should have concrete walls with an overhanging lip to prevent escape. The ponds should be in open sunlight and the water source should be warm, therefore a thermostatically controlled water heater will be required.
This turtle is naturally an aggressive and cannibalistic reptile. In captivity, these turtles frequently attack, injure and kill co-occupants of an enclosure. For this reason, they have to be segregated by size into different ponds. This is particularly critical for newly hatched Soft-shell Turtles.
Larger Trionyx sinensis farms may have a special pond for spawners, with a small location having a gentle sloping, clean sand bottom for egg laying and incubation. The turtles may start to spawn as early as the second year, but the eggs are irregular and the hatch is not very good. Therefore, turtles that are eight or nine years old are usually used.
Spawning usual takes place at night. The female selects a nesting site and digs a 20 to 25cm diameter hole with a depth of 8 to 12cm. Then it lays the eggs in it before covering it up. Each spawning pond should have an egg-laying site, normally a platform with several cm of deep sand. Each site has walkways extending into the water.
The eggs are greyish brown in colour; the unfertilized eggs develop white spots a few days after they are laid, and can be discarded. The egg-laying sites are checked every morning for signs. The eggs are dug out and must be handled with care while transferring. The fertilized eggs, those with small white caps, are transferred to a sand bed to incubate at about 30°C and are kept slightly moist. The eggs are arranged in rows with the white cap facing upward and buried under a 5cm layer of sand. Newly hatched turtles are removed daily and transferred to the nursery tank.
The hatching begins in about 50 days and the hatching rate is often as high as 80%. Young Trionyx are kept in nursery ponds, where they are fed twice a day on a diet of worms and crushed shrimp, which later may be supplemented with an eel feed, minced fish, and boiled egg yolk. In the wild, this species of turtle feeds on a wide variety of fresh fish, crustaceans, insects and rodents. Therefore, in captivity it is essential to feed them a varied diet. Despite the fact that the shell is softer than other chelonians these turtles do require calcium and phosphorus in their diet, given in the form of vitamin and mineral supplements. Vitamin D3 is essential for the assimilation of these minerals, which is why a suitably balanced supplement (Vionate) must be provided with all food given to those in captivity.
A sheet is sometimes spread over the nursery pond to keep the ponds warm, but should be removed if the temperature exceeds 32°C. Within a year, the juvenile turtles reach 200g and can be transferred to an adult turtle grow-out pond.
A study of factors affecting the hatching rate of Trionyx sinensis showed that sand and temperature were the most important ones. Fine sand produced higher hatching rate than coarser sand, because it could keep more water and humidity, and it does not cloud the water so much. (Kanika Kanjanachatree, Phuket Community College; Vudhichai Janekarn, Marine Biological and Fishery Research Institute, Phuket; Arkom Wangmuang, Phuket Community College; http://www.clib.psu.ac.th/acad_41/kkan2.htm)
In general, socialization with other species is not possible, but sometimes walking catfish, Clarius, are added to the ponds to eat the unwanted food and to maintain the water quality. Filtration is also important to reduce foul smells and to keep the water clean. Good air circulation in the top layer of the water is needed to prevent the turtle breathing stagnant air.
Many reptiles carry the naturally forming bacteria Salmonella. It must be stated that salmonella bacteria can only be contracted by ingestion (via the mouth). Good hygiene is, therefore, very important.
The adult turtles can eat crabsticks, prawns (with the shells on), small rodents, crickets, waxworms, trout, salmon, earthworms etc., mixed with either corn or soybean meal. The rate of growth is a function of the temperature, which ideally is 20° to 28°C.
 
Age (years)
Size (g)
Pond surface area (m2)
0-1
3-7
0.02
1-2
7-120
0.20
2-3
120-200
0.30
3-4
200-600
0.50
Tab.1: The approximate growth and pond requirements for the Soft-shell Turtle (allowing
winter hibernation)
The Soft-shell Turtles are harvested at about 600g, which may be reached in one to three years (Tab.1). Harvesting is started by dragging a net along the bottom of the pond. After the initial collection of the turtles, the ponds are drained and the farmer wades in and removes the remaining turtles by hand.
Live domestic Soft-shell Turtles or similar species are sold for around 10 to 12 US$/lb. The typical marketing size is 800g to 1kg. Individual turtles are put into plastic nets for easy handling. Whole frozen turtles in various sizes are sold for around 4 US$/lb. The price of frozen meat is around 16 US$/lb.
There are no published trade statistics available, because the market is very small.


References

Matthhew Landau. 1992. Introduction to Aquaculture. John Wiley & Sons, inc.

Sepang Today Aquaculture Centre, Malaysia. Aquaculture training school

S. Ishizaki, Yoshoku (Fish Culture), Midori Shobo, Tokyo (1977)
S. Kazi et al., Yogyo-koza, Vol V. Midori Shobo, Tokyo (1979)

S. A. Pasachnik. Senior Seminar 2002. Introduced Species in Hawaii. Earlham College

Chelonian Research Foundation

Cayman Turtle Farm. Turtle Culture, Fern Wood. C.E. Nash (Editor), Production of Aquatic Animals, World Animal Science. 1991

http://www.redtailboa.net Contributed by: Stuart Dodsworth of www.reptiletrust.com

Tom Asakawa. 1999. Soft-shell Turtle Market Japan. U.S. Embassy Tokyo Japan

The care of Trionyx (soft shelled turtles). Pritchard. 1979 Encyclopedia of Turtles

Claudia Kellner, April 2004