Expert topic: Black-spotted frog
by Liu Fenglei, He Zhuliu, Dong Qiufen and Zhang Song, Guangzhou Nutriera Biotechnology Co., Ltd, China
The black-spotted frog (Pelophylaxnigromaculatus) is an amphibious animal of the species Ranidae and the genus Pelophylax. It is a beneficial species with economic and scientific research values,and it has been listed in the IUCN red list of Threatened Species since 2004. Therefore, it is not allowed to catch wild black-spotted frogs in China.
Black-spotted frogs have been studied in China for a long time, and it is recorded in the Compendium of Materia Medical. As the meat has high protein and low fat, the southerners even depict itas delicious as chicken"s meat and it has been a popular dish forthe people.
In addition to its nutritional value, it has some medicinal effects such as improving liver and kidney functions, promoting bodyimmunity, anti-aging properties, beneficial lung functions andeyesight etc. In addition, extracted frog oil can be used as a regulator of human body metabolism and beauty.
The black-spotted frog is mainly distributed in China, Japan, North Korea, South Korea and Russia. It can adapt to wide geographical environments, and can be found in different habitats including meadows, leafy, mixed pine, broadleaved forests, bush land, and even deserts.
Furthermore, the species is also present in suitable modifiedhabitats. Within these, its inhabits are various types of stagnant water bodies, including river pools, channels, lakes, reservoirs,ponds, swamps, ditches and paddy fields. Chinese scientists have achieved full-scale artificial farming and have formulatedfeed technology for this species. The black-spotted frog industryhas been developing rapidly. It"s widely farmed in more than 10 provinces of China, and it has become a common aquaculture product.
With commercial farming technology, the black-spotted frog has developed very rapidly and is booming in China.
In 2015, the commercial farming area of the black-spotted frog was about 1,647 acres. But it grew sharply in 2016 and 2017 withfarming areas about 6,590 acres and 13,180 acres respectivelyand is becoming an increasing trend in 2018. Central China is the main black-spotted frog farming area, in which Hubei province accounts for the largest breading area of nearly 4,942 acres,followed by Hunan province (3,945 acres), Sichuan province (1,647 acres) and other provinces (3,945 acres).
At present, the average yield of black-spotted frog is 150~330kg/ acres. The annual production of the black-spottedfrog is about 70,000 tonnes, and the commercial feed demand is 100,000 tonnes in China.
The fry of the black-spotted frog are obtained by means ofnatural reproduction in an artificial nursery. The area of a frogpond is approximately 200m2 with a ditch surrounding the middle resting area; it is for frog farming and also laying eggs.
The stocking density of the broodstock is three to four pairs/m2. The body weight of broodstock is normally more than 50g, and each female can lay 1,000-1,500 eggs. When the spring comes
with stable and suitable temperatures, the farmers fill the ditchwith water and the black spotted frog naturally breeds and lays eggs in the ring-shaped ditch where eggs develop into tadpoles.
To prevent cannibalism, the farmers collect the frog eggs and hatch them together, and then transfer the tadpoles to the nursery ponds.
Black-spotted frog is farmed alongside the Yangtze River basin because it is suitable to survive with the subtropical monsoon climate that has warm and humid temperature, rainfall and
four distinct seasons. The black-spotted frog has a hibernationhabit, and the suitable temperature for growth is 20-30 °C. Theblack-spotted frog lays eggs from March to April, and the tadpole growth period is from March to May, the metamorphosis period is from May to June, the growth period of the frog is from May to October, and the hibernation period is from October to February of the following year.
For commercial farming, the black- spotted frog hatchingfor five-10 days, the tadpolegrowth period is about 45-55 days, the metamorphic periodis about 30 days, and thefroglet to the frog farming period is about 60-120 days. Actually it"s believed that the black-spotted frog doesn"t consume static feed. Farmers only feed the frogs with living Tenebrio molitor and maggots. But by the way of mixing the living Tenebrio molitor with the commercial diet to feed the frogdynamically, the black-spotted frog can"t distinguish the Tenebriomolitor and commercial feed.
According to this characteristic, a special elastic feeding tray was developed and designed for black-spotted frog feeding. When the black-spotted frog jumps onto the feeding tray, the gauze vibrates, and the feed vibrates as living feed movements thereby stimulating the frogs to eat.
With some improvements, the bait tray is no longer restricted to the elastic gauze, and the plastic plate can also be used as a feeding tray. With this feeding tray, the farmers started to use extruded feed for their frogs since 2015.
Thanks to the extruded feed, black-spotted frog farming is developing rapidly. Many aquafeed mills in Hunan, Hubei
and locations nearby are trying to produce frog feed, but with different feed quality and performance. The current black-spotted frog feeds on the market can be divided into two types: mashed feed, which is specially used for feeding tadpoles in the early stage, and extruded feed, which is for the frog growth. The feedprotein ranges from 36 percent to 42 percent, with prices 0.48-0.60 USD/kg, and the farmers always prefer feed with 40 percent protein for their frogs.
According to the conditions of the pond, three farming methods can be used. Firstly, black-spotted frog eggs can directly move to the pond with a density of 120-200 eggs/m2 for hatchery production. The farmers also can stock about 60-100 tadpoles/m2 or 50-80 froglets/m2. Artificial farming can greatly shorten the black-spotted frog growth cycle.
With better nutrient conditions, a froglet (size of 1.5-1.7g/pcs) can only take 50 days to an adult frog, which can reach themarket size of 30g/pcs.
Black-spotted frog dishes are popular in central and southern China, but Chinese laws protect the wild frogs. Farmers there also have a positive respect for the black-spotted frog, because the wild black-spotted frog has a strong ability to catch pests
and protect crops from pests. People only consume the farmedblack-spotted frog, but the annual production 70,000 tonnes can"t meet the increasing remand, which will promote more artificialfarming in the area.
Farmers can get a good return from frog farming. Normally the harvest season is from August to October with relative low pricessuch as 3.62 USD/kg, but farmers still can get good profits. In the first half of a year, the prices are much higher due to limitedsupply.
Currently, green house farming technology is under research, so consumption requirements will be met for the whole year.
Artificial farming of the black-spotted frog is now boomingwith a huge development potential. Scientists and experts are doing research on the hatchery part to improve productivity, and frog healthcare probiotics will be combined with extruded feed nutrition. Production procedures and management standards will be made for a long-term green and sustainable development.