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  1. Identity
    1. Biological features
    2. Images gallery
  2. Profile
    1. Historical background
    2. Main producer countries
    3. Habitat and biology
  3. Production
    1. Production cycle
    2. Production systems
    3. Diseases and control measures
  4. Statistics
    1. Production statistics
    2. Market and trade
  1. Status and trends
    1. Main issues
      1. Responsible aquaculture practices
    2. References
      1. Related links
    Identity


    Rana catesbeiana  Shaw, 1802 [Ranidae]
    FAO Names:  En - American bull frog,   Fr - Grenouille-taureau américaine,  Es - Rana toro americana
       
    Biological features
    One of the largest frogs of the genus Rana, which can reach up to 20 cm in snout-to-vent length (SV-L), and up to 800 g in weight.
    Body robust, with wide, flat head. Skin smooth and plain (no wrinkles, warts or spikes), dominantly pale green with brown spots on the dorsal and lateral parts of the body, including limbs and head. Abdominal side white. In adult males, upper abdomen temporarily turns yellowish as sexual maturity approaches. Anterior limbs short. Posterior legs robust and long (representing up to 50 percent of total body length, and up to 40 percent of total body weight). Both anterior and posterior limbs possess inter-digital swimming webs. Sexual dimorphism is present in this species, although it is only conspicuous when pre-adult stage is reached.
    Images gallery
    photo of ranaRana catesbeianaBreeding pen Semi-natural bullfrog breeding pen (Central Brazil)
    Contorlled environment breeding penControlled-environment breeding pen (Yucatan, Mexico)Nursery tankNursery tank, attached to a tadpole rearing tank (Guatemala)
    Profile
    Historical background
    The American bullfrog is native to North America. Its natural geographical distribution extends from the south-eastern Canadian province of New Brunswick in the north, southwards through eastern United States to Florida, Alabama and the south-eastern part of Texas. It has been introduced to a number of other regions, including Central and South America, the Caribbean islands, and Northeast and South-eastern Asia.

    The first documented attempts to cultivate the American bullfrog date back to the late XIX century in the United States. Primitive farms consisted of fenced earthen ponds, where tadpoles were stocked to feed on natural productivity. Young frogs would congregate along the edge of the pond to feed on insect larvae hatched on decomposing meat or other kitchen wastes deliberately placed as spawning substrates. Poor yields soon discouraged such pioneering attempts. By the late 1930s, bullfrogs had been introduced in Brazil, and the first frog farm outside the United States was established. Success was marginal due to the lack of sufficient food, cannibalism and disease problems. Bullfrog farming re-gained popularity in Brazil in the mid 1970s. Small ventures multiplied and academic groups got involved in research until late 1980s, developing a range of culture facility designs and culture techniques for bullfrogs, whose systems are described in the production section of this fact sheet.

    Taiwan Province of China imported the first batch of bullfrogs as a potential alternative aquaculture species in the 1950s. A research programme aimed at the cultivation of Rana catesbeiana was then established.

    The first attempts to cultivate this species in Mexico began in the early 1960s, when this species was introduced. The first farm was established with the objective of meeting the growing demand for live frogs in the United States. The farm had breeding, tadpole rearing and fattening facilities and eventually became an extensive tadpole-producing facility for stocking natural water bodies that later became frog fishing grounds.

    Between 1968 and 1990, two research groups in United States, at the University of Michigan, and at Louisiana State University, carried out research on culture techniques for bullfrogs as laboratory animals, and on its reproductive physiology, pathology and nutrition.

    In the early 1990s Thai farmers also began culturing frogs, and R. catesbeiana (along with Rana tigerina, a species native to Southeast Asia) became a popular culture species, technically supported by Chulalongkorn University.

    Between 1991 and 2001, the Center for Research and Advanced Studies (Cinvestav) of Mexico, carried out a comprehensive applied research programme for its cultivation, resulting in further advances in reproductive physiology, nutrition, pathology and ecophysiology, which led to the development of an inundated-type culture system that is currently in commercial use in a number of regions of Mexico and Central America.
    Main producer countries
    Although production of this species is reported to FAO by only two countries, commercial farms also exists in Mexico, Guatemala, Salvador, Panama, Ecuador, Argentina, Thailand, Indonesia, the Lao People's Democratic Republic, Viet Nam and Malaysia, while experimental farms exist in the United States of America, Cuba and Puerto Rico. It is likely that production from the other commercial farms is reported to FAO under the more general statistical category 'frogs (Rana spp.)'.

    Main producer countries of Rana catesbeiana (FAO Fishery Statistics, 2006)
    Habitat and biology
    Bullfrogs readily adapt to and occur throughout a wide range of climatic conditions. They are found in temperate regions, where they hibernate to withstand below-freezing ambient temperatures, and also in tropical regions, where temperatures reach 40 °C during summer months.

    The reproductive physiology of bullfrogs is highly influenced by temperature, photoperiod, ambient humidity, and barometric pressure. Consequently, the closer a population is to the Equator, the wider the length of its reproductive period. While year-round spawning is common in bullfrog stocks from Panama and Ecuador, wild stocks in Mississippi (United States of America) have a three-month reproductive season.

    Metamorphosis of tadpoles is dependent upon two types of ecological factors:
    • Adequate environmental conditions (temperature, water quality, availability of food).
    • Competitive interactions (intra- and inter-specific competition and presence of predators).
    All these factors act as natural selection 'sieves', thus only allowing the fittest individuals to survive through to adult stages. In culture situations, where such factors are artificially eliminated, genetic variability expresses itself through size disparities and vulnerability of the weakest organisms.

    In general, bullfrogs from the northern hemisphere (i.e. Asia, North and Central America) reproduce from March through August, while populations from countries south of the Equator (i.e. Brazil, Uruguay and Argentina) reproduce from September through February. The fecundity of bullfrogs is a function of age, rather than body mass. In farmed females, between 1 300 and 33 000 laid eggs have been recorded from first-spawning and 3-year females, respectively.

    Embryonic development and timing to metamorphosis are highly temperature-dependent. In tropical regions (>26 °C) hatching occurs within 48 hours. The concentration of dissolved oxygen is of particular importance at this stage, therefore egg masses have to be kept near the surface. DO levels should be >3 mg/litre. Newly-hatched larvae are approximately 10 mm in length and attach to smooth surfaces by means of an oral sucker. They have a yolk sac that is consumed in approximately 72 hours at ≥26 °C. Immediately after the yolk sac is exhausted, larvae become free-swimming, filter feeding tadpoles.

    Ontogenic transition of feeding habits include filter-feeding of phytoplankton, grazing on benthic algae, detritophagy and a gradual shift towards animal protein ingestion, before reaching the metamorphic climax when nourishment becomes briefly autogenic. After tail resorption, froglets become carnivores.

    Farmed frog stocks can achieve a survivorship of more than 50 percent. Genetic variability expresses through a significant asynchrony in growth and timing to sexual maturity within every cohort, therefore, under tropical conditions, fitter individuals can reach market size (>180 g), in 3 months after metamorphosis, and sexual maturity in as early as 7 months after hatching, while weakest may take over one year.
    Production
    Production cycle

    Production cycle of Rana catesbeiana

    Production systems
    Seed supply 
    Various strategies are employed by bullfrog farmers to obtain seed. These include collection of egg masses or tadpoles from the wild, as well as semi-natural breeding in captivity (semi-controlled reproduction), and more recently, environmental and hormonal manipulation for controlled reproduction.

    Collection from the wild

    Many small farmers of Latin America, in areas where wild bullfrog populations occur, collect tadpoles during the breeding season. Smaller tadpoles (<50 mm) are transported in oxygen-saturated water in plastic bags at 1 500-2 000/litre. Metamorphosing tadpoles are also collected. These are placed on soaked cotton sheets, and transported in perforated cardboard boxes at 250/m2 of box bottom area.

    Semi-natural reproduction

    This consists of stocking adult males and females in breeding pens where practically no management other than feeding is practiced. Breeding pens are of two types. Asian farmers employ 10-20 m2 square concrete tanks, with 1 m walls and an 8-12 cm permanent water layer. Water flows through the tank continuously. Breeders are stocked at 1-5/m2 , and a sex ratio of 1 male: 1-3 females. Feeding consists of 40 percent protein floating pellets, provided once a day at 2.5-3 percent bodyweight/day.

    Latin American bullfrog farms generally employ a semi-dry type of breeding pen. This consists of an area of variable dimensions (they range from 10 to 1 600 m2 ), constructed of cinder block or agricultural shade cloth. Some pens also have a top mesh to prevent avian predation. Between 75 and 90 percent of the total floor surface area of the pen is covered by grass, while the rest has shallow (<10 cm) concrete-lined puddles. These latter are used as spawning sites and can be small (1 m2 ), for one breeding couple at a time, or large enough for collective breeding (20-60 m2 ). Feeding points and shelters are also present. Feeding consists of a 40 percent protein pellet, fed once daily at 2.5-3 percent bw/day, together with 2-3 percent bw/day fly (Musca domestica) larvae.

    Controlled reproduction

    Controlled reproduction involves the manipulation of ambient and water temperature, ambient humidity and photoperiod in indoor breeding facilities. Such strategies are usually sufficient to stimulate reproduction throughout the year, especially in thermally stable latitudes. However, hormonal stimulation is occasionally employed. Intensive bullfrog farms in Mexico and Guatemala employ indoor breeding facilities, which retain heat through a greenhouse effect. Buildings are divided into three sections:
    1. A series of 3-5, 25 m2, sex-segregated broodstock-holding tanks.
    2. A collective meeting area for males and females.
    3. A series of small (1 m2) spawning puddles.
    The temperature within the building oscillates between 28 ºC and 42 °C in a 24-hour cycle most of the year. Water temperature remains constant at 26-28 °C. Light bulbs are evenly distributed in the building, and are automatically time-regulated to maintain a photoperiod of 10D:14L Ambient humidity is kept at 95-98 percent, by using water sprinklers. Breeders are stocked at 10/m2 in section 1, from which ripe individuals are transferred to section 2 at a male: female ratio of 1:1. The stocking density is reduced to 1/m2. Breeders spawn in section 3.

    Hatchery

    Most farms use their tadpole rearing tanks to incubate fertilized spawns. However, some others have specific incubation facilities. These involve concrete buildings where eggs are placed in small (1 m2) plastic or fibreglass containers. Fertilized eggs are kept in a shallow (5-8 cm), static, chlorine-free, clean water layer in a shaded, ventilated (25-26 °C) site. No aeration is employed. Hatching takes place within 48 hours at 26 °C.
    Nursery 
    Tadpole rearing

    Once tadpoles reach the first-feeding stage, they are transferred to the tadpole rearing tanks. Phytoplankton inoculation is carried out for the first two weeks, and then supplementary feeding is provided 2-4 times a day. The recommended stocking density is 50/m2.

    Water quality is maintained by running freshwater continuously through the tank (1-1.5 times/day), or through aeration. Culling is a routine procedure to lower intra-specific competition. Timing to metamorphosis varies greatly among individuals. Precocious tadpoles become froglets in 45 days, while most of the population achieves this in 90-120 days, and a small portion of the cohort (7-12 percent) will metamorphose after one year or more, even in tropical conditions.

    Nursery

    Nursery tanks are only used in the wet, Mexican system. These are 5.0 x 2.5 x 0.40 m and attached to the tadpole rearing tanks (see photograph in the images gallery). Here froglets are trained to feed on inert, floating pellets. Through routine culling, weaker, slow-growing individuals are removed. Froglets are stocked at between 50 and 75/m2. A 2 cm water layer is maintained permanently. Young frogs are fed ad libitum at least 6 times a day with 1/16', 40 percent crude protein, floating crumbles, until they reach 30-45 g, which normally takes between 30 and 45 days at 26 °C.
    Ongrowing techniques 
    Ongrowing systems can be classified into two major types: dry, and semi-dry and wet (inundated) systems.

    Dry systems

    These include the Brazilian designs mentioned in the following table.

    SystemMain physical characteristicsCountries
    AquaterrariumEarthen or concrete, shallow, narrow, long open canals with sloped, grass-covered banks and terraces Brazil, Mexico
    Tank-IslandSquare 20-30 m2 walled, roofless, grass-covered floor, with a central concrete platform (10% surface area), surrounded by a shallow (<0.10 m) canalBrazil, Taiwan Province of China
    Confinement RoomsSquare, 12 m2, concrete floored, walled rooms. Floor is a ramp with its lower part under a water layer and roofedBrazil
    AmphifarmConcrete, closed buildings containing 8-12, 20-25 m2, concrete floored on-growing rooms. Floor has two narrow canals, pre-fabricated shelters and feeding troughsBrazil, Ecuador
    GreenhousesWooden or concrete 4-8 m2 tanks with partially flooded floor. Tanks are placed in wooden or metallic-framed, plastic or tarpaulin-roofed building Brazil, Argentina, Uruguay, México, Guatemala
    RanaboxVertical array of wooden or fibreglass, heated boxes with water and feed traysBrazil, Argentina


    Semi-dry and wet systems

    This category comprises a number of systems employed in Southeast Asia, as well as some Latin American versions employed in Mexico, Guatemala, Argentina and Uruguay. The following table summarizes the main operational and productive characteristics.

    Wet surface area30-50% of total bottom area of fattening tank100% of total bottom area of fattening tank
    Water dynamicsStaticFlow-through
    Nursery stageNoYes
    Average yield 12-16 kg/m214-22 kg/m2
    Type of feedSupplementary + live (fly larvae)100% supplementary feed
    Functional versatilityLimitedHigh
    Feed supply 
    Specific frog feed is used in some Asian countries, while Latin American farmers employ chiefly tilapia or trout feeds.
    Harvesting techniques 
    Once frogs reach market size, they are prepared for harvest. Frogs are starved for 24 hrs before harvest. In semi-dry systems, ongrowing rooms are drained and frogs are collected manually. Harvesting is carried out in much the same way in wet systems although, in some farms, iced water is pumped into the tanks to hypothermally anaesthetize the frogs to allow for better handling.
    Handling and processing 
    Processing of frogs is carried out in certified processing facilities. Frogs are hypothermally anaesthetized (12´at 4 °C) and then slaughtered. Processing includes bleeding, skinning and cutting off the lower limbs, which are then thoroughly cleansed using chlorinated water. Then the legs are individually bagged, frozen and packed by size in master boxes for transport. Frog legs are kept frozen at -15±2 °C which gives them a shelf life of up to 6 months.

    Frogs for the live or scientific markets are manually rinsed and packed in 25-lb waxed perforated cardboard boxes. Live frogs are transported under cool and dry conditions by plane. Survival is usually up to 99 percent when the journey does not exceed 72 hrs.
    Production costs 
    The annual operating costs for a 36 tonnes/yr bullfrog farm (in Mexico) have been reported to total USD 67 560 (41 percent feed; 31 percent labour). Fixed investment costs were USD 130 000 (land USD 20 000; infrastructure USD 90 000; equipment USD 16 000; and initial broodstock USD 4 000).
    Diseases and control measures
    The major disease problems affecting American bullfrogs are included in the table below.

    In some cases antibiotics and other pharmaceuticals have been used in treatment but their inclusion in this table does not imply an FAO recommendation.

    DISEASEAGENTTYPESYNDROMEMEASURES
    'Red leg' disease.Occurrence of several bacteria, either synergistically or mono-specifically. The most common genera are Aeromonas, Pseudomonas, Klebsiella, Edwardsiella, Myma, StreptococcusBacteriaRed legs; red anusAntibiotics; biosecurity; movement of non-infected organisms only
    General oedemaMost common causative genera are Streptococcus and StaphylococcusBacteriaGeneral swellingAntibiotics; biosecurity; movement of non-infected organisms only
    'Swirling' diseaseMost commonly found genera in diseased organisms are Aeromonas, Streptococcus and StaphylococcusBacteriaAntibiotics; biosecurity; movement of non-infected organisms only
    TuberculosisMycobacterium spp.BacteriaTuberculosis; surface ulcers may appearAntibiotics; biosecurity; movement of non-infected organisms only
    MycosisAchlya spp., Saprolegnia spp.FungusUlcers, sometime with visible mycelia; skin reddeningFungicides; biosecurity
    EnvironmentalVarious (congenital, nutritional, environmental)Good management practices


    Suppliers of pathology expertise

    Assistance can be obtained from the following sources:
    • Dr. Marcio Hipolito, Instituto Biológico de Sao Paulo, Brazil send an email .
    • Dr. Putsatee Paryanonth, Chulalongkorn University, Bangkok, Thailand.
    • Dr. Victor Vidal, Center for Research and Advanced Studies (CINVESTAV), Merida, Mexico send an email.
    • Dr. Daniel Carnevia Instituto Nacional de Pesca, Montevideo, Uruguay.
    Statistics
    Production statistics
     
    The figure above is based on national statistical returns to FAO for aquaculture production of this species. Nearly all is from Taiwan Province of China (1551 tonnes in 2002), with very small annual production reported by Uruguay. Other frog aquaculture production is not identified by species, simply being reported as 'frogs, Rana spp.'; this category undoubtedly contains production of R. catesbeiana but the proportion is unknown. However, it is known that there is substantial production of this species in Brazil, Mexico, Ecuador and Guatemala.
    Market and trade
    In 1980, it was estimated that 3 percent of the global market of frogs (all species) was supplied by aquaculture, while the current (2002) estimated contribution is 15 percent, taking into account the calculated growth rate of the industry.

    Market statistics for frogs are scarce and unreliable. Some documented demand statistics place the United States of America as the highest consumer of frogs (all species), followed by France, Canada, Belgium, Italy and Spain.

    There are three major market niches for bullfrogs, namely:
    • Frog legs.
    • Live frogs.
    • Educational and scientific requirements.
    The market for frog legs is by far the largest niche worldwide. The main producers (capture and aquaculture) are Indonesia and Taiwan Province of China. Prices are weight-related, fluctuating from USD 3.86-10.14/kg at current (2004) prices.

    The demand for live frogs for food has increased especially amongst Asian groups living in Canada and the United States of America. Wholesaler prices range between USD 2.25 and USD 3.75/kg of whole frog, depending on weight. The main producers (capture and aquaculture) are Taiwan Province of China, Brazil and Mexico.

    Live bullfrogs for educational or scientific purposes are sold in the United States of America to processing companies. Three size-categories are marketed: 4-5', 5-6', and 6-7' (S-VL); prices range from USD 1.30-3.25 each.
    Status and trends
    Continued research efforts focusing on nutrition, pathology and reproduction are expected to result in important improvements that will boost production in the future. However, there is still much to be done on genetics. Marketwise, prices will tend to gradually increase, as trading of wild-caught frogs becomes restricted, thus being replaced by farmed animals; nonetheless, important efforts should focus on marketing and advertising, since frog meat and its attributes are far from being widely known.
    Main issues
    As in any other type of aquaculture, bullfrog farming can cause problems if not managed properly. The following table summarizes a series of externalities likely to be generated by frog farming, as well as the risks involved and some suggestions for their prevention or mitigation.

    ExternalityRisksMitigation strategies
    Organic dischargesEutrophication and ecological alteration of surrounding waters; organic pollution of water used for human consumptionOn farm wastewater treatment; wastewater re-use in agriculture; use of low-polluting feeds
    Release of antibioticsStimulation of natural bacterial resistanceDiscourage use of antibiotics; replace drugs with efficient management and prophylaxis
    Introduction of exotic speciesIntroduction of non-native pathogens; out-competition of local species; unwanted hybridizationImplement preliminary ecological impact studies; adopt strict bio-security measures to prevent escapes; quarantine introduced organisms
    Resources use conflictsWater or land that is or can be used in a more efficient way to generate more social benefitsMake a comparative cost/benefit analysis with other economic or social activities already in place or potential
    Collection of eggs and tadpoles from the wildDiminishes recruitment of commercially important frog fisheriesCarry out population dynamics studies; use aquaculture to re-stock natural fishing grounds


    Responsible aquaculture practices
    All countries request sanitary certification when buying frog legs but no CITES paperwork is required.

    It is important to develop specific regulatory frameworks for bullfrog farming, as it is becoming an important aquaculture activity in many regions. It should also follow the general principles adopted by the Code of Conduct for Responsible Fisheries, Article 9 (see http://www.fao.org).
    References
    Bibliography 
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