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.

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 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.

System	Main physical characteristics	Countries
Aquaterrarium	Earthen or concrete, shallow, narrow, long open canals with sloped, grass-covered banks and terraces	Brazil, Mexico
Tank-Island	Square 20-30 m2 walled, roofless, grass-covered floor, with a central concrete platform (10% surface area), surrounded by a shallow (<0.10 m) canal	Brazil, Taiwan Province of China
Confinement Rooms	Square, 12 m2, concrete floored, walled rooms. Floor is a ramp with its lower part under a water layer and roofed	Brazil
Amphifarm	Concrete, closed buildings containing 8-12, 20-25 m2, concrete floored on-growing rooms. Floor has two narrow canals, pre-fabricated shelters and feeding troughs	Brazil, Ecuador
Greenhouses	Wooden 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
Ranabox	Vertical array of wooden or fibreglass, heated boxes with water and feed trays	Brazil, 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 area	30-50% of total bottom area of fattening tank	100% of total bottom area of fattening tank
Water dynamics	Static	Flow-through
Nursery stage	No	Yes
Average yield	12-16 kg/m2	14-22 kg/m2
Type of feed	Supplementary + live (fly larvae)	100% supplementary feed
Functional versatility	Limited	High

Specific frog feed is used in some Asian countries, while Latin American farmers employ chiefly tilapia or trout feeds.

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.

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.

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).