Frog’s meat, appreciated for its delicate flavor and nutritional qualities, is featuring more and more among the most sought after of international cuisine. Despite the delicacy not yet having reached the same level of popularity as the other kinds of meat in Brazil, its breeding has great potential, and it may be raised to a more professional and productive level with the new techniques developed by the São Paulo State University (Unesp) in Botucatu. Among the novelties is the technique for producing single-sex batches with just female specimens.
This choice is made due to the fact that they do not contend for territory, unlike the pugnacious males who make the environment stressful, which results in lower productivity. The work carried out to date has also led to the production of a strain without any consanguinity with the population of bullfrogs (Rana catesbeiana), the species most bred in Brazil, which is originally from America and which appears at the top of the preferences of the main consumer markets, like France and the United States.
Impact on frog farming
Under the coordination of Cláudio ângelo Agostinho, from the Aquaculture Laboratory of the Animal Production and Husbandry Department of the Faculty of Veterinary Medicine and Zootechny (FMVZ) of Unesp, the researchers also developed new feed boxes and automatic feeders, which they are in a process of patenting. These are important novelties for frog farming in Brazil, although it is a sector that has few recent statistics about its economic and social impact. Some of the latest information tabulated was prepared by the Federal University of Viçosa (UFV), which estimated, in 2001, about 600 frog farms and 15 industrial concerns for slaughtering and processing, responsible for the production of 300 tons of meat a year. Figures from the São Paulo Fishing Institute show that the assessment made in 1998 by the Food and Agriculture Organization of the United Nations (FAO) showed for frog farming a turnover of US$ 47.8 million yearly.
In spite of the fact that nowadays only the meat – rich in proteins, calcium, iron, phosphorus, magnesium, and potassium, with a low level of cholesterol, is used commercially, the potential for putting the bullfrog to good use is regarded as exceptional. Its liver can be used to make pâtés. The tanned skin is used in the production of belts, bracelets, handbags, and shoes. And oil is extracted from the fat for the cosmetics industry, and even the inedible parts can be used in the make-up of animal feed.
Even with all the qualities of the bullfrog, the number of breeders has been falling. “In the 1980’s, there were over 2,000, and now this figure must be in the region of 600”, Agostinho explains. This happens in great measure, according to the researcher, due to the use of unsuitable installations and handling. Frog farms need, besides appropriate climatic conditions, land with a suitable topography, abundant water, on which they are fully dependent, and measures to avoid disputes between the animals.
In order to improve the results for the breeders and to expand frog farming in the country, the researchers from Unesp have developed methods that have been capable, at the same time, of increasing production at the frog farms and to avoid the dissemination of the specimens that escape, through carelessness of the breeders, to nature and thus bringing ecological problems, because the bullfrog contends for food and cannibalizes the native species.
Analyzing and controlling the genetic potential of specimens of bullfrogs from various commercial frog farms was the first scientific task for the group of researchers from Unesp. The main reason for this control is the common practice of endogamy (breeding among relatives) in the frog farms, which was already starting to cause the appearance of congenital defects and ailments, due to the lack of control over the origin of the animals. As a final result, a strain without consanguinity was achieved, using frogs originating from different regions and mated by artificial fertilization.
Agostinho collected individuals from four large frog farms in the cities of Brasilia, Viçosa, in Minas Gerais, and in Pirassununga and Franca, São Paulo – which had a population of reproducers of over 200 couples and populations free of endogamy. From that point onwards, new matings were carried out, and an examination using laparotomy (an abdominal incision) on the imagoes (three month old individuals, still sexually immature) made it possible to identify the females, by the presence of the ovary (an elongated and lobulated structure, while the testicles have a rounded format). The female imagoes can be masculinized, because despite having characteristics of an adult, are not yet capable of reproducing.
Once the females are identified, the cut is closed, and they start to be given the hormone methyltestosterone, which is added to their food in the proportion of 30 micrograms for each kilo of fish feed, during 40 days. With this treatment, the females become physiological males, with testicles and a regular production of semen. They are males that have the expression of their sexuality by the XX sexual chromosomes, and they are not infertile. They are used in mating with original XX females. “Accordingly, the resulting offspring will be made up exclusively of females”, Agostinho explains. “With these results, we showed that the technique of reversing the female imago into a male is possible, and one that is without precedent in Brazil and abroad.” A similar technique, transforming male breeders into females, has already been done for a few years by the São Paulo Fishing Institute in breeding trout. In this case, the transformation takes place at the fish’s larval stage.
The single sex female lineage of frogs should be of interest to the frog breeders, above all because in mixed batches losses occur, precisely at the slaughter stage, when the males reach maturity and start fighting, causing problems by contending for territory and for females. “The advantage of this method is that, without the typical fighting, the breeding stock develops without stress, in a quicker and more homogeneous manner”, Agostinho says. “Besides which, they are used only for breeding, and not to be slaughtered.” This eliminates the possibility of any hormone being swallowed by the consumers.
The measure also seeks to clear up the problem of frogs escaping from the frog farms into nature and the consequent damage to the native anura animals – which form the zoological order that includes frogs and toads – which, in Brazil, is one of the richest in the world. The constant escapes of frogs from the commercial frog farms can cause the local extinction of some species, due to the competition for food and from predatory behavior. The bullfrog shows high fecundity, and may produce from 10,000 to 20,000 tadpoles each time it spawns and mates up to seven times a year.
The reproductive profile of the bullfrog facilitates its dissemination in nature, mainly because some producers, when quit the business due to technical handling difficulties, abandon the frog farms and allow the animals to escape. “To get round this problem, we thought of preventing the reproduction of these animals by means of a single sex female lineage, because, in this case, the escape makes future mating impossible.”
Handing over the single sex lineage to Brazilian frog breeders is now provided for in an agreement between the Brazilian Agricultural Research Corporation (Embrapa) and the World Bank, in the Agricultural Technology for Brazil Support Project (Prodetab). The techniques will be passed on to producers selected according to the degree of their experience in the sector and the technical conditions of the frog farms.
Temperature and installations
The work that led to the development of the single sex female lineage had a sequel in the studies of the genotype-environment interaction in the laboratory, to find out whether the lineage developed is going to adapt itself to different regions of Brazil, given the climatic variations in the breeding establishments. For this study, the researcher uses populations that are not single sex.
The offspring was tested in the breeding systems used by the frog breeders. “Performance was similar for all the offspring. The next step will be to find out how the lineages respond to different temperatures”, the researcher says. “We have the capacity for monitoring over 6,000 animals, which are being marked and which, in May, will be put into bays with temperatures controlled at 25 °C, 28 °C, and 31 °C. The performance of each group will be checked over a three month period, after which they will be ready for slaughter”, Agostinho explains.
Besides the research into genetic improvement, the team from Botucatu also developed equipment to optimize the supply of food in the frog farms. This is because, after the metamorphosis of the tadpoles, the imagoes need food that show some kind of movement. The trick used to train the frogs to swallow the granulated feed consists of serving it inside a food trough together with a small quantity of fly larvae (similar to the larvae of the guava maggot), which make the granules of the feed attractive to the frogs, which, in nature, feed on larvae, insects, mice, and small birds. The equipment has the capacity for feeding up to imagoes.
After about 15 days of training in this food trough, the frogs begin to eat the granulated feed when it is thrown into the water. The food trough also serves as a shelter inside the bay, to reduce stress during the daily handling, which helps to speed up the process of growth and reduce the mortality rate.This is the moment when the second piece of equipment comes onto the scene, which the researchers call an automatic feeder. The device consists of a container with feed, fitted with temporizers that release small portions of granules, according to the programming based on the size and the quantity of the animals in the bay.
“It is a simple idea, but one that is going to cause a good impact”, Agostinho says. “By offering feed more times a day, the labor force can be reduced, and the competition for food diminished, since a satiated frog does not fight for food and gives the others an opportunity.” According to Agostinho, there is no record of automatic feeders applied to raniculture, on an international level. Still as prototypes, this equipment is arousing the interest of companies that are now studying its industrial manufacture.
1. Development of a Commercial Lineage of Bullfrog (Rana Catesbeiana): Production of Singe Sex Breeding Stock (nº 00/12652-2); Modality Regular Lines of Research Grants; Coordinator Cláudio ângelo Agostinho – Unesp; Investment R$ 19,820.00
2. Food trough and Shelter for Frogs (nº 03/09634-0); Modality Intellectual Property Support Program; Coordinator Cláudio ângelo Agostinho – Unesp; Investment R$ 12,000.00
3. Automatic Feeder of Feed for Frogs (nº 03/09636-3); Modality Intellectual Property Support Program; Coordinator Cláudio ângelo Agostinho – Unesp; Investment R$ 12,000.00