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Dennis Zensen

On December 12, 2007, I interviewed Dennis Zensen, the man charged with building and recruiting personnel for Ralston Purina’s Crystal River, Florida, shrimp research facility in 1968.  Zensen’s management style led to many shrimp farming discoveries in maturation, breeding, larval rearing and growout.  The Crystal River facility and the personnel trained there went on to make a major contribution to the development of shrimp farming in the Western Hemisphere.



Shrimp News: Tell me a little about your education.


Dennis Zensen: I was in the seminary for six years, planning to become a priest, when my parents ran into some problems, and I had to quit school. I went to work for the Van Camp Seafood Company, the people that do "Chicken of the Sea Tuna", worked my way up the ladder and wound up with a pretty good job. Then Ralston Purina acquired Van Camp, and I went to work for Purina, but didn't like my first job there. Hal Dean, the CEO of Purina, heard that I was thinking about quitting and summoned me to Purina's headquarters in St. Louis, Missouri, for a little talk. Hal had set up a new entity within the company called New Venture Management. I chatted with him and the man that was going to head up the new venture project and they offered me a job that I just could not refuse. I was hired to start new businesses for Purina..



Shrimp News: How did you get involved in shrimp farming?



Dennis Zensen: Since Purina was in the feed business, we werwhat and how to feed shrimp.  So I talked to some of Ralston Purina’s people who knew a whole lot about making trout and catfish feeds and they thought we could make shrimp feeds.  Originally, we just wanted to make feeds that we could sell to others, but then we decided to get into shrimp farming.  When we started the new shrimp project, I recruited Purina’s Dr. William MacGrath to develop shrimp feeds.  Many years later, Bill left Purina and managed a huge shrimp farm in Honduras.



Shrimp News: Who started the Ralston Purina project in Crystal River, Florida?



Dennis Zensen: That was my baby.  Environmentalists in Florida were jumping all over Florida Power for discharging warm water into the ocean.  I had some long talks with the CEO of Florida Power about using the warm water effluent to grow shrimp, telling him that the water would cool down in the shrimp ponds and could then be released into the ocean at ambient temperatures, which would dispatch all his environmental problems.  He bought that concept, and we signed a joint venture contract to study shrimp farming in thermal effluent.  We built a research facility on their land and some huge ponds, but never were able to produce enough seedstock for full-scale production.



Shrimp News: How much money did you spend on the Crystal River shrimp research facility?



Dennis Zensen: I don’t remember the exact numbers, maybe around two or three million dollars.



Shrimp News: Whom did you hire to run the shrimp facility?



Dennis Zensen: Bill More, and Yoshi Hirono to design and construct a shrimp hatchery that would take advantage of Florida Power’s thermal effluent.  That hatchery went on to become Purina’s famed Crystal River Research Center, an incubator for some of the first shrimp farmers in the Western Hemisphere.  We started doing experiments to see if we could get shrimp to reproduce in captivity, hoping to produce larvae and postlarvae for stocking the warm water ponds.  We chartered shrimp trawlers to capture wild broodstock, the local white shrimp (Penaeus setiferus).  We also had a lot of shrimp nauplii shipped up from Brazil, and we imported some tiger shrimp (Penaeus monodon) from Asia.


Hiring big trawlers to go out and catch gravid shrimp cost us a fortune.  On some trips, we only got ten or twenty gravid females, which cost us about a thousand dollars an animal.  We really needed to find a way to get them to breed in captivity.  We had divers go out at night with lights to see if they could observe their breeding behavior, a good idea, but it didn’t work.  We tried anything and everything to get them to breed, including a multitude of feeds and different water temperatures and salinities, but nothing seemed to turn them on.  Then one morning, one of the technicians noticed that some of the females had mated.  What happened?  We didn’t feed them any differently.  We didn’t change the water.  We didn’t know what happened, but, by accident, we discovered that the lights had been turned on or off in a particular sequence.  When we repeated the sequence, I don’t remember what it was, we got them to breed again.  And it worked every time after that, so we were no longer dependent on gravid females captured at sea.



Shrimp News: I’ve interviewed several of Crystal River’s first employees.  They say you gave them the time, tools and money to answer the basic question of how to breed and raise shrimp.  Is that right?



Dennis Zensen: Yes, that’s how I worked it.  When I arrived at Purina, I was really lucky because I got to spend a lot of time with Hal Dean, Purina’s chairman and chief executive officer.  He gave me a lot of advice on how to succeed in business.  I’ll never forget one thing that he said: “The secret is to coach, guide and counsel good people.”  That’s what I did with the crew at Crystal River.  I told them want we wanted to achieve, built them a research facility and let them figure it out, without bullying them or telling them how or what to do.  The coach, guide and counsel philosophy worked, and they worked like demons to answer the basic questions about shrimp farming—and succeeded!



Shrimp News: Were you successful in growing shrimp in the warm water effluent at the power plant?



Dennis Zensen: Not really.  We were never able to produce enough postlarvae to fill the growout ponds.  We were probably a year away from having enough seedstock when Florida Power began to lose interest in the project.  The pressure from the environmentalists lessened, and they were not as interested in having a Purina project on their land.  So we started looking for sites in South America, specifically Panama.  We became very friendly with the president of Panama, Demetrio Lakas Bahas, who had graduated from Texas Tech University in 1963.  He cleared the way for us so that we could get whatever we wanted, and what we wanted was several thousand acres of land.  Our contact in the Panamanian Government was none other than the infamous Colonel Manuel Noriega.  I got to know Noriega, who spoke English, because he flew me around in his plane when we were looking for sites.



Shrimp News: Did you think Noriega would eventually become the military dictator of the country?



Dennis Zensen: No, there was no sign of that, but President Lakas was very nervous about him and was very careful about what he said about him.  They didn’t like each other.  I never guessed that Noriega would become the dictator of the country.  He just didn’t seem like that kind of a person.



We did get a few thousand acres, and it was ours to use at almost no expense, in perpetuity, as long as the project was successful and the government got its royalty on what came out of the ponds.  Then, Purina went through a big shakeout.  My boss was terminated; I was terminated and other people in the new venture wing were terminated—and all the projects that were under way just stopped, including the shrimp project.  Later, new management came in and rescued some of the projects, including the shrimp project.



Shrimp News: What did you do after you left Ralston Purina?



Dennis Zensen: I started Quincy Farms, a mushroom farm just north of Tallahassee, Florida.  The farm made a lot of money and eventually went public.  We became one of the largest mushroom growers in the United States, but then I decided not to expand into mushroom farming and took the company into the business of selling the mushroom spawn, or seed.  I had a lot of good contacts in the insurance industry, and on Wall Street and was able to raise about 20 million dollars to get a company, Sylvan, Inc., started.  Its shares were traded on the NASDAQ stock exchange for a while, but later, after a new round of financing and an ownership change, the company returned to private ownership.  Today, we have ten spawn plants scattered around the world.  I’m retired now, but still on the board of directors and the largest single stockholder.  I’m also on the boards of all the Sylvan companies around the world.



Source: Dennis Zensen.  Telephone Interview by Bob Rosenberry, Shrimp News International.  December 12, 2007. Published on January 18, 2008.


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