TWIN FALLS — Bullfrogs have fascinated Steve Rivas since he was 6 years old.

“Everything about them fascinates me,” Rivas said. About 15 years ago, his mother gave him a poster he had made in elementary school detailing the life cycle of a bullfrog. He keeps it hanging on his office wall.

One of the fascinating characteristics of bullfrogs is also what makes it difficult to grow them under farm conditions. Bullfrogs are aquatic herbivores as larva but become semi-aquatic carnivores as adults. Essentially they are two different animals in one body.

Rivas began experimenting with methods for raising bullfrogs in 1989 as soon as he graduated from the College of Southern Idaho’s Technical Aquaculture Program.

He remembers visiting Tolief Rangen after graduation to thank him for a scholarship. Rangen asked him what he planned to do and Rivas said he planned to get a job and turn bullfrogs into farm animals.

Rangen told him that bullfrogs wouldn’t eat pellets, but if Rivas could figure out a way to get them to do it, he should come back and Rangen would manufacture the pellets for him.

It took five years of trial and error — and raising maggots in the living room — to get bullfrogs on pelleted feed. Tadpoles were easier to get on feed than the adults who rely heavily on movement to trigger feeding. But eventually Steve and his wife Lisa found a formula that worked and Rana Ranch Commercial Bullfrogs was in business.

At first Rivas expected to sell bullfrogs as pets or for pond stocking, but the medical community quickly evolved into the primary market for his stock. Since retiring from the CSI Hatchery in July 2015, Rivas has been focusing on his selective breeding program to develop uniform animals for medical research.

“They are looking for cookie-cutter frogs,” Rivas said. “The frogs I supply this year must be the just like the frogs they got last year.”

Even though most researchers don’t tell him what they are working on, bullfrogs have qualities in their skin, eyes and ears that make them ideal subjects for research on hearing loss, nerve damage, Alzheimer’s and cancer. They shed their skin as they grow and researchers have discovered a fungus grows on that shed skin which may also have medicinal purposes.

Once he determined that medical researchers were his primary market, he had to rethink his production practices. Bullfrogs spawn like crazy but the breeding season is very short and he needs to supply different sized frogs to customers throughout the year.

Fortunately bullfrogs are poikilothermic which means their metabolism and growth can be regulated by temperature. Rivas takes advantage of their high fertility to spawn a large number of larva that he raises to a certain size and then holds at that size until he needs them to change into frogs. That ensures he has frogs of varying sizes throughout the year to meet customer needs. He is also using temperature to extend the spawning season.

Rivas refer to frogs by their spawn year, but they don’t begin having birthdays until they go on feed and begin the morphology process. Most of his regular customers give him enough lead time to ensure he has enough frogs at the right size to meet demand.

Many researchers prefer using his farm-raised bullfrogs to wild caught ones because they are used to being handled and don’t startle easily. He has designed his tanks to offer bullfrogs an environment that matches wild conditions as much as possible even under high stocking rates. He estimates that his bullfrogs have kept thousands of their wild cousins from being captured for use in medical labs.

Even though bullfrogs present unique challenges, Rivas says they are not that much different than other raising aquaculture species. Water and nutrition are key for growing both fish and bullfrogs.

Rivas has a permit to raise bullfrogs in Idaho, a requirement since bullfrogs are considered a non-native species in the state. He warns customers that releasing bullfrogs into areas where they historically have not been present can be a threat to native animals.

Still, he thinks there are other species that could make farm animals if someone has ambition and is willing to work hard. And it doesn’t if the species is one a potential entrepreneur has been interested in since they were young.

“(The medical community is) looking for cookie-cutter frogs. The frogs I supply this year must be the just like the frogs they got last year.” Steve Rivas, bullfrog farmer