Texas Parks and Wildlife Department Inland Fisheries biologists are stalking a killer lurking in Texas waters.
By Larry D. Hodge
Since February 2001, TPWD Inland Fisheries workers have been engaged in a grim struggle against a nearly invisible enemy, a tiny floating plant commonly known as golden alga. The story of that battle is a scientific detective thriller with more than a few surprising twists — and it’s far from over.
Golden alga — Prymnesium parvum — made its first confirmed appearance in Texas in 1985, when it killed more than 100,000 fish in the Pecos River. It’s been implicated in the deaths of 17.5 million fish valued at more than $7 million, severely hampered the operation of two TPWD fish hatcheries and struck crippling blows at local economies dependent on fishing and tourism. And it may be expanding its range. Its presence has been confirmed in the Canadian, Red, Brazos, Colorado, Pecos, Trinity and Sulphur river systems.
Even at 400 times magnification, golden alga appears tiny. Turning in tight, jerky circles like a carnival bumper car, the one-celled organism gives no clue of its deadly potential. But on a pleasant September day at Lake Diversion, southwest of Wichita Falls, biologist Tom Dorzab shows me what golden alga can do. A fish kill is in progress, and dead shad, catfish and freshwater drum rim the lake. Golden alga, once a rare visitor, is making its third appearance in the lake in less than three years.
At the Dundee State Fish Hatchery, which draws its water supply from the lake, the staff is well acquainted with the threat: In 2001 golden alga wiped out Dundee’s entire production of striped bass. That same year, golden alga caused fish kills on Possum Kingdom Reservoir, Lake Granbury, Colorado City Lake, E.V. Spence Reservoir, Moss Creek City Lake and Lake Whitney. In 2002, golden alga struck the Possum Kingdom hatchery, which had not been in production the year before. In all, 23 Texas lakes have been affected.
Golden alga is not going away. And some way has to be found to deal with it.
Protecting the Hatcheries
Since the first outbreak at Possum Kingdom Lake, TPWD Inland Fisheries biologists and researchers have been working to learn as much as they can about golden alga. They have two goals: First, to be able to prevent or control outbreaks in hatcheries, and second, to determine what can be done to protect reservoirs and streams. They feel confident they have learned a lot about the first scenario; the second remains a work in progress.
Winston Churchill once said about Russia, “It is a riddle wrapped in a mystery inside an enigma: but perhaps there is a key.” That statement might well apply to golden alga, which is present in marine environments throughout the world. It was unknown in fresh water in the Western Hemisphere until TPWD pollution biologist Joan Glass found it during a 1988 fish kill on tributaries of the Clear Fork of the Brazos. “I had never seen or heard of anything like it,” she recalls. “All the usual water quality parameters were normal, the water had living aquatic insects in it, but there were dead fish everywhere. Ranchers were asking if it would kill their cattle, and I’m saying ‘I don’t even know what it is.’” The alga was later identified by an expert who had seen it in hatchery ponds in Israel.
Whether golden alga has always been here or was transported to Texas by air currents or some other means remains a mystery. What is known is that it seems to prefer to live in water with some salinity. As we’ll see later, that trait is also one key to its control in hatcheries.
Scientists are better acquainted with the “hows” of golden alga behavior than with the “whys.” Normally present in slightly salty waters, its numbers usually remain low and it causes no problems. Sometimes, however, for reasons that are not clearly understood, golden alga “blooms,” multiplying so rapidly that within days it can impart a golden hue to water. Blooms usually occur during the cooler months, when golden alga seems to have a competitive advantage over other kinds of alga that grow best in warm waters. However, both Lake Diversion and the Dundee State Fish Hatchery have experienced golden alga blooms and fish kills during the hottest part of the year, August.
Golden alga appears to pose no health threats to humans, livestock or wildlife. It becomes dangerous to fish, mussels, clams and other gill-breathing creatures only when it begins to produce toxins. Gills are selectively permeable — they admit oxygen and excrete carbon dioxide but keep water out. Golden alga toxins destroy gill cells, in effect transforming them into open doors that admit water and everything in it. Golden alga toxins and other chemicals in the water get into the fish’s blood and circulate throughout its body. Death comes within hours and sometimes minutes.
Rainfall patterns may play a part in fish kills. “We don’t know why, but we have noticed that after there is a major rainfall, we often get an increase in P. parvum in Lake Diversion,” says Tom Dorzab. Scientists suspect that water refilling a lake following a drought may wash in substances — perhaps residues from agriculture, horticulture and sewage treatment plants or septic systems — that trigger a bloom.
“One of the things suggested in a lot of the literature is the possibility there are nutrient ratios that have changed historically because of human impacts that might be causing some of the blooms,” says Gerald Kurten, the Inland Fisheries regional director who supervises the Dundee and Possum Kingdom hatcheries. (See the sidebar “Keeping Golden Alga Happy.”) “Have farming and residential development around reservoirs played a part? We haven’t found a smoking gun yet.”
Both the Possum Kingdom and Dundee fish hatcheries draw their water supply from lakes infested with golden alga. The water from both lakes is slightly saline, making it ideal for hatching and rearing striped bass, a species that normally spends part of its life in saltwater. Striped bass and hybrid striped bass (a cross between striped bass and white bass) are stocked in many lakes in Texas. They do not reproduce in Texas’ fresh water, because the regulated river conditions (below and above major reservoirs) are not sufficient for egg hatch. Annual stockings are needed to maintain the striped bass fishery at Possum Kingdom reservoir and other popular fisheries around the state such as lakes Buchanan and Whitney.
Dundee is TPWD’s main hatchery for striped bass and hybrid striped bass. Tom Dorzab managed the hatchery at the time of the first fish kills there, and he recalls the events of February through June 2001 with obvious discomfort.
“We started having trouble with our rainbow trout dying in February, while Possum Kingdom Reservoir was having so much trouble,” he remembers. “We sent a sample of water to Austin, and they said it looked like Prymnesium parvum. We moved all our smallmouth and largemouth brood fish to the A. E. Wood Hatchery to protect them and continued to look for ways to control the alga. We’d had some mortality in our ponds for years, and it usually came late in the production cycle. So we went about preparing our striped bass ponds for production as usual, thinking we had time to find something to treat the water with if golden alga became a problem.”
On the short list of “something to treat the water with” was ammonium sulfate, commonly available as 21-0-0 commercial fertilizer (21 percent nitrogen, zero percent phosphorus, zero percent potassium). But ammonium sulfate is a double-edged sword: While it will kill golden alga, too much of it will also kill fish. And as biologists soon learned, how much is too much depends on factors that vary hour by hour, such as the temperature and pH of the water.
The plan developed at Dundee was to watch the ponds and apply ammonium sulfate if fish started dying. “We stocked 53 ponds with striped bass and hybrid striped bass fry,” says hatchery biologist Dennis Smith. About 200,000 fry are stocked per acre-foot of water. Since it’s difficult to see the tiny fish once they are stocked in a pond, ponds are sampled with a seine periodically to check on fry numbers and growth rates. Dorzab and Smith were in for a shock. “We didn’t catch anything in the seines,” Smith says. “We drained the ponds, and there were no fish left.” Golden alga had silently wiped out the fish while they were less than half an inch long.
“That kicked us into action,” says Dorzab. “We knew we had a big problem. We formed the golden alga hatchery work group, and very quickly we devised a project to try to get some survival.” TPWD personnel went to Lake Texoma to obtain more brood fish, and the resulting fry were stocked, again with the intent of treating the water if and when golden alga became a problem. In three weeks all those fish were dead, too. Methods of detecting golden alga were just being developed, and the fry had been put into water that was already toxic. The entire year’s production of striped bass — 5 million fish — had been lost.
“The atmosphere around here was pretty depressing,” Dorzab says. “Spawning is always a very stressful time — we work on 24-hour schedules and everybody is a walking, talking zombie. Now we’d gone through spawning twice and didn’t have anything to show for our efforts. I felt very frustrated. We are here to raise fish, and we didn’t have any fish.” Frustrated but still capable of dark humor, biologists compiled a list of possible future actions to combat the alga that ended with this bold-faced, italicized item: nuclear air strikes.
More research was needed. “We designed another project using koi carp, and we treated the ponds before we put the fish in,” Smith says. “We treated some ponds with ammonium sulfate, some with copper sulfate — another known algicide — and left others untreated as control ponds. The results were dramatic. None of the fish in the control ponds survived. There was some survival in the ponds treated with copper sulfate, but we harvested fewer fish and less weight of fish than we had stocked. In the ponds treated with ammonium sulfate, we harvested 10 times the weight of fish we had stocked — production was even better than what we normally expect. Based on that, we were confident we had a treatment that would work.”
But there was one possible problem. “We were nervous about using ammonium sulfate, because as fish culturists we have had it drilled into our heads that ammonia will kill fish, and we were applying it at pretty high levels,” says Dorzab.
“The expert opinion was that we could not raise striped bass in the level of ammonia it took to kill the alga,” Smith adds. Ironically, ammonia affects fish in much the same way as golden alga toxins do, by disrupting gill action. Ammonia destroys the gills’ ability to remove carbon dioxide from the fish’s blood, and the buildup of CO2 in the blood is eventually fatal.
During the winter of 2001-2002, Smith scoured scientific journals and tested different levels of ammonia using hybrid striped bass fry donated by a fish farm in Arkansas. Approximately the same figure for how much ammonium sulfate to use kept turning up. Using that as a guide for treating the ponds, Dundee produced 4.5 million stripers and hybrid stripers in 2002, and morale at the hatchery rose markedly. “We felt we had really accomplished something,” Smith says.
And indeed they had, partly due to an odd twist. The reason the striped bass are able to tolerate the level of ammonia needed to kill the alga is the presence of salt in the water. The very thing that seems to allow golden alga to survive also makes it possible to kill it without harming the fish.
The cure is not without cost. While ammonium sulfate is relatively cheap, monitoring golden alga levels and treating incoming water to kill any P. parvum present is very expensive. The workload for hatchery personnel has also quadrupled, says Kurten, and they have had to be intensively trained to recognize the alga. “It’s like they have gone from being nurses to being brain surgeons in one or two years,” he says.
Significant fish kills in hatcheries appear to be unlikely in the future if control programs can be properly maintained and improved. Feral fish populations remain in danger, however. In February 2003, golden alga appeared in the Canadian, Pecos, Colorado and Brazos river systems. Fish kills occurred on Lake Granbury, Possum Kingdom, Lake Whitney, O. H. Ivie and nine other West Texas lakes. The kills illuminated one inescapable fact facing Inland Fisheries managers: It makes no sense to grow fish and stock them into waters where they will soon die.
Protecting Streams and Reservoirs
A fish kill at a hatchery impacts the public indirectly. Fewer fish for stocking means fewer fish to catch in future years, and the value of fish lost is a small item in a much larger state budget. A fish kill in a public stream or reservoir is an altogether different matter. The number of anglers and tourists falls, and the effects ripple throughout the local economy. Guide and hotel bookings drop. Grocery store, restaurant, bait shop and service station sales fall. Jobs may be lost in industries that have nothing to do directly with fishing.
The Possum Kingdom Chamber of Commerce predicted the loss to the local economy from the 2001 fish kill at $16 million to $18 million over four years. Hotel/motel tax revenues in the nearby city of Graham fell 16 percent in 2000-2001 from the year before and have yet to rebound to pre-kill levels. John Bryan of Graham, a long-time fishing guide on Possum Kingdom, says he used to guide 170 to 180 trips a year, but now he books about 50. His income from guiding has been slashed by two-thirds. “That’s a pretty big pill to take three years in a row,” he says. “At one time there were 12 to 14 guides on this lake. Now there is only me and one other.”
In order to lessen the economic impact and restore the fishery as quickly as possible, TPWD gives priority to restocking lakes that have suffered kills. In the case of Possum Kingdom, in the two years following the 2001 kill TPWD stocked 435,000 channel catfish, 71,000 blue catfish, 6.2 million striped bass, 65,000 smallmouth bass, and 1.5 million Florida largemouth bass into the lake. In addition, size and possession limits for largemouth and striped bass were changed to protect the larger brood fish that survived.
“We closely monitor the fish populations at Possum Kingdom,” says Mark Howell, the district biologist. “All indications from our surveys are that the stocked fish have done very well, particularly the largemouth bass. Growth rates are better than before the kill, because there is now a very abundant shad prey base. As for striped bass, three times as many are showing up in our surveys as we found in 2001.”
Golden alga is a nasty little pest, and one of the nastiest things about it is that once you have it, it won’t go away. Its spores, or cysts, settle into sediments in the bottoms of ponds, lakes or streams — even if they dry up — and remain dormant until conditions are right for another bloom. There is no preventive treatment for natural bodies of water — but there is hope.
With the help of Representative Jim Keffer of Eastland, TPWD obtained $1.2 million in funding from the 78th Texas Legislature to find ways to deal with the golden alga problem. Additional monies were obtained from U.S Fish and Wildlife Service and Sport Fish Restoration grants. Part of the money was used to bring experts from around the world to Fort Worth last October to share information about golden alga as a first step toward learning to control it.
“One of our main goals is to come up with real management strategies and not just pour money into research that doesn’t give us answers we need,” says Larry McKinney, director of TPWD’s Coastal Fisheries Division.
TPWD is also proceeding with basic research needed to understand how P. parvum works in the hope that eventually its devastating effects can be prevented or at least diminished. Data about past blooms will be examined to determine if contributing environmental factors can be identified. The level and breadth of P. parvum distribution in Texas will be determined. A DNA-based test for presence of the alga will be developed, along with genetic databases, to make detection easier and to make possible research into what makes P. parvum tick.
“Right now we don’t have a lot of answers,” Joan Glass says, “but humans have always solved their problems if given some time and a chance to get their heads together. I think we will get to the point where we can control golden alga. It hasn’t been thoroughly researched before, and that’s what we’re working on.”
“We know so much now that we realize we know so little,” adds Gerald Kurten.
That realization is the first step on the road to a solution.