Striped Bass Hybrids: The Frankenfish
Innovative KDWP fish culture project producing home-grown hybrids
PRATT - One might call it Frankenfish. The striped bass/white bass hybrid - more commonly called the " wiper" - is the undisputed terror of Kansas fishing waters. No fish, pound-for-pound, fights as hard as a wiper, and this tenacity has made it an increasingly popular quarry for the state's anglers.
Producing enough wipers to fill the demands of Kansas anglers is no easy task, however. Striped bass (or stripers) have been stocked in several Kansas reservoirs, but extreme summer water temperatures can limit their survival. Even in waters where stripers survive, their populations can't reliably provide wild females needed for a wiper production program.
For this reason, Kansas historically relied on fish trades with other states for wipers. However, this left the program at the mercy of annual fluctuations of available fish in other states. In addition, trading for fish from other states ran the risk of accidental introduction of unwanted species, as happened when white perch were sent to Kansas and inadvertently stocked in Wilson and Cheney reservoirs.
There had to be an answer, and the Kansas Department of Wildlife and Parks (KDWP) Milford Fish Hatchery would provide it. In 1993, the hatchery launched an experimental program to maintain a domestic striped bass broodstock population in the hatchery. If successful, the need for trades could be eliminated and control of the hatching process increased.
The first step was to stock hatchery ponds with striped bass fry, 100,000 to 200,000 per pond. These ponds contained no other fish and were high in zooplankton, a necessary food source for the growing fry. After 30 days, the fish were 1 to 3 inches long and ready to be transferred to culture tanks inside the hatchery. Here, they were trained to eat a pelleted food and grown to an average length of 4 inches before being transferred to raceways outside the hatchery. This would be their permanent home.
Four feet deep, 8 feet wide, and 100 feet long, the concrete raceways contained flowing water at a constant temperature of 58 degrees, ideal for stripers. Here, they thrived on their artificial cuisine and cool temperatures until they were old enough to breed - at age four.
Thus, the first domestic striped bass spawning in a Kansas hatchery occurred in 1997 and has continued annually. But rearing the fish proved much easier than spawning and producing wipers. To enhance egg development, the fish had to be switched from pellets to a live fish diet 30 to 45 days before spawning. Usually in early May, 12 females were selected for propagation and transferred to tanks inside the hatchery. Here, the were gradually acclimated to water temperatures of 66-68 degrees, ideal for spawning. All environmental factors - from lighting to disturbance and handling - could be controlled here, reducing stress on the fish.
After three days in their new environment, the fish were injected with human chorionic gonadotropin (HCG), a human hormone that facilitates successful reproduction. HCG speeds ovulation and induces a more predictable spawn. Eggs became fully-developed in just 18-30 hours after injection, requiring round-the-clock attention.
At this point, the culture process becomes even trickier. Eggs remain fertile only 30 minutes after ovulation, so the fertilization process must be timely and precise. Milt (fluid containing sperm) from wild white bass is stripped from the males precisely into pans with the eggs. The eggs accept milt for only two minutes, and once the milt is activated by water, it remains viable for only 30 to 60 seconds.
A female striped bass may produce more than one million eggs, depending on the size of the fish. Fertilized eggs are placed in special hatching jars where they can be continually monitored and dead eggs removed. Once the eggs hatch, the fry swim to the top of the jar and through a common trough emptying into a fry holding tank. These new wiper fry stay here for 9 days. From there, they may be stocked directly into state waters or placed in hatchery ponds and raised to fingerling size or larger for later stocking.
The early efforts were a learning process, with low hatch rates. By 2004, however, the success rate was up to 30 percent, providing a treat for anglers across the state through a process that is rare in the United States. Milford Hatchery is one of a handful of places that maintains a domestic broodstock solely for spawning.
For more information on this subject, pick up a copy of the March/April issue of Kansas Wildlife & Parks magazine. Look for the article entitled "Wipers For the Future," by Derek Schneidewind. For detailed information on wiper stocking in Kansas, visit the Fish Stockings.