RAISING FROGS
by Skip Kemp and John W. Jensen
by Skip Kemp and John W. Jensen
Frog legs are a special culinary treat to many persons and are served in some of the finer restaurants. Frogs supplied to these markets are almost exclusively harvested in the wild and most are imported.
There are several species sold but the bullfrog (Rana catesbeiana) has the most potential for culture. Many attempts have been made to grow food-size frogs but to date none have been profitable. Experts say that frogs can be feasibly grown only in warmer areas of the world which have a year round growing season or where there is enough sunlight in winter to economically heat greenhouses.
Techniques for successful culture of laboratory frogs have been developed, however the densities, required for profitable food-size frog operations cannot be supported in ponds.
Adult frogs lay eggs in shallow water during spring. The eggs hatch in 1-3 weeks (depending upon water temperature) into tadpoles which are the larval form of frogs. Tadpoles have gills which become rudimentary as lungs are developed in about 2-3 weeks.
Growth to metamorphosis is temperature and food related. This transformation takes place after 8-12 weeks. In more northerly latitudes this may take as long as 1-2 years. From metamorphosis 6-8 months are required before frogs reach marketable size (1/2 pound). It may take another 1-2 years in the North or as little as 4 month in the more tropical areas of the world.
Frog culture as it is practiced today is strictly limited to laboratories. The most important factor in producing frogs is food supply. Tadpoles will feed on almost any soft animal or plant material, even fish feeds. Because they feed slowly there is a great loss of nutrients through leeching into the water. Feeds for tadpoles must be water stable to prevent such loss. Practical diets are only in the experimental stage at present.
Once the legs are developed and the tail is absorbed frogs will only accept living food. In artificial production systems, frogs prefer fish and tadpoles. Their cannibalistic habit can be overcome by providing food in excess. Top minnows (Gambusia) are a good source of food because they can be easily grown. Frogs will also accept live crayfish, worms and crickets.
The second most important production factor is disease control. Very high mortalities sometime occur due to bacterial infections, the most severe being the "red leg' disease. In most cases individuals showing symptoms of disease should be discarded as there is no reliable treatment. Sanitation is the best means for controlling disease. Change water daily or supply flowing water to effectively keep facilities clean and no chemical cleansers will be necessary.
As with other aquacultural enterprises success will be related to effort spent in marketing. One should not attempt to enter frog culture without allocating time and money for marketing. The frog culturist will not be besieged with orders for frogs and must actively pursue sales. Several potential markets exist which require varying degrees of development. The first one which comes to mind is the food-size market for restaurants. Probably the largest market is for smaller frogs and tadpoles used in research laboratories and for educational purposes. Thirdly, it has been suggested that there will be a market for frog skins to be use in making leather. This surely will require a lot of development. Other areas of frog culture which need development are harvesting techniques, processing methods and distribution systems.
Growth and survival of frogs can be enhanced by modifying some ponds. Most of these modifications are fairly expensive.
1. Bullfrogs have a migratory nature and are susceptible to predation. A low, small mesh fence 3 to 4 feet high can be erected around the pond serving to contain frogs and exclude such predators as cats, foxes, raccoons, snakes and turtles.
2. Snakes, turtles, bass and other predatory fish can be eliminated from the pond by various means.
3. Emergent shoreline vegetation can be planted. This will attract insects for food, and provide shade during the day. It may also provide places for frogs to hide from water birds.
4. Adult frogs are territorial often requiring up to 21 feet of shoreline for feeding and survival. Anything which can be done to increase to shoreline will increase the carrying capacity of frogs for a given area. This can involve digging long narrow trenches in the pond and depositing the earth as long peninsulas.
5. Frogs are more able to capture food from shallow waters. The best depth is 2 to 6 inches. When constructing ponds for growing frogs, the majority of the area should be at this depth. Deeper areas are needed however which will not freeze in winter so that frogs will have places to hibernate in bottom muds.
6. Lights can be installed to attract flying insects at night, increasing food supply.
It appears that growing food-size frogs for profit is not likely to be feasible for some time. Techniques have been developed for culturing small frogs but this seems to have more potential for laboratories to grow them for their own use. Changes can be made to farm ponds to enhance the growth of bullfrogs. However, these changes are expensive and often detract from other more desirable uses of the ponds.