By Dianna Troyer
For Idaho Farm Bureau Federation
The bellow of a bullfrog is like the sound of a cash register ringing at Rana Ranch near Twin Falls.
To meet the needs of three dozen loyal clients, Steve Rivas and his wife, Lisa Ault, raise and sell about 6,000 bullfrogs annually for medical research.
Like the metamorphosis of a tadpole to a frog, their business model has transformed considerably – from their living room where they fed maggots to their wild-caught frogs, to an efficient quarter-acre farm where the finicky bullfrogs thrive in temperature-controlled tanks and dine on a proprietary pelleted food.
“We were told it’s impossible to raise bullfrogs as farm animals, but we didn’t listen and didn’t give up,” said Rivas, 67, who worked as an instructor at the College of Idaho’s aquaculture program in Twin Falls until he retired in 2015.
He and Ault overcame numerous problems while developing Rana Ranch. How could bullfrogs be fed efficiently, considering they are finicky eaters and cannibalistic? How could their growth be controlled to meet clients’ specific size needs? Once mature, how could they be shipped?
Through years of trial and error, the Twin Falls residents devised meticulous protocols – hard-won trade secrets they decline to share.
“We still haven’t perfected bullfrog culture. It’s an art and a science, just like every other type of farming,” Rivas said. “We’ve been successful at developing a small, obscure farm that supplies an obscure and vital niche market. Our clients are willing to pay top dollar – an average of $45 a pound for our clean and robust frogs.”
Their clients include universities, medical schools, hospitals, drug companies, and labs where they are used to research diverse diseases including cancer, Alzheimer’s, hearing loss and nerve damage.
“Many researchers have told us our bullfrogs have helped them to understand diseases, and they’ve been instrumental in developing new treatments and remedies,” Rivas said.
“Besides being used in medical research, our bullfrogs are used to train doctors in surgery including microsurgery,” he said. “They’re also used in dissection, physiology, and psychology labs.”
They have shipped frogs to 43 states not only for biological research but to stock lakes, wetlands, ornamental koi ponds, water gardens, and golf course water features.
“I’ve always liked that distinct bellowing sound they make during breeding season,” Rivas said. “A semi-tame bullfrog can be a real character in an ornamental pond.”
Rivas started Rana Ranch while teaching at CSI, naming it after the frog’s scientific name, Rana catesbeiana. His career and the ranch are a natural extension of his lifelong fascination for reptiles, amphibians, and fish he caught and raised as a child. A poster he drew in elementary school showing a frog’s life cycle hangs on his office wall.
After graduating from CSI’s aquaculture program in 1989, Rivas took a leap of faith and caught six wild bullfrogs from the nearby Snake River, believing they could be developed into an aquaculture species.
“We kept them in three plastic garbage cans in our living room for more than a year,” he said. “In 1991, we started raising them at an aquaculture farm about 20 miles from town.”
Three years later, they placed an ad in Reptile Magazine, intending to sell bullfrogs as pets. They only sold a few, but fortunately a university lab employee read the ad and contacted him.
“A lightbulb came on, and we sent flyers to 20 universities,” he said. “Sales took off from there.”
As their business grew, their feeding program evolved from raising maggots to a proprietary pellet fed in a specific way.
“Bullfrogs are sight feeders and only eat live food, so for several years we raised up to 100 pounds of housefly maggots a week,” Rivas said. “They grab anything that moves, but if it doesn’t keep moving in their mouth they’ll spit it out. It prevents them from ingesting floating or moving sticks, leaves, or other inedible things.”
The frogs grabbed the experimental pellets, “but getting them to swallow them was the hard part,” he said. “It was a happy day in 1994 after about 100 experiments that Lisa found a way to get the bullfrogs to eat pellets – no more maggots. I have a lot of respect for the biomass production capacity of housefly larvae, but maggot farming is a disagreeable endeavor.”
A local mill makes the pelleted feed.
“Once we had them on a pelleted diet, we spent several more years doing feed trials to develop nutritious diets for all their life stages and ages,” said Ault, who graduated from CSI’s aquaculture program in 1992. “It’s complicated. Depending on their life stage, they’re two totally different animals: aquatic herbivores or semi-aquatic carnivores. Much but not all of our feed is plant based.”
In 1993, they moved to their present location, where they rent space at a local aquaculture farm closer to home that provides hot and cold gravity-fed water. Cold water, about 55 degrees Fahrenheit, is piped directly from a spring, while 102-degree water flows from an artesian well.
They installed Fiberglas troughs with locked tops to protect the tadpoles and frogs from predators. In each trough, Rivas installed cold and warm water lines, allowing the frogs to grow year-round instead of hibernating.
Controlling growth with temperature
“Hands-on training at CSI and raising them in clean cold and warm water are the keys to farming bullfrogs the way we do,” Rivas said. “Being (cold-blooded), their metabolism and growth can be regulated by temperature. We can put them into semi-hibernation to hold them at different stages of growth to save on feed, maintenance, and time. We’ve spawned bullfrogs as early as March and as late as August.”
Although he started with frogs caught in 1989, “we didn’t have real success with spawning until 2004,” Rivas said. “Before that, we bought wild-caught tadpoles from private ponds and from CSI for years. It wasn’t until 2009 that we were able to supply all of our tadpoles from our own broodstock.”
With gravity flow of 15 gallons per minute of water, Rivas keeps about 10,000 large late stage tadpoles on hand.
“Tadpoles can take up the whole water column, while bullfrogs take up floor space,” he said. “It’s a more efficient use of our limited trough space to keep mostly tadpoles and morph them into bullfrogs as we need them. Generally, a newly morphed frog that has lost its tadpole tail matures into a 5 1/2-inch frog within about six months.”
He usually maintains about 3,000 bullfrogs in four sizes. They range from medium at 4 inches and 4 ounces to super jumbo, exceeding 5 1/2 inches and weighing more than 11 ounces.
To tend to his farm, Rivas works about two hours a day feeding frogs and cleaning the troughs. Ault spends two to three hours a week counting, measuring, weighing, and sorting frogs for shipment.
Most are shipped during the school year, September to May, with sales slowing down from Thanksgiving through New Year’s.
Having overcome issues dealing with food and rates of growth, Rivas had to figure out how to get the bullfrogs to clients. Relying on UPS Next Day Air, they ship the frogs in six different-sized cardboard boxes. He cuts sheets of RMAX, a rigid foam plastic thermal insulation board, and lines each box.
“The RMAX keeps the temperature moderated and makes the boxes extremely durable,” he said. “Clients tell us they like our frogs because they’re accustomed to captivity and people, tolerate handling well, and aren’t easily startled or stressed.”
Rivas emphasizes the farm is sustainable and no herbicides, pesticides, non-organic fertilizers or electricity are used. Manure is composted and effluent water is used for irrigation.
Having developed their frog-farming techniques, Rivas said they could raise millions of bullfrogs.
“But that would put us into the food market,” he said, “and that isn’t what we want to do at this point in our lives.”